Orthodontic Treatment of Impacted Teeth. Adrian Becker

also serve to enable us to diagnose the dental age of the patient’s individual unerupted permanent teeth. However, because developmental variation is found within these different groups of teeth, the developmental stage of a single tooth cannot be used as an indicator for overall dental development and dental age must be evaluated employing a comprehensive, all‐round assessment. Only then can a definitive determination be offered.

      Accurate assessment of dental age is critical in deciding when to treat a patient in general and in regard to the treatment of impacted teeth in particular.

      We are now in a position to define the terms that we shall use throughout this text, as follows:

       Retained deciduous tooth: This term has a positive connotation and refers to a tooth that remains in place beyond its normal, chronological shedding time due to the absence, or retarded development, of the permanent successor. A radiograph of the permanent successor is required in order to determine the presence and developmental status of the unerupted permanent tooth.

       Over‐retained deciduous tooth: In contrast, this term has a negative connotation and refers to a tooth whose unerupted permanent successor exhibits root development in excess of two‐thirds of its expected final length (Figure 1.3). Here too, a radiograph of the permanent successor is required in order to determine the status of the deciduous tooth and its implied treatment.Fig. 1.3 The mandibular left second deciduous molar is retained (extraction contraindicated), since the root development of its successor is inadequate for normal eruption. The right maxillary deciduous canine, in contrast, is over‐retained (extraction advised), since the long root of its successor illustrates delayed eruption.

        Permanent tooth with delayed eruption: This term refers to an unerupted tooth whose root is developed in excess of two‐thirds of its expected final length and whose spontaneous eruption may nevertheless be expected within a reasonable time.

       Impacted tooth: This refers to a tooth whose root is developed in excess of two‐thirds of its expected final length, but which is not expected to erupt in a reasonable time.

      When assessing the dental age of the patient, it is important to emphasize that one should not include the maxillary lateral incisors, the mandibular second premolars and the third molars in this calculation. The development timetable of these teeth is not always in line with that of the patient’s other, ontologically more stable teeth [9, 10]. These are the same teeth that are most frequently congenitally missing in cases of partial anodontia (hypodontia) or oligodontia. Indeed, reduced size, poorly contoured crown form and late development of these teeth are all considered microforms of congenital absence [9–12]. The variation in their timing is, however, always expressed as lateness and they are never seen in a chronologically more advanced state of development than the other teeth. If the individual dental age of any of these variable groups of teeth is advanced, then so too is the dental age of the entire dentition in which they are to be found.

      In summary, therefore, we may assert as follows:

       All orthodontists must have at their fingertips the ages at which the permanent teeth normally erupt.

       Permanent teeth normally erupt when approximately two‐thirds of their final root length has developed.

       The remainder of the root reaches apexification approximately 2½–3 years after eruption.

       Determining the closed apex of the tooth on a radiograph is usually an easy and accurate parameter to establish.

       Determining the completed proportion of the root of a tooth, whose final completed length is unknown, is not an assessment that can be performed accurately. It rather falls into the realm of informed guesswork.

      Having now set out the principles upon which dental age may be assessed, we must turn to the practical side of translating these principles into clinical terms in a logical, systematic and didactic manner. The simplistic way of adopting the above principles would be to take the panoramic radiograph or full‐mouth periapical survey and then work around each dental arch from one tooth to the next, individually and from left to right, upper to lower, evaluating each tooth in turn. This would then require coordinating all the individual results and computing a final figure that is the dental age of the patient. The resulting conclusion would have to be compared against the values seen on an idealized chart of the norms for a given population [1, 4, 13]. Although this method delivers accuracy, it requires a considerable time and it is likely to take an hour or so to reach the final conclusion. It is an arduous and tedious endeavour, which does not lend itself to the conditions that are present in a busy clinical orthodontic practice.

      What is recommended is a simple, logical but systematic approach that can be employed chairside to reach a similar conclusion in just a few minutes, even at the initial orthodontic consultation visit. This method will rely on the same criteria of establishing the development of crown and root, but must do so in a step‐by‐step manner, starting from a different point of departure. The ‘starting point’ of this systematic approach has, for reasons that will be explained in the following paragraphs, been set at the cut‐off dental age of 9 years.

Assessing dental age in the clinical setting – the Jerusalem method

      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,