Thulasidas Shreedevi, Givan Daniel A, Lemons Jack E, O'Neal Sandra Jean, Ramp Lance C, Liu Perng-Ru
Graduate Prosthodontics Resident, Department of Restorative Sciences, School of Dentistry, University of Alabama, Birmingham, AL.
J Prosthodont. 2015 Feb;24(2):127-35. doi: 10.1111/jopr.12182. Epub 2014 Jun 27.
To investigate the effects of abutment design to correct for implant angulation and aging on the fracture resistance of zirconia abutments. Greater understanding of the fracture strength of the zirconia abutments under various clinical conditions may lead to improvement of clinical protocols and possibly limit potential failures of implant prosthetics.
Test specimens consisted of an implant-zirconia abutment-zirconia crown assembly with implant apex positioned at 0°, 20° to the facial (20F), and 20° to the lingual (20L) with respect to a constant crown contour. To keep the abutment design as the only variable, CAD/CAM technology was used to generate monolithic zirconia crowns identical both in external and internal dimensions and marginal contours to precisely fit all the abutments in an identical fashion. The monolithic zirconia abutments were designed to fit the constant crown contours and the internal connection of the implant at the three angulations. The customized abutments for the three implant angulations varied in emergence profile, screw hole location, and material thickness around the screw hole. Half the specimens from each group were subjected to steam autoclaving and thermocycling to simulate aging of the restorations in vivo. To mimic the off-axis loading of the central incisor, the specimens were loaded at the recommended cephalometric interincisal relationship of 135° between the long axis of the crown supported by the implant and the Instron force applicator simulating the mandibular incisor. The force applicator was positioned 2 mm from the incisal edge and loaded at a 1 mm/min crosshead speed. Data were evaluated by 2-way ANOVA (α = 0.05) and Tukey's HSD.
The 20F group had the highest fracture values followed by the 0° group, and the 20L group had the lowest fracture values. Aging did not yield any significant difference in fracture force magnitudes.
Within the limitations of this study, tilting the implant apex to the lingual significantly reduced the fracture strength of angle-corrected zirconia abutments. Accordingly, while the angle between the occlusal force application and the long axis of the implant decreases, the resistance (force) to fracture decreases.
研究基台设计对种植体角度校正的影响以及老化对氧化锆基台抗折性的影响。深入了解不同临床条件下氧化锆基台的抗折强度，可能会改进临床方案，并有可能减少种植修复体的潜在失败。
测试样本由种植体-氧化锆基台-氧化锆全冠组件组成，种植体根尖相对于恒定的全冠外形分别位于0°、向唇侧20°（20F）和向舌侧20°（20L）。为使基台设计作为唯一变量，采用计算机辅助设计/计算机辅助制造（CAD/CAM）技术制作整体式氧化锆全冠，其外部和内部尺寸以及边缘轮廓均相同，以便以相同方式精确适配所有基台。整体式氧化锆基台设计为适配恒定的全冠外形以及种植体在三种角度下的内部连接。针对三种种植体角度定制的基台在穿出轮廓、螺丝孔位置以及螺丝孔周围的材料厚度方面有所不同。每组样本的一半进行蒸汽高压灭菌和热循环处理，以模拟修复体在体内的老化情况。为模拟中切牙的非轴向加载，样本在种植体支持的全冠长轴与模拟下颌切牙的英斯特朗力施加器之间呈135°的推荐头影测量切牙间关系下加载。力施加器位于距切缘2 mm处，并以1 mm/min的十字头速度加载。数据采用双向方差分析（α = 0.05）和图基 Honestly Significant Difference（HSD）检验进行评估。
20F组的抗折值最高，其次是0°组，20L组的抗折值最低。老化在抗折力大小方面未产生任何显著差异。
在本研究的局限性范围内，将种植体根尖向舌侧倾斜会显著降低角度校正后的氧化锆基台的抗折强度。因此，当咬合力施加方向与种植体长轴之间的角度减小时，抗折（力）能力会降低。
