Objectives: We evaluated retentive characteristics and morphological changes of a stud attachment system (Locator®) for implant-retained overdentures after cyclic loading onto implant abutments.
Methods: An acrylic mandibular model with two Straumann implants placed at varying implant angles (0°, 10°, 15°, 20°) was used for repeated insertion (baseline, 50, 500, 5000, and 10,000 cycles) in a 37°C water bath. Single-implant overdenture design was used as a control. Attachments were embedded in resin housings and mounted in a coil cycler electromechanical fatigue machine. Vertical tensile dislodging forces were recorded at a cross-head speed of 80 mm/min after cyclical loading to 77.5N, 155N, or 310N at 2Hz (n=5). Tested specimens were observed with a measurescope. Peak load-to-dislodgement was measured and compared by ANOVA and Scheffé multiple comparison tests (p≤0.05).
Results: The peak load-to-dislodgement values ranged from 126.8±20.9N to 30.2±2.9N and single-implant controls were statistically significant lower than two-implant groups after 10,000 cycles (p<0.05). A 32.8% to 58.6% retention decrease was recorded for single-implant controls and two-implant groups after 10,000 cycles. No significant differences in retentive values were observed in two-implant systems after 10,000 cycles (p>0.05). Microscopic examination of the matrix portion revealed wear and deterioration of liner of Locator® attachment systems, especially the white liner for angle abutments, and supported the change of retention after cyclic insertions and loadings.
Conclusions: The Locator LR attachment system provides adequate retention for more than 10,000 cycles of chewing. Wear and deterioration of attachment systems are possible mechanisms for the decrease of retention.
Supported partially by the University of Washington Dental Alumni Association and Restorative Department Spencer Fund 65-4909.