A microcomputed tomography evaluation of the marginal fit of cobalt-chromium alloy copings fabricated by new manufacturing techniques and alloy systems

Statement of problem. Although new digital manufacturing techniques are attracting interest in dentistry, few studies have comprehensively investigated the marginal fit of fixed dental prostheses fabricated with such techniques. Purpose. The purpose of this in vitro microcomputed tomography ( a) study was to evaluate the marginal fit of cobalt-chromium (Co-Cr) alloy copings fabricated by casting and 3 different computer-aided design and computer-aided manufacturing (CAD-CAM)-based processing techniques and alloy systems. Material and methods. Single Co-Cr metal crowns were fabricated using 4 different manufacturing techniques: casting (control), milling, selective laser melting, and milling/sintering. Two different commercial alloy systems were used for each fabrication technique (a total of 8 groups; n=10 for each group). The marginal discrepancy and absolute marginal discrepancy of the crowns were determined with ACT. For each specimen, the values were determined from 4 different regions (sagittal buccal, sagittal lingual, coronal mesial, and corona) distal) by using imaging software and recorded as the average of the 4 readings. For each parameter, the results were statistically compared with 2-way analysis of variance and appropriate post hoc analysis (using Tukey or Student t test) (alpha=.05). Results. The milling and selective laser melting groups showed significantly larger marginal discrepancies than the control groups (70.4 +/- 12.0 and 65.3 +/- 10.1 jim, respectively; P<.001), whereas the milling/sintering groups exhibited significantly smaller values than the controls (P=.004). The milling groups showed significantly larger absolute marginal discrepancy than the control groups (137.4 +/- 29.0 and 139.2 +/- 18.9 p.m, respectively; P<.05). In the selective laser melting and milling/sintering groups, the absolute marginal discrepancy values were material-specific (P<.05). Nonetheless, the milling/sintering groups yielded statistically comparable (P=.935) or smaller (P<.001) absolute marginal discrepancies to the control groups. Conclusions. The findings of this in vitro CT study showed that the marginal fit values of the Co-Cr alloy greatly depended on the fabrication methods and, occasionally, the alloy systems. Fixed dental prostheses produced by using the milling/sintering technique can be considered clinically acceptable in terms of marginal fit.