A Study on the increase of supporting alveolar bone during intrusion of tooth

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Intrusion is one type of tooth movement and teeth are usually intruded by about two-four mm into the alveolar bone. I this situation, the alveolar crest is also resorbed, ad consequently the relationship between supporting alveolar bone and tooth is maintained. This is due to the supra-alveolar fibers which are stretched downward with the intruded tooth. Intrusion produces no increase of the supporting bone. In this study we attempted to increase the supporting bone during the intrusion of a tooth by cutting the supra-alveolar fibers (septotomy). Mandibular third premolars (P3) of beagle dogs were used as materials. The P3 on both side were intruded for 4 weeks with skeletal anchorage system. Septotomy was performed every weeks around the P3 on one side of the mandible. Some of the P3 used as controls. After the intrusion, the dogs were fixed with formalin, and P3 with the surrounding bone were dissected out, dehydrated, embedded in resin. Then the specimen were observed with micro CT. Three dimensional images of the alveolar bone of P3 was constructed. The control P3 (without intrusion) was evenly surrounded by the alveolar bone. After 4 weeks, the P3 was intruded by about 2 mm with buccal movement. The lingual alveolar bone height was same with that of the control. The buccal alveolar crest was moved downward and the alveolar bone height considerably decreased. P3 with septotomy showed different aspects. Width of lingual alveolar bone increased, though the location of alveolar crest was not changed. The location of the buccal alveolar crest moved upward, indicating the increase of the alveolar bone height. The results suggest that intrusion with septotomy induces the increase of supporting bone.