The aims of this in vitro study were: to evaluate the repeatability of producing the semi-precision attachment; to establish their estimated longevity by a simulated, repeated denture placement/removal procedure of denture; and to investigate the wear of their components. Four types of semi-precision attachments were evaluated. The attachments represented polymer-to-metal type of friction: Vario-Kugel-Snap, Vario-Soft, Strategy OT and ASC-52, which exhibited metal-to-metal type of friction. Tensile dislodging force was applied to sample to register peak load-to-dislodgment and also to determine the displacement curve. Then the cyclic axial loading tests were performed with insertion/separation machine. To detect worn areas, the surface of each sample was examined under a scanning electron microscope. The large variability of initial retentive force and shape of displacement curves was noted within Vario-Soft and Vario-Kugel-Snap group. After the first period of loading (up to 300 cycles), the mechanical properties of all samples were stabilised. The mean retention force of attachments with polymer matrix after 3000 cycles was approximately half the recommended value, while samples of ASC-52 (with metal-to-metal friction) withstood 8000 cycles. Results suggest that the inaccuracies of casting and laboratory procedure have only limited influence on the fit of the semi-precision attachments. The attachment with metal-to-metal type of friction exhibits the highest wear resistance (simulated up to 8 years of usage) compared to attachments with polymeric matrix (up to 3 years). All attachments exhibited wear of metal patrix, what can minimise the chance of re-activation in a long run.
© 2010 Blackwell Publishing Ltd.