Comparison of butt-joint endocrowns and ferrule prepared endocrowns constructed with different CAD/CAM materials in terms of fracture strength and failure mode, an in vitro study

Our in-vitro study aimed to estimate the influence of different preparation designs and types of constructed material on fracture resistance of endocrown restorations. Seventy intact human mandibular molar teeth were utilized in our study. Ten of them with no preparation considered as the control group. The remaining 60 teeth (experimental group) were root canal treated and were divided into 2 major groups based on preparation design: 1. Butt-joint endocrown preparation performed group (n=30); 2. Endocrown preparation was performed with the ferrule group (n=30). The two main groups were further divided into 3 subgroups based on the type of CAD/CAM restoration materials used. The first subgroup (n=10) of endocrowns were made with IPS e.max CAD (Ivoclar Vivadent Inc, NewYork, USA), the second subgroup (n=10) of endocrowns were made with monolithic zirconia (GC Initial zirconia meiningen/Austria), and the third subgroup (n=10) of endocrowns were made by reinforced composite (BRILLIANT Crios COLTENT). All endocrowns were cemented by self-adhesive resin cement (BisCem BISCO, USA) and thermally aged with 5000 cycles in a water bath between 5º C and 55º C. The fracture strength test was done by using a universal testing machine. Fracture resistances were measured in Newton (N), and failure modes were classified. The data were analyzed using two-way ANOVA and Bonferroni post hoc (α = .05) tests. Concerning the preparation designs, fracture resistance in butt-joint design (2754.6 ± 1268 N), was higher than that of ferrule design (1998.7 ± 1064.8 N) with a statistically significant difference. Concerning the materials used, the fracture resistance in zirconia (3703.6 ± 859.9 N) was statistically significantly higher than those of both IPS e.max (2119.7±768.8 N) and BRILLIANT Crios composite (1306.6 ± 420.6). The fracture resistance of IPS e.max CAD was statistically significantly greater than composite. The fracture mode analysis showed a lower percentage of favorable failure in butt-joint design groups with no significant difference, while ferrule design groups had a higher percentage of favorable failure except the zirconia group with a statistically significant difference. In conclusion, the butt-joint design endocrowns had higher fracture strength than ferrule design endocrowns; the monolithic zirconia material had the highest fracture strength while the BRILLIANT Crios reinforced composite had the lowest fracture strength. Keywords: Endocrown, Fracture strength, Butt-joint, Ferrule, CAD/CAM.