Objective: This study aimed to investigate the effect of occlusal thickness design on fracture resistance of endocrowns restored with lithium disilicate ceramic and zirconia.
Methods: A total of 24 artificial first mandibular molars were randomly divided into four groups with six teeth in each group as follows: group lithium disilicate ceramic-2 mm (lithium disilicate ceramic, with an occlusal thickness of 2 mm and a retainer length of 4 mm); group lithium disilicate ceramic-4 mm (lithium disilicate ceramic, with an occlusal thickness of 4 mm and a retainer length of 2 mm); group zirconia-2 mm (zirconia, with an occlusal thickness of 2 mm and a retainer length of 4 mm); and group zirconia-4 mm (zirconia, with an occlusal thickness of 4 mm and a retainer length of 2 mm). After adhesive cementation (RelyX Ultimate Clicker), all specimens were subjected to thermocycling (10 000 cycles). The specimens were subjected to fracture resistance testing at a 135° angle to the teeth at a crosshead speed of 0.5 mm·min⁻¹ in a universal testing machine. Data were analyzed with ANOVA and Tukey's HSD test by SPSS 15.0. The failure modes were classified.
Results: The fracture resistances of groups lithium disilicate ceramic- 2 mm, lithium disilicate ceramic-4 mm, zirconia-2 mm, and zirconia-4 mm were (890.54±83.41), (2 320.87±728.57), (2 258.05±557.66), and (3 847.70±495.99) N respectively. Group zirconia-4 mm had the highest fracture resistance, whereas group lithium disilicate ceramic-2 mm had the lowest.
Conclusions: The fracture resistance of molar endocrown with zirconia is higher than that with lithium disilicate ceramic. Increasing the occlusal thickness can improve the fracture resistance but increase the risk of fracture of abutment.
目的 探讨二硅酸锂陶瓷和氧化锆制作的下颌第一磨牙髓腔固位冠的牙合面厚度设计对抗折性能的影响。 方法 根据修复设计（冠部材料及厚度）的不同，将24个下颌第一磨牙树脂仿真牙随机分成4组，每组6个。二硅酸锂2 mm组：采用二硅酸锂陶瓷制作修复体，牙合面厚度2 mm，固位体长4 mm；二硅酸锂4 mm组：采用二硅酸锂陶瓷制作修复体，牙合面厚度4 mm，固位体长2 mm；氧化锆2 mm组：采用氧化锆制作修复体，牙合面厚度2 mm，固位体长4 mm；氧化锆4 mm组：采用氧化锆制作修复体，牙合面厚度4 mm，固位体长2 mm。使用树脂水门汀粘接系统（RelyX Ultimate Clicker）粘接后，冷热循环10 000次。将万能试验机与牙长轴呈135°，位移速度0.5 mm·min⁻¹，在颊尖加载，测定抗折力及折裂方式，并用SPSS 15.0软件进行方差分析和多重比较。结果 二硅酸锂2 mm组、二硅酸锂4 mm组、氧化锆2 mm组、氧化锆4 mm组的抗折力分别为（890.54±83.41）、（2 320.87±728.57）、（2 258.05±557.66）和（3 847.70±495.99）N。氧化锆4 mm组的抗折力最高，二硅酸锂2 mm组的抗折力最低。结论 磨牙髓腔固位冠使用氧化锆较二硅酸锂陶瓷有更高的抗折力，增加修复体牙合面厚度可提高抗折力，但基牙折裂风险也增加。.
Keywords: endocrown; fracture resistance; lithium disilicate ceramic; retainer; thickness; zirconia.