非均匀的粘结剂层的厚度对全瓷冠应力分布的影响

Effect of nonuniform adhesive layer thickness on the stress distribution of all-ceramic crowns

目的:探讨非均匀的粘结剂层的厚度对轴向加载的全瓷冠应力分布的影响。方法:建立四个轴对称的二维有限元的In-Ceram全瓷冠模型,粘结剂层的厚度分别为均匀厚度25μm组,100μm组,咬合面25μm轴壁和肩台100μm组及咬合面100μm轴壁和肩台25μm组。通过轴向均匀加载540牛顿对全瓷冠的各组分的应力大小和分布进行分析。结果:只有当粘结剂层为均匀厚度100μm时,饰面瓷的拉应力峰值比均匀厚度25μm时降低12%;只有当粘结剂层为均匀厚度100μm和咬合面厚度25μm、轴壁肩台厚度100μm时,粘结剂层的拉应力峰值较均匀厚度25μm分别降低了33.3%和33.1%;核瓷所受的拉应力水平最高。当咬合面粘结剂层的厚度为25μm时,核瓷拉应力峰值降低。饰面瓷的拉应力峰值存在于朝向核瓷侧的咬合面线角区,应力值较低;核瓷的拉应力峰值存在于咬合面线角区的内面上,而粘结剂的拉应力峰值则位于轴龈线角并向轴壁抬起处。结论:从材料的机械性能角度分析,粘结剂层在修复体各部位对全瓷修复体的应力所起到的作用是不同的,要结合修复材料的机械性能和受到的应力水平来决定修复体粘结剂层的厚度。

Objective： To investigate the effect of nonuniform adhesive layer thickness on the stress distribution of axially loaded all-ceramic crowns. Methods： Analyses were performed by analyzing four different axisymmetric two-dimensional finite element models constructed by various adhesive layer thickness groups.These were groups of uniform adhesive layer thickness of either 25μm（group 25μm）and100μm（group100μm）, associated with group of 100μm in occlusal region and 25 μm in remaining region（group 25-100μm） and correspondingly reverse one （group 100-25）.All models were loaded with a uniformly vertical 540N force downward, on the top of the crown.Two-dimensional finite - element stress analyses were performed. Results： The porcelain peak tensile principal stress of group 100μm decreased by 12% compared to group 25 μm and was the lowest in all the four groups. With regard to the adhesive layer peak tensile stress, both group 100μm and group 100-25 μm were lower than the other groups and decreased by 33.3% and 33.1%, respectively in comparison with group 25 μm. When 25 μm adhesive layer thickness occurred in occlusal region, the core ceramic peak tensile stresess lowered, but were still the highest among the all-ceramic crowns. For all the groups, the porcelain tensile stresses were located around the inner surface of the axial/occlusal region, the core ceramic on the inner surface of the axial/occlusal line angle region, while the adhesive layer in the chamfer region turning up toward axial region. Conclusions： Taking mechanical properties of materials into consideration, nonuniform adhesive layer thickness plays an important role in the stress distribution of all-ceramic crowns. The adhesive layer locations have different effects on the stress distribution.Particular emphasis should be placed on the determination of adhesive layer thickness in term of material properties and stress level.