Influence of restorative material and margin relocation on the fracture resistance of teeth restored with CAD/CAM endocrowns

Aim To evaluate the resistance to load of composite and lithium silicate CAD/CAM endocrowns cemented on maxillary molars with or without margin relocation in a standardised proximal box. Methodology Sample size was calculated making reference to the results of a preliminary study (a=0.05; b=0.20; d=500.0; r=280.0). Thirty-two intact extracted maxillary molars of comparable size were root-filled and randomly allocated to four experimental groups (n = 8): composite endocrown without margin relocation; composite endocrown with margin relocation; lithium silicate without margin relocation; lithium silicate with margin relocation. The tested CAD/CAM materials were Lava Ultimate and Celtra DUO for composite and lithium silicate groups, respectively. The margin relocation procedure involved the preparation of a standardized mesial box and restoration with a flowable composite. The endocrowns were obtained with the Cerec 3 CAD/CAM system making use of a custom-designed phantom model and luted with self-adhesive cement. The restored teeth underwent thermomechanical aging (1 250 000 cycles, 1 Hz, 5–55°C) and were axially loaded to fracture with a universal testing machine. Fracture types were qualitatively assessed. Maximum load to fracture were compared amongst groups with a two-way analysis of variance and Duncan post hoc test (P < 0.05). Results No specimens exhibited appreciable defects after the thermomechanical aging. The mean maximum load values exceeded the threshold of the masticatory forces in all the tested groups. The composite endocrown without margin relocation obtained the greatest resistance values (1910.6 373.1 N), while the lithium silicate with margin relocation obtained the lowest (1314.9 326.1 N). For both tested materials, margin relocation slightly but not significantly reduced the resistance values. Most specimens had non-restorable fractures. Conclusions Under the conditions of the present study, margin relocation did not influence the resistance to fracture of teeth restored with CAD/CAM endocrowns. A trend of improved resistance to load of endocrown restorations was observed for the tested composite material in comparison to lithium silicate.