Fracture resistance and failure modes of endocrowns manufactured with different CAD/CAM materials under axial and lateral loading

Objectives The purpose of this in vitro study was to evaluate the fracture resistance and failure modes of endocrowns made of three computer-aided design/computer-aided manufacturing (CAD/CAM) materials subjected to thermo-mechanical cycling loading. Materials and Methods Eighty mandibular molars were divided into four groups (n = 20): one (C E) was restored with lithium disilicate glass-ceramic conventional crowns, three were restored with endocrowns made of three different CAD/CAM materials; (E E) lithium disilicate glass-ceramic, (E V) zirconia-reinforced lithium silicate glass-ceramic, and (E C) resin nano-ceramic. After cycling loading, half of the samples from each group were loaded axially and the other half was loaded laterally. Fracture resistance was recorded in Newton (N) and failure modes were classified. Two-way ANOVA, Bonferroni post hoc (alpha = .05), Chi-square, and multiple logistic regression tests were used to analyze data. Results Statistically significant interaction were recorded between fracture resistance (N) and loading (P < .001), and groups (conventuional crown and endocrowns; P < .001). Endocrowns presented higher fracture strength than conventional crowns. Fracture resistance was significantly larger under axial loading. The numbers of irreparable failures were extremely important in the endocrowns groups (Groups E E, E V, E C), and only conventional crowns (Group C E) showed almost no irreparable failures under axial loading. Conclusion Lithium disilicate glass-ceramic recorded the highest fracture resistance under axial and lateral loading. Clinical Significance The number of irreparable failures with all endocrown materials tested do not suggest yet the use of this type of restorations in posterior teeth.