Purpose: To test the hypothesis that the concentration of 10-methacryloxydecyl dihydrogen phosphate (MDP) in zirconia primers has no effect on the chemical bonding efficacy of methacrylate resins to yttria-stabilized tetragonal zirconia (Y-TZP). Materials and Methods: Shear bond strength testing was performed to evaluate the efficacy of experimental primers containing 5, 10, 15, 20 or 30 wt% MDP (5M, 10M, 15M, 20M, 30M) in improving composite-zirconia bond strength. Bonding without use of MDP-containing primer served as the negative control (Ctr0). Bonding with a commercially available MDP-containing primer served as the positive control (CtrM). Thermogravimetric analysis (TGA), inductively coupled plasma-mass spectrometry (ICP-MS), x-ray photoelectron spectroscopy (XPS), Fourier transform-infrared spectroscopy (FT-IR), and computational simulation of infrared spectra were used to confirm the formation of Zr-O-P bond between MDP and Y-TZP. Results: Results derived from TGA, ICP-MS, XPS, and FT-IR suggested that MDP chemically bonded with Y-TZP. Simulation of IR data supported the FT-IR results. There was a higher concentration of phosphorus on the 10M-conditioned Y-TZP surface when compared with the other groups, suggesting bettter formation of Zr-O-P bond in the 10M group. Shear bond strengths were significantly lower for group 5M (p 0.05), compared to groups 10M to 30M, which were not significantly different from one another (p > 0.05). Conclusions: MDP improves resin bonding of zirconia through the formation of Zr-O-P bonds with zirconia. 10 wt% MDP appears to be the most optimal concentration for synthesizing zirconia primers for resin bonding. Keywords: adhesion, bond strength, MDP, phosphate ester monomer, surface treatment, yttria-stabilized tetragonal zirconia