Methods: Four attachments for implant overdentures were tested. There were 10 specimens of Locator-abutment (Zest Anchors, Escondido, CA, USA) using the LR-blue matrices and 30 specimens of TiSi-snap-abutment (bredent medical, Senden, Germany) in combination with vinylpolysiloxane (VPS) as matrices. VPS was provided in 3 different shore hardness (25, 50, 65 SH). 10 specimens were fabricated of each hardness. Overall, 40 specimen were tested. Retentive forces were measured after 0, 100, 200, 500, 1000 and 5000 removals in artificial saliva (Zwick Universal testing machine). After 5000 removals all the specimens completed 10000 thermocycles (5 / 55 °C) and final measurements of the retentive force were taken. An ANOVA–analysis for repeated measurements was performed.
Results: No change of retention force was observed for VPS after repeated dislodging and thermocycling. The locator attachments revealed a highly significant decrease of retention forces up to 58% (p<0.001).
Conclusions: VPS attachments provided constant retention forces simulating 5 years of clinical use in vitro. Retention force of VPS attachments increased with higher Shore-A-hardness. Clinical studies are necessary to prove the longevity of VPS attachment systems under clinical conditions.