Evaluating the Passivity of Implant-Supported Monolithic Zirconia Three-Unit Fixed Partial Denture Screwed to Multi-Unit Abutments with and without a Titanium-Base

PURPOSE: This study aimed to evaluate the passive fit of two-unit monolithic zirconia screw-retained fixed partial dentures (FPDs) on multi-unit abutments (MUAs), by comparing restorations fabricated with and without a titanium base (T-base). MATERIALS AND METHODS: To simulate a three-unit fixed partial denture (FPD), two implant analogs were embedded in polymethyl methacrylate (PMMA) and connected to parallel multi-unit abutments (MUAs). Fifty monolithic zirconia restorations were fabricated and divided into two groups: Group 1 consisted of restorations cemented to T-bases, while Group 2 included screw-retained restorations without T-bases. The passive fit of each restoration was evaluated using the Sheffield (one-screw) test and scanning electron microscopy (SEM) by measuring vertical marginal discrepancies (VMD) at six predefined reference points per restoration. Data were statistically analyzed using two-way ANOVA, followed by Tukey's post-hoc test for multiple comparison. The level of significance was set at α = 0.05. RESULTS: There were no statistically significant differences in VMD values between restorations with and without T-bases (P = .395). All recorded VMD values were below 150 µm, a threshold considered clinically acceptable. The lowest mean VMD was observed at the molar lingual site in Group 2 (17.24 ± 17.18 µm). CONCLUSION: The use of a titanium base did not significantly affect the passive fit of monolithic zirconia FPDs on MUAs. The results highlight the clinical reliability of screw-retained monolithic zirconia restorations, both with or without T-base and provides a foundation for future studies involving more complex restorative designs and conditions.