Conformity of removable partial denture designs to agreed principles based on materials used - A preliminary study

Abstract

Removable partial denture (RPD) designs may differ based on types of materials used. The aim of the study was to investigate how a sample of non-metal clasp (NMC), acrylic and metal RPD designs complied with biomechanical design principles. This cross-sectional study examined 60 clinical designs of NMC, acrylic and metal RPDs at 3 commercial dental laboratories in the Cape Town Metropole, at the stage when the dentures were ready for transport to dentists. Retention, indirect retention, support, soft tissue cover, and cross-arch design features were recorded and compared with “ideal” control designs developed by 2 experts in the specialty of prosthodontics. Fifty five % of the clinical designs had no rests, hence were mucosa supported. None of the NMC and only 35% of acrylic RPDs had some rests. A total of 35 clinical designs required indirect retention, but it was only provided in 14 (40%) of them. Eighty five % of acrylic RPDs had no clasps; metal RPDs had more clasps than required while NMC RPDs had slightly less clasps than required. Ratio teeth covered/replaced was most favourable for metal (0.91), followed by acrylic (1.83) and NMC (1.80) RPDs. Cross – arch stabilization was absent in 22% of clinical designs, all of them from the NMC group. Of the 3 types of RPDs, metal RPDs complied best with requirements in terms of tissue support (mostly tooth and mixed tooth/mucosa), retention, cross-arch stabilization and “open” design. Acrylic RPDs provided crossarch stabilization but were lacking in all other aspects. Except for direct retention, NMC RPDs did not conform to any of the agreed biomechanical requirements for RPDs assessed in this study.