Farzin Mitra, Derafshi Reza, Giti Rashin, Taghva Masumeh
Dept. of Prosthodontics, School of Dentistry, Shiraz University of Medical Sciences, Shiraz, Iran.
Dept. of Prosthodontics, Biomaterials Research Center, School of Dentistry, Shiraz University of Medical Sciences, Shiraz, Iran.
J Dent (Shiraz). 2021 Jun;22(2):132-137. doi: 10.30476/DENTJODS.2020.85080.1114.
Retrieval of cement-retained implant-supported restorations is challenging in cases of screw loosening or periodontal problems.
The purpose of this study was to evaluate the effect of the screw access hole on the fracture resistance of zirconia-based cement-retained restorations with and without an access opening.
In this study thirty-three cement-retained implant-supported zirconia-based molar crowns were fabricated and divided into 3 groups (n=11). As the control group, group 1 consisted of conventional cement-retained crowns. Group 2 comprised conventional cement-retained crowns in which a hole was created in the location of the screw. Group 3 consisted of cement-retained crowns in which a ledge was created in the location of the screw access channel. The specimens were cemented to their abutments and their access openings were filled with composite resin. A compressive load was applied to the specimens using a universal testing machine until they fractured. The mean fracture resistance values of the samples were compared by using the one-way ANOVA and Tamhane post-hoc test (a=0.05).
The mean fracture resistance values were 1270.18± 12.67 N in group 1 (the control group), 960.09±210.67 N in group 2 (conventional), and 1357.81±361.68 N in group 3 (the special design). The fracture resistance value was higher in the special design group than that of the conventional design (= 0.018) and the fracture resistance value of the conventional design group was less than that of the control group (= 0.042). No statistically significant difference was detected between the control group and the special design group in fracture resistance values.
Preparing a screw access hole in cement-retained implant-supported zirconia-based crowns decreased the fracture resistance of the restoration. Designing a ledge in the zirconia framework around the access hole may increase the fracture resistance of the restoration.
在螺丝松动或存在牙周问题的情况下，取出水泥固定的种植体支持修复体具有挑战性。
本研究的目的是评估螺丝通道孔对有无通道开口的氧化锆基水泥固定修复体抗折性的影响。
在本研究中，制作了33个水泥固定的种植体支持的氧化锆基磨牙冠，并分为3组（n = 11）。作为对照组，第1组由传统的水泥固定冠组成。第2组包括在螺丝位置制作了一个孔的传统水泥固定冠。第3组由在螺丝通道位置制作了一个台阶的水泥固定冠组成。将标本粘固到基台上，其通道开口用复合树脂填充。使用万能试验机对标本施加压缩载荷，直至其断裂。通过单因素方差分析和Tamhane事后检验（α = 0.05）比较样本的平均抗折值。
第1组（对照组）的平均抗折值为1270.18±12.67 N，第2组（传统组）为960.09±210.67 N，第3组（特殊设计组）为1357.81±361.68 N。特殊设计组的抗折值高于传统设计组（P = 0.018），传统设计组的抗折值低于对照组（P = 0.042）。对照组和特殊设计组在抗折值上未检测到统计学上的显著差异。
在水泥固定的种植体支持的氧化锆基牙冠上制备螺丝通道孔会降低修复体的抗折性。在通道孔周围的氧化锆框架中设计一个台阶可能会增加修复体的抗折性。
