Digital Evaluation of the Trueness and Fitting Accuracy of a Three-Unit Fixed Zirconium Bridge Fabricated from Different Types of Zirconia and Different Marginal Cement Space Thickness

Abstract

Objective The aim of this study was to measure the internal, marginal fitness, and trueness of a three-unit fixed zirconium bridge fabricated using two types of zirconia and different marginal cement space thicknesses. Methods and Materials Thirty-two aluminum master models, constructed by computer numerical control (CNC) milling machines using aluminum rod, representing two prepared aluminum abutments (the upper first premolar and the first molar) were chosen due to differences in shape and dimensions, which may affect adaptation. It may also be considered one of the most common cases in clinical practice and a missing second premolars were used to fabricate a three-unit fixed partial zirconium bridge. A master model was scanned with an intraoral scanner. Fixed dental prostheses (FDPs) were fabricated with two designs (single-layer high-translucent [HT] Katana and ultra-translucent multilayer (UTML] zirconia Katana) and two marginal cement space thicknesses (0 and 25μm for HT and ML). These specimens are divided according to marginal cement space and type of zirconia into four groups, each containing eight samples. Group A: 25-μm marginal cement space with single-layer HT zirconia. Group B: 25-μm marginal gap with UTML zirconia. Group C: 0 μm marginal gap single-layer HT zirconia. Group D: 0 μm marginal gap with UTML zirconia. Fitness and trueness of the fabricated three-unit FDPs were evaluated by scanning the silicone replica of the cement space and analyzing the thickness of the silicone replica in the three-dimensional inspection software (Geomagic Control X, Morrisville, North Carolina, USA). Results Highest mean value of internal gap was recorded at the molar abutment of group D (95.05, ± 3.42 μm), while the lowest was recorded at the premolar abutment of group A (57.12, ± 2.43μm). For marginal gap, the lowest marginal gap was also recorded at the premolar abutment of group A (36.14, ± 3.94μm), and the highest was at the molar abutment of group D (84.74, ± 2.98 μm).For trueness, group A showed the lowest root mean square (RMS) of mean with both abutments compared with group D, which recorded the highest RMS of mean for trueness. Conclusion The marginal cement space thickness affects the FPD internal, marginal fitness, and trueness; single-layer HT (Katana) zirconia shows better fitness and trueness than UTML (Katana).