Evaluation of strain distribution on an edentulous mandible generated by cobalt-chromium metal alloy fixed complete dentures fabricated with different techniques: An in vitro study.

Statement of problem. Fixed complete dentures (FCDs) have been used in the treatment of completely edentulous patients for over 40 years. However, few reports have investigated misfit values and strain distribution in the context of FCDs fabricated with new technologies. Purpose. The purpose of this in vitro study was to evaluate misfit values and strain distribution in FCDs and their relation to the fabrication technique of the cobalt-chromium (Co-Cr) metal framework. Material and methods. Four implants were placed in the interforaminal region of a mandibular cast at the bone level. The Co-Cr metal alloy frameworks were fabricated using the following techniques: computer-aided design and computer-aided manufacturing (CAD-CAM), milling from hard blocks, CAD-CAM milling from soft blocks, and direct metal laser sintering (DMLS). The superstructures of equal sizes with acrylic resin bases and acrylic resin denture teeth were fabricated on the Co-Cr metal alloy framework, and a digital microscope was then used to measure the misfit between the abutments and the implants. The stress formed after the application of torque was measured with a strain-gauge stress analysis technique. Data were statistically analyzed using 1-way ANOVA and the Tukey Honestly Significant Difference test (alpha=.05). The correlation between the misfit and the strain values was evaluated with the Pearson Correlation test (alpha=.001). Results. The lowest mean misfit values (99 +/- 17 mu m) were observed in the hard block group (P<.05) and the highest in the DMLS group (139 +/- 29 mu m). A statistically significant positive relationship was found between the misfit and the stress distribution after torque application (P<.05). Moreover, the lowest misfit group, hard blocks, had the lowest mean strain values (81.1 +/- 54 MPa) after torque application. Conclusions. Within the limitations of this in vitro study, the fabrication technique used for Co-Cr metal alloy frameworks appears to influence the passive fit significantly (P<.05). The hard-block technique was found to be the most precise fabrication technique for Co-Cr metal alloy frameworks. A significant relationship was observed between the amount/distribution of misfit and the strain on the FCD (P<.05).