Orthodontic Treatment of Impacted Teeth. Adrian Becker

reason, where a rotated tooth is exposed, the bony opening should be extended around the crown of the tooth, towards the mid‐buccal area of the crown (provided that this can be done easily), while limiting further surgical damage. In this example, flap replacement may be completed and the pigtail ligature may be tied onto the newly placed attachment and drawn in the direction of the target site in the dental arch.

      During exposure of the crown of a tooth, instrumentation of the enamel surface will hamper neither the eruption process nor the quality of the treated result. On the other hand, exposure and instrumentation of the root surface are potentially damaging. Exposing root surface presupposes that the natural attachment of the tooth at the CEJ will have been ruptured and, in consequence, renewed attachment will probably only be able to be established more apically. Indeed, there are yet more undesirable results of exposing root surface: periodontal fibres are severed and cementum exposed and subjected to drying (from the suction and air syringe) and contact with foreign substances (etchant, bonding materials). This can in due course lead to the initiation of a resorption process on the root surface, as well as to ankylosis and to total failure of eruption, as we shall read in Chapter 10. Even more common possible consequences include seriously reduced bone support, long clinical crowns and poor gingival attachment and quality.

Pathological pressure necrosis

      Kokich advised against the use of the closed eruption technique for the exposure of canines that are deeply impacted in the palate, preferring an open surgical approach. The method he described [15] demands the removal of sufficient bone to create an opening whose diameter is larger than the crown of the tooth. The cavity is extended from crown tip to CEJ and concurrently the follicle is removed in its entirety. Kokich’s rationale for this procedure was that contact made between the follicle of an advancing unerupted tooth and the alveolar bone causes the same resorption of the bone as is seen in the normal, unaided eruption process of teeth. He claimed that the proximity of bare enamel to alveolar bone does not physiologically initiate resorption, ‘since there are no cells in the enamel to resorb the bone’. His contention was that ‘resorption will eventually occur through pathological pressure necrosis, but it will occur slowly’. Accordingly, when an impacted tooth is located in mid‐palate, the advice given was to perform an open exposure and maintain its patency, pending natural, spontaneous eruption, which may or may not occur. The confident but unsupported claim was that ‘these palatally displaced canines will erupt on their own … in about 6 to 8 months’ [15]. This is an interesting theory, except that this hypothesis has not been tested on a random sample of impacted canine cases and, more importantly, neither has there been an evaluation of the periodontal outcome nor the orthodontic success of such a sample.

Reparatory bone deposition begins in the organizing blood clot, soon after the surgical exposure. It therefore follows that, unless the widest part of the crown of the impacted tooth has been drawn fully outside the bony plate during a very short time period, it must be expected that bone will re‐form over and around areas of the crown of the tooth. According to Kokich’s hypothesis, this will cause the natural movement of the tooth to slow down or perhaps even stop, due to the ‘pathological pressure necrosis’ that will have occurred. One may be permitted to enquire what ‘pathological pressure necrosis’ is if not the undermining resorption and hyalinization of the alveolar bone that occur in every orthodontic tooth movement. However, there are no studies or case presentations reported in the literature, nor are there any clinically or histologically detectable post‐treatment signs of pathology, which may give credence to the existence of a different and histopathological phenomenon. Notwithstanding this, its manifestation would obviously not augur well, either for patients whose teeth are deeply impacted in bone, or for others for whom several weeks or months may elapse after the surgical exposure and before orthodontic traction is applied.

      In Chapter 18 we describe many of the more common reasons for failure to resolve the impactions and how these may be avoided. There are illustrations of cases of successful resolution of impaction as much as a year or more after the surgical exposure had been performed; cases where success was achieved after a significant gap in the treatment following an initially failed treatment by another practitioner. In these cases, before treatment was started, much mature bone had been laid down, providing an impediment in the path of the impacted tooth, and yet the second attempt at treatment was both successful and rapid and did not need re‐exposure of the tooth.

      Four decades ago, it was shown that the presence of an intact follicle was a prerequisite for the process of normal unassisted eruption [48]. Experience with routine biomechanical traction of impacted teeth has taught us, however, that even in the absence of a follicle, light orthodontic traction is capable of encouraging the resorption of bone that is needed for the assisted eruption of an exposed tooth.

      In Chapter 10 we have pointed to anecdotal clinical evidence that contradicts Kokich’s view. The chapter deals in detail with impacted maxillary canines that are associated with root resorption of their immediate neighbours. In the more extreme examples of this anomaly, the canine crown and the resorbed incisor root are intimately related and are situated in the middle of the ridge, surrounded by bone on all sides. Here the exposure has to be carefully planned to avoid surgical trauma to the incisor root area. It is clearly out of the question to carry out broad clearance of bone and of dental follicle to the full width and length of the crown of the canine and down to the CEJ. Nevertheless, these teeth can routinely be drawn through the surrounding bone and the impaction resolved, as with any other impacted tooth, with the application of light forces suitably directed, and in most cases with considerable speed.

      Similarly, in Chapter 21 we describe the treatment of patients with cleidocranial dysplasia (CCD). Here surgical exposure is required on multiple impacted teeth, deeply displaced low down in the basal bone. For reasons outlined in that chapter, exposure of the canine and premolar teeth will typically be aimed at the buccal aspect of the teeth. It will avoid both the deliberate broad removal of bone surrounding the remainder of the crown of the tooth and exposing of the occlusal surface of the crown of the tooth superiorly. This method seems not to have any retarding effect on the eruptive response of the tooth to occlusally directed light forces, despite the fact that it may often have to resorb a thick layer of bone in the process. This is even the case where alveolar bone in CCD patients is considered to be particularly dense and the largely acellular cementum on the roots of their teeth is associated with slower resorption [49].

       Bone graft and the impacted canine

A 9‐year‐old female patient was accepted for treatment by an orthodontic resident in the cleft palate unit of the Hebrew University‐Hadassah School of Dental Medicine in Jerusalem. The patient, who was in the middle period of the mixed dentition, had a unilateral cleft lip and palate of the left side (Figure 5.10a). The palate was very narrow and V‐shaped and she had a bilateral and anterior crossbite.

      When the patient was admitted for the autogenous bone graft that would close off the cleft (Figure 5.10c, d), the lateral incisor on the distal side of the cleft was transposed with the unerupted maxillary canine (Figure 5.10b). These two anterior occlusal radiographs were recorded the day before and the day after the placement of the graft, for the purpose of checking the outcome of the procedure.

      A rehabilitation treatment plan was established for the orthodontic part of the overall correction. The plan was to align the two teeth in their transposed relationship, rather than attempt to correct it. This was based on the periodontal assessment of the long‐term relative merits of the two therapeutic possibilities. It was considered that moving the lateral incisor bodily into the area of the former cleft, where there was a glaring deficiency of alveolar