Abstract
Purpose : To obtain maximum attractive force for magnetic attachments, the degree of flatness of the keeper surface is very important. This study evaluated the flatness of keeper surfaces fabricated on copings using the cast-bonding and the direct-bonding techniques.
Materials and Methods : Specimens were made with keepers from the Hyper Slim 3513 magnetic attachment system (Hitachi Metals, Tokyo, Japan) using both the cast-bonding and the direct-bonding techniques. In the cast-bonding technique, the coping with the keeper was waxed up and cast according to conventional laboratory procedures. In the direct-bonding technique, the keeper was cemented on the cast housing with resin cement. The 3-dimensional shape of the keepers was measured using non-contact laser beam equipment (NH-4N, Mitaka Kohki, Tokyo, Japan), and the flatness was statistically analyzed with the Mann-Whitney U-test at a significance level of α=0.05.
Results : The keepers fabricated with the cast-bonding technique had a convex curvature, whereas the direct-bonding technique produced a flatter keeper surface. There was a significant difference (p<0.01) in the flatness between the two techniques.
Conclusion : The direct-bonding keepers were significantly flatter than the cast-bonding keepers, whose surfaces bulged in the center. The direct-bonding technique thus allowed optimal retentive force for the magnetic attachment.
