Читать книгу Essentials of Orthognathic Surgery - Johan P. Reyneke - Страница 8
ОглавлениеThere must be clear and effective communication between the orthodontist and the maxillofacial surgeon from the outset of treatment to achieve the best results from surgical therapy. Through this close relationship, a full exchange of information and data can be made. Each practitioner involved in the patient’s care should be familiar with the standard records required, and the data on the patient should be shared regardless of who actually performs the investigations. Treatment should commence only after both the orthodontist and the surgeon have consulted with the patient, a treatment plan has been jointly prepared, and both clinicians have a copy of the patient’s records. Orthognathic surgeons should have a thorough understanding of orthodontic treatment principles to enable them to communicate sensibly, to plan realistically, and to know what can be expected from the orthodontic treatment. Conversely, orthodontists should understand the surgical possibilities, limitations, and requirements to make the partnership ultimately advantageous to the patient.
A systematic examination is necessary to adequately evaluate and plan treatment for patients with dentofacial deformities. In routine cases, this evaluation includes the following:
General patient evaluation
Sociopsychologic evaluation
Esthetic facial evaluation
Radiographic evaluationLateral cephalometricPosteroanterior cephalometricFull-mouth periapicalPanoramic
Occlusion and study cast evaluation
Temporomandibular joint evaluation
General Patient Evaluation
Hereditary tendencies in the development of dentofacial deformities
The term dentofacial deformity is generally used to describe a significant disproportion of the jaws in association with malocclusion. Jaw deformities are thought to be more common among individuals with genetic backgrounds that are crossed between different racial and ethnic groups as compared with those from isolated human populations. It is assumed that about one-third of children who present with a severe Class III malocclusion will have a parent with the same problem and that one-sixth of these children will have siblings with the same problem. A short face growth pattern with a deep bite malocclusion is more frequently found in Caucasians, while bimaxillary protrusion with anterior open bite and microgenia is more prevalent among individuals of African descent.
Knowledge and an understanding of normal facial growth and development as well as the effect of malformations on associated facial structures is useful in diagnosis and treatment planning as well as to limit complications during treatment. Factors that are known to alter facial growth and cause dental malocclusion and skeletal deformities may include the following: (1) syndromes, (2) hereditary factors, (3) environmental and neuromotor effects, (4) trauma, and (5) pathology (eg, tumors).
Medical history
The patient’s medical history can be obtained by means of a questionnaire that the patient fills out at the first consultation. The questionnaire should be thorough so that no important areas are overlooked. The data are used to focus follow-up questions. Existing medical problems must be further evaluated and discussed with the appropriate physician or specialist. The potential for these medical problems to complicate general anesthesia or reconstructive surgery must be evaluated. Risk management and potential complications related to any medical problem should be discussed with the patient and carefully documented. Other medical specialists treating the patient should be consulted as necessary, and reports on existing conditions and drugs the patient may be taking should be obtained. It is also important to look for and recognize congenital syndromes because these patients may have unusual growth patterns and may respond unpredictably to orthodontic or surgical treatment.
Dental evaluation
History
Previous restorative, orthodontic, orthognathic surgery, periodontal, and facial pain treatment should be reviewed. The dental history is often an important barometer of the patient’s probable commitment to future treatment.
General evaluation
Oral hygiene and previous dental treatment are good indications of the patient’s “dental IQ” and motivation for future treatment. Caries, periodontal and periapical pathology, and the presence of unerupted and/or impacted teeth should be noted. The need for implants should be evaluated for possible inclusion in the final treatment plan. However, final prosthetic decisions are deferred until surgical orthodontic treatment has been completed.
Periodontal considerations
The prognosis for any periodontally affected teeth is established and the effect of orthodontic and surgical treatment considered. Periodontal disease and inadequately attached gingiva must be managed before commencement of orthodontic treatment. Long-term management, further periodontal treatment, and prognosis should be discussed with the periodontist and the patient.
Occlusal–oral function evaluation
Mastication, swallowing, mouth breathing, modified eating habits, and maximum mouth opening are documented. Snoring and breathing during sleep (eg, obstructive sleep apnea) should be noted and investigated. The effect of the dentofacial deformities on speech should be noted and the patient referred for pretreatment speech evaluation. Tongue thrust, thumbsucking, and lip-biting habits should be noted and their effect on the deformity evaluated.
Sociopsychologic Evaluation
Evaluation of the patient’s sociopsychologic makeup is often neglected. It is important to consider the patient’s motives for treatment and to determine the patient’s expectations from treatment. There are two basic causes of patient dissatisfaction with the treatment outcome: (1) failure of the clinician to clearly inform the patient of realistic and probable treatment results (especially esthetic results), and (2) overoptimistic expectations of the patient regarding the results of treatment.
At the first consultation, the patient should be introduced to the concept of orthognathic surgery gently but confidently. It is imperative that from the start, the clinician provides the patient with a realistic and understandable overview of orthognathic treatment principles and general treatment possibilities in relation to the patient’s specific dentofacial problem. Understanding the patient’s concerns, motivations, and expectations will provide insight into the patient’s psychologic health.
The clinician should refrain from overwhelming the patient with overt enthusiasm about the benefits of treatment, but rather should allow the patient to make his or her own decision. Some patients may need time to discuss future treatment with family or friends. Further counseling about realistic treatment expectations may be necessary, and it may even be best to delay treatment until the patient seeks psychologic guidance and is able to cope with treatment realities.
The perception of one’s own appearance is often the “motor” behind direction in life. Surgical-orthodontic change of facial appearance inevitably has an effect on this motor. The following are some relevant questions for the patient to consider:
What does the patient (and/or the patient’s parents) think is wrong? Many individuals are able to identify, explain, and prioritize their concerns, which may vary from functional to esthetic problems. A patient is often referred by his or her dentist for treatment for conditions unfamiliar to the patient or family. The patient may be seen by the dentist not because of their own concerns but those of their parents. For these patients, it is paramount to explain their specific problems and the reasons for correction, including the risks of nontreatment, the treatment required, and the associated risks of treatment. It may come as a shock to the patient and family members that the patient may need surgery. It is therefore important to comprehensively discuss with the patient (and family when necessary) the concepts related to surgery combined with orthodontic treatment. The advantages and disadvantages of combining orthodontics with surgery, alternative treatments, and compromises should be discussed; if possible, results from previously treated patients should be reviewed. This information will help the patient and family to make an informed decision regarding treatment.
Why is treatment required? The motivation for treatment is often a good predictor for the patient’s cooperation during treatment.
Why is treatment required now? The timing of seeking treatment is influenced by various factors including finances, onset of symptoms, and late diagnosis, among others.
What is expected from treatment? The expectations and priorities of patients differ. For patients with severe facial deformities, the esthetic change is more important than functional occlusal correction. Patients who need correction of their malocclusion but prefer not to have any esthetic facial change can present a treatment challenge to the surgeon and the orthodontist.
Figure 2-1 shows a sociopsychologic evaluation form, which should give the clinician an overview of the patient’s sociopsychologic status, indicating any existing problems and possible need for consultation with a psychologist.
Fig 2-1 Sociopsychologic evaluation form.
Esthetic Facial Evaluation
The clinical assessment of the face is probably the most valuable of all diagnostic procedures. The esthetic facial evaluation should be performed in a systematic fashion with the patient standing or seated comfortably. Primary emphasis should be placed on frontal esthetics because that is how people see themselves. Data should be recorded on a special form that can also serve as a checklist. Only abnormal and pertinent data should be recorded. Balance and proportion between the various facial structures in the individual are more important than numeric values. It is also important to compare the facial proportions with the patient’s general build and posture (ie, corporofacial relationship).
The clinical examination of the face should always be done with two questions in mind:
1 Would orthodontic-surgical treatment be able to correct the dental, skeletal, and soft tissue structure diagnosed as abnormal?
2 How would the orthodontic-surgical correction of the abnormal structures influence the facial structures considered to be normal?
It is often possible to correct the malocclusion of patients with dentofacial deformities by means of compromised orthodontic treatment, meaning an orthodontic-dental compromise for a skeletal jaw discrepancy resulting in an acceptable long-term functional and stable occlusion and facial esthetics. The fear of surgery, financial issues, unsatisfactory surgical experience of the orthodontist, and feasibility of correction by compromised orthodontic treatment will influence the orthodontist to implement orthodontic treatment for a skeletal deformity.
The patient should be examined in natural head posture, with the teeth in centric occlusion and the lips relaxed. Natural head posture is the position in which the patient orients his or her head and that feels most natural. Figure 2-2 illustrates the profound effect a change in head posture may have, for example, on chin position, chin-throat angle, and chin-throat length. Skeletal and soft tissue changes can therefore only be planned with the head in natural posture and the lips relaxed to ensure appropriate soft tissue changes. Orthodontic and surgical treatment are planned to produce ideal function in centric occlusion. All examination data should therefore be recorded in centric occlusion. However, patients with vertical maxillary deficiency and severely closed bites are an exception to this rule. Because of the inadequate height of the maxilla, these patients’ bites are overclosed, leading to distortion of their lips. To accurately evaluate these patients’ lips and maxillary incisor–upper lip relationships, they should be evaluated in an open bite posture. A wax bite can be placed between the teeth to increase the vertical dimension until the lips just part. The lack of tooth exposure, lip shape and thickness, anteroposterior position of the chin, labiomental fold, upper lip length, nasolabial angle, and soft tissue thickness can now be assessed more meaningfully. Figure 2-3 illustrates the profound changes in soft tissue characteristics in a patient with vertical maxillary deficiency in centric relation and in the open bite position.
Fig 2-2 Clinical assessment of the chin and throat area is possible only when the head is in natural posture. Note the differences with the head tilted down (a), tilted up (b), and with the head in natural posture (c). The white line represents the Frankfort horizontal (FH) plane.
Fig 2-3 Individual with vertical maxillary deficiency. Note the change in the shape of the lips and lower facial height with the teeth in occlusion (a) and with the mandible rotated open until the lips just part (b).
It is imperative that the patient be examined with the lips in a relaxed position, because it is impossible to assess the relationship between the soft tissue and the hard tissue when the lips are forced together. Figure 2-4 demonstrates the effect of muscular compensation on the lips and chin. Note the change in the interlabial gap, labiomental fold, chin and lip shape, and maxillary tooth exposure. The sella-nasion (S-N) plane and Frankfort horizontal (FH) plane have traditionally been used as horizontal planes of reference for various cephalometric and clinical assessments. However, patients do not carry their heads with the S-N or FH planes parallel to the floor. Cephalometric landmarks should not dictate head posture used for facial assessment and treatment planning. The clinical evaluation should therefore be carried out with the head in the natural posture.
Fig 2-4 The profile of the lower third is profoundly different when the lips are forced together (a) versus in repose (b).
Frontal analysis
From the frontal view, it is particularly important to assess facial form; transverse dimensions; facial symmetry; the vertical relationship in the upper, middle, and lower thirds of the face; the lips; and the nose.
Facial form
The relationship between the facial width and vertical height has a strong influence on facial harmony. Facial form and harmony should also be correlated with the patient’s overall body build. When correcting facial form, the overall body build of the individual should be considered (ie, short and stocky versus long and thin). The height-to-width proportion of the face is 1.3:1 for females and 1.35:1 for males. The bigonial width should be approximately 30% less than the bizygomatic dimension (Fig 2-5). Short, square facial types are often associated with a Class II deep bite malocclusion, vertical maxillary deficiency, masseteric hyperplasia, and macrogenia, whereas long, narrow facial types are often associated with vertical maxillary excess, a narrow nose, mandibular anteroposterior deficiency, microgenia, a high palatal vault, and an anterior open bite malocclusion (Figs 2-6 and 2-7; Table 2-1).
Fig 2-5 Facial form. The facial height (trichion [Tr]–soft tissue menton [Me′]):bizygomatic width (Za-Za) should be 1.3:1 (females) and 1.35:1 (males). The bigonial width (Go-Go) should be approximately 30% less than the bizygomatic width.
Fig 2-6 In this individual, the bigonial width is greater than the bizygomatic width because of bilateral masseter muscle hypertrophy.
Fig 2-7 Individual with a long, narrow face. The bizygomatic width is more than 30% greater than the bigonial width.
Transverse dimensions
The rule of fifths is a convenient method for evaluating transverse facial proportions. The face is divided into five equal parts—each the approximate width of the eye—from helix to helix of the outer ears (Fig 2-8).
Fig 2-8 Transverse facial proportions.
Table 2-1 | Comparison of broad and narrow faces
| Broad face | Narrow face | |
| Facial height | Square, short | Long |
| Bigonial width | Masseter hypertrophy | Decreased intergonial distance |
| Nose | Broad nose | Narrow nose |
| Chin | Macrogenia | Microgenia |
The outer fifths are measured from the center helix of the ears to the outer canthus of the eyes. Prominent ears may have a profound effect on facial proportions and can be corrected by otoplasty. In patients with masseter hypertrophy, the face appears square, and the gonial angles fall well outside the canthus line. A more harmonious facial form can be established in these patients by means of bilateral reduction of the masseter muscles and contouring the mandibular angles (Fig 2-9). Intergonial width can be increased by subperiosteal angle implants (Fig 2-10).
Fig 2-9 (a) The bigonial width is increased because of bilateral masseter muscle hypertrophy. The gonion falls lateral to a vertical line drawn through the outer canthus of the eye. (b) Transverse facial harmony has been restored by bilateral masseter muscle and mandibular angle reduction.
Fig 2-10 (a) This patient wanted to make his oval face more square. (b) The angles of the mandible were augmented by the placement of bilateral subperiosteal angle implants.
The medial three-fifths of the face are measured from the outer to the inner canthus of the eyes. The outer border should coincide with the gonial angles of the mandible. In patients with masseter muscle hypertrophy, the gonial angles will fall well lateral to this line (see Fig 2-9a). In patients with long faces, there will be a tendency for the gonial angles to be medial to these lines. It should be noted that the width of the mouth should approximate the distance between the inner margins of the irises of the eyes (Fig 2-11).
Fig 2-11 Vertical lines drawn through the medial canthi should coincide with the ala of the nose, whereas vertical lines drawn through the medial margins of the irises of the eyes should coincide with the corners of the mouth.
The middle fifth is delineated by the inner canthus of the eyes. In patients with hypertelorism, this fifth will be out of proportion with the other four-fifths. The ala of the nose should coincide with these lines (see Fig 2-11). For patients in whom maxillary advancement and/or superior repositioning is considered and the ala falls outside of the lines, control of alar width is indicated during surgery (see chapter 5).
Facial symmetry
To assess facial symmetry, an imaginary line is drawn through the soft tissue glabella (G'), pronasale (Pn), center of the philtrum of the upper lip and lower lip, and soft tissue pogonion (Pog'; Fig 2-12). For more accurate assessment, these points should be marked on the patient’s face one at a time while other parts of the face are blocked out.
Fig 2-12 Facial symmetry. Important midline structures are the midpoint between the eyebrows (G), nasal bridge (NB), nasal tip (Pn), midpoint of the philtrum of the upper lip (Ph), dental midlines (DM), and midpoint of the chin (Pog').
The maxillary and mandibular dental midlines should be assessed in relation to the facial midline, as well as in relation to each other. These observations will play an important role in the decision-making process regarding surgical or orthodontic correction of dental midlines. It is also important to evaluate the mandibular dental midline in relation to the midline of the chin. This information will assist in treatment planning for correction of mandibular asymmetry by means of mandibular surgery, genioplasty, or both. The presence of a transverse cant in the occlusal plane should be noted and correlated with the asymmetry. Surgical correction of an occlusal plane cant will often play a significant role in the total correction of facial asymmetry and should not be corrected orthodontically (see chapter 4).
No face is perfectly symmetric, but the absence of any obvious asymmetry is necessary for good facial esthetics. Posteroanterior cephalometric radiography or CBCT imaging for 3D virtual treatment planning are indicated in the presence of a clinically significant asymmetry. This will allow the clinician to distinguish between bone, soft tissue, or a combination of the two as etiologic factors.
Vertical relationship
In the vertical dimension, the face can be divided into three equal parts (Fig 2-13): (1) upper third (hairline [trichion] to the glabellar area), (2) middle third (glabellar area to subnasale [Sn]), and (3) lower third (Sn to soft tissue menton [Me']).
Fig 2-13 The face is divided into thirds by drawing horizontal lines through the trichion (Tr), G, subnasale (Sn), and soft tissue menton (Me'). The lower third can be divided into an upper third (from Sn to stomion superius [Sts]) and a lower two-thirds (from stomion inferius [Sti] to Me').
Upper third of the face
Fortunately, deformities that exist in the upper third of the face can usually be masked by an appropriate hairstyle. However, it is important to record deformities in this area because they may indicate craniofacial deformities.
Middle third of the face
The nose, center of the lips, and middle of the chin (in the lower third of the face) should fall along a true vertical line (Table 2-2). Generally, no sclera is seen above or below the iris in a relaxed eyelid position with the patient looking straight ahead in natural head posture. Individuals with a midface deficiency tend to show sclera below the iris of the eye (Fig 2-14).
Table 2-2 | Comparison of excessive and deficient midface dimensions
| Excessive middle third | Deficient middle third | |
| Vertical maxillary dimension | Excessive | Deficient |
| Cheeks | Sallow | Full |
| Sclera showing | Visible below the iris | Normal |
| Cheekbones | Flat | Prominent, broad |
| Paranasal areas | Flat | Full |
| Nose | Narrow, long | Short, broad |
Fig 2-14 Sclera shows below the irises of the eyes in this individual with midface deficiency.
Sequential evaluation of the cheekbones, paranasal areas, alar eminences, and upper lip relation (in the lower third) should be performed. The cheekbone–nasal base–lip contour is a convenient contour line to evaluate the harmony of the structures of the midface (zygoma, maxilla, and nasal base) with the paranasal area and upper lip. This line starts just anterior to the ear, extends forward through the cheekbone, and then runs anteroinferiorly over the maxilla adjacent to the alar base of the nose, ending lateral to the commissure of the mouth. The line should form a smooth, continuing curve (Fig 2-15). An interruption of the curve may be an indication of an apparent skeletal deformity. Figure 2-16 illustrates a clear interruption of the line in the maxillary area, indicating maxillary anteroposterior deficiency. In Fig 2-17, there is a double break with one indicating maxillary deficiency and the other an interruption in the lower part because of mandibular anteroposterior excess.
Fig 2-15 Cheekbone–nasal base–lip contour. The cheekbone area (CC) is divided into three parts: (1) zygomatic arch, (2) middle area, and (3) subpupillary area. The maxillary point (MxP) is the most medial point on the curve. The nasal base–upper lip contour (blue) extends inferiorly from MxP. The line should curve gently, without interruptions, ending lateral to the corner of the mouth.
Fig 2-16 (a) Interruption of the curve at MxP. (b) Individual with maxillary anteroposterior deficiency. There is an interruption in the cheekbone–nasal base–lip contour at MxP.
Fig 2-17 (a) Interruption of the curve at MxP and below MxP. (b) An individual with maxillary anteroposterior deficiency and mandibular prognathism. The cheekbone–nasal base–lip contour is interrupted with a double break, at MxP and also below MxP.
Lower third of the face
The middle third to lower third vertical height of the face should have a 5:6 ratio (Table 2-3). The length from Sn to stomion superius (Sts; called the upper lip length) should make up one-third of the lower third facial height. The distance from stomion inferius (Sti) to Me', the lower lip length, should equal two-thirds of the lower third face height (see Fig 2-13).
Table 2-3 | Comparison of excessive and deficient lower face height
| Excessive lower third | Deficient lower third | |
| Vertical maxillary dimension | Excessive | Deficient |
| Lip appearance | Increased interlabial gap | Overclosed |
| Smile | Gummy | Toothless |
| Maxillary incisor exposure | Excessive | Little or none |
| Chin | Microgenia | Macrogenia |
| Malocclusion | Class II with or without anterior open bite | Class III closed bite or Class II deep bite |
Normal upper lip length is 20 ± 2 mm for females and 22 ± 2 mm for males, measured from Sn to upper lip inferior (Sts). If the upper lip is anatomically short, there is a tendency for the interlabial gap to be larger than normal and for increased maxillary tooth exposure with normal lower facial height. This condition should not be confused with skeletal vertical maxillary excess. The distance from lower lip superior (Sti) to Me' is 40 ± 2 mm for females and 44 ± 2 mm for males. The lower lip may often appear short because of posture caused by maxillary incisor interference in patients with deep bite. The upper lip length should be related to lower anterior dental height.
With the patient’s lips in repose, the amount of maxillary incisor exposure beneath the upper lip should be noted (Fig 2-18). For individuals in whom the maxillary incisors are not visible under the upper lip, the tooth-lip relation should be evaluated with the mandible rotated open until the lips just separate (Fig 2-19). The relation of the dental midline to the facial midline is an important aspect to note because dental midlines can be coordinated and/or corrected either orthodontically or surgically. The etiology of dental midline shifts may be dental or skeletal. Dental factors that may cause midline shifts include spaces; missing teeth; tooth rotations; malpositioned teeth; crowding; crowns, fixed partial dentures, fillings, or implants (which can all change the size of teeth); and tooth size discrepancy.
Fig 2-18 Excessive maxillary incisor exposure and increased interlabial gap. Normal maxillary incisor exposure under the upper lip is 1 to 4 mm. This measurement will be influenced by upper lip length, vertical maxillary length, lip thickness, and the angle and anteroposterior position of the maxillary incisors.
Fig 2-19 Individual with vertical maxillary deficiency. (a) It is not possible to assess maxillary incisor–lip relationship with the teeth in occlusion. (b) The lack of maxillary incisor exposure is evident with the mandible rotated open until the lips part and the upper lip is relaxed and not influenced by the lower lip.
In faces with asymmetry involving the mandible, it is critical to note the midline of the chin and its relation to the mandibular dental midline. The chin is evaluated for symmetry, vertical relation, and shape. The cant of the occlusal plane is evaluated, especially in individuals with facial asymmetry, by asking the patient to bite on a wooden spatula and then relating the occlusal plane to the interpupillary line (Fig 2-20). The maxillary dental arch level (between the maxillary canine tips) must be distinguished from the mandibular dental arch level (between the mandibular canine tips). However, with this assessment it is necessary to make sure that the orbits are on a horizontal plane because there may be an orbital deformity influencing this observation. Patients who present with facial asymmetry and a cant in the occlusal plane will require an anteroposterior cephalometric radiograph for further analysis.
Fig 2-20 The cant in the occlusal plane can be evaluated in relation to the interpupillary line by asking the patient to bite on a wooden spatula. During this assessment, make sure that the interpupillary line is parallel to the floor.
The amount of gingiva exposed during smiling is also noted. The ideal tooth exposure during smiling is the full tooth crown to 2 mm of gingiva, which occurs in females more often than males. When examining the smile, it should be kept in mind that the amount of tooth exposure is influenced by (1) the vertical length of the maxilla, (2) lip length, (3) maxillary incisor crown length, (4) amount of lip action with smile, and (5) shape of Cupid’s bow of the lip.
Surgical superior repositioning of the maxilla is indicated only when excessive gingival exposure is found in combination with an increased interlabial gap, increased maxillary incisor exposure, and increased vertical height of the lower third of the face. The amount of surgical superior repositioning will be dictated by the amount of tooth exposure, lip length, crown length, and age and sex of the patient. Keep in mind that superior repositioning of the maxilla will tend to shorten the upper lip. The upper lip will lengthen with age, especially in males. If necessary, surgical repositioning should err on the long side because overcorrection gives the patient a toothless and aged look.
One should never plan treatment based on the smile pattern. For example, an individual may exhibit a normal maxillary tooth–lip relationship (1 to 4 mm) that increases during smiling to expose up to 7 mm of gingiva (“gummy smile”). If superior repositioning is planned according to the amount of gingiva exposed during smiling, the maxilla will need to be superiorly repositioned by 6 mm to establish the ideal full tooth exposure. However, this will result in no tooth exposure and a toothless look in repose.
Lips
The lips are extremely critical to overall esthetics. Lip symmetry should be evaluated; if asymmetry exists, its etiology should be determined (eg, cleft lip, facial nerve dysfunction, underlying dentoskeletal asymmetry, scarring caused by previous trauma, or congenital unilateral microsomia or macrosomia).
The lower lip generally exhibits 25% more vermilion than the upper lip, and the lips should be 0 to 3 mm apart in repose. An increased overjet will result in an everted lower lip and excessive vermilion exposure due to the effect of the maxillary incisors on the lip. There are specific racial differences in lip thickness and shape that one must bear in mind for the purposes of treatment planning. To accurately evaluate the maxillary incisor–lip relationship in patients with closed bites, the lips should be relaxed and the jaws moved apart until the lips are slightly parted (closed bites may be the result of maxillary vertical deficiency or severe deep bites). Accentuation of Cupid’s bow of the upper lip may lead to exposure of the maxillary central incisors only. This exposure of the maxillary central incisors will not be evident on a lateral cephalometric radiograph because only the central incisors can be seen. Therefore, the amount of superior repositioning of the maxilla in patients with vertical maxillary excess should be assessed clinically and not radiographically.
Nose
Although the nose has not always been considered part of orthognathic correction, it comprises an important aspect of the overall facial esthetics, and the form and function of the nose can be affected by orthognathic surgery. Many orthognathic surgeons also perform rhinoplasty as part of overall dentofacial correction. In many instances, nasal reconstruction may be part of the orthognathic treatment plan; sometimes, rhinoplasty and orthognathic surgery can be performed simultaneously. Control of the nasal form should also be considered, especially in patients requiring superior repositioning and/or advancement of the maxilla (see page 292.)
The functional and esthetic nasal evaluation should be included in the examination of the orthognathic patient. An intranasal examination should be performed to identify a possible existing deviated nasal septum, hypertrophied turbinates, or nasal polyps. Esthetic concerns should be noted, and the nose should be evaluated from a frontal and profile view.
A discussion of detailed esthetic parameters of the nose is beyond the scope of this text. However, important esthetic factors to consider are the width of the nasal base, the distance from the base of the nose to the anterior extent of the nares, and from the anterior aspect of the nares to the tip of the nose. The prominence of the dorsum, the shape of the nasal tip, and the acuteness of the supratip break must also be considered in relation to the intended orthognathic surgery and the physical and/or relative esthetic effects surgery may have on these structures. The length of the columella and the nasolabial angle as well as the projection and shape of the nares should be considered; these aspects may be negatively affected by maxillary surgery.
Because orthognathic surgery can have a relative and anatomical effect on nasal form and esthetics, simulta-neous rhinoplasty and orthognathic surgery should be limited to small corrections to the nasal dorsum only. Formal rhinoplasty should be deferred to a second procedure. Figure 2-21 demonstrates the profound relative change of the nose following orthognathic surgical correction of a Class III malocclusion.
Fig 2-21 Corrective facial changes following orthognathic surgery may have a profound relative and/or anatomical effect on the nose. (a) Preoperative view showing a nose that appears large with a prominent dorsum. (b) The nose appears to have a normal shape and form following correction of a Class III occlusion by superior repositioning of the maxilla via a Le Fort I osteotomy, mandibular setback by means of a bilateral sagittal split osteotomy, and advancement genioplasty.
Although the face is divided into equal thirds to simplify clinical examinations and for schematic descriptive purposes, an orthognathic surgical procedure may affect the soft tissue in one or more of these thirds. Ferretti and Reyneke described the division of the face from the frontal view into five areas of surgical influence (Fig 2-22).
Fig 2-22 The face can be divided into oculonasal (1), maxillary (2), and mandibular (3) complexes. The mandibular complex includes the genial subcomplex (4).
Profile analysis
Upper third of the face
The supraorbital rims normally project 5 to 10 mm beyond the most anterior projection of the globe of the eye. Frontal bossing, supraorbital hypoplasia, exophthalmos, or enophthalmos should be distinguished.
Middle third of the face
It is helpful to examine the middle and lower thirds of the face in isolation, and masking the lower third with a card eliminates any undue influence that this third may have on the perceptions of the face as a whole. The middle third of the face can also be blocked out to evaluate only the lower third in relation to the rest of the face (Fig 2-23). The nose, cheeks, and paranasal areas are sequentially evaluated.
Fig 2-23 (a) The mandibular complex (including the chin) is blocked out, revealing the deficient paranasal flattening and poor upper lip support. (b) The middle third of the face is blocked out, showing the mandible and chin in good relation to the rest of the face. This observation is confirmed when only the upper lip and maxilla are blocked out (c).
Nose
The shape of the dorsum is noted as normal, convex, or concave. The projection of the nasal bridge should be anterior to the globes (5 to 8 mm). The appearance of the nasal tip is evaluated for the presence of a supratip break and for tip definition and projection (Fig 2-24). It is important to distinguish between a dorsal hump and a turned-down tip because each has different treatment implications. The possible effect of maxillary surgery on the nose should be kept in mind when evaluating the proportions of the base of the nose (Fig 2-25).
Fig 2-24 The nasal tip projection is evaluated by the Goode method. If BC is greater than 55% to 60% of AB, the nasal tip usually appears disproportionately overprojected.
Fig 2-25 (a) Vertical ala–columella relationship. (b) Columella-lobule relationship with a ratio of approximately 2:1. (c) The general shape of the alar base should resemble an isosceles triangle, with the lobule neither too broad nor too narrow.
Cheeks
The globes generally project 0 to 2 mm ahead of the infraorbital rims, whereas the lateral orbital rims lie 8 to 12 mm behind the most anterior projection of the globes (Fig 2-26). The cheeks should exhibit a general convexity from the apex of the cheekbone to the commissure of the mouth. This line of convexity, called the cheekbone–nasal base–lip curve contour, requires simultaneous frontal and profile examination. This line starts just anterior to the ear, extending forward through the cheekbone, then antero-inferiorly over the maxilla adjacent to the alar base of the nose, and ending lateral to the commissure of the mouth (Fig 2-27). The line should form a smooth, continuing curve with no interruptions. An interruption of the curve may indicate an apparent skeletal deformity. Figure 2-28 illustrates a clear interruption of this line in the maxillary area, indicating maxillary anteroposterior deficiency. In Fig 2-29, the interruption in the line is in the maxillary area, indicating maxillary anteroposterior deficiency, and inferior to the upper lip section, indicating mandibular anteroposterior excess.
Fig 2-26 The lateral orbital rim lies 8 to 12 mm behind the globe, and the globe projects 0 to 2 mm ahead of the infraorbital rim.
Fig 2-27 (a) Cheekbone–nasal base–lip curve contour. (b) Note the smooth, uninterrupted curve of the contour line in an individual with good facial proportions.
Fig 2-28 (a and b) An interruption in the curve of the contour line at MxP, indicating maxillary anteroposterior deficiency. (c) An improvement in the curve after advancement of the maxilla.
Fig 2-29 (a and b) A double break in the contour line in an individual with maxillary anteroposterior deficiency and mandibular anteroposterior excess. (c) The curve in the contour line is more harmonious after surgical advancement of the maxilla and mandibular setback.
Paranasal areas
The clinician should carefully assess the paranasal area because it plays an important role in distinguishing between middle third deficiency and mandibular anteroposterior excess. The ratio of the linear distance (horizontally) from nasal tip to Sn and from Sn to alar base crease is normally 2:1 (Fig 2-30). A ratio closer than 1:1 indicates maxillary anteroposterior deficiency. An increased ratio indicates decreased nasal projection. Patients with a Class III malocclusion, decreased nasal projection, and a short nose should be treated by mandibular setback rather than maxillary advancement. The possibility of rhinoplasty as a second procedure should be discussed with the patient.
Fig 2-30 Nasal projection. The projection of the nose is measured horizontally from Pn to Sn and is normally 16 to 20 mm. From the nasal base (Nb), the ratio of Pn-Sn to Sn-Nb should be 2:1.
Lower third of the face
A systematic examination of the lower third of the face includes evaluation of the lips, labiomental fold, nasolabial angle, chin, and chin-throat area.
Lips
The protrusion, retrusion, and soft tissue thickness of each lip is evaluated with the lips in repose. The upper lip usually projects slightly anterior to the lower lip. The position of the lips relates to the underlying dental position, such as maxillary dental protrusion or lack of upper lip support caused by, for example, Class II, division 2 malocclusion or excessive orthodontic retraction of maxillary incisors. An individual with an excessive increase in lower lip vermilion and a deep labiomental fold often also has a Class II, division 1 malocclusion.
The anteroposterior lip position may be assessed with the help of the esthetic line of Ricketts (E-line) or esthetic plane of Steiner (S-line) as guidelines (see the following sections on cephalometrics). The Sn-Pog' line, also called the lower facial plane, is an important guide in assessing the lip position and planning orthodontic and surgical positioning of the incisors, as well as surgical positioning of the chin. The upper lip should be 3 ± 1 mm ahead of this line and the lower lip 2 ± 1 mm ahead of this line. Extractions followed by retraction of incisors behind the Sn-Pog' line should be avoided. Keep in mind that this assessment is influenced by the anteroposterior position of the chin and the soft tissue thickness of the lips (Fig 2-31).
Fig 2-31 Effect of the chin position on the Sn-Pog′ line. (a) Effect in an individual with mandibular anteroposterior deficiency (lips ahead of the line). (b) With the chin in normal horizontal relationship to the maxilla, the upper lip should be 3.5 mm and the lower lip 2.5 mm ahead of Sn-Pog′. (c) Effect in an individual with mandibular prognathism (lips on the line). In all three cases, the upper lip position has not changed; however, a change in Pog′ position results in a change in the lip position relative to the Sn-Pog′ line.
Labiomental fold
The lower lip–chin contour should have a gentle S-curve, with a lower lip–chin angle of at least 130 degrees (Fig 2-32). The angle is often acute in patients with Class II mandibular anteroposterior deficiency because of impingement of the maxillary incisor on the lower lip or macrogenia. The angle is flattened in individuals with microgenia or lower lip tension caused by Class III malocclusion. The surgeon considering genioplasty should assess not only the anteroposterior position of the Pog' but also the chin shape and the labiomental fold.
Fig 2-32 Labiomental fold. The lower lip–chin angle should be at least 130 degrees.
Nasolabial angle
The nasolabial angle, which is measured between the inclination of the columella and the upper lip (Fig 2-33), should be in the range of 85 to 105 degrees (Table 2-4). In females, a slightly larger angle is acceptable; whereas in males, a smaller angle is considered esthetically pleasing. Patients with mandibular anteroposterior deficiency have increased nasolabial angles, and this angle is usually acute in individuals with Class III occlusion. Surgical or orthodontic retraction of maxillary incisors should be avoided in individuals with large nasolabial angles. Where crowding necessitates tooth extraction, the nasolabial angle should influence the decision to extract first versus second premolars. Surgical repositioning of the maxilla also affects the nasolabial angle. In general, the maxilla should never be moved posteriorly, especially in combination with superior repositioning. This surgical movement leads to loss of lip support, increase in nasolabial angle, increase in nasal projection, and flattening of the nasal base. These changes result in poor esthetics and a premature aging effect. The maxilla should be moved posteriorly only in individuals with true maxillary protrusion, which occurs very rarely.
Fig 2-33 The nasolabial angle, measured between the inclination of the columella of the nose and the upper lip, should be 85 to 105 degrees.
Table 2-4 | Comparison of acute and obtuse nasolabial angles
| Acute angle | Obtuse angle | |
| Maxillary incisor position | Protruding | Upright or retroinclined |
| Nasal projection | Drooping nasal tip | Prominent or hanging columella |
| Occlusion | Class III | Class II |
| Bite | Deep bite | Open bite |
| Maxillary vertical dimension | Deficient | Excessive |
Chin
Although the chin forms a prominent esthetic feature of the face, it has no clearly defined function. Anatomically the chin is considered to be the soft tissue structure below the labiomental fold. Chin projection should be in good balance with the entire profile. The anteroposterior position of Pog', however, is not the only determining factor for good chin esthetics. When examining the chin, the clinician should consider the entire complex of structures forming the lower third of the face from Sn to Me'. It is difficult to isolate individual parts constituting this complex because the examiner should evaluate the size, shape, and position of each structure in relation to the other structures as well as the chin complex in relation to the rest of the face. At this stage, the middle third of the face should be masked and the relationship of the chin to the rest of the facial structures evaluated. Various soft tissue cephalometric analyses are available to assist in clinical evaluation of the anteroposterior chin position. However, the chin should be evaluated in all three dimensions. The width of the chin should be assessed in relation to the overall facial shape. A narrow chin often has a knobby appearance, and if surgical advancement of the chin is planned, widening of the chin should be contemplated. The labiomental fold, chin shape, relationship to the dental midline, symmetry, and cant of the lower border should be considered.
Chin-throat area
The presence of a double chin and adipose tissue should be noted. The lower lip–chin-throat angle (normally 110 degrees) provides chin definition (Fig 2-34). The distance from the neck-throat angle to Pog' (submandibular length) should be approximately 42 mm. These observations are pertinent when considering mandibular setback or advancement procedures, genioplasty (advancement or reduction), or submental liposuction (Table 2-5).
Fig 2-34 Lip-chin-throat angle and submandibular length.
Table 2-5 | Comparison of acute and obtuse lip-chin-throat angles
| Acute angle | Obtuse angle | |
| Mandibular anterposterior dimension | Excessive | Deficient |
| Submandibular fat | None | Present |
| Occlusion | Class III | Class II |
Radiographic Evaluations
Lateral Cephalometric Radiographic Evaluation
The information from lateral and (if indicated) posteroanterior cephalometric radiographs forms an important part of the database for orthognathic surgical treatment planning. Although clinical evaluation must be the primary diagnostic tool in determining surgical treatment of the orthognathic patient, cephalometric analysis is a helpful diagnostic guide. It enables the clinician to quantify, classify, and communicate dentofacial deformities; create a treatment plan via a visual treatment objective; help plan for tooth extractions; monitor progress during treatment; study specific changes during and after treatment to evaluate treatment results; and study facial growth.
The lateral cephalometric radiograph should be taken with the patient’s head in a natural posture, the teeth in centric occlusion, and the lips in repose. There are three exceptions to this requirement:
1 Where there is a clinically significant difference between the centric occlusion and centric relation, a second radiograph should be taken with the teeth in centric relation.
2 In patients with maxillary vertical deficiency, a second radiograph should be taken with the mandible rotated open until the lips just part. The maxillary incisor–upper lip relationship, upper lip length and shape, and the amount of maxillary downgraft can be more accurately evaluated on this radiograph.
3 In patients with severe Class III malocclusion and overclosed bites, it is difficult to assess the lips, tooth-lip relationship, and the relationship between the maxilla and mandible. A second radiograph should be taken with the mandible rotated until the lips just part.
The primary objective of treatment is not to make the patient’s cephalometric measurements normal, but rather to make the occlusal function normal and the facial appearance harmonious. For most patients, function and esthetics go hand in hand.
Cephalometric analysis involves measuring, comparing, and relating various linear and angular measurements of the hard and soft tissue structures of the face. The following analysis, a compilation of measurements useful in making a diagnosis and developing a treatment plan, is divided into lateral cephalometric analysis of soft tissue, hard tissue (skeletal analysis), and dental relationships.
Although soft tissue analysis is discussed as part of cephalometric analysis, it should be emphasized that the primary soft tissue examination of the facial esthetics guided by cephalometric analytic values should be done clinically. A patient’s cephalometric analysis and photographs should be part of the permanent records, but controlled, reliable records of the clinical examination are necessary for accurate diagnosis and correct treatment. The diagnosis should not be based only on the examination of photographs and cephalometric analysis.
Soft tissue analysis
Soft tissue landmarks
Lateral soft tissue landmarks, shown in Fig 2-35, include the following:
Fig 2-35 Soft tissue cephalometric landmarks.
Soft tissue glabella (G′): The most anterior point of the forehead
Soft tissue nasion (N′): The deepest point of concavity in the midline between the forehead and the nose
Pronasale (Pn): The most anterior point of the nose
Subnasale (Sn): The point at which the columella of the nose merges with the upper lip in the midsagittal plane
Labrale superior (Ls): The mucocutaneous border of the upper lip vermilion
Stomion superius (Sts): The lowest point of the vermilion of the upper lip
Stomion inferius (Sti): The uppermost point of the lower lip vermilion
Labrale inferior (Li): The mucocutaneous border of the lower lip
Soft tissue pogonion (Pog′): The most anterior point of the chin in the midsagittal plane
Soft tissue menton (Me′): The lowest point on the contour of the soft tissue chin, found by dropping a perpendicular line from a horizontal line through the skeletal menton
Soft tissue planes
Soft tissue planes are shown in Fig 2-36 and include the following:
Fig 2-36 Soft tissue planes. (1) Facial plane. (2) Upper facial plane. (3) Lower facial plane. (4) S-line. (5) E-line (esthetic plane).
Facial plane: Extends from N' to Pog′
Upper facial plane: Extends from G' to Sn
Lower facial plane: Extends from Sn to Pog'
S-line: Formed by connecting Pog' to a point midway between Pn and Sn
E-line: Extends from Pn to Pog'
Soft tissue vertical evaluation
Relationship of middle to lower facial third height
The distance from G' to Sn (middle facial third height) and from Sn to Me' (lower facial third height) is measured. The ratio should be approximately 1:1. In most orthognathic surgical patients, abnormalities are in the lower third of the face (Sn-Me'). In patients in whom the lower third of the face is increased in relation to the upper third, either vertical maxillary excess or an increase in the vertical anterior height of the mandible should be expected (Fig 2-37). A decrease in lower vertical height could be caused by either vertical maxillary deficiency, vertical deficiency of the anterior mandible, or an overclosed bite.
Fig 2-37 Soft tissue vertical evaluation. Vertical measurements are made perpendicular to the FH plane. MFH, middle facial third height; ULV, upper lip vermilion height; ULL, upper lip length; ITE, incisor tooth exposure; LFH, lower facial third height; LLV, lower lip vermilion height; ILG, interlabial gap; LLL, lower lip/chin length.
Upper lip length
Upper lip length measured from Sn to Sts should be 22 ± 2 mm for males and 20 ± 2 mm for females (see Fig 2-37). Patients with relatively long upper lips tend to have less maxillary incisor exposure, whereas individuals with short upper lips tend to have an increased interlabial gap with increased maxillary incisor exposure (Table 2-6). When vertical repositioning of the maxilla is contemplated, upper lip length should be considered to plan the correct amount of superior repositioning of the maxilla for each individual.
Table 2-6 | Comparison of increased and decreased lip lengths
| Increased lip length | Decreased lip length | |
| Maxillary incisor exposure | Decreased | Increased |
| Differential diagnosis | Vertical maxillary deficiency | Vertical maxillary excess |
| Smile | Toothless | Gummy |
| Lip seal | Adquate | Increased interlabial gap |
Lower lip/chin length
The lower lip/chin length is measured from Sti to Me' and should be 44 ± 2 mm for males and 40 ± 2 mm for females (see Fig 2-37). An increase in the vertical dimension may indicate an increased anterior vertical height of the mandible. In contrast, a decrease may indicate a short anterior mandibular height. This dimension may also be short in individuals with both deep bites and everted lower lips.
Ratio of upper lip length to lower lip/chin length
The upper lip length (Sn-Sts) should be approximately half the length of the lower lip and chin (Sti-Me′; see Fig 2-37). A decrease in the vertical relation indicates either a long upper lip or a vertical deficiency of the anterior mandibular height. An increase in the ratio may be caused by either a short upper lip or a vertical excess of the anterior mandible.
Interlabial gap
When the lips are relaxed, they should be touching slightly, although an interlabial gap of 1 to 3 mm is still considered normal (see Fig 2-37). An increased interlabial gap (ie, larger than 4 mm) is usually an indication of lip incompetence due to vertical maxillary excess. Patients with a short upper lip, however, also tend to have an increased interlabial gap (Table 2-7).
Table 2-7 | Comparison of increased and decreased interlabial gaps
| Increased interlabial gap | Decreased interlabial gap | |
| Maxillary incisor exposure | Increased (assess with teeth in occlusion and lips relaxed) | None or little |
| Smile exposure | Gummy | Less than the full incisor crown exposed |
| Lip competence | Mouth breathing | Overclosed appearance |
| Vertical maxillary dimesnion | Excessive | Deficient/deep bite |
| Upper lip | Short | Long |
| Vermilion exposure | Excessive | Less |
Maxillary incisor exposure
When the patient’s lips are relaxed, 1 to 4 mm of the maxillary incisors should be visible under the upper lip. Lack of tooth exposure may be an indication of maxillary vertical deficiency; more than 4 mm of tooth exposure may indicate vertical maxillary excess (see Fig 2-37). The upper lip length should be kept in mind with this assessment.
Patients with relatively normal upper lips and excessive incisor exposure under the upper lip will have vertical maxillary excess. This assessment can be made only with the lips in repose. Lack of tooth exposure under an upper lip of normal length is an indication that the maxilla is vertically deficient. Vertical maxillary deficiency can be assessed only with the bite opened until the lips begin to part.
Upper and lower lip vermilion height
The upper lip vermilion height should be 25% less than the lower lip vermilion height. In short, the ratio of Ls-Sts to Sti-Li should be 3:4 (see Fig 2-37). Vermilion heights may vary depending on race, a fact that should be kept in mind during evaluation. Increased lower lip vermilion exposure may be due to lower lip eversion caused by lip incompetence in patients with vertical maxillary excess. The lower lip is also often everted in Class II deep bite cases or Class II, division 1 cases where the lower lip is rolled outward by the maxillary incisors.
Table 2-8 summarizes the vertical soft tissue relationships.
Table 2-8 | Summary of vertical soft tissue relationships
| Vertical relationship | Measurement | Normal value |
| Middle facial height: lower facial height (MFH:LFH) | G'-Sn:Sn–Me' | 1:1 |
| Upper lip length (ULL) | Sn–Sts | 20 ± 2 mm (females) 22 ± 2 mm (males) |
| Lower lip/chin length (LLL) | Sti–Me' | 40 ± 2 mm (females) 44 ± 2 mm (males) |
| Upper lip length: lower lip/chin length (ULL:LLL) | Sn–Sts:Sti–Me' Sn–LLV:LLV–Me' | 1:2 1:0.9 |
| Interlabial gap (ILG) | NA | 0 to 3 mm |
| Maxillary incisor tooth exposure (ITE) | Sts–Maxillary incisor tip | 1 to 4 mm |
| Upper lip vermilion:lower lip vermilion (ULV:LLV) | Ls–Sts:Sti–Li | 3:4 |
NA, not applicable.
Soft tissue anteroposterior evaluation
Nasolabial angle
The nasolabial angle is formed by a line tangent to the columella and a line tangent to the upper lip. A value of 85 to 105 degrees is considered normal. In males, the angle is usually more acute, whereas in females, a more obtuse angle is considered to be attractive (Fig 2-38).
Fig 2-38 The nasolabial angle is formed by a line tangent to the columella and a line tangent to the upper lip (Sn-Ls).
The nasolabial angle is influenced by the position of the upper lip supported by the maxillary incisors and the inclination of the columella of the nose. Excessive orthodontic retraction of the maxillary incisors will undermine upper lip support, leading to an unattractive increase of the nasolabial angle. The angle is more acute in Class III cases and more obtuse in Class II cases. The following factors that may influence the nasolabial angle should be considered during treatment planning:
Lip support. The existing maxillary incisor–upper lip relationship must be assessed.
Lip strain. Strained lips tend to move posteriorly once tension has been released. Tense lips, however, move less anteriorly with tooth or bone movement.
Lip thickness. Thin lips respond more readily than thick lips to tooth movement.
Magnitude of the overjet. If orthodontic retraction of maxillary incisors is contemplated, the larger the overjet, the more retraction that will be necessary. This retraction may lead to an increase in the nasolabial angle and loss of lip support.
The final anteroposterior position of the maxillary incisors and anteroposterior lip position are affected by interdental crowding or spaces in the anterior maxillary dental arch, tooth size discrepancies (maxillary versus mandibular), extraction versus nonextraction, extraction pattern (first versus second premolars), and existing tooth angulation.
Lip prominence
A line is drawn from Sn to Pog' (lower facial plane). The perpendicular distance of the Ls ahead of the Sn-Pog' line should be 3 ± 1 mm, whereas the Li should be 2 ± 1 mm anterior to the Sn-Pog' line (Fig 2-39a).
Fig 2-39 (a) Lip prominence in relation to the lower facial plane. The distance of Ls and Li to Sn-Pog′ is measured. Ls to Sn-Pog′: 3 ± 1 mm. Li to Sn-Pog′: 2 ± 1 mm. (b) Lip prominence in relation to SnV. The distances of Ls and Li are measured to the line drawn parallel to true vertical through the Sn. Ls to SnV: 1 to 2 mm. Li to SnV: 0 mm. (c) Lip prominence in relation to the E-line. Li should be 2 ± 2 mm behind Pn-Pog′.
The anteroposterior position of the upper lip is an indication of soft tissue support by the maxillary incisors and plays an important role in orthodontic or surgical positioning of the maxillary incisors. Thus, it should be kept in mind during treatment planning. The Li tends to be further ahead of Sn-Pog' in Class II cases (with Pog′ posteriorly situated) and behind the line in Class III cases (with Pog' anteriorly situated).
A vertical line drawn through the Sn perpendicular to “true horizontal” is called the subnasale vertical (SnV), and the upper lip should be 1 to 2 mm ahead of SnV. The lower lip should be on or just posterior to SnV (Fig 2-39b). In cases of mandibular anteroposterior deficiency, the lower lip tends to be more than 1 mm posterior to SnV. In patients with mandibular anteroposterior excess and/or maxillary anteroposterior deficiency, the lower lip will be anterior to the SnV. The distance of the most prominent part of the lower lip is measured to the E-line (Pn-Pog'). The lower lip should be 2 ± 2 mm behind the E-line (Fig 2-39c).
This evaluation is influenced by the nose and chin prominence and could also be used for planning the final chin position. The lower lip would tend to be ahead of this line in individuals with Class II mandibular anteroposterior deficiency, in whom Pog' is situated posteriorly and the lower lip everted.
Maxillary and mandibular anteroposterior position
A vertical line perpendicular to the constructed horizontal plane is drawn through G'. Pog' should be 1 to 4 mm behind the line. For maxillary anteroposterior assessment, Sn should be 6 ± 3 mm ahead of this line (Fig 2-40).
Fig 2-40 Maxillary and mandibular anteroposterior position. Sn should be 6 ± 3 mm ahead of the vertical line drawn through G′, and Pog′ should be 1 to 4 mm behind this line.
In patients with maxillary anteroposterior deficiency, Sn will be less than 3 mm ahead of the line, or in severe cases, even behind the line. Pog′ ahead of the line indicates possible mandibular anteroposterior excess. In mandibular anteroposterior deficiency, Pog′ will be more than 4 mm behind the line. It is important, however, to evaluate the anteroposterior position of the chin in conjunction with other features (particularly the shape of the chin) to distinguish among microgenia, macrogenia, and mandibular anteroposterior deficiency.
Chin prominence
Soft tissue chin prominence can be evaluated by measuring the distance to a line drawn through N' perpendicular to the FH. This line is also known as 0-degree meridian; Pog' should be 0 ± 2 mm ahead of it (Fig 2-41). A more prominent chin would be more than 2 mm ahead of the 0-degree meridian, whereas a horizontally deficient chin would be more than 2 mm posterior to the line.
Fig 2-41 Chin prominence. Anteroposterior evaluation of the chin to the 0-degree meridian and to a line perpendicular to the FH through Sn. Pog′ should be 0 ± 2 mm ahead of the 0-degree meridian and 3 ± 3 mm behind the SnV.
Another vertical line that is helpful in assessing the horizontal prominence of the chin is a line drawn perpendicular to FH through Sn. Pog' should be 3 ± 3 mm behind this line (see Fig 2-41). A horizontally excessive chin would be on or ahead of the vertical line, whereas a deficient chin would be more than 6 mm posterior to this line.
It is extremely important, however, to use the above measurements only as a guide when assessing chin position. Chin prominence must be evaluated in conjunction with other factors, such as chin shape, depth of the labiomental fold, microgenia, macrogenia, lower lip position, and mandibular anteroposterior excess or deficiency.
Lower lip–chin–throat angle
The lower lip–chin–throat angle is contained between a line drawn from Li to Pog' and a submental tangent line. An angulation of 110 ± 8 degrees is considered normal. For this assessment, the radiograph must be taken in natural head posture (Fig 2-42). This angle will be more acute in patients with mandibular anteroposterior excess and/or macrogenia. It will be more obtuse in cases of mandibular anteroposterior deficiency and/or microgenia.
Fig 2-42 Lower lip–chin–throat angle.
Chin-throat length
The chin-throat length is measured from the angle of the throat to Me′ (Fig 2-43). A distance of 42 ± 6 mm is considered normal. This measurement is only meaningful with the patient’s head in natural posture. The distance will be excessive in individuals with mandibular prognathism and short in those with a recessive mandible (Table 2-9). This measurement is significant in differentiating between mandibular anteroposterior excess and maxillary deficiency. Mandibular setback would obviously reduce this length.
Fig 2-43 Chin-throat length.
Table 2-9 | Comparison of increased and decreased chin-throat lengths
| Increased chin-throat length | Decreased chin-throat length | |
| Mandibular anteroposterior dimension | Excessive | Deficient |
| Occlusion | Class III | Class II |
| Chin | Macrogenia | Microgenia |
Facial contour angle
The angle of facial convexity is formed by lines drawn from G′ to Sn and from Sn through Pog′. The line from G′ to Sn is also called the upper facial plane, whereas the lower facial plane is formed by the line from Sn to Pog′. The mean angulation is estimated to be –12 degrees. A clockwise angle is expressed as positive; a counterclockwise angle is negative. Males tend to have a straighter profile (–11 ± 4 degrees); a slightly more convex profile is considered esthetically pleasing for females (–13 ± 4 degrees; Fig 2-44a). It is important, however, to differentiate among the various facial deformities that may produce the same facial contour angle. The measurement of the angle does not reveal the localization of the deformity.
Fig 2-44 (a) Facial contour angle. (b and c) Both individuals have a facial contour angle of –12 degrees, but they have different vertical deformities. (b) Vertical maxillary excess. (c) Vertical maxillary deficiency. (d to f) The facial contour angle in all three individuals is –20 degrees, indicating a convex profile. The convexity, however, is caused by different deformities: (d) mandibular anteroposterior deficiency, (e) maxillary anteroposterior excess, and (f) vertical excess of the maxilla with clockwise mandibular rotation. (g to i) The facial contour angle in all three individuals is –7 degrees. This concavity is caused by different deformities: (g) mandibular anteroposterior excess, (h) maxillary anteroposterior deficiency, and (i) maxillary vertical deficiency with counterclockwise mandibular rotation.
In Figs 2-42b and 2-44c, both individuals have normal anteroposterior relations according to the facial contour angle (ie, –12 degrees). However, the vertical height of one is long (see Fig 2-44b), and the mandible has rotated clockwise; the other has a short vertical height (see Fig 2-44c) due to maxillary anteroposterior deficiency with the mandible rotated counterclockwise.
In Figs 2-44d to 2-44f, all three patients have a Class II malocclusion and an increased facial contour angle (ie, –20 degrees). Their identical facial contour angles, however, are produced by entirely different skeletal patterns. Figure 2-44d shows mandibular anteroposterior deficiency. Figure 2-44e shows maxillary anteroposterior excess, and Fig 2-44f shows vertical maxillary excess, with clockwise (backward) rotation of the mandible.
Figures 2-44g to 2-44i show Class III malocclusion and a more concave profile with decreased facial contour angle (ie, –7 degrees) produced by three entirely different skeletal patterns. Figure 2-44g shows mandibular anteroposterior excess. Figure 2-44h shows maxillary anteroposterior deficiency, and Fig 2-44i shows a maxillary vertical deficiency with counterclockwise (forward) rotation of the mandible.
E-line (Ricketts)
In relation to the E-line (Pn to Pog´), the upper lip should lie approximately 4 mm behind it whereas the lower lip should lie about 2 mm behind it (Fig 2-45). The profile contained by this line should form a reasonably symmetric Cupid’s bow. Dental support for the upper and lower lips will affect these values and distort the shape of the Cupid’s bow. In the assessment, the clinician should keep in mind the effect of the anteroposterior chin position (Pog′).
Fig 2-45 E-line (Pn-Pog′).
S-line (Steiner)
The upper and lower lips should touch the S-line (drawn from Pog′ to the midpoint of the S-shaped curve between Sn and Pn; Fig 2-46). Lips behind this line may indicate lack of lip support or a prominent chin. Lips may fall ahead of this line because of dental protrusion or a deficient chin.
Fig 2-46 The S-line follows Pog′ to the midpoint of the S-shaped curve between Sn and Pn.
Z-angle (Merrifield)
The Merrifield Z-angle is formed by the intersection of FH and a line connecting Pog′ and the most protrusive lip point (upper or lower; Fig 2-47). The average Z-angle is 80 ± 9 degrees. An angle greater than 80 degrees is indicative of mandibular anteroposterior excess, whereas an angle of less than 80 degrees suggests an anteroposterior deficiency of the mandible. The Z-angle also indicates the relationship of the lips to the chin, as well as possible chin prominence or deficiency.
Fig 2-47 The Z-angle is formed by the intersection of FH and a line connecting Pog′ and the most protrusive lip point (upper or lower).
Lip thickness
Upper lip thickness is measured horizontally anterior to the bone from 2 mm below A-point to the anterior border of the upper lip (Fig 2-48). Upper lip strain is measured from the vermilion border to the labial surface of the maxillary central incisor and compared with lip thickness above this point.
Fig 2-48 Soft tissue thickness of the upper lip.
The two measurements above should be within 1 mm of each other. A distance between the vermilion border and tooth surface that is more than 1 mm less than the upper lip thickness is indicative of upper lip strain, which may be caused by maxillary dental protrusion. The difference reflects the strain factor and gives the clinician an indication of how far the incisors would have to be retracted before the lip would assume normal form and thickness and start responding to incisor retraction by moving posteriorly. Thin lips would respond more readily than thick lips to orthodontic tooth movements. Racial differences in facial soft tissue thickness should be taken into account.
Anteroposterior soft tissue relationships are summarized in Table 2-10.
Table 2-10 | Summary of anteroposterior soft tissue relationships
| Anteroposterior relationship | Normal value |
| Nasolabial angle | 85 to 105 degrees |
| Lip prominence: Ls to Sn-Pog' Li to Sn-Pog' Ls to SnV Li to SnV | 3 ± 1 mm ahead 2 ± 1 mm ahead 1 to 2 mm ahead 0 mm |
| Chin prominence: Pog' to 0-degree meridian Pog' to Sn (perpendicular to FH) Lower lip-chin-throat angle | 0 ± 2 mm ahead 3 ± 3 mm ahead 110 ± 8 degrees |
| Chin-throat length | 42 ± 6 mm |
| Facial contour angle | –11 ± 4 degrees (males) –13 ± 4 degrees (females) |
| E-line to Ls E-line to Li | –4 mm –2 mm |
| S-line to Ls S-line to Li | 0 mm 0 mm |
| Z-angle | 80 ± 9 degrees |
Skeletal analysis
Hard tissue landmarks
Hard tissue landmarks, shown in Fig 2-49, include the following:
Fig 2-49 Hard tissue cephalometric landmarks.
Glabella (G): The most anterior point of the frontal bone
Nasion (N): The most anterior point on the frontal nasal suture in the midsagittal plane
Orbitale (Or): The lowest point on the inferior orbital rim
Sella (S): The center of the sella turcica, as on the lateral cephalogram, which is located by inspection
Pterygomaxillare (Ptm): The apex of the teardrop-shaped pterygomaxillary fissure (lowest point of the opening)
Basion (Ba): The point where the median sagittal plane of the skull intersects the lowest point in the anterior margin of the foramen magnum
Anterior nasal spine (ANS): Anterior tip of the nasal spine
Posterior nasal spine (PNS): The most posterior aspect of the palatal bone
A-point, or subspinale: The most posterior midline point in the concavity where the lower anterior edge of the anterior nasal spine meets the alveolar bone overlying the maxillary incisors
B-point, or supramentale: The most posterior midline point in the concavity of the mandible between the alveolar bone overlying the mandibular incisors (infradentale) and the pogonion
Pogonion (Pog): The most anterior point of the chin
Gonion (Go): The point defined by using two lines, one tangent to the inferior border of the mandible and the other tangent to the posterior border of the ramus; found by bisecting the angle formed by the two lines and extending the bisector through the curvature of the mandible
Gnathion (Gn): The lowest, most anterior midline point on the symphysis of the mandible (midway between the Me and the Pog)
Menton (Me): The most inferior point on the symphysis of the mandible in the midline
Porion (Po): The most superior point of the external auditory meatus (anatomical point); the machine porion is the uppermost point on the outline of the rods of the cephalometer
Condylion (Co): The most posterosuperior point on the head of the condyle
Hard tissue planes
Hard tissue planes, shown in Fig 2-50, include the following:
Fig 2-50 Hard tissue planes. (1) True horizontal plane (HP). (2) Constructed horizontal plane (cHP). (3) Anterior cranial base (S-N). (4) Basion-nasion (Ba-N) plane. (5) Frankfort horizontal (FH) plane. (6) Pterygoid vertical (Ptv). (7) Functional occlusal plane. (8) Occlusal plane. (9) Dental plane (A-Pog). (10) Mandibular plane (Go-Gn).
True horizontal plane (HP): A line perpendicular to a plumb line on the radiograph will be the HP for a specific patient.
Constructed horizontal plane (cHP): A horizontal plane constructed by drawing a line through N at an angle of 7 degrees to S-N (see point 2 in Fig 2-48). This plane tends to be close to true horizontal.
Anterior cranial base (S-N): Formed by a line drawn from S to N.
Basion-nasion (Ba-N) plane: Extends between Ba and N and divides the face and the cranium.
Frankfort horizontal (FH) plane: Extends from Po to Or.
Pterygoid vertical (Ptv): A vertical line perpendicular to the FH and drawn through the distal outline of Ptm fissure.
Functional occlusal plane: A line through the cusp contacts of the molars and premolars.
Occlusal plane: Formed by a line drawn through the mesial cusp contact of the molars and dividing the incisor overbite.
Dental plane: Extends between A-point and Pog.
Mandibular plane: Extends from Go to G.
Skeletal anteroposterior relationships
Mandibular plane angle (Steiner)
The mandibular plane is drawn between Go and Gn. The mandibular plane angle is formed between the mandibular plane and the anterior cranial base (S-N). Its mean is 32 degrees (Fig 2-51). This angle interprets the difference between anterior and posterior facial heights. Individuals with high mandibular plane angles tend to have Class II malocclusions, vertical maxillary excess, and anterior open bites. Patients with low mandibular plane angles tend to be vertically deficient and have deep bites.
Fig 2-51 Mandibular plane angle is formed by the intersection of the mandibular plane and the anterior cranial base (S-N).
SNA angle (Steiner)
The SNA angle is formed between the anterior cranial base (S-N) and a line drawn through N and A-point. Its mean is 82 degrees (Fig 2-52). The SNA angle gives an indication of the anteroposterior position of the maxilla relative to the anterior cranial base. An angle less than 82 degrees is indicative of maxillary anteroposterior deficiency, whereas an increased angle may indicate maxillary protrusion.
Fig 2-52 Steiner analysis for maxillary and mandibular anteroposterior positions relative to the anterior cranial base (S-N). SNA is 82 degrees. SNB is 80 degrees. The maxillomandibular relationship is indicated by the ANB angle (mean, 2 degrees).
SNB angle (Steiner)
The SNB angle is formed between the anterior cranial base (S-N) and a line drawn through N and B-point. Its mean is 80 degrees (see Fig 2-52). The angle gives an indication of the anteroposterior position of the mandible relative to the anterior cranial base. Patients with mandibular anteroposterior excess will have an angle greater than 80 degrees. Those with mandibular deficiency will have a decreased angle.
ANB angle (Steiner)
The ANB angle is formed between A-N and N-B. Its mean is 2 degrees (see Fig 2-52). The angle provides an idea of the anteroposterior discrepancy between the maxilla and the mandible. In Class III cases, the angle is less than 2 degrees or even negative; in Class II cases, the angle is increased.
In spite of its shortcomings, Steiner analysis continues to be a popular method of evaluating the anteroposterior relationship of the maxilla and mandible. However, this analysis should not be used to make an absolute diagnosis of sagittal skeletal disharmony because vertical and rotational jaw dimensions relative to the anterior cranial base often have a significant effect on the measurements (see the next section).
Wits appraisal
Most cephalometric analyses, like Steiner analysis, relate the maxillary and mandibular anteroposterior position to the cranium. Measurements from the cranial base, however, do not always provide a reliable expression of the anteroposterior relationship between the maxilla and mandible. The Wits appraisal is a linear measurement between the maxilla and mandible and is not influenced by the cranium.
Points BO and AO are established by dropping perpendicular lines from the A-point and B-point, respectively, onto the occlusal plane (Fig 2-53). The mean in males is BO 1 mm ahead of AO. In females, BO and AO coincide. The measurement between BO and AO indicates the anteroposterior discrepancy between the maxilla and the mandible. A small discrepancy may indicate that a patient can be treated orthodontically, whereas a large discrepancy may indicate that surgical correction will be required.
Fig 2-53 Wits appraisal. Vertical lines are drawn perpendicular to the occlusal plane (OP) from A-point and B-point. The points of contact on the OP are labeled AO and BO, respectively.
Clockwise or counterclockwise rotations of the maxillomandibular complex relative to the anterior cranial base do not affect the Wits appraisal measurements. However, these rotations significantly affect Steiner analysis. This is a good example of how two cephalometric analyses may render quite contradictory measurements; however, the observations assist in treatment planning. Figures 2-54a to 2-54c illustrate three cases with the same Wits measurements (0 mm) but ANB angles of +2, +8, and –2 degrees and very different facial profiles. Surgical rotation of the maxillomandibular complex may be indicated for correction in the cases depicted in Figs 2-54b and 2-54c. The case in Fig 2-54d has an ANB angle of –1 degree, indicating a mild Class III discrepancy between the jaws. The Wits appraisal for this case, however, is 8 mm, indicating a substantial jaw discrepancy; the patient could not be treated by orthodontic means alone.
Fig 2-54 The effect of rotation of the maxillomandibular complex relative to the anterior cranial base and the ANB angle. (a) Normal relation: ANB angle is +2 degrees. (b) Counterclockwise rotation resulting in an ANB angle of +8 degrees. (c) Clockwise rotation with an ANB angle of –2 degrees. In all three cases, the Wits appraisal (blue line) indicates a normal relationship (0 mm) between the maxilla and mandible. (d) An ANB angle of –1 degree indicates a mild Class III jaw relationship (Steiner). According to the Wits appraisal, the discrepancy between the maxilla and mandible is severe (8 mm).
Facial angle (Downs)
The facial angle is the inferior inside angle in which the facial line (N-Pog′) intersects the FH. Its mean is 82 to 95 degrees (Fig 2-55). The facial angle indicates the relative anteroposterior position of the mandible to the cranium.
Fig 2-55 Facial angle. The mean is 82 to 95 degrees.
Maxillary depth (McNamara)
The maxillary depth is the horizontal distance between N and A-point. It is calculated by drawing a line through N perpendicular to FH until A-point is reached (Fig 2-56). Its mean is 0 mm. A-point is expressed as a positive value anterior to the line and as a negative value posterior to the line. The maxillary depth is an indication of the anteroposterior position of the maxilla in relation to the cranium.
Fig 2-56 Maxillary depth. A line is drawn through N perpendicular to FH. A-point (maxillary position) is expressed as positive anterior to the line and as negative posterior to the line.
Anteroposterior and vertical relationships (McNamara)
The lower anterior facial height is measured from ANS to Me, and the midfacial length is measured from Co to A-point. The distance from Co to Gn constitutes the mandibular length (Fig 2-57). There should be a correlation between the lower anterior facial height (ANS-Me), the length of the midface (Co-A), and the mandibular length (Co-Gn). The correlations are listed in Table 2-11.
Fig 2-57 Lower anterior facial height: ANS-Me. Midfacial length: Co-A. Mandibular length: Co-Gn.
Table 2-11 | Normative standards (mm) in McNamara analysis
| Midfacial length (Co-A) | Mandibular length (Co–Gn) | Lower anterior facial height (ANS–Me) |
| 80 | 97–100 | 57–58 |
| 81 | 99–102 | 57–58 |
| 82 | 101–104 | 58–59 |
| 83 | 103–106 | 58–59 |
| 84 | 104–107 | 59–60 |
| 85 | 105–108 | 60–62 |
| 86 | 107–110 | 60–62 |
| 87 | 109–112 | 61–63 |
| 88 | 111–114 | 61–63 |
| 89 | 112–115 | 62–64 |
| 90 | 113–116 | 63–64 |
| 91 | 115–118 | 63–64 |
| 92 | 117–120 | 64–65 |
| 93 | 119–122 | 65–66 |
| 94 | 121–124 | 66–67 |
| 95 | 122–125 | 67–69 |
| 96 | 124–127 | 67–69 |
| 97 | 126–129 | 68–70 |
| 98 | 128–131 | 68–70 |
| 99 | 129–132 | 69–71 |
| 100 | 130–133 | 70–74 |
| 101 | 132–135 | 71–75 |
| 102 | 134–137 | 72–76 |
| 103 | 136–139 | 73–77 |
| 104 | 137–140 | 74–78 |
| 105 | 138–141 | 75–79 |
Maxillary-mandibular anteroposterior relationship (McNamara)
The clinician should be aware that in McNamara analysis, the effective lengths of the midface and the mandibular length are related and are expressed as small, medium, and large. The maxillomandibular differential is determined by subtracting the midfacial length from the mandibular length. In small individuals (mixed dentition stage), the difference should be 20 to 23 mm. In medium-sized individuals, there should be a difference of 27 to 30 mm, and in large individuals, the difference should be 30 to 33 mm (Fig 2-58).
Fig 2-58 Maxillomandibular anteroposterior relationship. The maxillomandibular differential of 24 mm shown here would be ideal for a small to medium individual. The maxillomandibular ratio of 1:1.24, however, indicates a discrepancy in the relationship between the jaws. According to McNamara’s normative standards (see Table 2-11), a midfacial length of 97 mm would be better related to a mandibular length of 126 to 129 mm. This may indicate a slight anteroposterior deficiency of the mandible.
The graph in Fig 2-59 illustrates the relationship between midfacial length, mandibular length, and lower anterior facial height. A discrepancy greater or smaller than the normative values would indicate a disharmonious relationship between the maxilla and mandible. Alternative analysis should be used to identify which jaw is at fault. The midfacial length is measured from Co to A-point, whereas the mandibular length is measured from Co to the anatomical Gn. The linear relationship between the midfacial length and the length of the mandible is called the ratio of effective maxillary to mandibular length. Any specific maxillary (midfacial) length will correspond to a specific mandibular length within a given range (see Table 2-11). The normal adult ratio should be maxilla (Co-A) to mandible (Co-Gn) = 1:1.3.
Fig 2-59 The relationship between midfacial (maxillary) length and mandibular length is generally linear and dependent on size rather than on age or sex. An individual with a maxillary length of 100 mm should have an effective mandibular length of 130 mm. The difference between the maxillary and mandibular lengths in this instance would be 30 mm. (Adapted from McNamara and Brudon, 1993, with permission).
During normal growth, the ratio decreases from 1:1.25 for an 8-year-old child to the adult value. The effective mandibular length increases faster than the length of the maxilla, at the rate of 0.005 mm per year (ratios of 1:1.26 at 10 years of age, 1:1.27 at 12 years, 1:1.28 at 14 years, and 1:1.29 at 16 years). The clinician should be aware that a change in this value may indicate disproportionate growth, but it does not indicate which jaw is at fault.
The esthetic effect of the effective maxillary and mandibular lengths is closely related to the anterior facial height and, therefore, the angle formed between A-point, Co, and Gn. This angle normally decreases as an individual ages (Fig 2-60).
Fig 2-60 The esthetic effect of the change in lower anterior facial height and backward (a) and forward (b) rotation of the chin. In both a and b, the midfacial lengths (97 mm) and mandibular lengths (121 mm) are the same. In a, the lower anterior facial height (ANS-Me) is 78 mm, whereas in b, it is 60 mm. The angle between Co-A and Co-Gn is 35 degrees in a but 25 degrees in b.
Skeletal anteroposterior relationships are summarized in Table 2-12.
Table 2-12 | Summary of skeletal anteroposterior relationships
| Anteroposterior relationship | Normal value | |
| Maxilla | To anterior cranial base (SNA) To mandible (ANB) To mandible (Wits appraisal) Maxillary depth: A-point to N perpendicular to FH To mandibular length: Co-A:Co-Gn | 82 degrees 2 degrees AH 1 mm behind BO (males) AO and BO coincide (females) 0 mm 1:1.3 |
| Mandible | Mandibular plane angle S-N to Go-Gn To anterior cranial base (SNB) To maxilla (ANB) To maxilla (Wits appraisal) To maxillary length: Co-Gn:Co-A | 32 degrees 80 degrees 2 degrees BO 1 mm ahead of AO (males) BO and AO coincide (females) 1.3:1 |
Skeletal vertical relationships
Midface to lower face skeletal height
Skeletal vertical relationships are measured from N to ANS and from ANS to Me. A vertical line is drawn perpendicular to the FH anterior to the face. In turn, perpendicular lines are drawn to the vertical line from N, ANS, and Me, and the distance is measured from N to ANS and from ANS to Me (Fig 2-61). The normal values are 53 mm from N to ANS and 65 mm from ANS to Me. However, the relationship between the vertical heights is more important than the measurement. A ratio of 5:6 is normal. In most individuals with vertical dentofacial deformities, the lower measurement (ANS-Me) will be affected, which in turn will affect the relationship with the upper measurement (N-ANS). The ANS-Me distance will be increased in individuals with vertical maxillary excess, vertical mandibular excess, and open bites. The lower measurement (ANS-Me) will be decreased in individuals with vertical maxillary deficiency, closed bites, deep bites, and vertical mandibular deficiency.
Fig 2-61 Midface and lower face skeletal heights. N-ANS:ANS-Me = 5:6.
Analysis of dental relationships
Maxillary incisor evaluation
Maxillary incisor position
Steiner analysis. According to the Steiner analysis, the relative location of the maxillary incisor is determined by relating the angulation of the incisor to the N-A line. The most anterior point of the maxillary incisors should be 4 mm ahead of N-A, with an axial inclination of 22 degrees to this line (Fig 2-62a).
Fig 2-62 (a) Maxillary incisor position (Steiner): 22 degrees to N-A, 4 mm ahead of N-A. (b) An alternative measurement of maxillary incisor angulation. The angle between the cranial base (S-N) and maxillary incisor (apex to incisor tip) should be 106 ± 4 degrees.
The linear relationship of the incisor tip to N-A provides information on the anteroposterior position of the incisor to the maxilla, but not to the entire facial complex. In orthognathic cases, this measurement can be helpful in determining the preoperative positioning of the tooth if the relation of the maxilla to the cranial base is also considered. In individuals with dentofacial deformities, the N-A line is often not a reliable basis to assess the incisor position because of the skeletal disharmony between cranial base and maxilla. In these cases, a vertical line through A-point should be substituted for N-A (Fig 2-62b). A helpful additional measurement is the angulation between a line through the maxillary incisor (apex to incisor tip) and a line through the anterior cranial base (S-N), which should be 106 ± 4 degrees (see Fig 2-62b).
Fig 2-63 Maxillary incisor position (McNamara). The labial surface of the incisor should be 4 to 6 mm ahead of the vertical line through A-point.
McNamara analysis. An important relationship, especially in orthognathic patients, is that of the incisors to the underlying basal bone of each jaw. In the McNamara analysis, the position of the maxillary incisors to their respective bone bases is determined by drawing a vertical line through A-point parallel to N and perpendicular to FH. The facial surface of the maxillary incisor should be 4 to 6 mm ahead of the line (Fig 2-63).
In maxillary dental protrusion cases, the incisor will be more than 6 mm ahead of the vertical line through A-point and will be an indication for orthodontic retraction. Where the maxillary incisors are upright (eg, in Class II, division 2 malocclusions), the incisor tip will be less than 4 mm ahead of this line or may be even behind it.
Mandibular incisor evaluation
Mandibular incisor position
Steiner analysis. The relative location of the mandibular incisors is determined by its relation to the N-B line (Fig 2-64). According to the Steiner analysis, the mandibular incisor angulation to the N-B line should be 25 degrees, and the most labial portion of the tooth crown should be 4 mm anterior to the line. However, the N-B line often is not reliable to assess the mandibular incisor position in patients with dentofacial deformities because of a lack of harmony between the mandible and the cranial base.
Fig 2-64 Mandibular incisor position (Steiner): 25 degrees to N-B line, and 4 mm ahead of N-B.
The angular and linear measurements give an indication of the relationship of the mandibular incisors to the mandible. In individuals with Class III malocclusions and compensated incisors, the angle will be smaller and the incisor tip closer to the N-B line or even behind it. Protrusive incisors would produce a larger angle, and the labial surface would be more than 4 mm ahead of N-B. These measurements can also serve as a guide in planning for extractions and preoperative orthodontic positioning of the mandibular incisors.
McNamara analysis. As in the maxilla, in the mandible, it is important to determine the relationship of the mandibular incisors to the mandibular bony base. According to the McNamara analysis, the labial surface of the mandibular incisors should be 4 mm ahead of a true vertical line drawn through the B-point and at an angle of 25 degrees to the line (Fig 2-65a).
Fig 2-65 (a) Class I occlusion; incisor to vertical line through B-point: 4 mm and 25 degrees. (b) Class II malocclusion with mandibular incisor protrusion; incisor to vertical line through B-point: 11 mm and 42 degrees. (c) Class III malocclusion with compensated mandibular incisors; incisor to vertical line through B-point: 2.5 mm and 10 degrees.
An increase in this measurement indicates mandibular dental protrusion. In some racial groups, this measurement may be normal, but in Caucasians, it is often seen in Class II malocclusion with mandibular skeletal deficiency (Fig 2-65b). In Class III dental and skeletal relationships, the mandibular incisors are often compensated and are closer to this line or even behind it (Fig 2-65c).
Downs analysis. According to the Downs analysis, the ideal inclination of the long axis of the mandibular incisors to the mandibular plane is 90 ± 7 degrees (Fig 2-66). In individuals with Class III malocclusion and compensated mandibular incisors, this angle tends to be small. It tends to be larger when the lower incisors are protrusive (eg, in bimaxillary protrusion or Class II, division 1 malocclusion).
Fig 2-66 Mandibular incisor position (Downs). The axial inclination of the mandibular incisor to the mandibular plane (Go-Gn) is 90 ± 7 degrees.
Interincisal angle (Downs)
The interincisal angle is formed by a line through the incisal edge and the apex of the root of the maxillary and mandibular central incisors (130 ± 6 degrees; Fig 2-67). The more protrusive the incisors, the smaller the angle. Low angles indicate protrusion of the incisors and are often associated with Class II, division 1 malocclusions. High angles are frequently associated with Class II, division 2 deep bites.
Fig 2-67 Interincisal angle.
Maxillary molar to pterygoid vertical (Ricketts)
The distance from the pterygoid vertical (back of the maxilla) to the distal surface of the maxillary first molar (Fig 2-68) should be equal to the patient’s age + 3 mm. The distance will increase as the maxilla grows forward. For example, a 12-year-old child has a normal distance of 15 mm; an 18 year-old adult, 21 mm. It stabilizes at 24 mm in the adult, around age 21. This measurement helps determine whether a malocclusion is due to the maxillary or mandibular molar position. It is also useful in deciding whether extractions or headgear may be indicated and is indicative of the anteroposterior position of the maxilla. A small value indicates that the molar is too far distal, and thus headgear and distalization should be avoided; large values indicate the opposite. This measurement is influenced by previous maxillary tooth extractions allowing mesial drifting of the molar.
Fig 2-68 Maxillary molar position. The distance from Ptv to the first molar should be the patient’s age + 3 mm.
Mandibular anterior dental height
The mandibular anterior dental height is measured from the mandibular incisor tip to the inferior border of the mandible. The average mandibular dental height is 44 ± 2 mm for males and 40 ± 2 mm for females (Fig 2-69). An increase in the mandibular vertical height of the face of a patient with normal upper lip length and normal maxillary incisor exposure may be caused by the anterior vertical height of the mandible. In this patient, vertical reduction genioplasty may be indicated.
Fig 2-69 Mandibular anterior dental height: 44 ± 2 mm for male patients and 40 ± 2 mm for female patients.
Occlusal plane angle
According to the Steiner analysis, the occlusal plane angle is formed between a line drawn through the region of the overlapping cusps of the first premolar and first molar bisecting the incisal overbite (the occlusal plane [OP]) and the anterior cranial base (S-N). The mean angle is 14 degrees (Fig 2-70). According to the Downs analysis, the angle is measured between the occlusal plane and the FH plane and should be 9 degrees.
Fig 2-70 Occlusal plane angle. Angle between OP and anterior cranial base (S-N).
The occlusal, palatal, and mandibular plane angles are often used in describing an individual as “high angle” or “low angle.” High-angle individuals tend to have relatively long anterior facial heights, whereas low-angle individuals tend to have vertically short anterior facial heights.
The numeric values of tooth positions given in Table 2-13 should be considered a guide to diagnosing abnormal tooth positions and to determining final dental, skeletal, and soft tissue positions. The clinician must subjectively evaluate the positioning of the teeth to determine whether they are positioned in the central trough of bone.
Table 2-13 | Summary of dental relationships
| Dental relstionship | Normal value | |
| Maxillary incisor | Angle to N-A Distance to N-A Distance to A-point vertical | 22 degrees 4 mm ahead 4 to 6 mm ahead |
| Mandibular incisor | Angle to N-B Distance to N-B Distance to B-point vertical Angle to mandibular plane | 25 degrees 4 mm ahead 4 mm ahead 90 ± 7 degrees |
| Interincisal angle | Maxillary to mandibular incisor | 130 ± 6 degrees |
| Maxillary first molar | Molar to Ptv | Patient's age + 3 mm in growing individuals |
| Mandibular anterior dental height | Incisor tip to mandibular border | 44 + 2 mm (males) 40 + 2 mm (females) |
| Occlusal plane angle | Occlusal plane to S-N Occlusal plane to FH | 14 degrees 9 degrees |
Posteroanterior Cephalometric Radiographic Evaluation
In addition to lateral cephalometric radiography, individuals with facial asymmetry require posteroanterior radiographic evaluation of the facial bones. It would certainly be advantageous to obtain a CBCT image or multislice CT to facilitate virtual treatment planning (Fig 2-71). CBCT allows images to be obtained with the patient in a standing or seated position with the teeth in the preferred occlusion and the soft tissue in repose. As always, accurate image acquisition also applies here. Multislice CT scanning is performed with the patient in supine position, which will inherently falsify the 3D facial soft tissue mask of the patient, and gravity may distort the facial soft tissue in this position and interfere with the accuracy of the image. Also, careful attention should be paid to the wax-bite or registration device so the lip position or morphology will not be disturbed when taking a CT scan. (See “Virtual Surgical Planning” in chapter 3.)
Fig 2-71 The 3D CT scanned image of a patient with hemifacial microsomia. The skeletal asymmetry and agenesis of the left mandibular ramus and condyle is clearly demonstrated and allows for accurate virtual treatment planning.
Hard tissue cephalometric landmarks
Posteroanterior hard tissue landmarks, shown in Fig 2-72, include the following:
Fig 2-72 Posteroanterior hard tissue cephalometric landmarks.
Spheno-frontal (SF) point: Where the smaller wing of the sphenoid bone crosses the medial orbital ridge
ANS: The center point at the base of the nose
Jugulare (J): The most superior and medial point on the zygomatic buttress
Mastoid (M): The most inferior point on the mastoid bone
A: The contact area between the maxillary incisors. Note: This is distinct from A-point.
B: The contact area between the mandibular incisors. Note: This is distinct from B-point.
Y: The most lateral point on the buccal surface area of the first maxillary molar (YL on the left and YR on the right)
Z: The most lateral point on the buccal surface area of the first mandibular molar (ZL on the left and ZR on the right)
Go: The most inferior posterior point at the angle of the mandible
Me: The most inferior point at the anterior mandibular area
CH: The most inferior lateral point on the anterior inferior border of the mandible (CHL on the left and CHR on the right)
Transverse posteroanterior cephalometric planes
Transverse posteroanterior cephalometric planes, shown in Fig 2-73, include the following:
Fig 2-73 Transverse posteroanterior and vertical planes. (1) Cranial base plane. (2) Mastoid plane. (3) J-plane. (4) Occlusal plane. (5) S-plane. (6) Chin plane.
Cranial base plane (C-plane): A horizontal line connecting the left and right SF points and extending laterally to the cranium
Mastoid plane (D-plane): A line connecting the left and right mastoid points
S-plane: The connecting line between the left and right Go of the mandible
J-plane: A line drawn from the left J-point to the right J-point, which is divided into two halves (IR and IL) by the geometrically constructed vertical axis (GM)
Occlusal plane: A plane formed by a line connecting the occluding points of the maxillary and mandibular buccal cusps left and right
Chin plane (CHP): A line drawn on the inferior border of the chin at maximum bone contact, through Me
Vertical posteroanterior cephalometric line
The vertical cephalometric line is called the geometrically constructed vertical axis (GM; see Fig 2-73). It is constructed by dividing the C-plane and the D-plane, connecting these two midpoints, and extending this line to the chin.
Triangular analysis
Triangles are constructed for evaluation of the symmetry of the maxilla, mandible, and chin. The maxillary triangle is constructed by connecting the midpoint of the C-plane (C-point) with points J on either side of the GM. These connecting lines are called the HR line and the HL line. The base of the triangle is divided in two halves, IR and IL, by GM (Fig 2-74a).
Fig 2-74 (a) Maxillary triangle. (b) Mandibular triangle. (c) Chin triangle and vertical line through B-point perpendicular to CHP.
The mandibular triangle is constructed by connecting C-point with Go bilaterally using lines PR and PL. The base of the mandibular triangle is halved into SR and SL by GM (Fig 2-74b).
The chin triangle is constructed by connecting the C-point with CHR and CHL; the long legs of the triangle are called KR and KL. A line is drawn from B-point perpendicular to CHP to evaluate the mandibular incisor midline in relation to the midline of the chin. The base of this triangle is divided into two halves, GR and GL, by GM (Fig 2-74c).
By measuring the long legs of the triangles, cants in the maxilla, mandible, and chin can be evaluated in relation to the cranial base, as well as to each other. By comparing the left and right sides of the bases of the triangles, transverse discrepancies on rotations can be assessed. Midline asymmetries of the nasal spine, Me, and dental midlines can be evaluated. Any discrepancy between the mandibular dental midline and the midpoint of the chin can be evaluated by the vertical line perpendicular to CHP (see Fig 2-74c).
Vertical and transverse dentoalveolar assessment
The vertical relationship between the basal bones and the dental and alveolar structures is evaluated by dropping perpendicular lines from the J-plane at YR and YL to the occlusal plane and from the S-plane to the occlusal plane at ZR and ZL. Transverse discrepancies are assessed by measuring the distances both from YR and YL and from ZR and ZL to the GM line. Vertical discrepancies are assessed by measuring the vertical heights from the J-plane to the occlusal plane, comparing left and right side heights. Mandibular dentoalveolar vertical discrepancies can be examined by measuring the vertical heights from the occlusal plane to the S-plane at ZR and ZL (Fig 2-75).
Fig 2-75 Vertical dentoalveolar assessment.
The posteroanterior cephalometric analysis is helpful in assessing facial asymmetry. Also, in combination with the lateral cephalometric analysis, it gives the clinician a better dimensional understanding of dentofacial deformities. The lateral and posteroanterior cephalometric analyses of an individual with severe facial asymmetry involving the maxilla, mandible, and chin are demonstrated in Fig 2-76.
Fig 2-76 (a) Severe facial asymmetry. Note the severe rotation of the triangles. (b) The severe asymmetry is also evident on the lateral cephalometric tracing. The 3D nature of the facial asymmetry, a common finding in such cases, is well demonstrated.
Limitations of Cephalometric Analysis
Although cephalometric analysis is important in both diagnosis and development of a treatment plan, it has the following limitations:
Most individuals with dentofacial deformities have anatomical variations in the location of the cephalometric landmarks used as a baseline in many analyses, such as S, N, and Or. These anatomical variations often lead to incorrect conclusions from the analysis.
The clinician must not base interpretations on single cephalometric measurements.
The clinician must recognize the limitations as well as the advantages of cephalometry and be sure to integrate measurements with clinical findings.
The art of cephalometric interpretation lies in understanding abnormal findings and identifying the etiologic factors behind these cephalometric abnormalities in patients with dentoskeletal deformities.
Although cephalometric analysis forms an important part of the database for diagnosis and treatment planning, it should not take precedence over the clinical evaluation of the patient.
Full-Mouth Periapical Radiographic Evaluation
If a patient has any indication of periapical or periodontal pathology and/or dental caries, periapical radiographs should be taken to obtain a more detailed understanding of the pathologic condition. Periapical radiography can also more accurately assess the deviation of roots in areas of intended interdental osteotomies.
Panoramic Radiographic Evaluation
Panoramic radiography is an excellent means to establish an overview of the paranasal sinuses, bony temporomandibular joint (TMJ), periapical and periodontal pathology, dental caries, position of the inferior alveolar canal, position of the lingula, position of the mental foramen, tooth root lengths in relation to the maxillary sinus, and mandibular symphysis. Any suggestion of temporomandibular pathology should be further investigated by more specific radiographic examination. In addition, the panoramic radiograph can detect root deviations in areas of intended interdental osteotomies (although not as accurately as can a periapical radiograph), unerupted and/or impacted teeth, and previously undetected pathologic conditions. The information obtained is valuable not only in the pretreatment assessment but also in the determination of the relative position of anatomical structures, which is important during the actual surgical procedure. Figure 2-77 shows a panoramic radiographic evaluation form. It is essential that an immediate preoperative panoramic radiograph is available at the time of surgery because it gives the surgeon a valuable overview of anatomical structures relevant in most orthognathic surgical procedures (eg, position of the inferior alveolar canal, mental foramen, tooth roots, impacted third molars [if present], and maxillary sinuses).
Fig 2-77 Panoramic radiographic evaluation form. This evaluation should be used during the pretreatment assessment, at the presurgical examination, and at the time of surgery.
Occlusion and Study Cast Evaluation
Occlusal functional evaluation
The basic aims of occlusal functional evaluation are to determine the compatibility of centric occlusion (CO) and centric relation (CR); to note the difference between CO and CR, if present; to note any bite of convenience or occlusal slide; and to note interocclusal rest space. Figure 2-78 is a sample functional evaluation form.
Fig 2-78 Functional evaluation form.
Study cast analysis
Intra-arch relationship
In the study cast analysis, arch form and symmetry, missing teeth, tooth rotations, and overerupted teeth are noted. Maxillary and mandibular occlusal curves are studied. Crowding and the need for extractions are determined. Bolton discrepancies of tooth sizes are studied. Any tooth size discrepancies should be noted and compensated for during the preoperative orthodontic treatment stage. Tooth size discrepancy influences arch compatibility and leads to poor occlusal fit at surgery.
Interarch relationship
The study cast analysis also includes examination for incisor overjet and overbite, as well as Angle classification for molars and canines. The clinician evaluates coordination of dental midlines and crossbites while moving the dental casts into a Class I malocclusion to get an idea of general arch compatibility.
If the possibility of establishing an acceptable occlusion, accommodating the teeth, or providing for tooth size discrepancies is at all questionable, a Kesling diagnostic setup should be used. This setup also can be used to test for various extraction patterns.
If a crossbite exists with the teeth in CO and it is corrected when the dental casts are moved into a Class I occlusion, the crossbite is considered relative. If the crossbite still exists after the dental casts have been positioned in a Class I relationship, the crossbite is considered absolute (see chapter 5, Fig 5-38).
A sample form for study cast analysis is presented in Fig 2-79.
Fig 2-79 Study cast analysis form.
TMJ Evaluation
The TMJ is an important component of the orthognathic mechanism and should be examined with care. Pathologic conditions may be present in the joint at the outset, may develop during treatment, or may even develop long after treatment. Therefore, the clinician should diagnostically and prognostically evaluate the joint before orthodontic-surgical treatment begins. A basic TMJ examination evaluates three areas: (1) mandibular movements, (2) TMJ signs and symptoms, and (3) mouth opening and deviations.
Careful documentation of TMJ pretreatment status is very important (Fig 2-80). The correct positioning of the condyle in the fossa is a critical aspect of the orthognathic surgical procedure, and information gathered at the pretreatment evaluation may be useful during surgery. The patient should also understand that correction of the dentofacial deformity and malocclusion will not necessarily correct a TMJ problem. Some clinicians believe it to be advantageous to perform TMJ surgery and orthognathic surgery simultaneously.
Fig 2-80 TMJ evaluation form.
According to an evidence-based systematic review of temporomandibular dysfunction, Rinchuse and McMinn came to the following conclusions:
There is evidence-based support for the use of occlusal splints and biofeedback to treat temporomandibular joint disorders (TMDs).
There is no evidence supporting the treatment of TMDs by occlusal adjustments in orthodontic patients.
Occlusion, which was once considered to be the primary and sole cause of TMDs, now is only recognized as having a secondary role in causing it (if any role at all).
Orthodontic treatment to improve the occlusion does not cause TMDs.
Several clinicians studied the effect of orthognathic surgery on patients with signs and symptoms of TMDs. When comparing and contrasting their findings, some observations can be made (Onizawa et al 1995, Panula et al 2000, Dervis et al):
Patients scheduled for orthognathic surgery did not have significantly different TMD signs and symptoms than patients in the control group.
TMD signs and symptoms frequently improved in patients following orthognathic surgery.
Not all TMD patients improved following orthognathic surgery. For some patients, the signs and symptoms got worse.
Masticatory muscle and joint tenderness frequently improved following orthognathic surgery.
In most patients, the maximum mouth opening decreased following orthognathic surgery; however, this was clinically insignificant.
Airway Considerations in Orthognathic Surgery
It has been estimated that anywhere between 9% to 24% of men and 4% to 9% of women between the ages of 30 to 60 years are affected by obstructive sleep apnea (OSA). It is further estimated that 80% to 90% of those affected remain undiagnosed. Though, historically, cephalometric evaluations and clinical evaluations have been relied on in treatment planning for corrective jaw surgery with an end result of dental stability, skeletal stability, and a pleasing esthetic outcome, the impact on the airway must now be factored in for all treatment plans. Orthognathic surgery can either dramatically improve the airway or potentially compromise it.
Features of patients with compromised airways include those with maxillary and/or bimaxillary retrusion, lower facial height, large tongue, elongated soft palate, inferior hyoid position, and those who tend to have a head-up posture in an effort to dilate the airway in addition to one of these other symptoms (Fig 2-81).
Fig 2-81 (a) Note short chin-throat length (1), narrow oropharyngeal airway (2), and mandibular retrusion (3) and large distance from hyoid cartilage to mandible (4) in a patient with an obstructed airway. (b) CBCT scan shows significant narrowing at the base of the tongue in the naso and oropharynx region (arrows). The patient’s head is up here, but a head-down position results in near complete obstruction.
Individuals with high mandibular plane angles in addition to steep occlusal planes are often accompanied by a skeletal Class II pattern. However, it is possible to have a skeletal Class III high-angle skeletal structure with a short chin-throat dimension that may also present with a narrow oropharyngeal airway dimension (Fig 2-82). Lateral cephalometric analysis has been the most widely reported in the literature for evaluating the posterior airway space (PAS); however, an intraoperative fiber-optic pharyngoscopy can be used as well. With the prevalence of CBCT scanning, volumetric area measurements are possible, and these can also be correlated with compromised airways.
Fig 2-82 Patients with a high mandibular plane and Class III malocclusion often have good chin projection but narrowed airways (arrow). Linear movements can exacerbate airway problems, especially with the mandible moving backward along a steep occlusal plane.
Landmarks and measurements
Cephalometric airway analysis reveals that the soft palate anteroposterior (AP) dimension in a normal individual is approximately 10.0 mm. A retrognathic patient will have 7.4 mm of PAS, and a prognathic patient will typically have 12.5 mm or more. The dimensions of the tongue base are 11.0 mm, 8.3 mm, and 12.8 mm, respectively, for normal, retrognathic, and prognathic patients. Early studies indicate that a PAS less than 11.0 mm and a mandibular plane to hyoid distance of greater than 15.4 mm was associated with OSA. Those with a posterior airway space of less than 5.0 mm and a hyoid distance of greater than 24.0 mm tended to demonstrate the worst respiratory deficiencies. Recent studies disputed this and indicated that no one skeletal or soft tissue parameter can be directly linked to OSA; however, it is important that one pay close attention to airway dimensions so that treatment planning can be used to achieve positive effects on the airway, if warranted, or to at least minimize the effects of surgical movements.
Important cephalometric landmarks to be mindful of are the potential changes in the vertical and AP positions of the PNS and D-point (Fig 2-83). Recent studies have demonstrated that significant airway volume changes occurred when PNS moved vertically and D-point (which essentially corresponds to the genial tubercles) moved in a horizontal or an upward vertical direction. The data further indicated that there was an increase or decrease of 2% of the total airway volume for every millimeter of directional change in these points. Furthermore, certain vertical and horizontal movements tend to impact various areas of the airway differently. When PNS was moved inferiorly, the oropharynx tended to have a smaller total volume; however, the nasopharynx enlarged. If PNS moved superiorly, then airway volume increased, but it was at the expense of the nasopharyngeal airway; when the airway lengthened, the nasopharyngeal airway narrowed as a result. With this in mind, one needs to be cautious with maxillary movements that result in the PNS moving upward. These should be offset with advancement of both jaws to promote airway increases as well as increases in the minimal cross-sectional area. Simple autorotation of the mandible after a posterior impaction of the maxilla is not nearly as predictable relative to its impact on improving the airway as is a mandibular advancement in the correction of the skeletal Class II malocclusion. Therefore, it may be strongly considered that both jaws be surgically corrected in patients with airway issues.
Fig 2-83 Important anatomical landmarks when treatment planning include the PNS and D-point, which corresponds to the approximate position the genioglossal tubercles though centered in the symphysis (arrows). Movement of PNS downward and D-point upward and forward have positive effects on airway volume.
Vertical movements of the genial tubercles, or D-point, significantly affect the oropharyngeal airway in total airway volume, largely due to the positional changes of the suprahyoid musculature. It appears, however, that more sagittal movements of D-point have the greatest impact on Class II patients, and vertical movements have the greatest impact on Class III patients. With these changes in mind, it is important that the surgeon’s treatment plan take into consideration the skeletal geometry of their movements and how they will affect the airway. According to Steiner, a mandibular plane angle of 32 degrees (SN-mandibular plane; see Fig 2-51) is considered normal. As an example, a high angle (> 40 degrees) Class II malocclusion is best treated from an airway standpoint, with a counterclockwise rotation of the maxillomandibular complex, because this results in all of the favorable skeletal movements that have been shown to increase airway volume and minimal cross-sectional area, namely movement of PNS downward and D-point forward and upward (Fig 2-84).
Fig 2-84 This patient had severe OSA. (a) Presurgical frontal view. (b) Presurgical profile view. (c) Presurgical occlusion. (d) The surgical plan consists of a large counterclockwise rotational advancement, closing the open bite in the mandible. (e and f) CBCT images confirm marked airway compromise. (arrows). (g and h) The upward and forward movement of the mandible restulted in significant postsurgical facial and skeletal changes. (i and j) The postoperative CBCT scans confirm a significant improvement in the airway anatomy (arrows).
Class II patients
Some amount of maxillary advancement is often incorporated. Two-jaw surgery in Class II patients has a predictable improvement in the airway when the mandible is advanced. This improvement is even more pronounced when both jaws come forward or are rotated in a counterclockwise direction. (Chapter 3 discusses these treatment planning concepts in more detail.) In patients with Class II skeletal deformities, orthognathic surgery is used both to give the patient a better esthetic appearance and to alleviate airway concerns from a retrognathic mandible. Hernández-Alfaro et al (2011) performed a study on this topic. A retrospective evaluation of 30 patients who underwent maxillomandibular advancement, maxillary advancement, or mandibular advancement was performed. Three groups of 10 subjects each were established: group 1, bimaxillary surgery (Le Fort I maxillary osteotomy and mandibular bilateral sagittal split osteotomy with maxillomandibular advancement); group 2, maxillary advancement (Le Fort I maxillary osteotomy); and group 3, mandibular advancement (bilateral sagittal split osteotomy). Pre- and postoperative CBCT scans were taken in each case, and the changes in pharyngeal airway volume were compared.
A statistically significant increase in the pharyngeal airway volume occurred systematically. The average percentage of increase was 69.8% in group 1 and 78.3% in group 3. Group 2 exhibited a lower magnitude of increase (37.7%).
Class III patients
Class III patients are far more complicated because the skeletal deformity may have a mixed nature. In addition, the situation might include isolated maxillary hypoplasia, isolated mandibular hypoplasia, or a combination of maxillary hypoplasia and mandibular hyperplasia. The goal of a recent study by Rosário et al (2016) was to investigate whether advancement of the maxilla alone would affect the volume of the upper airway. CBCT scans were taken before and after surgery in 14 patients with a Class III skeletal deformity undergoing maxillary advancement exclusively. The effects of the procedure led to a mean increase in volume of 3.22 cm3. Patient age and sex were not factors in the results.
As one might expect, mandibular setback surgery demonstrates a decrease in airway volume. In a study by Tselnik and Pogrel (2000), 14 patients had their pharyngeal airway space evaluated after mandibular setback surgery. Lateral cephalograms were obtained before surgery, immediately after surgery, and at long-term follow-up between 6 months and 2 years. The mean setback distance was 9.7 mm, which resulted in a long-term mean decrease in tongue base to posterior pharyngeal wall length of 4.77 mm. The area of the pharyngeal airway space decreased long-term an average of 1.52 cm2. It was observed that outcome measurements increased at the immediate postoperative radiograph before decreasing at the long-term follow-up radiograph. This was thought to be from forward movement of the hyoid bone after surgery to preserve airway opening in the immediate postoperative period to prevent airway collapse. It is clear that individuals with short necks, obese individuals, or those with large tongues who have mandibular setbacks may be predisposed to the development of OSA, and patient selection should be carefully managed when planning isolated mandibular surgeries in those populations.
Given that there is improvement in the airway with isolated maxillary advancement and worsening of the airway dimensions with isolated mandibular setback, the better approach is strong consideration for two-jaw procedures. A small amount maxillary advancement can be effectively used to mitigate the negative impact of the mandibular setback. With that in mind, the authors rarely perform isolated mandibular procedures but instead opt for isolated maxillary advancement in those that can esthetically tolerate the surgical movement or a two-jaw procedure in those Class III patients who cannot.
Class III patients with normal mandibular plane angles can often be treated with linear movements. Class III patients with a high or low mandibular plane angle malocclusion can be more complicated and often require rotational movements. Low-angle (SN-mandibular plane < 22 degrees; see Fig 2-51) Class III patients often have overprojected chins due to vertical deficiency and/or overclosure. High-angle Class III patients, on the other hand, often have a short chin-throat dimension but a well-shaped chin. This scenario of course can lead to inadequate skeletal support for the airway. Low-angle Class III patients esthetically benefit from clockwise movements to deemphasize the chin and magnify the movement of the midface, but high-angle Class III patients often benefit esthetically from counterclockwise movements. Though this sounds counterintuitive, a counterclockwise rotation point around the incisors or B-point results in minimal chin movement and proportionately more posterior incisor movement. The D-point is often superior movement, which has a very positive effect on airway dimensions (Fig 2-85).
Fig 2-85 Patients with high mandibular plane angle Class III occlusion treated with counterclockwise rotation of the maxillomandibular and advancements benefit because the D-point moves upward and forward, the incisors move backward, and the airway is enhanced. Presurgical (a) and postsurgical (b) CBCT scans demonstrate the advantage of this approach (red rectangles).
Orthognathic surgery can impact the airway whether or not a patient has OSA, so the changes in the airway must be carefully considered during treatment planning.
Conclusion
Generations of surgeons have focused mainly on the original three pillars of orthognathic surgery treatment planning: dental decompensation and stability, skeletal correction and stability, and a pleasing esthetic outcome. Now there is a fourth pillar of treatment planning: providing skeletal support of the airway and surgical movements that enhance the airway or at least mitigate any deleterious effects.
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