Load-Bearing Capacity of All-Ceramic Fixed Partial Dentures - Do In Vitro Tests Overestimate Strength?

To assess the impact of the testing model on the load-bearing capacity of monolithic zirconia three-unit fixed dental prostheses (FDPs) and to discuss its implications for transferring in vitro results to clinical reality.

Thirty-two CAD- designed three-unit FDPs milled from zirconia were resin-bonded to four different types of die models (n=8 each): PM (models made from PMMA); FR (fiberglass-reinforced polymer models), NP (CoCr-alloy models), and TM (tooth mobility simulation models). Load-to- failure testing was performed, and data were analyzed (P < 0.05).

The mean fracture values were 1676 ± 210 MPa in group TM, 1820 ± 203 MPa in group PM, 2266 ± 138 MPa in group FR, and 4847 ± 496 MPa in group NP. All direct pairwise comparisons, except for TM and PM, showed significant differences. The results suggest that the nature of the underlying model has significant impact on the fracture values of all-ceramic FDPs in in vitro testing. Therefore, the validity of in-vitro tests regarding clinical relevance must be questioned, emphasizing the necessity of a close-to-reality and highly standardized testing method.