Effect of primers on bonding of metal bracket to zirconia

Abstract

The use of zirconia in conservative aesthetic dentistry has become more common. With this trend, it’s been extensively investigated to get acceptable bond strength with zirconia surface. But these studies are all focusing on resin luting cement with “naked” zirconia. Therefore, the aims of this study were to compare shear bond strength of resin cement to zirconia surface with using different primers and determine the effective surface treatment method for metal bracket bonding, zirconia primer or conventional porcelain primer.Zirconia blocks(Zirkonzhan) were milled and embedded in cylinder-shaped acrylic resin required for using testing machine. Specimens were randomly assigned to four groups (n=10): NZ, Non-glazed surface / Sand blasting + Zirconia primer; GZ, Glazed surface / Sand blasting + Etching + Zirconia primer; GP, Glazed surface / Sand blasting + Etching + Porcelain primer and GZP, Glazed surface / Sand blasting + Etching + Zirconia primer + Porcelain primer. Mandibular incisor stainless steel metal bracket was bonded to target surface with resin cement and all specimens underwent thermal cycling for 2,000 cycles (5 ℃ to 55 ℃) with a dwelling time of 30 seconds.Shear bond strengths of specimens were measured using a universal testing machine at a cross-head speed of 1 mm/min. Scanning electron microscopy, 3D optical profiler and stereoscopic microscopy were used for imaging the zirconia surface before and after surface roughening and debonding. The data were analyzed by one-way ANOVA and Fisher’s exact test (p<.05).The group GZ, using zirconia primer on glazed surface showed significantly lower shear bond strength than other groups. As for group NZ, GP and GZP, there was no statistically significant difference among them. While specimens in group NZ and GP showed adhesive failure between the resin cement/bracket base or complex adhesive and cohesive failure, all specimens in group GZ failed at the zirconia/resin cement interface. Based on the results of this study, it does not seem proper to use a zirconia primer to bond metal bracket on the surface of full contour zirconia crown with resin cement. In such situations, the use of porcelain primer is more appropriate.