SURFACE PREPARATION FOR ORTHODONTIC BONDING TO PORCELAIN

This study evaluated the effect of various porcelain surface treatment s on the tensile strength of orthodontic brackets bonded to a feldspat hic metal ceramic porcelain. The porcelain was fused to Rat gold alloy tabs and divided into six groups that were subjected to sandblasting, silane application, intermediate resin, or etchants (9.6% hydrofluori c acid or 4% APF gels). Two brackets were bonded onto each porcelain/m etal tab (n = 60) with Bis-GMA resin (Concise, 3M Corp., St. Paul, Min n.) or 4-META resin (MCP-bond, Sun Medical Co. Ltd., Tokyo, Japan). Th e samples were stored in 37 degrees C water, thermocycled 1000 times f rom 5 degrees C to 55 degrees C, and tested in tension. Alignment and uniform loading during testing were secured by engaging a hook in a ci rcular ring soldered onto the bracket slot before bonding. Similar con trol brackets (n = 12) were bonded with Concise to extracted caries-fr ee mandibular incisors. Bond failure sites were classified according t o a modified Adhesive Remnant Index (ARI) system. Silane application t o the sandblasted porcelain surface significantly increased the bond s trengths according to analysis of variance and Duncan's multiple range test. The quality of the bonds was further enhanced by the addition o f the intermediate resin. Etching the porcelain with 9.6% hydrofluoric acid provided similar bond strengths, but the 4% APF gel was less eff ective. The MCP-bond was not significantly better than Concise in bond strength to sandblasted porcelain. Several difficulties associated wi th the clinical interpretation of laboratory data on bonding to dental porcelains are discussed, and clinical trials are necessary for final evidence of efficacy.