Chemical interaction between 10-methacryloyloxydecyl dihydrogen phosphate and methacryloxypropyltrimethoxysilane in one-bottle dental primer and its effect on dentine bonding

Abstract

In the present study, we investigated the chemical interaction between 10-methacryloyloxydecyl dihydrogen phosphate (10-MDP) and methacryloxypropyltrimethoxysilane (gamma-MPS) in one-bottle primer solutions and its effect on dentine bonding performance. Solutions containing 10 wt% 10-MDP and/or gamma-MPS at 0, 1, 5, 10, or 15 wt% were prepared, providing 10 experimental groups (labeled MDP/MPSxx or MPSxx, where MDP indicates the presence of 10 wt% MDP and xx is the wt% of gamma-MPS in the solution). Phosphoric-acid-etched dentine blocks were prepared from human molars and conditioned in the solutions before being used to build resin-dentine-bonded specimens, which were subsequently subjected to microtensile bond strength (μTBS) testing after 24-h or six-months water storage. Interfacial nanoleakage was evaluated by SEM observation. All the primer-conditioned samples showed significantly higher initial μTBS values than that of the control group, and six-months water storage significantly lowered the μTBS for all the groups; however, the decreases for MDP/MPS10 and MDP/MPS15 were significantly greater than those for MDP/MPS1 and the control solution. Furthermore, MDP/MPS10 and MDP/MPS15 groups also showed more serious nanoleakage. Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, and X-ray diffraction analyses were used to investigate the chemical affinity between 10-MDP and hydroxyapatite (HAp). In XRD analysis, the intensities of peaks assigned to 10-MDP-calcium salts were lower for the solutions containing gamma-MPS. Overall, the results indicate that the copresence of gamma-MPS (above 10 wt%) and 10-MDP in one-bottle primer solutions inhibit the formation of 10-MDP-calcium salts, leading to increased long-term nanoleakage and decreased bonding durability.