Surface preparation for orthodontic bonding to porcelain.

This study evaluated the effect of various porcelain surface treatments on the tensile strength of orthodontic brackets bonded to a feldspathic metal ceramic porcelain. The porcelain was fused to flat gold alloy tabs and divided into six groups that were subjected to sandblasting, silane application, intermediate resin, or etchants (9.6% hydrofluoric acid or 4% APF gels). Two brackets were bonded onto each porcelain/metal tab (n=60) with Bis-GMA resin (Concise, 3M Corp., St. Paul, Minn.) or 4-META resin (MCP-bond, Sun Medical Co. Ltd., Tokyo, Japan). The samples were stored in 37 degrees C water, thermocycled 1000 times from 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 circular ring soldered onto the bracket slot before bonding. Similar control brackets (n=12) were bonded with Concise to extracted caries-free mandibular incisors. Bond failure sites were classified according to a modified Adhesive Remnant Index (ARI) system. Silane application to the sandblasted porcelain surface significantly increased the bond strengths according to analysis of variance and Duncan's multiple range test. The quality of the bonds was further enhanced by the addition of the intermediate resin. Etching the porcelain with 9.6% hydrofluoric acid provided similar bond strengths, but the 4% APF gel was less effective. The MCP-bond was not significantly better than Concise in bond strength to sandblasted porcelain. Several difficulties associated with the clinical interpretation of laboratory data on bonding to dental porcelains are discussed, and clinical trials are necessary for final evidence of efficacy.