高嵌体修复下颌第一磨牙近中邻[牙合]面缺损的生物力学分析

Biomechanical analysis of mesial-occlusal defect repair in mandibular first molar with onlay repair

目的应用三维有限元法探讨髓腔深度对E-Max铸瓷高嵌体修复下颌第一磨牙近中邻[牙合]面(mesial-occlusal,MO)缺损的应力大小及分布情况。方法选取1名牙周健康、牙列完整、咬合正常、左侧下颌第一磨牙形态标准的哈尔滨医科大学附属第二医院口腔颌面外科的志愿者作为建模对象,采用锥形束CT(conical beam CT,CBCT)扫描数据结合逆向工程软件建立下颌第一磨牙根管治疗后MO缺损的有限元模型,选择2种不同[牙合]面覆盖方式的高嵌体,A组为全覆盖式的高嵌体,B组为保留远中边缘嵴式的高嵌体。根据髓腔制备深度分为2 mm.3 mm.4 mm.5 mm组,各组分别施加280 N的垂直载荷和105 N的舌向45度载荷,观察修复体、黏结剂层及剩余牙体组织的应力大小和分布情况。结果A组中各结构的应力值随着髓腔深度的增加而增大,髓腔深度为2 mm时,各结构的应力值相对最小;B组在髓腔深度为5 mm时,垂直加载下,各结构应力值最小,斜向加载下,黏结剂和牙本质的应力值最大;B组与A组的应力大小相似,但斜向加载时,除牙釉质外各结构应力值均变小。结论增加髓腔深度,全覆盖式高嵌体易脱落和折裂,而保留边缘嵴式高嵌体本身能得到有效保护,值得临床推广。

Objective To explore the depth of the medullary cavity of E-Max ceramic onlay repair of mandibular first molar mesial adjacent surface(mesial-occlusal,MO)defect stress size and distribution by the three-dimensional finite element method.Methods The finite element model of MO defect of mandibular first molar after root canal treatment was established by using conical beam CT(CBCT)scanning data and reversed engineering software,two different face cover means high onlay were selected,group A was full of cover type onlay,group B retained the far edge of crest type onlay.They was divided into 2 mm,3 mm,4 mm,5 mm group according to the preparation of the medullary cavity depth,a vertical load of 280 N and a tongue load of 105 N at 45°were applied to each group,observed the restoratio,the adhesive layer and the rest of the tooth body stress size and distribution of the organization were analyzed.Results The stress value of each structure in group A increasead with the increase of the medullary cavity depth.When the medullary cavity depth was 2 mm,the stress value of each structure was relatively minimum.In group B,when the pulp cavity depth was 5 mm,the stress value of each structure was the lowest under vertical loading,while the stress value of binder and dentin was the highest under oblique loading.The stress of group B was similar to that of group A,but under oblidue loading,the stress of all structures decreased except tooth enamel.Conclusion When the depth of medullary cavity increases,the full cover type onlay is easy to fall off and break.While retaining the marginal ridge type onlay itself can be effectively protected,it is worthy of clinical promotion.