IMPROVING ORTHODONTIC BONDING TO GOLD ALLOY

Flat tabs of cast gold alloy (n = 156) were subjected to either of thr ee surface treatments: (1) roughening with diamond bur, (2) aluminum o xide sandblasting, and (3) sandblasting plus tin electroplating. Mandi bular incisor edgewise brackets were bonded with Concise (BIS-GMA resi n) (Unitek, Monrovia, Calif.) or Superbond C&B (4-META metal bonding r esin) (Sun Medical Co. Ltd., Kyoto, Japan), or with Concise after appl ication of an intermediate resin. All-Bond 2 Primers A and B (Bisco De ntal Products, Itasca, III.), or B alone. All specimens were stored in water at 37 degrees C for 24 hours, and 60 were then thermocycled 100 0 times from 5 degrees C to 55 degrees C and back. The tensile bond st rength testing was performed in a Lloyd 1000R machine (Fareham, Hants, England). Alignment and uniform loading during testing were secured b y engaging a hook in a circular ring soldered onto the bracket slot be fore bonding. Similar control brackets (n = 24) were bonded with Conci se to extracted human premolars and lower incisors according to a rout ine procedure. Bond failure sites were classified by a modified ARI sy stem. The results showed that sandblasting produced significantly stro nger bonds to gold alloy than roughening with diamond bur. Superbond C &B provided significantly stronger bonds to gold allay than Concise. T here were generally insignificant differences in bond strengths betwee n the water stored and the thermocycled specimens. Bond failures of Co ncise to sandblasted plus tin-plated gold alloy invariably occurred at the gold/adhesive interface, whereas those of Superbond C&B occurred within the adhesive or in the adhesive/bracket interface. The bond str engths obtained with Superbond C&B and sandblasted gold alloy surfaces were comparable to those of the brackets bonded to conventionally etc hed human teeth with Concise. Tin-plating improved the orthodontic bon d strengths to sandblasted gold alloy only marginally. The bond streng th of Concise to sandblasted gold alloy was significantly improved wit h the intermediate application of A1l-Bond 2 primers A and B. It is co ncluded that successful bonding to gold alloys is feasible with severa l combinations and clinical recommendations for bonding brackets and l ingual retainer wires to high-noble alloy surfaces are discussed.