Shear bond strength of brackets bonded to porcelain surface: in vitro study

PURPOSE To compare the effects of different porcelain surface treatment methods on the shear bond strength (SBS) and fracture mode of orthodontic brackets. MATERIALS AND METHODS Seventy feldspathic porcelain disk samples mounted in acrylic resin blocks were divided into seven groups (n=10) according to type of surface treatment: I, Diamond bur; II, Orthosphoric acid (OPA); III, hydrofluoric acid (HFA); IV, sandblasted with aluminum oxide (SB); V, SB+HFA; VI, Neodymium:yttrium-aluminum-garnet (Nd:YAG) laser; VII, Erbium:yttrium-aluminum-garnet (Er:YAG) laser. Brackets were affixed to treated all-porcelain surfaces with a silane bonding agent and adhesive resin and subjected to SBS testing. Specimens were evaluated according to the adhesive remnant index (ARI), and failure modes were assessed quantitatively under a stereomicroscope and morphologically under a scanning electron microscope (SEM). Statistical analysis was performed using one-way analysis of variance and the post-hoc Tukey test, with the significance level set at 0.05. RESULTS The highest SBS values were observed for Group V, with no significant difference between Groups V and III. SBS values for Group I were significantly lower than those of all other groups tested. The porcelain/resin interface was the most common site of failure in Group V (40%) and Group III (30%), whereas other groups showed various types of bond failure, with no specific location pre-dominating, but with some of the adhesive left on the porcelain surfaces (ARI scores 2 or 3) in most cases. CONCLUSION The current findings indicate that a diamond bur alone is unable to sufficiently etch porcelain surfaces for bracket bonding. Moreover, SB and HFA etching used in combination results in a significantly higher shear-bond strength than HFA or SB alone. Finally, laser etching with either an Nd:YAG or Er:YAG laser was found to be more effective and less time-consuming than both HFA acid and SB for the treatment of deglazed feldspathic porcelain.