Retentive force and fitness accuracy of cobalt-chrome alloy clasps for removable partial denture fabricated with SLM technique

Purpose: Evaluating the fitness accuracy and retentive force of cobalt-chrome (Co-Cr) alloy clasps fabricated using the selective laser melting (SLM) technique. Methods: Premolar and molar abutment models with a 0.5-mm undercut depth, 1.5-mm-thick occlusal rest seats, and guiding planes were designed and fabricated using a milling machine. On these models, Akers clasps with 0.25- and 0.5-mm undercut depths were designed and fabricated with SLM and a traditional lost wax casting method. Based on the manufacturing methods, abutment types, and undercut depths, the clasps were divided into eight groups (10 per group). The fitness accuracy of the clasps was evaluated by measuring the gap distance between the clasps and abutments using a silicone film method. The initial retentive force and changes in retention up to 7,200 insertion/removal cycles of the clasps were also measured. The data were analyzed using multiple linear regression, paired t-tests, and one-way ANOVA (a=0.05). Results: For both the SLM and cast clasps, the fitness accuracy of the rest was greater than that of the clasp tip and shoulder. No significant difference was found in the fitness accuracy between the SLM and cast clasps, regardless of the abutment type and undercut depth before or after insertion/removal cycles (p>0.05). There was also no significant difference in the initial retentive force between the SLM and cast clasps (p>0.05). After 7,200 insertion/removal cycles, the SLM clasp exhibited a greater residual retentive force (p<0.05). Conclusion: The SLM technique for manufacturing the clasps of removable partial dentures has promising clinical applications.