Change in the retentive force of Akers clasp for zirconia crown by repetitive insertion and removal test

Abstract

PurposeThe objective of this study was to evaluate the suitability of monolithic zirconia crowns (MZC) as abutment teeth of Akers clasps on removable partial dentures (RPD) by determining the change in retentive force after repetitive insertion/removal test. MethodsMZC and silver palladium copper alloy (Ag–Pd) full-metal crowns (FMC) for the mandibular second premolar were fabricated. Resin patterns of Akers clasps made with a 3D printer were casted with Ag–Pd or cobalt chromium alloy (Co–Cr). Clasp retentive force was measured with combinations of the crown and clasp materials. After measuring the initial retentive force of the clasp, repetitive insertion/removal test was carried out. The surface of the crown before and after the test was observed with an optical microscope and a scanning electron microscope; some specimens were subjected to element analysis by an electron probe microanalyzer. ResultsThe initial retentive force of the Co–Cr clasp was greater than the Ag–Pd clasp for both MZC and FMC. Clasp retentive force decreased with increasing number of insertion/removal cycles, and least reduction in force was observed for the Ag–Pd clasp on MZC. Wear marks were detected where FMC contacted the clasp. Discoloration of MZC due to wear of the Co–Cr clasp was observed. ConclusionsWhen repetitive insertion/removal of the clasp was performed on MZC, retentive force decreased depending on clasp materials. However, the amount of decrease in retentive force was comparable or small compared to conventional FMC. As a result, it was suggested that MZC could be used on abutment tooth for RPD.