Orthodontic Treatment of Impacted Teeth. Adrian Becker

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