Retentive force and magnetic flux leakage of magnetic attachment in various keeper and magnetic assembly combinations.

Statement of problem. Magnetic attachments are commonly used for overdentures. However, it can be difficult to identify and provide the same type and size of magnetic assembly and keeper if a repair becomes necessary. Therefore, the size and type may not match. Purpose. This study evaluated the retentive force and magnetic flux strength and leakage of magnetic attachments in different combinations of keepers and magnetic assemblies. Material and methods. For 6 magnet-keeper combinations using 4 sizes of magnets (GIGAUSS D400, D600, D800, and D1000) (n=5), retentive force was measured 5 times at a crosshead speed of 5 mm/min in a universal testing machine. Magnetic flux strength was measured using a Hall Effect Gaussmeter. Data were statistically analyzed using a 1-way ANOVA, and between-group differences were analyzed with Tukey's HSD post hoc test (alpha=.05). Results. The mean retentive force of the same-size magnet-keeper combinations was 3.2 N for GIGAUSS D400 and 5.1 N for GIGAUSS D600, but was significantly reduced when using larger magnets (P <.05). Magnetic flux leakage was significantly lower for corresponding size combinations. Conclusions. Size differences influence the retentive force and magnetic flux strength of magnetic attachments. Retentive force decreased due to the closed field structure becoming incomplete and due to magnetic field leakage. (J Prosthet Dent 2011;105:266-271)