Methods: Mechanical (Zest Locator) and magnetic (Magnedisc 800; Neomagnet) attachments were embedded in overdenture housings (n = 5). Overdenture attachments were tested on mandibular models with two parallel Branemark implants placed by a servo-hydraulic testing machine (Model 8511, Instron) in a 37°C water bath at 0.2 Hz for repeated dislodgment for 5,400 cycles. Specimens also were loaded sinusoidally in a coil cycler electromechanical fatigue machine (Proto-Tech, Portland, OR) at 2 Hz for 50,000 cycles from zero to 78 N in a 37°C water bath. Vertical tensile dislodging forces were captured at a cross-head speed of 50 mm/min after every 900 cycles of repeated insertion. Statistical analysis: ANOVA and Scheffe post-hoc tests at a ≤ 0.05.
Results: For the mechanical attachments, the peak load-to-dislodgement force ranged from 3.9 (0.2) to 37.8 (2.7) N after 50,000 cycles of loading. A 64.8% decrease in retentive force was observed after 50,000 cycles loading (p < 0.05) and a 73.9% decrease occurred after 5,400 cycles of placement and removal (p < 0.05). Microscopic examination of the specimens revealed wear and degradation consistent with the loss of retention. No differences in retentive values were observed for the magnetic attachments at baseline or after 50,000 cycles (p > 0.05).
Conclusions: The mechanical attachments tested in the current study were more susceptible to loss of retentive force and physical deterioration than magnetic attachments tested under identical conditions.
Partially supported by the University of Washington Department of Restorative Dentistry Spencer Fund 65-4909.