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

牙齿侵入是牙齿移动的一种类型，牙齿通常会侵入牙槽骨约2-4毫米。在这种情况下，牙槽骨也被吸收，从而维持了支持牙槽骨和牙齿的关系。这是由于牙槽上的纤维随着牙齿的侵入而向下伸展。侵袭不会增加支撑骨。在这项研究中，我们试图通过切断牙槽上的纤维(中隔)来增加牙齿侵入时的支撑骨。以比格犬下颌第三前磨牙(P3)为材料。用骨性支抗系统侵入双侧P3，持续4周。每周一次在一侧下颌骨P3周围行中隔切开术。部分P3用作对照。侵入后，用福尔马林固定，取出P3及其周围骨，脱水，包埋于树脂中。然后对标本进行显微CT观察。建立P3牙槽骨的三维图像。对照组P3(无侵袭)均匀地被牙槽骨包围。4周后，P3被侵犯约2 mm，并伴有颊向移动。舌侧牙槽骨高度与对照组相同。颊槽骨向下移动，牙槽骨高度明显降低。鼻中隔切开术的P3表现出不同的方面。舌侧牙槽骨宽度增加，但牙槽突位置无明显变化。颊牙槽突位置上移，提示牙槽骨高度增加。结果提示，鼻中隔切开可导致支持骨量增加。

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.