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.