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目的通过建立埋伏牙三维有限元模型,分析不同工况下埋伏牙的牙周应力,从而为临床上正畸牵引治疗埋伏牙提供基础实验依据。方法选取1例上颌尖牙完全骨埋伏患者,利用螺旋CT技术与三维有限元方法建立统一坐标系下上颌埋伏尖牙及其支持组织的三维有限元模型。保持牙尖位置不变,调整埋伏牙长轴的倾斜角度,使牵引力方向与牙体长轴的夹角分别为0°、45°和90°。在每个模型埋伏牙牙尖处施加50、100、150g的牵引力,分析比较9种工况下牙周膜等效应力云图和牙齿瞬间位移云图的特点。结果当牵引力方向与牙体长轴一致时(0°),埋伏牙上各点的瞬间位移为沿牵引力方向,趋向于整体移动,牙周组织应力集中区域出现在牙尖及根尖点处,最大应力值出现在牙尖处;当牵引力方向与牙体长轴呈45°和90°夹角牵引时,埋伏牙趋向于以沿牵引力方向的倾斜移动,旋转中心在牙颈部附近,应力集中区域出现在牙尖及面向牵引力侧,最大应力值出现在牙尖处;同一种牵引角度下,随着牵引力大小的增加,埋伏牙牙周组织应力值逐渐增加,但应力集中区域变化不明显。结论当牵引力方向与牙体长轴一致时,埋伏牙趋向于整体移动,牙周组织应力分布较为均匀,有利于其牵引;当牵引力方向与牙体长轴不一致时,埋伏牙趋向于倾斜移动,牙周组织应力分布不均匀,不利于其牵引。较小的牵引力值有利于埋伏牙的牵引。
OBJECTIVE To establish a three-dimensional finite element model of impacted teeth and analyze the periodontal stress of the impacted teeth under different working conditions so as to provide basic experimental evidences for clinical orthodontic traction treatment of impacted teeth. Methods One case of maxillary canine anterior maxillary ambulation was selected. The three-dimensional finite element model of the maxillary impacted canine and its supporting tissues under the uniform coordinate system was established by using spiral CT and three-dimensional finite element method. Maintain the position of the cusp, adjust the tilt angle of the long axis of the impacted tooth so that the angle between the traction direction and the long axis of the tooth body is 0 °, 45 ° and 90 °, respectively. The force of 50,100,150g was applied to the ambushed tooth cusp of each model, and the characteristics of the equivalent stress contour of the periodontal ligament and the instantaneous displacement cloud pattern were analyzed and compared. Results When the direction of traction was consistent with the long axis of the tooth (0 °), the instantaneous displacement of each point on the impacted tooth was along the direction of the traction and tended to move integrally. The stress concentration area of periodontal tissue appeared at the cusp tip and apex, When the direction of traction and the long axis of the tooth is at an angle of 45 ° and 90 °, the ambushed teeth tend to move with a tilt in the direction of the traction force. The center of rotation is near the dental neck and the stress concentration In the same traction angle, with the increase of the traction force, the stress value of the periodontal tissue of the impacted tooth increased gradually, but the change of stress concentration area was not obvious. Conclusion When the direction of the traction force is consistent with the long axis of the tooth body, the ambushed teeth tend to move as a whole and the stress distribution in the periodontal tissue is more uniform, which is beneficial to traction. When the direction of the traction force is inconsistent with the long axis of the tooth body, the ambushed teeth tend to tilt, Periodontal tissue stress distribution is not uniform, is not conducive to its traction. Smaller traction values favor the traction of the impacted teeth.