This study aimed to determine the optimal concentration of 10-methacryloyloxydecly dihydrogen phosphate (MDP) in primers used as surface treatment agents for zirconia. Prototype primers with adjusted MDP concentrations were used to measure the contact angles and, tensile bond strength and water resistance tests.

Zirconia blocks for computer-aided design and computer-aided manufacturing (CAD/CAM) were used for the contact angle measurements and tensile bond strength tests. The surfaces of the blocks were treated with prototype primers containing adjusted concentrations of MDP (1% to 15%). Composite- or methyl methacrylate-based resin luting cements were used to measure the tensile bond strength tests. Additionally, the adhesive interface was evaluated after the tensile bond test. Zirconia microbeads were treated with a prototype primer and evaluated for water resistance.

One-way analysis of variance and Tukey’s multiple comparison test were performed on the obtained values. Surface treatment with prototype primers containing 2% and 3% MDP exhibited higher water resistance and suitable adhesion to the resin luting cements. Therefore, an MDP concentration of 2% or 3% in primers appears to be appropriate for the surface treatment of zirconia.