Objective: The use of zirconia has increased dramatically for dental applications; however, establishing a reliable bond with dental materials has both been difficult and inconsistent. Air-abrasion creates increased surface area needed for attachment and phosphate primers and monomers (MDPs) have demonstrated marginal success in promoting adhesion. This study compares an earlier reported plasma fluorination technique with commercially available zirconia adhesive primers and the potential long-term viability.
Methods: Yttria-stabilized zirconia (LAVA, 3M ESPE) plates were highly polished (Ra ~200nm) prior to pretreatments. After primer and fluorination treatment, contact angles were measured to quantify surface hydrophobicity before and after ethanol clean. Additionally, simple shear bond and cyclic fatigue tests were performed to evaluate adhesion strengths. Single factor ANOVA at a confidence of 5% was performed on mechanical tests, and failure surfaces were analyzed using optical and scanning electron microscopy. X-ray photoelectron spectroscopy (XPS) was also used to determine the chemical modification of YSZ surfaces exposed to varying fluorination times.
Results: Plasma fluorination produce the lowest contact angle (7.8°) and highest adhesive strength (37.3 MPa) suggesting this pretreatment facilitates a more chemically active surface for increased chemical bonding. XPS deconvolution of the Zr 3d and Y 3d XPS core level spectra revealed formation of both ZrF4 and YF3. In addition, seven-coordinate ZrO2F5 and/or ZrO3F4 phases were deconvolved, retaining similar atomic coordination as the parent oxide and believed to have formed by substitutional displacement of oxygen by fluorine.
Conclusions: It is hypothesized that these new phases have the potential to increase hydroxylation at the surface making it more reactive, thus allowing for covalent bonding between ZrOxFy and resin cement. It is also believed that this surface treatment can increase long-term viability of zirconia restorations over other adhesive techniques. This research was supported through RTI International fellows program.
Keywords: Adhesion, Cements, Ceramics, Surfaces and Zirconia
See more of: Dental Materials 1: Adhesion - Bond Strength Testing and Mechanisms