牵张成骨区成骨方式的有限元分析

背景：有研究报道牵张间隙内存在软骨内成骨及膜内成骨两种成骨方式,也有研究认为在只有轴向牵张力作用而无其他方向外力干扰情况下,牵张新骨仅以膜内成骨一种方式成骨。目的：研究不同咬合状态下牵张区新生组织所处的力学环境,并验证该环境是否具有诱导和促进成软骨的能力,解释成骨方式不一致的矛盾。方法：建立下颌骨双侧牵张成骨模型,设定牵开距离为1 cm,固定后4周,在骨面咀嚼肌附着部位施加肌肉力来模拟实际咀嚼运动。选择双侧后牙咬合、左侧磨牙咬合及前牙咬合状态进行模拟分析,考察压应力/张应力、剪应力、范式应力变化。结果与结论：①双侧后牙咬合状态：范式应力及剪应力自舌侧向颊侧力值有所增加。自远中舌侧下缘至远中颊侧上缘,压应力逐渐转为张应力。②前牙咬合状态：范式应力及剪应力自舌侧面逐渐向颊侧减小。压应力/张应力在舌侧面压应力较大,向颊侧逐渐减小,过渡为张应力。③左侧磨牙咬合状态：左侧牵张区各应力和双侧后牙咬合状态下的各应力分布特点很相近,但最大值均要比双侧后牙咬合状态下的相应力值小。右侧牵张区范式应力在远中面的上缘和下缘出现应力最大值,近中颊侧下缘出现应力最小值,之间为过渡区。剪应力与范式应力特点相似。压应力/张应力则主要出现在近中下缘。说明在固定早期若牵张器不够稳定,咀嚼运动可以在新生组织内形成一个促使软骨形成的力学环境,为成骨方式不一致的矛盾指出了明确的答案。

Finite element analysis of osteogenesis model of mandibular distraction zone

BACKGROUND:Some studies have reported that there exist two kinds of ossification ways, intramembranous ossification and endochondral ossification in the distraction gap. Others also reported that there will be only intramembranous ossification when the tensions forces axial without other direction of external interference.OBJECTIVE:To investigate the level of stress of different occlusal conditions suffered by new tissues, and to verify whether the environment can induce and promote endochondral ossification in order to explain the issue of osteogenesis inconsistent.METHODS:We established a clinical bilateral mandibular distraction osteogenesis model and set the distance of 1 cm. After consolidation for 4 weeks, we exerted muscle force in the site of masticatory muscles’ attachment in order to simulate the actual chewing movement. We selected three basic occlusion statuses, namely clenching in the intercuspal position, left unilateral molar clenching and incisal clenching. The three-dimensional finite element analysis was used to investigate the level of stress (stress/tensile stress, shear stress, the stress paradigm).RESULTS AND CONCLUSION:①Status of clenching in the intercuspal position: the value of Von Mises stress and shear stress was increased from lingual lateral to the buccal. The compression stress was gradually turned into a tensile stress from lingual and distal lower edge to buccal and distal upper edge. ②Status of incisal clenching: the value of Von Mises stress and shear stress was decreased from lingual lateral to the buccal. Pressure stress was gradually turned into a tensile stress from lingual lateral to the buccal. ③Status of left unilateral molar clenching: the stress distribution of left distract region was very similar to that of the intercuspal position status, but the maximum values were lower than the intercuspal position status. The maximum value of Von Mises stress existed at the upper and lower edge of distal lateral. The minimum value existed at the buccal and mesial lower edge. There is a transition zone between the maximum and minimum value. The characteristics of shear stress were similar to that of Von Mises stress. Compression/tensile stress mainly exited at the mesial lower edge. This indicates that masticatory movement can create a mechanical environment promoting the cartilage formation especially when the fixation is not stable enough and provide a accurate solution to the issue of osteogenesis inconsistent.