The change in retentive force of magnetic attachment by abrasion.

Magnets are frequently applied to removable dentures as retentive attachments. A magnet-retained removable overdenture might be slightly shifted from side to side by eccentric movement in the mouth, and the surface of magnetic attachment may be worn as a result. However, the relationship between the retentive force of magnetic attachment and its surface abrasion has not been reported. The purpose of this research is to investigate this relationship. Ten Mgfit DX 400 magnetic attachments for natural tooth roots were used for this experiment. The magnetic attachments were embedded in autopolymerizing acrylic resin, and ten pairs of specimens were fabricated. A 5-mm repeated gliding motion was applied on each pair of specimens until 30 000, 50 000, or 90 000 cycles had been achieved. The abrasion machine was under 5 kg loading, and the slide speed was 60 times/min. The retentive force of magnetic attachment was measured with a tension gauge at (1) before gliding; (2) after 30 000 gliding cycles; (3)after 50 000 gliding cycles; or (4) after 90 000 gliding cycles. The average change of retentive force of ten magnetic attachments after 30 000, 50 000, and 90 000 gliding cycles was 0.016 N, 0.003 N, and -0.008 N, respectively. The change was statistically analyzed using a paired-sample t test, which showed that the number of gliding cycles did not affect the retentive force of magnetic attachment significantly. The surface of magnetic attachment after gliding was observed by a microscope, and the abrasion of this attachment surface is clearly seen.