Internal porosities, retentive force, and survival of cobalt-chromium alloy clasps fabricated by selective laser-sintering

Abstract

Purpose: The purpose of this study was to evaluate internal porosities, retentive force values and survival of cobalt-chromium (Co-Cr) alloy clasps fabricated by direct metal laser-sintering (DMLS) and compare them to conventionally cast clasps.

Methods: Embrasure clasps were digitally designed fitting teeth 35 and 36 on identical metal models (N = 32). Sixteen clasps were fabricated using DMLS (group DMLS) and another sixteen clasps were additively manufactured from wax and then cast from a Co-Cr alloy (group CAST). Internal porosities were examined using micro-focus X-ray (micro-CT) and analyzed applying Kolmogorov-Smirnov test, Mann-Whitney test, and T test (significance level: p < 0.050). A universal testing machine was used to determine the retentive force values at baseline and after 1095, 5475, 10,950 and 65,000 cycles of simulated aging. Data were analyzed employing Kolmogorov-Smirnov test, one-way ANOVA, and Scheffé's post-hoc test (significance level: p < 0.050). Survival was estimated for 65,000 cycles of artificial aging using Kaplan-Meier analysis.

Results: Micro-CT analysis revealed a higher prevalence (p < 0.001), but a more homogeneous size and a significantly smaller mean (p = 0.009) and total volume (p < 0.001) of internal porosities for group DMLS. The groups showed mean initial retentive force values of 13.57 N (CAST) and 15.74 N (DMLS), which significantly declined over aging for group CAST (p = 0.003), but not for group DMLS (p = 0.107). Survival was considerably higher for group DMLS (93.8%) than for group CAST (43.8%) after 65,000 cycles of aging.

Conclusions: Clasps made by laser-sintering could be an alternative to conventional cast clasps for the fabrication of removable partial denture frameworks.

Keywords: Additive manufacturing; CAD/CAM; Clasp; Removable partial denture; Retentive force.