NMR study on the demineralization mechanism of the enamel and dentin surfaces in MDP-based all-in-one adhesive.

The acidic monomers utilized in all-in-one adhesives play a key role in the enamel and dentin bonding performance. The purpose of this study is to investigate the mechanism by which 10-methacryloyloxydecyl dihydrogen phosphate (MDP) demineralizes the enamel and dentin surfaces prepared by a diamond bur in three types of experimental MDP-based all-in-one (EX) adhesives containing different amounts of water (46.6, 93.2 and 208.1 mg/g). The enamel and dentin reactants of EX adhesives were analyzed using solidstate phosphorous-31 nuclear magnetic resonance and X-ray diffraction. Increased amount of water led to increases in the efficacy by which MDP demineralizes the enamel and dentin surfaces. However, the rate of calcium salts of MDP produced slowed down at the water concentrations above 93.2 mg/g. The dentin yielded greater amounts of di-calcium salts of the MDP monomer and dimer than the enamel, which develops a different type of layered structure of MDP from the enamel.

Demineralization capacity of commercial 10-methacryloyloxydecyl dihydrogen phosphate-based all-in-one adhesive.

OBJECTIVE: We determined the amounts of calcium salt of 10-methacryloyloxydecyl dihydrogen phosphate (MDP-Ca salt) and dicalcium phosphate dihydride (DCPD) with an amorphous phase developed during the application of commercial MDP-based all-in-one adhesives to enamel and dentin. This is because the demineralization by MDP and following calcium salt formation of MDP may be limited by an ionic bond formation of MDP to hydroxyapaptite in the enamel and dentin and following intermediary layer formation of MDP, since MDP forms a chemically-stable adsorption layer. METHODS: Scotchbond Universal Adhesive, Clearfil Tri-S Bond ND, Clearfil Tri-S Bond ND Quick, G-Bond Plus and our designed MDP-based all-in-one adhesive were used. Enamel and dentin reactant residues of each adhesive were prepared by varying the adhesive application periods: 1, 30 and 60min, and were analyzed using phosphorous-31 nuclear magnetic resonance and X-ray diffraction. RESULTS: Increasing the adhesive application period to enamel and dentin led to the increased amount of MDP-Ca salt in contrast to amorphous DCPD. In the dentin, each adhesive showed a saturated value on the production amount of MDP-Ca salt when the adhesive was applied more than 30min. In contrast, in the enamel, each adhesive showed an intermediate value on the saturated production amount of MDP-Ca salt that the respective adhesive exhibited. This is due to MDP employed demineralizes the enamel and dentin until MDP was completely consumed yielding MDP-Ca salt. CONCLUSION: Commercial MDP-based all-in-one adhesives would not form an intermediary layer of MDP on hydroxyapatite throughout their application period to enamel and dentin. CLINICAL RELEVANCE: The rate of MDP-Ca salt produced by the demineralization of enamel and dentin depends on the components that constitute commercial adhesive more strongly than on the concentrations of MDP and water in the respective adhesive. This is because HEMA-containing adhesive shows a slower production rate of MDP-Ca salt than HEMA-free adhesive in the enamel and dentin samples.

Effect of the demineralisation efficacy of MDP utilized on the bonding performance of MDP-based all-in-one adhesives.

OBJECTIVES: The amounts of calcium salt of 10-methacryloyloxydecyl dihydrogen phosphate (MDP-Ca salt) and dicalcium phosphate dihydride (DCPD) with an amorphous phase produced by the demineralisation of enamel and dentin were determined using commercial MDP-based 2-hydroxyethyl methacrylate (HEMA)-containing and HEMA-free all-in-one adhesives. The effect of the amount of MDP-Ca salt produced on bonding performance to enamel and dentin was then characterized. METHODS: Three types of commercial HEMA-containing adhesives (Scotchbond Universal Adhesive, Clearfil Tri-S Bond ND, Clearfil Tri-S Bond ND Quick), a commercial HEMA-free adhesive (G-Bond Plus) and an experimental HEMA-free adhesive were used. The reactant residues of each adhesive were prepared after interacting with enamel and dentin samples for 60 s. The amounts of MDP-Ca salt and amorphous DCPD produced were determined using a phosphorous-31 nuclear magnetic resonance technique. Enamel and dentin bond strengths were measured for each adhesive, with and without thermocycling. RESULTS: The amounts of MDP-Ca salt and amorphous DCPD formed after interacting with enamel and dentin differed among the five adhesives and were independent of their pH values. Enamel showed a strong positive-correlation of the bond strength of the all-in-one adhesives to the amount of MDP-Ca salt produced, however, the dentin showed a weak negative-correlation. CONCLUSION: The HEMA-free all-in-one adhesives showed a greater efficacy to demineralise the enamel and dentin than the HEMA-containing all-in-one adhesives. The dentin showed a different effect of the amount of MDP-Ca salt produced on the bonding performance compared with enamel. CLINICAL SIGNIFICANCE: The enamel bond strength of MDP-based all-in-one adhesives strongly contributes to the demineralisation efficacy by the incorporation of MDP, in contrast to the dentin bond strength. However, the efficacy of MDP-based all-in-one adhesives to demineralise the enamel and dentin is not directly related to the pH value of the MDP-based all-in-one adhesive.