Fracture Resistance of Straight and Angulated Zirconia Implant Abutments Supporting Anterior Three-Unit Lithium Disilicate Fixed Dental Prostheses

Purpose: The purpose of this study was to evaluate fracture resistance of straight and angulated zirconia implant abutments supporting anterior three-unit lithium disilicate fixed dental prostheses (FDPs). Materials and Methods: Four different test groups (n = 8) representing anterior three-unit implant-supported allceramic FDPs were fabricated to fit an in vitro model with two implants. Groups 1 and 2 simulated a clinical situation with an ideal implant position for maxillary left central and right lateral incisors from a prosthetic point of view, which allowed for the use of a straight, prefabricated zirconia and titanium abutment. Groups 3 and 4 simulated a situation with a compromised implant position that required an angulated (15-degree) abutment. Tapered internal-connection implants (Direct's Legacy, 13-mm length, 3.7-mm diameter, Implant Direct) mounted in epoxy resin models were used in this study. Lithium disilicate (IPS e.max press, Ivoclar Vivadent) three-unit FDPs were fabricated and cemented using self-adhesive resin cement. The samples were subjected to thermocycling (2 × 3,000 × 5°C/55°C) and mechanical loading (TCML; 50 N × 600,000 cycles). Fracture resistances were determined for all the samples that survived aging. Kruskal-Wallis analysis of variance and Mann-Whitney U tests were performed to test for differences in fracture strength values at a 5% significance level. Results: All samples subjected to TCML survived without mechanical failure. The highest fracture loads were associated with FDPs supported by implants with 0-degree abutment angulations compared with those FDPs supported by 15-degree abutment angulations (group 1: 538.7 ± 24.77 N; group 2: 542.17 ± 21.64 N; group 3: 523.57 ± 19.71 N; group 4: 528.37 ± 24.57 N). This difference in load-bearing capacity was not statistically significant (P > .05). Conclusion: The use of angulated zirconia abutments for compensation of nonideal implant locations is possible without reducing the load-bearing capacity of implant-supported anterior three-unit lithium disilicate FDPs. Keywords: abutment angulations, all-ceramic FDPs, fracture resistance, zirconia abutment