Читать книгу Orthodontic Treatment of Impacted Teeth - Adrian Becker - Страница 19

There are several criteria that are appropriate to the appraisal of tooth development when using full‐mouth periapical radiographs or a panoramic film. The information that is available regarding the ages at which the various stages of dental development occur is based on the classic random studies that have been carried out over many decades of the local populations of the researchers involved. The figures for the mean ages at which these stages occur, in the hypothetical child, are as follows:

1 The first signs of the presence of a tooth are discernible radiographically with the initiation of calcification of incisal edges and cusp tips. Thereafter, one may observe the formation of the completed crown as well as progressive degrees of root formation (usually expressed in fractions), and thence the fully closed root apex. Since orthodontic treatment is largely performed on a relatively older section of the child population, the stages of actual formation of the root become the only relevant factors.

2 The accuracy with which one may assess fractions of an incomplete, immeasurable and merely ‘expected’ final root length is not reliable and is very much a matter of individual observer variation.

3 The stage of tooth development that is easiest to define with confidence and with accuracy is that which relates to the closure of the root apex. So long as the dental papilla at the root end remains discernible, the apex is open and Hertwig’s root‐forming, epithelial sheath is in an active stage of increasing root length. However, once fully closed, the papilla disappears and a continuous lamina dura will be seen on a periapical radiograph, closely following the root outline. These are the specific diagnostic signs of that landmark event. Apexification is therefore the most important single factor upon which a system of assessment may be faithfully and easily made of the dental age of a given patient in the clinical environment.

4 From population studies, we learn that the first permanent tooth to erupt in the mouth is the mandibular central incisor, closely followed by the first permanent molars, and this occurs at the age of 6 years.

5 Root development of the permanent teeth is completed approximately 2.5–3 years after their normal eruption [4]. This allows us to conclude that, at the age of 8.5–9 years, the child’s mandibular incisors will be the first teeth to exhibit closed apices and will usually be closely followed by the four first permanent molars. This being the case, it is clear that the age of 9 years must be the basic starting point from which to commence the evaluation of the child’s dental age. If mandibular incisors or molars demonstrate root closure, then the tentative diagnosis would be that the patient has a dental age of at least 9 years. If the apices are still open, then the conclusion would be that the child has a lower dental age.

It should be emphasized, however, that the exercise is aimed at ranking a specific child’s dental development vis‐à‐vis the above hypothetical mean. Whether or not the evaluated tooth has actually erupted is entirely irrelevant to this equation.

Let us examine the progressive diagnostic path in its correct order (see also Table 1.1):

1 If the mandibular central incisor roots are complete, we may presume that the patient is at least 9 years old (dental age), i.e. this figure is derived from 6 years (the normal age of eruption as determined by two‐thirds root length development), with the addition of 2.5–3 years to apexification.

2 We may then proceed and check for closed apices of the first molars (9–9.5 years).

3 At 9.5 years, the mandibular lateral incisors roots will have completely developed.

4 The next teeth in the expected eruption series are the maxillary central incisors, whose closed apices would indicate a dental age of 10 years.

5 Because their rate of development is variable, it would be wise to bypass the assessment of the maxillary lateral incisors at this point in the diagnostic process and move on to examine the later teeth.

6 Apexification of the mandibular canines and first premolars (12–13 years).

7 Thereafter, the maxillary first premolars (13–14 years).

8 In common with the maxillary lateral incisors, the mandibular second premolars are also developmentally variable teeth and their assessment should also be bypassed for the present calculation.

9 Next there are the maxillary canines (14–15 years).

10 The final stage of development relates to the four second molars (15 years).

Table 1.1 Apexification age of individual tooth types.

9 years	Mandibular central incisors
9–9.5 years	First molars and mandibular lateral incisors
10 years	Maxillary central incisors
11 years	Maxillary lateral incisors
12–13 years	Mandibular canines
13–14 years	Maxillary first premolars
14–15 years	Second premolars and maxillary canines
15 years	Second molars

This stage‐by‐stage apexification determination will lead us to the last tooth in this sequence with a closed apex (Figure 1.4), which indicates the dental age of the patient. Once the determination is completed, it is valuable to return to the maxillary lateral incisor and the mandibular second premolar. If these are developing normally, then their age of eruption would be 8 years and 11 years, respectively, with an apexification date of 11 and 14 years, respectively. Retarded development of these individual teeth may be age assessed according to the above criteria for calcification. An illustration of this situation would be where the overall dental age assessment is diagnosed as 12 years, yet the right maxillary lateral incisor might match a 9‐year‐old child and the left mandibular second premolar might even be characteristic of someone 8 years of age.

In contrast to the above process of examination and assessment and in the case of a dental age less than 9 years, none of the permanent teeth will have completed their root development. Here clinicians will have no choice but to rely on their own estimation of the degree of root development, of the degree of crown completion and, in the very young, of the stage of initiation of crown calcification (Figure 1.5). This is most conveniently carried out by working backwards from the expected development at age 9 years and, with this as a base, comparing the dental development status of the patient, beginning with the mandibular central incisors and the first permanent molars.

Fig. 1.4 Root apices are closed in all first molars, all mandibular and three of the maxillary incisors, excluding the left lateral incisor. Canine and premolar apices are open.

Fig. 1.5 No closed apices. Dental age assessment 7–7.5 years.

By way of illustration, at a dental age of 6 years the length of the roots of the mandibular central incisors and the first permanent molars will be seen to be one‐half to two‐thirds developed. Confirmation of this will come from a comparison, which may be made with the development stage reached by the other teeth, where one would anticipate that unerupted maxillary central incisors will have reached one‐half root length, mandibular canines one‐third root length, first premolars one‐quarter root length, and so on.

As already noted, however, variations do occur, particularly with maxillary lateral incisors, mandibular second premolars or third molars. This may lead to certain apparent contradictions. It is therefore recommended to exclude consideration of these teeth when making the relevant assessments and thereby not only simplifying the process, but also contributing to the accuracy of the resulting assessment.

In addition, as stated above, early development of these teeth in relation to the development of the remainder of the dentition does not appear to occur. Indeed, individual variability is expressed only in terms of degrees of lateness. Accordingly, the developmental status of these teeth is available as corroborative evidence for the determination of dental age, but only if their own developmental stage is shown to be in line with the remainder of the dentition.

In a similar way, one should not incorporate abnormal features in the calculation process of the assessment of dental age. Unusually small teeth, coniform premolars, mandibular incisors and peg‐shaped lateral incisors are all wont to develop very much later than normally shaped and sized teeth of the same series; indeed, sometimes as much as three or four years later. Thus, in diagnosing dental age for a patient with an abnormality of this nature, a general determination of the dentition should point out that this abnormal tooth may display a much lower dental age. A 14‐year‐old patient who has a complete permanent dentition, including the second molars, may yet exhibit a mandibular second deciduous molar. The radiographs (Figure 1.6) show the apices of the first molars, central and lateral incisors, mandibular canines and premolars to be closed, while the maxillary canines and the second molars are almost closed. However, the unerupted mandibular second premolar has an open root apex and presents a development stage equivalent to about a quarter of its expected eventual length, or even less. Correspondingly, although we may assess the dental age of the dentition as a whole to be 11‐12 years, we would have to point out that the dental age of the unerupted second premolar is approximately 7 years. The conclusion here, in the context of this terminology, is clearly that the second premolar, individually, does not exhibit delayed eruption and the deciduous second molar is not over‐retained. Thus, it would not be appropriate to extract the deciduous tooth at this point, but rather to wait for at least a few years, during which time the tooth may be expected to shed normally.

Fig. 1.6 Late‐developing second mandibular premolars with retained (not over‐retained) deciduous second molars in a child with a dental age of 11–12 years. The contrast and brightness of this poorly contrasted picture have been adjusted in the relevant areas to clearly show the stage of development of these tooth buds.

In summary, there are four different parameters that can explain the existence of certain deciduous teeth that are inconsistent with the chronological age of the patient. Each of these parameters has clinical repercussions and labelling a patient as one particular grouping will in fact dictate the nature of the treatment required:

1 A late‐developing dentition: In this condition the dental age of the patient has developed slower than his chronological age. This is evident radiographically by a lesser root formation in the entire dentition than that which is expected at the chronological age. Typically, this is accompanied clinically by the continued and symmetrical presence of all the deciduous molars and canines on both sides of the jaw. Here, the extraction of deciduous teeth is contraindicated, since the teeth are expected to exfoliate normally when the appropriate dental age is reached.

2  A normally developing dentition with over‐retained deciduous teeth: In this condition and despite the fact that the dental age of the patient correlates with her chronological age, the radiograph demonstrates one or more permanent teeth, which show well‐developed roots but have remained unerupted, i.e. beyond their due eruption time. In most examples of this condition, the anomaly tends to be localized in a single section of the dentition. This may be due to an ectopic siting of the permanent tooth bud, which has stimulated the resorption of only a portion of the root of its deciduous predecessor. Shedding has not occurred due to the continued presence of the remaining part of the root or of another unresorbed root. Indeed, sometimes the condition may be found symmetrically in a single dental arch or even in both arches. In this condition the recommended treatment is extraction of the over‐retained tooth or teeth.

3 A normally developing dentition with single or multiple late‐developing permanent teeth: This condition is commonly found in relation to the maxillary lateral incisor and the mandibular second premolar teeth. Normal shedding of the tooth is expected to occur when the root of the permanent tooth reaches two‐thirds to three‐quarters of its expected length. Accordingly, extraction of the deciduous predecessor is to be avoided.

4 A combination of the above: Sometimes one may see features of all of these three alternatives in a single dentition. In such a case the recommended treatment would need to be multiple and selective, each condition treated in its appropriate way.

The importance of a careful diagnosis and differentiation of the above conditions cannot be over‐emphasized. All the aspects of planning and timing of treatment of the patient with impacted teeth depend entirely on a correct diagnosis.