Alammari Manal Rahma, Abdelnabi Mohamed Hussein, Swelem Amal Ali
Oral and Maxillofacial Prosthodontic Department, Faculty of Dentistry, King Abdulaziz University, Jeddah, Kingdom of Saudi Arabia,
Removable Prosthodontic Department, Faculty of Dentistry, Minia University, Minia, Egypt.
Clin Cosmet Investig Dent. 2018 Dec 31;11:1-8. doi: 10.2147/CCIDE.S193326. eCollection 2019.
Computer-aided design (CAD) and computer-aided manufacturing (CAM) monolithic crowns are gaining momentum. Limited evidence exists about the effect of tooth preparation total occlusal convergence (TOC) on marginal and internal gap distances in addition to load to fracture values.
The aim of this study was to evaluate, by microcomputed tomography (µCT), the influence of 12° and 20° TOC on marginal and internal adaptation of zirconia-reinforced lithium silicate (ZLS) crowns. Moreover, values of load to fracture with and without initial cyclic loading (CL) were compared.
Forty ZLS crowns were fabricated on dies with TOC of 12° and 20°, 20 crowns for each group. µCT was used to compare marginal and internal adaptation. Each specimen was measured at 140 points distributed on all tooth preparation surfaces for 2D gap distance assessment. 3D gap volume was also evaluated. Crowns were then cemented and divided into two subgroups; the first was stored in distilled water (no cyclic loading [NCL] subgroup), the second was subjected to CL (CL subgroup).
Factorial repeated measures ANOVA followed by Bonferroni post hoc in addition to independent and dependent -tests were used for statistical analysis. Marginal gap, absolute marginal discrepancy, and occlusal gap measurements showed significant differences between the measurement sites. Static load to fracture values showed significant differences between TOC groups for both NCL (=0.011) and CL (=0.025) subgroups.
An increase of TOC from 12° to 20° did not affect marginal and internal adaptation but resulted in higher values of load to fracture of ZLS crowns. CL simulating 1 year of service did not result in fatigue failure.
计算机辅助设计（CAD）和计算机辅助制造（CAM）整体式全冠正越来越受到关注。除了对断裂载荷值的影响外，关于牙体预备的全牙合面聚合度（TOC）对边缘和内部间隙距离的影响，现有证据有限。
本研究旨在通过显微计算机断层扫描（µCT）评估12°和20°的TOC对氧化锆增强硅酸锂（ZLS）全冠边缘和内部适配性的影响，并比较有无初始循环加载（CL）情况下的断裂载荷值。
在TOC为12°和20° 的代型上制作40个ZLS全冠，每组20个。采用µCT比较边缘和内部适配性。在所有牙体预备表面分布的140个点上测量每个标本，以评估二维间隙距离；同时也评估三维间隙体积值。然后将全冠粘固并分为两个亚组：第一组储存在蒸馏水中（无循环加载 [NCL]亚组），第二组进行CL处理（CL亚组）。
采用析因重复测量方差分析，随后进行Bonferroni事后检验以及独立和相关检验进行统计分析。边缘间隙、绝对边缘差异和咬合间隙测量结果显示，测量部位之间存在显著差异。NCL（P = 0.011）和CL（P = 0.025）亚组的静态断裂载荷值在TOC组之间均存在显著差异。
TOC从12°增加到20° 不会影响边缘和内部适配性，但会导致ZLS全冠的断裂载荷值更高。模拟1年使用期的CL未导致疲劳失效。
