Do clasps made of thermoplastic polymers ensure adequate retention for removable partial dentures? A systematic...

A consensus regarding the indications and performance of removable partial denture (RPD) clasps manufactured with thermoplastic polymers is lacking.

The purpose of this systematic review and meta-analysis was to evaluate the published literature on the retention forces of RPD clasps made of polymers and compare them with those made of cobalt chromium (Co-Cr).

A comprehensive search of studies published up to January 2024 was performed in PubMed/MEDLINE, Web of Science, and Cochrane Library databases according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement criteria and was registered in the Open Science Framework (https://osf.io/cw63x/?view_only=120a61789c0f496e92b3c8c64429af32). The population, intervention, comparison, outcome (PICO) question was "Do RPD clasps made of polymers have similar retention performances to those fabricated with Co-Cr alloy?". Continuous analyses were conducted using the mean difference (MD) and 95% confidence interval (CI), encompassing circumferential and double Akers clasps, as well as the initial and final times of the experiment. Heterogeneity analyses were performed, and forest plots were drawn.

The search in the databases and a manual search identified 158 articles, of which 8 were considered eligible. The meta-analysis revealed no significant difference in the comparison of the initial retention forces of circumferential clasp groups made of Co-Cr and polyetheretherketone (PEEK) with a 0.5-mm undercut and an MD of 0.63 N (95% CI -3.85 to 5.1, P=.780). For the other meta-analyses, the Co-Cr groups were favored. An improved linearity of retention values was observed for the polymer clasp groups.

Co-Cr clasps show the highest retention among identical designs, followed by polyaryletherketone (PAEK) and polyoxymethylene polymers. PEEK clasps (1.5 mm thickness, 0.5 mm undercut) are suitable for RPDs. Polymer clasps ensure stable retentive forces over time, with PAEK being a promising alternative for RPD clasps.