The effect of preparation designs on the fracture strength of anterior endocrowns prepared with two different materials

Purpose: The aim of our study is to compare the fracture strength resistance of endocrown restorations applied to central teeth with different preparation designs prepared with CAD/CAM technique from two different materials. Material and methods: In our study, 40 extracted human maxillary central teeth were used. The samples were cut 3 mm above the enamel cement level with the help of a separator. Standard root canal treatment was applied to the teeth. The teeth were randomly divided into 2 groups with ferrule (2 mm circumferential) and non-ferrule. After the preparation in the form of a butt joint was completed in the non-ferrule group, the preparation was completed in such a way that ferrule was formed in teeth containing ferrule, and the intracanal extensions of the samples were 3 mm. Then, these two groups (n=20) were randomly divided into 2 subgroups (n=10) in order to produce restorations with two different materials, zirconia-reinforced lithium silicate and lithium disilicate-containing CAD/CAM blocks. After the restorations were cemented with G-CEM Link Force, a dual cure total etch system, they were kept at 37°C for 24 hours. All samples were then subjected to a thermal cycle treatment of 5000 cycles between 5°C and 55°C. . With a universal testing machine, loading was performed at a 45° angle to the long axis from the palatal face of the tooth at a speed of 1 mm/min until fracture occurred. The maximum fracture strength (Newton) values of the restorations were recorded. The fracture types of the samples were examined and photographed. The obtained data were analyzed with the IBM SPSS Statistics Version 21 package program. The Mann Whitney U and Kruskal Wallis H Tests were used to examine the differences between the groups. Result: Mean breakage values of ferrule and non-ferrule groups were recorded as 561.23 N and 395.63 N, respectively. There is a statistically significant difference between the breakage values according to the presence and absence of ferrule. (p<0.05). A statistically significant difference was found between the mean breakage values (534.1 N) of endocrowns produced with lithium disilicate with a 2 mm circumferential ferrule and the mean breakage values (365.38 N) of endocrowns produced with lithium disilicate without ferrule (p<0.05). Although the mean breakage values (588.35 N) of endocrones produced with zirconium-reinforced lithium disilicate containing ferrule were higher than the mean breaking values (425.87 N) of the samples without ferrule, no statistically significant difference was found. There was no statistical difference between the materials in terms of refraction values. Conclusions: In the presence of ferrule, the refraction values of the samples were higher. While there was no significant difference between the fracture values of lithium disilicate and zirconium-reinforced lithium silicate endocrowns, all compared groups showed sufficient average fracture strength.