Department of Restorative Dentistry, School of Dentistry, Shahed University, Tehran, Iran.
Department of Epidemiology and Biostatistics, Faculty of Public Health, Tehran, Iran.
J Prosthodont. 2019 Jan;28(1):e172-e180. doi: 10.1111/jopr.12586. Epub 2017 Mar 8.
To evaluate the effect of overglazing and two polishing procedures on flexural strength and quality and quantity of surface roughness of a monolithic lithium disilicate ceramic computer-aided design (CAD) after grinding.
This in vitro study was conducted on 52 partially crystalized bar-shaped specimens (16 × 4 × 1.6 mm) of monolithic lithium disilicate ceramic. The specimens were wet polished with 600-, 800-, and 1200-grit silicon carbide papers for 15 seconds using a grinding/polishing machine at a speed of 300 rpm. Then, the specimens were crystalized and glaze-fired in one step simultaneously and randomly divided into four groups of 13: (I) Glazing group (control); (II) Grinding-glazing group, subjected to grinding with red band finishing diamond bur (46 μm) followed by glazing; (III) Grinding-D+Z group, subjected to grinding and then polishing by coarse, medium, and fine diamond rubber points (D+Z); and (IV) Grinding-OptraFine group, subjected to grinding and then polishing with a two-step diamond rubber polishing system followed by a final polishing step with an OptraFine HP brush and diamond polishing paste. The surface roughness (Ra and Rz) values (μm) were measured by a profilometer, and the mean values were compared using one-way ANOVA and Tamhane's test (post hoc comparison). One specimen of each group was evaluated under a scanning electron microscope (SEM) for surface topography. The three-point flexural strength values of the bars were measured using a universal testing machine at a 0.5 mm/min crosshead speed and recorded. The data were analyzed using one-way ANOVA and Tamhane's test (α = 0.05).
Statistically significant differences were noted among the experimental groups for Ra, Rz (p < 0.0001), and flexural strength values (p < 0.009). The lowest Ra and Rz values were found in the grinding-OptraFine group (0.465 ± 0.153), which were significantly lower than those in glazing (p < 0.03) and grinding-glazing (p < 0.001) groups. The Ra and Rz values were not significantly different between the two polishing systems (p = 0.23 and p = 0.25, respectively). The highest flexural strength was found in the glazing group (283.350 ± 49.854 MPa) without significant differences compared to grinding-glazing (p = 0.98) and grinding-OptraFine groups (p = 0.86). The lowest flexural strength was found in grinding-D+Z group (225.070 ± 17.299), which was significantly different from the value in glazing (p < 0.03) and grinding-glazing (p < 0.04) groups. SEM analysis of polished surfaces revealed regular morphology with some striations.
The OptraFine system created smoother and more uniform surfaces in terms of quantity (p < 0.03 for Ra, p < 0.01 for Rz) and quality of roughness compared to glazing. The flexural strength of lithium disilicate ceramic after polishing with the OptraFine system was similar to that after glazing (p = 0.86). Despite similar surface roughness after polishing with the two systems, the D+Z system reduced the flexural strength of ceramic (p < 0.03).
评估上釉和两种抛光程序对整体式硅酸锂陶瓷计算机辅助设计（CAD）在研磨后的弯曲强度以及表面粗糙度的数量和质量的影响。
本体外研究使用 52 个部分结晶的条形样本（16×4×1.6mm）进行，这些样本为整体式硅酸锂陶瓷。使用研磨/抛光机以 300rpm 的速度用 600、800 和 1200 号碳化硅砂纸对样本进行湿抛光 15 秒。然后，样本同时进行结晶和上釉烧制，并随机分为四组，每组 13 个样本：（I）上釉组（对照组）；（II）研磨上釉组，先用红色带金刚石修整器（46μm）进行研磨，然后上釉；（III）研磨-D+Z 组，先用粗、中、细金刚石橡胶点（D+Z）进行研磨，然后进行抛光；（IV）研磨-OptraFine 组，先用两步金刚石橡胶抛光系统进行研磨，然后用 OptraFine HP 刷和金刚石抛光膏进行最后抛光步骤。使用轮廓仪测量表面粗糙度（Ra 和 Rz）值（μm），并使用单向方差分析和 Tamhane 检验（事后比较）比较平均值。每组的一个样本在扫描电子显微镜（SEM）下评估表面形貌。使用万能试验机以 0.5mm/min 的十字头速度测量棒材的三点弯曲强度值，并记录。使用单向方差分析和 Tamhane 检验（α=0.05）对数据进行分析。
实验各组的 Ra、Rz（p<0.0001）和弯曲强度值存在显著差异（p<0.009）。研磨-OptraFine 组的 Ra 和 Rz 值最低（0.465±0.153），与上釉（p<0.03）和研磨上釉（p<0.001）组相比，显著更低。两种抛光系统的 Ra 和 Rz 值没有显著差异（p=0.23 和 p=0.25）。上釉组的弯曲强度最高（283.350±49.854MPa），与研磨上釉组（p=0.98）和研磨-OptraFine 组（p=0.86）相比无显著差异。研磨-D+Z 组的弯曲强度最低（225.070±17.299），与上釉组（p<0.03）和研磨上釉组（p<0.04）相比差异显著。抛光表面的 SEM 分析显示出规则的形态，有一些条纹。
与上釉相比，OptraFine 系统在数量（Ra 为 p<0.03，Rz 为 p<0.01）和粗糙度质量方面创造了更光滑和更均匀的表面。用 OptraFine 系统抛光后的硅酸锂陶瓷的弯曲强度与上釉相似（p=0.86）。尽管两种系统抛光后的表面粗糙度相似，但 D+Z 系统降低了陶瓷的弯曲强度（p<0.03）。
