Clinical study of the internal gaps of zirconia and metal frameworks for fixed partial dentures

The aim of this clinical study was to compare the internal gaps between abutment teeth and posterior fixed partial dentures (FPDs) fabricated utilizing milled zirconia and cast gold-alloy frameworks. As part of an ongoing randomized controlled clinical trial, 32 three-unit FPDs (16 zirconia and 16 metal-ceramic) in 25 patients were randomly selected for adaptation measurements. During the bisque-stage ceramic try-in, an A-silicone impression material was placed between the abutment teeth and the framework. The internal gap, corresponding to the thickness of the replica, was measured under magnification at the following locations: cervical, axial, and occlusal (cusp-tips and central). The internal gaps of FPDs with zirconia frameworks were significantly larger in cervical, axial, and centro-occlusal regions (cervical: 189.6 ± 71.8  μ m vs. 118.6 ± 31.5  μ m; axial: 140.5 ± 38.3  μ m vs. 95.7 ± 18.1  μ m; and centro-occlusal: 192.0 ± 66.5  μ m vs. 153.1 ± 69.8  μ m). The cervical gaps next to the pontics were significantly larger compared with those of the outer walls in both types of FPDs (zirconia: mean difference 67.7 ± 114.7  μ m; metal-ceramic: mean difference 30.0 ± 71.2  μ m). Posterior three-unit FPDs incorporating milled zirconia frameworks exhibited larger internal gaps than those constructed using conventional metal-ceramic techniques.