Retention Characteristics of Magnetic Overdenture Attachments After Cyclic Loading

Objective: The purpose of this study was to compare retention characteristics of various neodymium-iron-boron alloy magnetic attachment systems including the Neomagnet (Neo), the Magnedisc (Ma), and an experimental magnet (SN) before and after cyclic loading.

Method: Magnetic specimens were embedded in resin housings and mounted in a coil cycler electromechanical fatigue machine. Stainless steel keepers with or without titanium nitride coating were used for sinusoidal loading treatments (baseline, 50K, and 100K cycles) from zero to 320 N in a 37°C water bath. Vertical tensile dislodging forces were recorded at a cross-head speed of 120mm/min before and after cyclic loading (n=5). 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 all attachment systems ranged from 1.9±0.2 N to 4.1±1.2 N after 100K cycles. An 18% decrease in retention was recorded for the Ma system after 100K cycles (p<0.05). No differences in retentive values were observed after 50K cycles (vs. baseline, p>0.05). Microscopic examination of the specimens revealed wear and corrosion products coated, and supported the change of retention after 100K cycles.

Conclusions: Long-term insertion and removal of magnetic overdenture attachments may compromise their retention. Wear of the attachment casing or induced corrosion of the magnet are possible mechanisms for the deterioration of retention.

Supported by the University of Washington School of Dentistry Fund RAC 75-5875 and Spencer Fund 65-4909.