Evaluation of the mechanism of cervical defect formation and development of the effective dentin adhesive system

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The efficacy of the experimental dentin bonding system to the cervical defect and the sound dentin cavity was evaluated by measuring the contraction gap width of the resin composite. Twenty extracted human teeth with and without cervical defect and twenty intact extracted human teeth were used. For ten teeth with cervical defect, the defect surface was conditioned with neutralized 0.5 mol/L EDTA (pH 7.4) for 60 sec followed by rinse and dry. Then the cavity was primed with 35 vol % of gtyceryl mono-methacrytate solution for 60 sec followed by air blasting. The resin composite was filled in the cavity after application of the commercial dual-cured dentin bonding agent Ten minutes after the polymerization of the composite, the specimen was sectioned through the canter of the cavity and the maximum contraction gap width was measured on the section of the cavity using the light microscope. For ten specimens with cervical defect, the dentin priming was omitted though other steps were performed in the same methods. The cervical cavity was prepared in the twenty intact human teeth and restored with the resin composite mediated with the experimental dentin bonding system with and without dentin priming. The gap formation was prevented completely in the primed cavity regardless of the kind of the dentin. When the priming was omitted, the complete cavity was observed in the seven specimen of the cervical defect though gap was observed in all of the specimens in the cavity prepared in the intact teeth. Thus it was concluded that the dentin in the cervical defect was more beneficial for dentin bonding than the sound dentin probably because the monomer diffusion and the water through was limited by the debris in the dentin tubules.