Hydroxylation of dental zirconia surfaces: characterization and bonding potential

Bioinert zirconia surfaces exhibit a low chemical bonding potential to resin-based luting agents. The aim was to hydroxylate dental zirconia surfaces and to examine tensile bond strength using commercial luting agents. The measured bond strength was compared with established mechanical conditioning techniques. Five acidic and one alkaline hydroxylation pretreatments were applied and compared with air abrasion and tribochemical silica coating. For the chemical characterization of hydroxyl groups and hydroxyl value, zirconia powders were used, chemically modified, and analyzed using Fourier-transformed infrared spectroscopy and a titrimetric method according to the ISO 4629 standard. All acidic pretreatment procedures exhibited increased hydroxyl values. The highest values were recorded after treatment with phosphoric acid or Piranha solution. Tensile bond strength was examined in a universal testing machine using the commercial dual-cure luting agents Multilink (Ivoclar, Liechtenstein) and Panavia F2.0 (Kuraray, Japan). Surface hydroxylation with Piranha solution in combination with the luting agent Multilink led to a bond strength of 12.47 +/- 3.25 MPa. Tribochemical silica-coated/silanized zirconia surfaces with Multilink produced the highest bond strength of 19.33 +/- 3.65 MPa. Using the luting agent Panavia F2.0, statistically homogenous values for the untreated (11.60 +/- 1.68 MPa) and for the hydroxylated surface (12.46 +/- 3,81 MPa) were measured. Bioinert zirconia surfaces were successfully hydroxylated in terms of tensile bond strength. Resin bonding with Multilink can be strongly increased by acidic treatment with Piranha solution. Bonding with Panavia F2.0 is not affected by hydroxylation, which is likely due to the incorporation of specific functional monomers.