Prosthodontics, Faculty of Dentistry, The University of Hong Kong, Hong Kong, China.
Private Practice, New Delhi, India.
J Dent. 2018 Aug;75:65-73. doi: 10.1016/j.jdent.2018.05.016. Epub 2018 May 26.
This study investigates the effect of selected surface finishing techniques on the biaxial flexural strength, surface roughness and phase transformation of a zirconia dental restorative material.
Fully-sintered zirconia discs (⌀19.5 mm × 0.85 mm) were treated on one side with a single or a combination of the following treatments: diamond and/or tungsten-carbide burs without water coolant in an air-turbine handpiece, air-particle abrasion, rubber-point polishing in a contra-angle handpiece, or no treatment (control). Biaxial flexural strength (BFS) (eleven groups, n = 10) was determined using a universal testing machine and surface roughness (thirteen groups, n = 6) was assessed using a profilometer. Results were analysed using one-way ANOVA and Student-Newman-Keuls Post-hoc test (α = 0.05) with Bonferroni correction. Specimens were observed under scanning electron microscopy (SEM) and x-ray diffraction (XRD) for their microstructure and crystalline phases respectively.
Grinding with diamond burs did not weaken zirconia (p > 0.0045) but produced rougher surfaces than the control group (p < 0.0038). Tungsten-carbide burs smoothened diamond ground specimens (p < 0.0038) for both grits of diamond. Specimens ground by tungsten-carbide burs have significantly reduced mean BFS (p < 0.0045) by up to two-thirds and SEM revealed fine surface cracks. Air-particle abrasion restored the mean BFS of tungsten-carbide ground specimens to control levels (p > 0.0045) and surface cracks were not observed. Phase transformation was not detected by XRD.
Dental zirconia ground dry with tungsten-carbide burs has a significantly reduced BFS and a smooth but defective surface. These defects may be removed and BFS restored by air-particle abrasion.
The use of tungsten-carbide burs for grinding dental zirconia should be cautioned. Diamond grinding does not weaken zirconia but requires further polishing.
本研究旨在探讨选定的表面处理技术对牙科修复用氧化锆材料的双轴弯曲强度、表面粗糙度和相转变的影响。
将完全烧结的氧化锆圆盘（⌀19.5mm×0.85mm）的一侧用以下处理方法中的一种或多种进行处理：在空气涡轮手机中不使用水冷却剂的金刚石和/或碳化钨车针、空气粒子喷砂、在角向机手中用橡胶点抛光、或不处理（对照组）。使用万能试验机测定双轴弯曲强度（BFS）（十一组，n=10），使用轮廓仪测定表面粗糙度（十三组，n=6）。结果采用单因素方差分析和 Student-Newman-Keuls 事后检验（α=0.05），并进行 Bonferroni 校正。用扫描电子显微镜（SEM）观察试件的微观结构，用 X 射线衍射（XRD）观察试件的晶体相。
金刚石车针打磨不会削弱氧化锆（p>0.0045），但表面粗糙度大于对照组（p<0.0038）。碳化钨车针使金刚石打磨的试件表面变得更光滑（p<0.0038），无论使用哪种粒度的金刚石。碳化钨车针打磨的试件的平均 BFS 显著降低（p<0.0045），降幅高达三分之二，SEM 显示出细小的表面裂纹。空气粒子喷砂可使碳化钨打磨试件的平均 BFS 恢复至对照组水平（p>0.0045），且未观察到表面裂纹。XRD 未检测到相转变。
牙科氧化锆经碳化钨车针干式打磨后，BFS 显著降低，表面光滑但有缺陷。这些缺陷可以通过空气粒子喷砂去除并恢复 BFS。
打磨牙科氧化锆时应慎用碳化钨车针。金刚石打磨不会削弱氧化锆，但需要进一步抛光。
