RELATIONSHIP BETWEEN SURFACE-AREA FOR ADHESION AND TENSILE BOND STRENGTH - EVALUATION OF A MICRO-TENSILE BOND TEST

Objectives. The purpose of this study was to test the null hypothesis that there is no relationship between the bonded surface area of denti n and the tensile strength of adhesive materials. Methods. The enamel was removed from the occlusal surface of extracted human third molars, and the entire flat surface was covered with resin composite bonded t o the dentin to form a flat resin composite crown. Twenty-four hours l ater, the bonded specimens were sectioned parallel to the long axis of the tooth into 10-20 thin sections whose upper part was composed of r esin composite with the lower half being dentin. These small sections were trimmed using a high speed diamond bur into an hourglass shape wi th the narrowest portion at the bonded interface. Surface area was var ied by altering the specimen thickness and width. Tensile bond strengt h was measured using custom-made grips in a universal testing machine. Results. Tensile bond strength was inversely related to bonded surfac e area. At surface areas below 0.4 mm(2), the tensile bond strengths w ere about 55 MPa for Clearfil Liner Bond 2 (Kuraray Co., Ltd.), 38 MPa for Scotchbond MP (3M Dental Products), and 20 MPa for Vitremer (3M D ental Products). At these small surface areas all of the bond failures were adhesive in nature. Significance. This new method permits measur ement of high bond strengths without cohesive failure of dentin. It al so permits multiple measurements to be made within a single tooth.