Orthodontic Treatment of Impacted Teeth. Adrian Becker

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.

When is a tooth considered to be impacted?

      Based on the principles set out by Grøn [13], it has been widely accepted that, under normal circumstances, a tooth erupts with a developing root and with approximately three‐quarters of its final root length. Typically, when they erupt the mandibular central incisors and first molars will have marginally less root development, whereas the mandibular canines and second molars will demonstrate slightly more root development. This is now generally accepted as a diagnostic baseline from which to evaluate the eruption of teeth in general.

Thus, where an erupted tooth shows less root development (Figure 1.7), it would be appropriate to label it as prematurely erupted. (This will usually be the consequence of the early loss of a deciduous tooth, particularly where extraction was dictated by the presence of periapical pathology, typically due to untreated caries.)

Fig. 1.7 The left mandibular premolars are prematurely erupted, with insufficient root development, due to premature extraction in a caries‐prone dentition.

      Conversely, where an unerupted tooth exhibits a more completely developed root, then the eruption process of this tooth must be presumed to have been impeded. (This may have been caused by any one of several aetiological possibilities, such as a failure of resorption of the roots of a deciduous tooth, or an abnormal eruptive path, the presence of a supernumerary tooth, or dental crowding, perhaps a much‐enlarged dental follicle/dentigerous cyst, or indeed any other forms of soft tissue pathology or disturbance in the eruption mechanism of the tooth.) One should not overlook the possibility that the cause of the non‐eruption may also be a thickened post‐extraction or post‐trauma repair of the mucosa.

      It is to be noted that if there is a history of very early extraction of one or two deciduous molars, we may find that there will be a substantial delay in the eruption of the premolars, indeed, even complete non‐eruption, caused by a thickened mucosa overlying the teeth. It is usually possible, for a period of a year or more, to palpate these teeth by virtue of their distinct outline being clearly visible and causing a bulging of the gum. However, eruption may not occur at all.

Impacted teeth and local space loss

Let us now look at the consequences of the inevitable time lapse between the performance of a surgical procedure to remove the cause of an impaction and the full eruption of the impacted tooth into the vacated space in the dental arch. The extent of this time‐span is linked to several factors, specifically the initial distance between the tooth and the occlusal plane, the stage of development of the particular tooth, the age of the patient and the manner in which hard and soft tissue may be laid down in the healing wound. There are consequences to this time period, which need to be addressed. Local changes in the erupted dentition, such as space loss and tipping of the adjacent erupted teeth, may occur as a result of the break in integrity of the dental arch caused by the surgical procedure. The surgical intervention is no less likely to elicit the drifting of neighbouring teeth than is any other factor that may be caused by loss of dental tissue and interproximal contacts.

      If an odontome or supernumerary tooth creates an obstacle to an unerupted permanent tooth, the result may be substantial vertical (and sometimes mesial, distal, buccal or lingual) displacement of the permanent tooth. In such a case, the ideal treatment would be to remove the obstructing body in order to leave the deciduous teeth intact, since the deciduous teeth would function to maintain arch integrity during the time lapse needed for the permanent tooth to erupt normally. However, in order to gain access to perform the necessary surgery, it is usually necessary to extract one or more deciduous teeth. This brings to the forefront the importance of interim space maintenance, particularly in the posterior area, during the lengthy time needed to allow for the long distance that a displaced permanent tooth may have to travel before it erupts into the mouth. Advance orthodontic planning is called for, preferably before or immediately subsequent to the surgical procedure. The interim space‐holding device should be retained until full eruption of the permanent tooth has occurred.

      The impaction of teeth is often associated with the lack of available space in the immediate area. This is frequently due to the drifting of adjacent teeth, as well as to crowding of the dentition in general. In these circumstances, the spontaneous eruption of an impacted tooth is unlikely to occur unless adequate or, preferably, excess space is available. It would be better to delay the excision of the associated pathological entity and permit this corrective treatment to be attempted,