Development of a novel surface modification for improved bonding to zirconia

Objective

This report presents a novel pretreatment technique, whereby the zirconia surface is converted to a more reactive zirconium oxyfluoride, enabling improved chemical bonding to other dental substrates via conventional silanation approaches.

Methods

The study leverages a novel gas-phase fluorination process that creates a thin oxyfluoride conversion layer on the surface of zirconia, making it more reactive for conventional adhesive bonding techniques. Zirconia specimens, polished and roughened, were pretreated and composite cylinders bonded using conventional adhesive techniques. All specimens were subjected to a force at a crosshead speed of 0.5 mm/min in an electro-mechanical testing device. Single-factor analysis of variance (ANOVA) at a 5% confidence level was performed for the bonding strength data. Optical microscopy and scanning electron microscopy (SEM) were used to evaluate and quantify failure surfaces.

Results

Shear bond strengths were analyzed using single-factor ANOVA (p < 0.05). Mechanical testing results revealed that fluorinated zirconia specimens (both rough and polished) displayed the highest shear bond strengths as compared to other commercially available treatments. X-ray photoelectron spectroscopy analysis helped determine that this novel pretreatment created a more reactive, 2-4 nm thick oxyfluoride conversion layer with approximate stoichiometry, ZrO₃F₄.

Conclusion

Simple shear bond mechanical tests demonstrated that a fluorination pre-treatment is a viable method to chemically modify zirconia to produce a reactive surface for adhesive bonding.