Bonding of Metal Attachments to Sandblasted Feldspathic and Zirconia Surfaces

Objectives: To evaluate the tensile bond strength (TBS) of metal orthodontic attachments to sandblasted feldspathic porcelain and zirconia with various protocols.
Methods: Thirty-six (36) feldspathic porcelain and 36 zirconia disc samples were prepared, ultrasonically cleansed, glazed, embedded in acrylic blocks, and sandblasted. Each material was divided into three groups according to one or more of the following surface treatments: hydrofluoric acid 4% (HF), silane (trimethoxysilyl-propyl-2-methyl-2-propeonic acid and acetone), Reliance Assure™ (RA) (Reliance Orthodontics) primer (biphenyl dimethacrylate, hydroxymethyl acrylate), Reliance Assure plus™ (RA plus) (Reliance Orthodontics) primer (bisphenol A-glycidyl methacrylate and ethanol), Z Prime™ plus (Bisco) zirconia primer (biphenyl dimethacrylate, 10-methacryloyloxydecyl dihydrogen phosphate, and ethanol). A round traction hook (TP Orthodontics) was bonded to each sample using Pad Lock™ light cure composite (Reliance Orthodontics) cured for 20 seconds. Static tensile bond strength tests were performed in a universal testing machine (Model 1125, Instron Corp) at 1mm/min cross-head speed. The adhesive remnant index (ARI) scoring was done in an optical microscope. Data obtained (MPa) were analyzed using ANOVA. ARI scores were analyzed using crosstabulation and Pearson chi-square test. Significance level was set at 0.05.
Results: No statistically significant mean difference in the TBS was found among the different bonding protocols for feldspathic and zirconia: (Mean ± S.D.; p-value) = (4.57±0.70; 0.369) and (5.29±0.55; 0.944) respectively. ARI scores for feldspathic was not statistically significant; p-value=0.569, for zirconia the results indicated that RA plus™, Z Prime™ plus and silane are significantly different; p-value=0.026. Silanization of zirconia samples resulted in more than 50% of the adhesive being left at the debonded site.
Conclusions: Silanization following sandblasting resulted in tensile bond strengths comparable to other bonding protocols for feldspathic and zirconia surfaces.