In vitro Shear Testing of Bonding Orthodontic Brackets on CAD/CAM Zirconia

Introduction: Developments in ceramic biomaterials (i.e. zirconia based ceramics) over the last 10 to 15 years have left us with the ability to provide very high strength restorations while also achieving superior esthetics to the patient. These ceramics have gained popularity quickly, but have different compositions when compared to porcelains and other inorganic non-metallic alternatives. Conventional bonding techniques intended for porcelains and other materials have been shown to be insufficient in bond strength to zirconia, so alternative protocols have been/are being investigated. A specific area that needs to be explored is bonding orthodontic brackets to zirconia based ceramics. Null Hypothesis: There will be no difference in shear bond strength between the different primer/adhesive groups after surface treatment of the zirconia blocks when bonded to orthodontic brackets. Specific Aim: The aim of this study is to evaluate the shear bond strength of orthodontic brackets on CAD/CAM zirconia using two surface treatment techniques and three different primer/adhesives. Methodology: 90 Lava Plus High Translucency Zirconia (3M ESPE) tiles embedded in acrylic resin cylinders were used. The polished zirconia surfaces was air-particle abraded with one of two materials. 45 specimens were air-particle abraded with CoJet Sand Blast-Coating Agent (CJ) of 30 um size. The micro-blasting unit was set at 40 psi and the specimens were abraded for 15 seconds at 5-10 mm distance. The other 45 specimens were air-particle abraded with 50 um aluminum oxide (AO) at 40 psi for 15 seconds at a distance of 5-10 mm. Each group of 45 (CJ and AO) was then further divided into 3 groups of 15. The 3 groups represent different primers consisting of: Scotchbond Universal (SB), Clearfil SE Bond Primer (CF), and Z-prime plus (ZP). The SB group had the primer gently rubbed onto the CJ and AO surfaces for 20 seconds followed by 5 seconds of oil free air. The CF group had the primer applied to the CJ and AO surfaces and left in place for 20 seconds followed by 5 seconds of oil-free air. The ZP group had 1 light coat applied to the CJ and AO surfaces followed by 5 seconds of oil-free air. Each group had a standard lower incisor orthodontic bracket bonded with 2000 grams of even pressure using Transbond XT (TB) as adhesive. Excess adhesive was removed. The adhesive was cured from the mesial, distal, incisal, and gingival for 3 seconds each. Once bonding of each specimen was complete it was stored in distilled water for 24 hours at 37¢ªC. They were then thermocycled 1000x at 5-55¢ªC intervals. Shear testing was performed with a Universal Testing Machine with a crosshead speed of 1mm/min. Following debonding each zirconia tile was given an ARI score to determine site of bond failure. Statistical Analysis: The data (MPa) was analyzed using a two-way analysis of variance (ANOVA). Multiple comparisons were made using Bonferroni post hoc tests. Level of significance was set at p<0.05. Expected Contribution: The long term goal of this research is to provide clinicians with the most efficient and optimal results when bonding orthodontic brackets to full zirconia restorations.