Methods: Attachments were embedded in overdenture housings and mounted in a universal testing machine. A stone mandibular model with two Branemark implants placed was used for repeated insertion (baseline, 500, and 5,500 cycles) in a 37°C water bath. Vertical tensile dislodging forces were recorded at a cross-head speed of 50 mm/min before and after every 500 cycles (n=5). Tested specimens were observed with stereoscopic microscope. Peak load-to-dislodgement was measured and compared by ANOVA and Scheffe′ multiple comparison tests (p≤0.05).
Results: The peak load-to-dislodgement for stud and bar-clip systems ranged from 23.3 ± 3.3N to 52.4 ± 1.6N at baseline and 9.6 ± 1.1N to 21.5 ± 4.7N after 5,500 cycles. A 38.5 to 68.8% decrease in retention was recorded for stud and bar-clip systems after 5,500 cycles (p<0.05). No differences in retentive values were observed in magnetic attachment systems between baseline and after 5,500 cyclic insertions (p>0.05). Microscopic examination of the matrix portion revealed wear and deterioration of stud and bar-clip attachment systems, and supported the change of retention after 5,500 cyclic insertions. No wear, but corrosion product deposition is disclosed on the surface of magnet attachment systems.
Conclusions: Long-term insertion and removal of overdenture attachments may compromise their retention. Wear and deterioration of the matrix portion of stud and bar-clip attachment systems are possible mechanisms for the decrease of retention.
Supported by the University of Washington School of Dentistry Fund RAC 75-5875 and Spencer Fund 65-4909.