4-Unit Molar Fixed Partial Dentures Made from Highly Translucent and Multilayer Zirconia Materials: An In Vitro Investigation

Abstract

Background: Modern zirconia blanks for the fabrication of dental CAD/CAM restorations provide a layer structure with color and strength transitions. Variation in the yttria content has a particular effect on the characteristics of the materials. The properties of dental restorations may vary depending on the milling position within the blank. Especially for wide-span fixed partial dentures (FPDs), relevant effects on clinical performance might result. This study investigated if the application of high-translucent zirconia and positioning within multilayer zirconia blanks affect the in vitro performance of 4-unit FPDs. Methods: 4-unit FPDs were fabricated from monolayer 3Y-TZP-A, 3Y-TZP, 4Y-TZP, 5Y-TZP, 4Y/5Y-TZP, and different positions within multilayer zirconia blanks (3Y-TZP/5Y-TZP). The FPDs were adhesively luted to resin abutment teeth, divided into groups (n = 8 each): “baseline” (24 h water-storage)/“TCML” (chewing simulation by means of thermalcycling and mechanical loading), and loaded to fracture. The statistics included mean and standard deviation, one-way ANOVA, Bonferroni post hoc test, and Pearson correlation (α = 0.05). Results: The mean fracture force values varied between 803.8 ± 171.7 N (5Y) and 1474.1 ± 193.0 N (3Y) (baseline) and 713.5 ± 190.9 N (5Y) and 1337.4 ± 205.6 N (3Y) (TCML). Significantly different (p = 0.000) results between the groups and individual significant differences (p ≤ 0.039) were found. Conclusions: Positioning within multilayer blanks affected the fracture force only slightly. Multilayer, 3Y-TZP-A, 3Y-TZP, and 4Y-TZP seem appropriate for the clinical application with 4-unit molar FPDs. Application of 5Y-TZP is critical.