In Vitro Aging and Fracture Tests on Differently Veneered Partially Stabilized Zirconia Anterior Crowns.

Objectives: To evaluate the fracture resistance of veneered incisor crowns made from highly translucent zirconia frameworks. Materials and Methods: Ninety-six all-ceramic single crowns were based on either a coping with minimum wall thickness or a cutback framework fabricated from highly translucent zirconia (5Y-PSZ). Each one-third of the specimens was finalized with different veneering ceramics using standardizations and glaze firing. Crowns were luted to cobalt-chromium dies with MDP-containing composite cement. Half of the entire sample underwent artificial aging (chewing simulation and thermocycling) before fracture load tests were conducted using a 6 mm steel sphere applied in a 90° angle to the oral aspect of the crowns with 1.3 mm distance to the incisal edge. Besides descriptive presentation of recorded forces at first damage (F_1d) and fracture (F_u), Kruskal Wallis and Mann-Whitney U tests were used to analyze data at α = 0.05. Results: Directly after manufacturing, incisor crowns of all test groups showed sufficient mean fracture resistances. After artificial aging, crack formation was observed in a high percentage for fully veneered crowns of all test groups, but only for one veneering ceramics with cutback crowns. Mean test forces of unaged crowns were F_1d,mean ≥ 422 N | F_u,mean ≥ 749 N (fully veneered) and F_1d,mean ≥ 644 N | F_u,mean ≥ 706 N (cutback) dropped significantly to F_1d,mean ≥ 131 N | F_u,mean ≥ 223 N (fully veneered) and F_1d,mean ≥ 324 N | F_u,mean ≥ 524 N (cutback) . Conclusions: Within the limitations of this laboratory study, 5Y-PSZ based anterior crowns can be a viable treatment option. Framework design, choice of the veneering ceramics and artificial aging show relevant effects on the fracture resistances. Concerted veneering ceramics should be used and partially veneering of the zirconia frameworks should be favored over full veneers.