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Introduction to the Use of Cephalometrics

Katherine Kula, MS, DMD, MS Ahmed Ghoneima, BDS, PhD, MSD

Cephalometrics refers to the quantitative evaluation of cephalograms, or the measuring and comparison of hard and soft tissue structures on craniofacial radiographs. It is an evolving science and art that has been woven into orthodontics and the treatment of patients. Cephalograms are an integral part of orthodontic records and are typically used for almost all orthodontic patients. The cephalometric analysis or evaluation helps to confirm or clarify the clinical evaluation of the patient and provide additional information for decisions concerning treatment.

The American Association of Orthodontists (AAO) developed the current Clinical Practice Guidelines for Orthodontics and Dentofacial Orthopedics,¹ which recommend that initial orthodontic records include examination notes, intraoral and extraoral images, diagnostic casts (stone or digital), and radiographic images. These radiographic images include appropriate intraoral radiographs and/or a panoramic radiograph as well as cephalometric radiographs. A three-dimensional cone beam computed tomograph (3D CBCT) can be substituted for a cephalometric radiograph; however, the routine use of a CBCT is not generally required in orthodontics, so cephalometric radiographs are the current standard.

The AAO Clinical Practice Guidelines¹ also recommend evaluating the patient’s treatment outcome and determining the efficacy of treatment modalities by comparing posttreatment records with pretreatment records. Posttreatment records may include dental casts; extraoral and intraoral images (either conventional or digital, still or video); and intraoral, panoramic, and/or cephalometric radiographs depending on the type of treatment and other factors. Many orthodontists also take progress cephalograms to determine if treatment is progressing as expected. In addition, board certification with the American Board of Orthodontics requires cephalograms and an understanding of cephalometry to explain the decisions for diagnosis, treatment, and the effects of growth and orthodontic treatment. Therefore, it is paramount that orthodontists understand how to use cephalometrics in their practice.

Basics of Cephalometrics

Cephalometrics is used to assist in (1) classifying the malocclusion (skeletal and/or dental); (2) communicating the severity of the problem; (3) evaluating craniofacial structures for potential and actual treatment using orthodontics, implants, and/or surgery; and (4) evaluating growth and treatment changes of individual patients or groups of patients. In general, a lateral cephalogram shows a two-dimensional (2D) view of the anteroposterior position of teeth, the inclination of the incisors, the position and size of the bony structures holding the teeth, and the cranial base (Fig 1-1a). A cephalogram can also provide a different view of the temporomandibular joint than a panoramic radiograph and a view of the upper respiratory tract.

Fig 1-1 (a and b) Lateral and frontal cephalograms.

In addition, cephalograms aid in the identification and diagnosis of other problems associated with malocclusion such as dental agenesis, supernumerary teeth, ankylosed teeth, malformed teeth, malformed condyles, and clefts, among others. They have also been used to identify pathology and can give some indication of bone height and thickness around some teeth. However, they are not very useful in identifying dental caries, particularly initial caries, and periodontal disease, so bitewing radiographs and periapical radiographs are needed for patients who are caries susceptible or show signs of periodontal disease. While some asymmetry can be diagnosed using a lateral cephalogram, an additional frontal cephalogram (Fig 1-1b) is needed to better identify which hard tissue structures are involved in the asymmetry.

Of course all of these conventional radiographs are 2D images. A 3D CBCT can replace multiple 2D radiographs and can allow the entire craniofacial structure to be viewed from multiple aspects (x, y, z format) with one radiograph (Fig 1-2). Intracranial and midline facial structures can be viewed without overlying confounding structures, and bilateral structures can be viewed independently. While the worldwide transition from 2D to 3D imaging is occurring quickly, it is still important for clinicians to understand what has been used for decades (2D), what additional 3D information is needed, and the limitations and potential of 3D imaging.

Fig 1-2 Software screen showing (a) coronal slice (green line in b and c), (b) sagittal slice (red line in a and c), (c) axial slice (blue line in a and b), and (d) 3D CBCT reconstruction of the same study.

The general purpose of this book is to introduce the orthodontic clinician to the use and interpretation of cephalometrics, both 2D and 3D, and to show the potential benefits of using 3D CBCTs. The purpose of this chapter is to provide the background for the current and future use of cephalometrics.

History of Cephalometrics

Prior to the use of radiographs, growth and development of the craniofacial complex was essentially a study of skull measurements (craniometry) (Fig 1-3) or soft tissue. Craniometry² dates back to Hippocrates in the 4th century BC and is still used today in physical anthropology, forensics, medicine, and art. It is used to determine the size of cranial bones and teeth, their relationship to each other, potential differences among groups of people, and evolutionary changes in the cranium and face. Some of the current cephalometric landmarks, planes, and angles have their origin in craniometry. For example, the Frankfort plane was established in 1882 during a meeting of the German Anthropological Society as a standardized method of orienting the skull horizontally for measurements.² The anthropologists agreed to define the Frankfort plane as a plane from the upper borders of the auditory meati (external auditory canals) to the inferior margins of each orbit. Later, this plane was modified for cephalometry to indicate that the right and left porion and left orbitale would be used to define the horizontal plane to minimize problems that asymmetry caused.

Fig 1-3 An original Broadbent craniostat used to standardize skull position and measurement. (Courtesy of Dr Juan Martin Palomo, Case Western Reserve University.)

Craniometry, however, had limitations. Each skull represented a one-time peek or snapshot at the development of one individual—in other words, a cross-sectional data point. There was little hope of a longitudinal study. Frequently, the reason for the death of the individual was unknown, resulting in an unknown effect on the growth and development of the skull. Thus, craniofacial development was interpreted based on the skulls of children who died because of trauma, disease, starvation, abuse, or genetics. Todd,³ the chairman of the Department of Anatomy at Case Western Reserve University School of Medicine, considered the measuring of these children’s skulls as studying defective growth and development; the longitudinal effect of orthodontic treatment on growth and development could not be assessed. Animal studies using dyes were obviously limited in providing interpretation of the effect of various factors on human growth and development. Soft tissue studies, particularly longitudinal, were also limited by the lack of reproducible data. Radiographs, however, provided the opportunity to study and compare multiple patients over decades.

The use and standardization of cephalograms continually evolved from their early beginnings in the late 1800s. Similarly, during that time, orthodontics had its inception as a dental specialty. Edward Hartley Angle classified malocclusion in 1899 and was recognized by the American Dental Association for making orthodontics a dental specialty.⁴ Angle established the first school of orthodontics (Angle School of Orthodontia in St Louis) in 1900, the first orthodontic society (American Society of Orthodontia) in 1901, and the first dental specialty journal (American Orthodontist) in 1907.

Shortly after the discovery of x-rays by Wilhelm Conrad Roentgen in 1895,⁵ the use of the first facial and cranial radiographs was reported as early as 1896 by Rowland⁶ and later by Ketcham and Ellis.⁷ By 1921, B. H. Broadbent was using lateral cephalograms in his private practice.⁷ In 1922, Spencer Atkinson reported to the Angle College of Orthodontia that he used lateral facial radiographs to identify the position of the first molar below the maxilla’s key ridge.⁷ Because the radiographs also showed soft tissue, Atkinson suggested that these lateral radiographs had the potential of relating the mandible and the maxilla to the face and to the cranial base.

Initially, the comparison of cephalometric radiographs to show the effects of growth and treatment was difficult because head position and distance from the cephalometric film were not standardized. In an attempt to standardize head position, in 1921 Percy Brown designed a head holder for taking radiographic images of the face.⁷ In 1922, A. J. Pacini reported standardizing head position for lateral radiographs by using a gauze bandage to hold the film to the head.⁸ Ralph Waldron followed in 1927 by constructing a cephalometer to measure the gonial angle on a roentgenogram taken 90 degrees from the profile.⁹ Martin Dewey and Sidney Riesner held the patient’s head in a clamp and took a profile view with the film cassette placed against the head.¹⁰ However, for several decades there was no universal standardization of cephalometric technique, meaning that identical radiographs of the same patient could not be reproduced.

It was obvious to Broadbent¹¹ that accurate and reliable longitudinal measurements of the head and face in three dimensions would be necessary to study growth and development of the teeth and the jaws as well as the effect of orthodontic treatment. Drawing on his previous experience of modifying Todd’s craniostat into a craniometer to standardize skull position and measurement (see Fig 1-3), Broadbent developed a craniostat that consisted of a head-holding device, two ear rods, and a nasion rest to stabilize the head of a living person relative to the radiographic film and the x-ray source (Fig 1-4). Broadbent even took impressions of the teeth while the patient was positioned in the craniostat and related them to the maxilla and mandible. He announced in 1930 that he had used a radiographic craniostat to study the longitudinal growth of the living face¹² and published a description of the invention in 1931.¹¹ Bolton’s cephalostat was modified later to include the standardization of head position for a roentgenogram from the frontal view (Fig 1-5). During the same year, a German orthodontist, H. Hofrath, also reported the development of a craniostat to standardize head position while taking lateral radiographs.¹³

Fig 1-4 An original Broadbent cephalometric craniostat consisting of a head-holding device, two ear rods, and a nasion rest to stabilize the head of a living person relative to the radiographic film and the x-ray source. (Courtesy of Dr Juan Martin Palomo, Case Western Reserve University.)

Fig 1-5 An original Bolton cephalostat modified to standardize head position for a frontal roentgenogram. (Courtesy of Dr Juan Martin Palomo, Case Western Reserve University.)

The standardization of cephalograms allowed comparison of the same head over time. Treatment effects and comparison with other individuals could also be studied. This so impressed Congresswoman Frances Bolton that she established a long-term research study at Case Western Reserve University to examine the growth and development of the teeth and the jaws in healthy children.

Early studies by Broadbent¹⁴ and other investigators of cranial and facial development emphasized the need to identify stable landmarks in order to superimpose the radiographs. Broadbent thought that at least in early childhood, certain cranial areas were more stable than the rapidly growing face. This led to the development of the Bolton-nasion plane of orientation and a registration point (R) in the sphenoidal area as the most fixed point in the head or face¹⁴ (Fig 1-6). The Bolton-nasion plane was a line drawn from nasion, the most forward position of the frontonasal suture, at the midline to the highest point (Bolton point) on the profile of the right and left condyles of the occipital bone posterior to the foramen magnum. Bolton point was chosen rather than the superior tip of the auditory meatus because the cephalostat’s ear rods masked the auditory canals. The bilateral occipital condyles were considered to produce a single image because they were essentially close enough to each other to be on the midplane of the skull. The center ray of the radiographic machine was considered to cause little magnification shadow. A point midway on a line drawn from the center of sella turcica on a perpendicular to the Bolton-nasion plane was called registration point (R) and was used to register superimpositions of the same individual or different individuals.

Fig 1-6 Bolton-nasion plane of orientation and registration point (R) in the sphenoidal area. The Frankfort horizontal and the perpendicular orbital plane were used for superimpositions.

To measure facial changes after registering the Bolton-nasion plane on R, the Frankfort horizontal plane was added to the initial record of each child, and the perpendicular orbital plane (the plane perpendicular to Frankfort horizontal through orbitale) was passed through the dentition. Measurements of changes were taken from these two planes, not directly from the Bolton-nasion plane.

During the next few decades, multiple centers evaluating growth and development using cephalograms were started, and numerous orthodontists provided their data in various formats to best describe their analysis of the craniofacial complex. Some parameters were used primarily for research, while others were specifically used for clinical analysis. Many analyses or groups of parameters assumed the names of the orthodontist best known for promoting them but included measures previously used in craniometry or by other orthodontists. In some cases (eg, mandibular plane, length of mandible, and cranial base) various orthodontists published somewhat different methods of defining the structures. Wilton Krogman and Viken Sassouni attempted to validate the clinical usefulness of approximately 70 existing cephalometric analyses in 1957.¹⁵ In some cases, these differences remain today because of strongly held opinions of the different schools of orthodontics. Unfortunately, this has also led to confusion for novices in this area and to intense discussion about which cephalometric values lend more to correct diagnosis and treatment analysis. In addition, comparison of various studies is complicated when different landmarks and planes are used.

Many cephalometric values were reported as simple descriptive statistics. Descriptive statistics, which are used to indicate the center or most typical value of a data set, are called measures of central tendency and include means and medians. The mean is the average of all the numbers for that data set, and the median is the data value in the middle of all the data arranged in ascending or descending order. Means or averages are provided more commonly than medians to clinically compare cephalometric values of groups. Research studies might report one or both values depending on the purpose and the sample in the study. However, data sets with the same mean can have considerable variation in the incorporated values. The descriptive statistics used to quantitatively describe these differences are called measures of dispersion (how widely the values are dispersed). The two measures of dispersion commonly used in cephalometrics are range and standard deviation. The range of a data set is the difference between the largest and the smallest value in that data set. The larger the difference, the greater is the dispersion of the data. The standard deviation tells how much deviation there is from the mean. The larger the standard deviation, the larger is the variation of the data. Usually, all data within a data set fall within three standard deviations (±3 SD) of the mean. Clinically, some orthodontists suggest that it is more difficult to treat patients whose cephalometric values are more than one standard deviation outside the mean; however, this also depends on the particular cephalometric value.

For the most part, it is assumed that the skeletal and dental cephalometric traits have values that, if plotted, would fall within a bell-shaped curve, a normal curve. That is, if the mean was determined and designated as zero, then when standard deviations are determined and marked on each side of the mean, the normal curve would be symmetric, and most of the data would fall within three standard deviations on each side. Depending on the range and the width of the standard deviations, the curve could be taller than wide or vice versa. However, normality should always be checked because not all data sets fit a bell-shaped curve. Unfortunately, many of the classic cephalometric studies did not report adequate statistics. Therefore, a careful reading of the literature is required for knowledgeable use of cephalometrics.

Many published cephalometric studies reported descriptive statistics to quantify the results of the cephalometric parameters for samples of the population they studied. In most cases, the study included a limited number of cases (sample) compared with the entire population. Samples were used because it was too difficult or expensive to study the entire population. Obviously, the more alike the individuals in a population, the more representative the selection of the sample would be for that population. However, the criteria for the samples used in some of the early cephalometric analyses were very limiting and probably did not truly represent the population. In other cases, the samples were so small and heterogenous that the results reported appear to have little value. Some criteria for subject selection included that the subjects must have acceptable, attractive,¹⁶ or award-winning faces.¹⁷

In one study¹⁸ of 79 adults with ideal occlusions, the cephalometric measures showed a large range of values from Class II to Class III maxillomandibular relationships, high-angle to low-angle mandibles, and incisor retrusion to protrusion. Although the means measured in the study were similar to those reported in other published studies, the ranges were considerably larger. A retrospective review of the faces indicated no extremely poor or unacceptable faces, showing that good occlusion was achievable even naturally without surgery. Thus, cephalometrics alone is never used for treatment decisions.

Various factors influence cephalometric values. For example, the measurement of 2D cephalometric parameters is influenced by the diverging rays of the cephalostat striking a multidimensional object that is at a distance from the recording film, causing magnification error. Prior to standardization of the distances of the object and the film from the x-ray source, the differential was unknown unless a standardizing object was included in the film. Magnification error also varies with different machines. Some early studies did not report or correct the magnification error when they were published. (Formerly, the American Board of Orthodontics required that cases submitted for board certification show a calibration device in the cephalogram to allow for correction of magnification error.) Despite these problems, the early studies were helpful in developing a better understanding of craniofacial growth and development and provided the basis for additional investigation. However, these original publications should be analyzed carefully before they are cited or used as a basis for clinical treatment.

One of the issues in determining craniofacial changes with early cephalometrics was the selection of cephalometric reference parameters called planes to compare skeletal and dental changes. For example, early in the development of cephalometry, William B. Downs¹⁹ realized that numerous measures were being used to describe the face. He sought to determine the range and the correlations of cephalometric values for individuals with excellent occlusions by comparing various cephalometric values from a group of 10 male and 10 female potentially growing adolescents (12 to 17 years old). Downs eventually came to the conclusion that he should evaluate the face by dividing the facial skeleton from the teeth and the alveolar processes. He would classify the skeletal pattern (maxilla versus mandible) alone and then determine the relationship of the teeth and alveoli to the facial skeleton. He suggested that the variability in values comparing the facial plane to sella-nasion (SN), the Frankfort horizontal, and the Bolton plane was so small that he was not sure why one was used instead of another to evaluate the face (Fig 1-7). Downs used the Frankfort horizontal because he felt that the SN and Bolton-nasion planes separated the cranium from the face, whereas the Frankfort horizontal allowed comparison of relationships involving only the face, the structures that orthodontic treatment (with or without surgery) could control. Using four faces, he demonstrated how the facial angle (facial plane to Frankfort horizontal) described the facial type better than the facial plane to SN or the facial plane to the Bolton plane when the position of the mandible was assessed (see Fig 1-7). Contrary to many cephalometric analyses that reported the mean measure, his comparisons for angle of convexity, AB plane, and mandibular plane angle were the numerical differences from the mean of the control group. For example, if the mean angle of convexity of the control group was reported as 180 degrees, a measurement of 185 degrees in a test patient would be reported as +5.0 degrees (a negative difference indicating concave profile and a positive difference indicating convex profile), not 185 degrees. Similarly, deviations from the means of the AB plane or mandibular plane angle were read as the difference from that mean without considering the variation within the control group. Downs thought that these differences would show the difficulty of treating the case. While Downs’s study was small, did not look at sex differences, and used growing individuals for whom some cephalometric values could change with age, his cephalometric parameters and values are still used today. Numerous parameters have been introduced following his study.¹⁵

Fig 1-7 Sella-nasion, Frankfort horizontal, and Bolton-nasion reference planes.

During the next few decades, numerous studies emphasized the importance of reliable and standardized landmarks, parameters, and references points to determine (1) the outcome of treatment for a single patient, (2) comparison of outcomes from multiple patients undergoing similar treatment, or (3) growth prediction with or without treatment. Unfortunately, some of these landmarks have changed slightly in definition or emphasis through the century of 2D cephalometry and will change for 3D cephalometry because of the addition of the third dimension. For example, in light of 3D investigation, it is currently in question whether A-point can be considered the most forward position of the maxilla.²⁰

3D CBCTs

3D CBCTs were first reported in 1994 and originally introduced commercially in Europe in 1996. However, it was not until 2001 that the first 3D CBCT was introduced commercially to the United States. Prior to 2007, few articles linked 3D CBCTs to orthodontics.²¹ Initial concerns about the high radiation dosage and its cost probably limited its use in orthodontics for a while but drove reengineering of the technology, which significantly reduced the radiation exposure and cost. Since 2007, hundreds of articles relating the use of 3D CBCTs to orthodontics have been published. The applicability of 3D CBCTs for associated orthognathic surgery and dental implants as well as need-specific orthodontics (eg, impacted teeth, craniofacial anomalies, bone thickness) has increased their usage in orthodontics and general dentistry. However, significant issues remain, including whether the landmarks and measures used in 2D cephalometry can be used in 3D cephalometry as well as the clinical relevance and use of 3D cephalometry for all orthodontic patients.

The evolution of 3D cephalometry has occurred more quickly than 2D cephalometry, probably due to worldwide digital communications. More than 50 years after the inception of lateral radiographs in orthodontics, Steiner²² indicated that cephalometrics was still not being used for clinical applications but was primarily a tool for academic studies of growth and development. On the other hand, it is predicted that in just 5 years, the global CBCT market will increase from $494.4 million in 2016 to $801.2 million in 2021, although the growth will probably not be limited to orthodontics.²³

Conclusion

Patient care is performed best by educated and discerning clinicians, so it is essential that clinicians not only understand the basics of 2D cephalometry and how it relates to 3D cephalometry but also keep up to date with the evolution of cephalometry and its associated technology, software, and applications.

References

1.American Association of Orthodontists. Clinical Practice Guidelines for Orthodontics and Dentofacial Orthopedics [amended 2014]. https://www.aaoinfo.org/system/files/media/documents/2014%20Cllinical%20Practice%20Guidelines.pdf. Accessed 25 August 2017.

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9.Basyouni AA, Nanda SR. An Atlas of the Transverse Dimensions of the Face, vol. 37 [Craniofacial Growth Series]. Ann Arbor: University of Michigan Center for Human Growth and Development, 2000:235.

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11.Broadbent BH. A new x-ray technique and its application to orthodontia. Angle Orthod 1931;1:45.

12.Broadbent BH. The orthodontic value of studies in facial growth. In: Physical and Mental Adolescent Growth [The Proceedings of the Conference on Adolescence, 17–18 October 1930, Cleveland, OH].

13.Hofrath H. Die Bedeutung der Rontgenfern und Abstandsaufname für die Diagnostic der Kieferanomalien. Fortschr Orthod 1931;1:232–258.

14.Broadbent BH. Investigations of the orbital plane. Dental Cosmos 1927;69:797–805.

15.Krogman WM, Sassouni V. Syllabus in Roentgenographic Cephalometry. Philadelphia: College Offset, 1957:363.

16.Tweed CH. The Frankfort mandibular incisor angle (FMIA) in orthodontic diagnosis, treatment planning, and prognosis. Angle Orthod 1954;24:121–169.

17.Riedal R. An analysis of dentofacial relationships. Am J Orthod 1957;43:103–119.

18.Casko JS, Shepherd WB. Dental and skeletal variation within the range of normal. Angle Orthod 1984;54:5–17.

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20.Kula TJ III, Ghoneima A, Eckert G, Parks E, Utreja A, Kula K. A 2D vs 3D comparison of alveolar bone over maxillary incisors using A point as a reference. Am J Orthod Dentofacial Orthopedics (in press).

21.Gribel BF, Gribel MN, Frazão DC, McNamara Jr JA, Manzi FR. Accuracy and reliability of craniometric measurements on lateral cephalometry and 3D measurements on CBCT scans. Angle Orthod 2011;81:26–35.

22.Steiner CC. Cephalometrics for you and me. Am J Orthod 1953;39:729–754.

23.Markets and Markets. CBCT/Cone Beam Imaging Market by Application. http://www.marketsandmarkets.com/Market-Reports/cone-beam-imaging-market-226049013.html?gclid=EAIaIQobChMI4_b899b31AIVyEwNCh1xXQseEAAYASAAEgJa0_D_BwE. Accessed 25 August 2017.