Comparison of Fracture Resistance and Failure Mode in Digitally Milled Restorations with Rapid Layering by Indirect Composite Resin: An In Vitro Study.

PURPOSE To evaluate the fracture resistance and failure mode of implant crowns made by polyether ether ketone (PEEK), zirconia, and chromium-cobalt frames, veneered by milled composite resin. MATERIALS AND METHODS Thirty-six implant analogs were mounted in acrylic blocks, and solid abutments were secured (n = 12). Single-unit frameworks were milled from PEEK, zirconia, or chromium-cobalt, and cemented to indirect composite veneers fabricated by the rapid layering technique. After thermal cycling, the fracture resistance test was performed at a speed of 0.5 mm/min, and the results were statistically analyzed by one-way analysis of variance (ANOVA) and Tukey post hoc test (P < .05). The failure mode was evaluated by a stereomicroscope ('L10). Veneer failure without damage to other components was considered desirable (repairable). RESULTS The mean fracture resistances of PEEK, zirconia, and chromium-cobalt specimens were 2,037.24, 2,567.05, and 2,032.10 N, respectively. The Tukey post hoc test showed no significant difference between the PEEK and chromium-cobalt groups (P = .99); however, the difference was significant between zirconia and PEEK or chromium-cobalt specimens (P = .001). Failure mode was desirable in all chromium-cobalt (12 specimens), 9 zirconia, and 7 PEEK-based specimens. CONCLUSION Zirconia-composite implant crowns had significantly higher fracture resistance. Given the range of maximum occlusal forces, all the specimens had clinically acceptable results. The failure mode was more desirable in chromium-cobalt, followed by zirconia-based crowns.