X-ray microtomographic evaluation of the absolute marginal fit of fixed prostheses made from soft Co-Cr and zirconia

Statement of problem.The absolute marginal fit of CAD-CAM presintered fixed partial dentures has been poorly documented. Purpose. The purpose of this in vitro study was to evaluate the marginal fit of presintered cobalt- chromium (Co-Cr) and zirconia 3-unit fixed partial dentures by using X-ray microcomputed tomography (mu CT). Material and methods. A metal model was prepared from a typodont to receive fixed partial dentures (N=12). The maxillary first premolar and first molar were prepared with a circumferential 1.2-mm chamfer and 2-mm occlusal reduction. The dies were scanned and assigned to 1 of 2 groups to receive the prostheses made of presintered Co-Cr or presintered zirconia (n=6). Each framework was seated on its model without load application. The abutments were scanned by using mu CT. A circle with 10 diameters, with a step of 18 degrees, was projected at the center of the obtained image. Absolute marginal discrepancy and marginal gap mean values were measured, and overextended and underextended margins determined. The data were analyzed by using the Levene t test and ANOVA (alpha=.05). Results. No statistically significant difference was found in the marginal fit between the materials tested (P=.939). The mean values were 66 +/- 14 mu m for Co-Cr and 61 +/- 12 mu m for zirconia. The absolute marginal discrepancy mean value for the premolar was 69 +/- 12 mu m and 41 +/- 9 mu m for the molar (P<.001). Overextension was predominant for both materials tested, with a higher percentage reported for the zirconia group. Conclusions. Presintered alloys presented clinically acceptable adaptation with a predominance of marginal overextensions.