What happened to the alveolar bone during retraction?

Professors Yanagita, Kuroda, Takano-Yamamoto, and Yamashiro are to be congratulated on successfully attaining a Class I occlusion on a skeletal Class III dental base, achieved by retracting the mandibular dentition using miniscrew anchorage (Yanagita T, Kuroda S, Takano-Yamamoto T, Yamshiro T. Class III malocclusion with complex problems of lateral open bite and severe crowding successfully treated with miniscrew anchorage and lingual orthodontic brackets. Am J Orthod Dentofacial Orthop 2011;139:679-89).

The posttreatment lateral cephalometric radiograph shows not only retraction of B-point but also marked reduction of the labiolingual alveolar bone width so that it appears that only the apex of the mandibular incisor roots remains in the alveolar bony envelope. In the absence of 3-dimensional imaging, I postulate that the actual bone coverage of the roots of the mandibular incisors resembles the images that Wehrbein et al reported in their study of the mandible of a deceased person who had undergone orthodontic treatment. In that article, the lateral cephalometric radiograph of the subject showed images of the mandibular incisor roots devoid of any labiolingual alveolar bone, except for the extreme apical area. The photographs of the dry mandible of the same subject showed that, instead of the incisor roots encased in bone, as is desirable, there were moderate bone dehiscences on the labial aspects of the mandibular incisors and severe dehiscences on the lingual aspects that resulted in only interradicular bone to provide lateral support to the incisors.

Sarikaya et al in their computed tomography scan study of alveolar bone thickness after retraction of anterior teeth also reported significant lingual bone loss that failed to recover by 3 months posttreatment. It was uncertain whether the lost cortical bone would regenerate.

I am concerned about the long-term prognosis of teeth that experience such severe dehiscences on the labial and lingual root surfaces and question whether we should continue to close our eyes when, in the pursuit of the ideal Class I occlusion, we seem to be bringing orthodontic tooth movement beyond the biologic limits of anatomy with our mechanotherapy.

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Apr 11, 2017 | Posted by in Orthodontics | Comments Off on What happened to the alveolar bone during retraction?
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