Statement of problem

Zirconia frameworks milled by computer-aided design and computer-aided manufacturing (CAD-CAM) often require clinical adjustments. In addition, zirconia prefabricated abutments can also require customization to achieve an adequate emergence profile. However, the influence of grinding adjustment on the surface characteristics and mechanical behavior of yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) and the best grinding protocol is unclear.

Purpose

The purpose of this in vitro study was to evaluate the effect of different grinding protocols on the surface characteristics, phase transformation, and mechanical behavior of Y-TZP for frameworks and implant abutments.

Material and methods

Bar-shaped specimens were fabricated according to ISO 6872-2016 and divided into 3 groups: GC (control, untreated), GA (grinding and finishing with medium and fine diamond rotary instruments using high-speed handpiece under constant water cooling), and GB (grinding and finishing with coarse and medium diamond rotary instruments, respectively, using slow-speed handpiece without water cooling). After specimen grinding, the topography and surface roughness were evaluated by using a laser confocal microscope, the Young modulus was measured by the impulse excitation technique, and crystallographic phase transformation was analyzed by X-ray diffraction. Specimens were then submitted to step-stress accelerated life testing (n=18). The surface roughness and Young modulus results were analyzed by 1-way ANOVA and the Tukey honestly significant difference test (α=.05). The data of step-stress accelerated life testing were analyzed by the survival probability considering the number of cycles and force until fracture.

Results

Statistically significant differences were found among groups considering surface roughness (GA>GB>GC) (P<.05) and Young modulus (GB>GA=GC) (P=.003). X-ray diffraction showed that grinding leads to phase transformation, GC showed only tetragonal phase, while GA and GB showed tetragonal and monoclinic phases. No statistically significant difference (P<.05) was found among groups submitted to the same loading profile when the survival probability was compared, but significant difference was found between the light and moderate loading (P=.002) and light and severe loading (P=.014) of GB when different loading profiles in each group were compared.

Conclusions

Although grinding protocols affected surface characteristics and promoted phase transformation, the mechanical behavior of Y-TZP was not impaired. Therefore, both the grinding protocols tested can be safely used based on the evaluated properties.

中文翻译：

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不同研磨方案对氧化钇稳定的氧化锆多晶表面特性和疲劳行为的影响：一项体外研究。

问题陈述

通过计算机辅助设计和计算机辅助制造（CAD-CAM）铣削而成的氧化锆框架通常需要进行临床调整。此外，氧化锆预制基台也可能需要定制以实现足够的出土轮廓。然而，磨削调整对氧化钇稳定的四方氧化锆多晶（Y-TZP）的表面特性和机械性能的影响以及最佳磨削方案尚不清楚。

目的

这项体外研究的目的是评估不同研磨方案对Y-TZP用于框架和种植体基台的表面特性，相变和机械性能的影响。

材料与方法

棒状样品按照ISO 6872-2016的标准制造，分为3组：GC（对照，未处理），GA（在恒定水冷条件下使用高速手机使用中，细金刚石旋转仪进行研磨和精加工）和GB （分别使用不带水冷的低速手机，分别用中，粗金刚石旋转仪器进行研磨和精加工）。样品研磨后，通过激光共聚焦显微镜评估其形貌和表面粗糙度，通过脉冲激发技术测量杨氏模量，并通过X射线衍射分析结晶相变。然后将样品进行阶跃应力加速寿命测试（n = 18）。表面粗糙度和杨氏模量结果通过1向ANOVA和Tukey诚实地显着差异检验（α= .05）进行分析。通过考虑循环次数和直至断裂的力的生存概率来分析阶跃应力加速寿命测试的数据。

结果

在考虑了表面粗糙度（GA> GB> GC）（P <.05）和杨氏模量（GB> GA = GC）（P = .003）的组之间，发现了统计学上的显着差异。X射线衍射表明，研磨导致相变，GC仅显示四方相，而GA和GB显示四方相和单斜晶相。比较生存概率时，在提交相同负荷曲线的各组之间未发现统计学上的显着差异（P <.05），但轻度和中等负荷（P = .002）和轻度和严重负荷（P = .002）之间存在显着差异。比较各组的不同负荷曲线时，GB的P = .014）。

结论

尽管研磨方案影响了表面特性并促进了相变，但并未损害Y-TZP的机械性能。因此，可以根据评估的特性安全地使用两种测试的磨削方案。