Effect of dissolution of collagen on adhesion to dentin

A new method of adherend surface treatment was evaluated to determine the effect of adhesion between dentin and adhesive resins. The pretreatment method consisted of the application of 40% phosphoric acid solution to dentin to remove the smear layer and decalcify the superficial dentin layer, followed by 10% sodium hypochlorite to dissolve and remove the exposed dentinal collagen and provide a fresh dentin apatite surface to which adhesive resin is applied. This method features a direct adhesion between the adhesive resin and dentin, with no resin-reinforced layer of dentinal collagen and adhesive resin. The adhesive tensile strength after storage in water at 37 degrees C for 24 hours measured 6.7 MPa with the phosphoric acid treatment alone, while the test method produced an initial adhesive strength as high as 9.7 MPa. After 10,000 thermal cycles (4 degrees C to 60 degrees C), the adhesive strength was 6.2 MPa, which was approximately 1.5 times greater than the value obtained with the method using the phosphoric acid solution alone.