Retention forces of 14-unit zirconia telescopic prostheses with six double crowns made from zirconia—an in vitro study

Abstract

The aim of this study was to evaluate the retention forces (RFs) of zirconia double-crown systems, with primary and secondary crowns made from zirconia in vitro. Ten maxillary models with six abutment teeth were prepared. Sixty inner crowns were fabricated from pre-sintered zirconia with a taper of 0°. Ten 14-unit telescopic prostheses (removable partial dentures, RDPs) were fabricated, using the same computer-aided design/computer-aided manufacturing system as that used for the inner crowns. The removal test was performed in a standardized setup using a universal testing device at a crosshead speed of 10 mm/min. Ten separation cycles were carried out for each single primary crown as well as for each 14-unit RDP in the presence of artificial saliva. The results were imported into a statistic program and analysed by a one-way ANOVA and post hoc tests. The level of significance was set at 5 %. The mean RFs of the single double-crown systems were in the range of 0.611-2.895 N, whereas the RFs for the whole RDP varied between 8.1 and 13.6 N. RF was dependent on the abutment tooth (p < 0.001) and on the model (p < 0.001). The results of this study indicate that the manufacturing of full-zirconia double-crown systems is possible as well as reproducible. The RFs are comparable to those reported from casted and electroformed double-crown systems. It has been shown that the RFs of the presented telescopic system are comparable to existing double-crown systems.