全瓷冠粘接界面缺陷对修复体应力的影响

Influence of Defects at Bonding Interface on Stress Distributions in Monolithic Ceramic Crown

目的探究当单层全瓷冠修复体与胶层之间存在由于口腔水环境下造成的脱粘以及粘结缺陷时对修复体内部应力分布的影响。方法以二硅酸锂CAD/CAM单层冠为研究对象,进行三维有限元实体建模。利用有限元软件ABAQUS定义瓷冠内表面与胶层上表面的7个脱粘状态(状态1~7),以及2种界面缺陷的情形(情况I、II)。对所建9个模型底部进行完全约束,并在咬合面分别用直径5 mm半球形解析刚体施加600 N竖向载荷以对其进行应力计算。结果在竖向咬合力作用下,瓷冠内部和胶层上表面应力集中主要出现在脱胶边界处以及缺陷的周边。瓷冠内部的第1主应力没有超过其极限抗拉强度,但胶层中的最大拉应力超过粘结剂的极限抗拉强度,即胶层会发生内聚破坏。结论瓷冠内壁的粘结完整在维持瓷冠内部整体应力处于较低水平方面有重要作用,粘结界面处缺陷的存在对瓷冠承载力的影响比单纯脱粘面积的增加对瓷冠承载力造成的影响更加显著。为保障全瓷冠修复体的承载能力,在口腔修复临床实践中更应该注意避免引入粘结缺陷。

Objective To explore the effects of the interfacial debonding caused by water environment in the mouth and the interfacial defects between the crown and cement on stress distributions in all-ceramic crowns.Methods The three-dimensional solid model of lithium disilicate CAD/CAM crowns for the first mandibular molar was established.Seven debonding states between inferior surface of the crown and top surface of the cement(Stage 1-7)as well as two interfacial defects(Case I and II)were defined in finite element software ABAQUS.The bottom of nine models was completely constrained.For stress calculation,the 600 N vertical load was applied at occlusal surface via an analytical rigid hemisphere with the diameter of 5 mm.Results Under occlusal vertical load,the stress on interior of the crown and top surface of the cement was mainly distributed at the boundary of the debonding areas and margin of the defects.The first principle stress on interior of the crown did not exceed its ultimate tensile strength,but the maximum tensile stress of the cement exceeded its ultimate tensile strength,leading to cohesive failure in the cement.Conclusions The axial wall played a critical role in maintaining the principal tensile stress of the crown at a lower level.The defects at bonding interface between the crown and cement had a more significantly impact on load capacity of the crown than the increase in debonding areas.In order to improve load bearing capacities of all-ceramic crowns,attention should be paid to avoid defects in clinical prosthodontic practices.