Implant angulation and fracture resistance of one-piece screw-retained hybrid monolithic zirconia ceramic restorations

OBJECTIVE: This study aimed to investigate the fracture resistance of one-piece screw-retained hybrid monolithic zirconia ceramic restorations in different implant angulations. MATERIALS AND METHODS: Three implant fixtures were embedded in acrylic resin blocks with 0°, 15°, and 25° angulations. For each group of implant angulations, 11 screw-retained one-piece monolithic zirconia restorations were made and bonded to the titanium inserts with a dual-cure self-adhesive resin. The complexes were screwed to the implant fixtures with titanium screws. The samples were thermocycled, subjected to compressive load, and fracture modes were recorded. One-way ANOVA and post hoc Tukey’s test were used for statistical analyses (α = 0.05). RESULTS: One-way ANOVA showed the fracture resistance to be significanltly different among the study groups (P = 0.036). The 15° group was significantly more resistant than 0° (P = 0.031). However, the 25° group was not significantly different from the 15° (P = 0.203) and 0° groups (P = 0.624). Fractures occurred only on the restorations, not at the screw levels. CONCLUSIONS: Tilting the implant up to 15° improves the fracture resistance of one-piece screw-retained hybrid monolithic zirconia restorations; however, increasing the tilt to 25° would not yield restorations with significantly better fracture strength than the straight implants. Accordingly, when angulated implants are indicated in the esthetic zones, one-piece screw-retained hybrid monolithic zirconia ceramic restorations can be used with acceptable fracture strength.