Читать книгу Orthodontic Treatment of Impacted Teeth - Adrian Becker - Страница 111

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].