Innovations in bonding to zirconia-based materials: Part I

Abstract
Objectives
Establishing a reliable bond to zirconia-based materials has proven to be difficult which is the major limitation against fabricating adhesive zirconia restorations. This bond could be improved using novel selective infiltration etching conditioning in combination with engineered zirconia primers. Aim of the work was to evaluate resin-to-zirconia bond strength using selective infiltration etching and novel silane-based zirconia primers.

Methods
Zirconia discs (Procera Zirconia) received selective infiltration etching surface treatment followed by coating with either of five especially engineered experimental zirconia primers. Pre-aged resin-composite discs (Tetric Ivo Ceram) were bonded to the treated surface using an MDP-containing resin-composite (Panavia F 2.0). The bilayered specimens were cut into microbars and the microtensile bond strength (MTBS) was evaluated. ‘As-sintered’ zirconia discs served as a control (α = 0.05). The broken microbars were examined using a scanning electron microscope (SEM).

Results
The combination of selective infiltration etching with experimental zirconia primers significantly improved (F = 3805, P < 0.0001) the MTBS values (41 ± 5.8 MPa) compared to the ’as-sintered’ surface using the same primers which demonstrated spontaneous failure and very low bond strength values (2.6 ± 3.1 MPa). SEM analysis revealed that selective infiltration etching surface treatment resulted in a nano-retentive surface where the zirconia primers were able to penetrate and interlock which explained the higher MTBS values observed for the treated specimens.

Keywords: Zirconia; Selective infiltration etching; Particle abrasion; Adhesion promotion; Silane coupling agent; Organophosphate cements; Resin composite; Zirconia primer