Regional measurement of resin-dentin bonding as an array

During the development of the microtensile bond-testing method, large varia tions in bond strengths were noted among serial sections. The reason for th ese variations is unknown. The purpose of this work was to determine the co nsistency of resin-dentin bond strengths across the occlusal surface of cor onal dentin by dividing composite resin buildups into an array of 1 x 1 mm beams, the top half consisting of composite resin, and the bottom half cons isting of dentin. Extracted human third molars had the occlusal enamel remo ved as a single section by means of a diamond saw. Resin composite buildups were made after the dentin was bonded with either One-Step or MacBond. Aft er being stored in 37 degrees C water for 1 day, the teeth were vertically sectioned at 1-mm increments into slabs of bonded teeth. Each slab was furt her subdivided by vertical sections into 1 x 1 x 8 mm beams. Each beam was assigned an x-y coordinate and tested for tensile bond strength. Two differ ent clinicians (A and B) performed the same procedures using One-Step in a parallel study. Using One-Step, clinician A obtained a large number of zero bonds in superficial dentin but fewer in deep dentin. This resulted in a v ery large standard deviation in bond strengths (mean +/- SD of 22 +/- 20 MP a in superficial dentin acid 27 +/- 14 MPa in deep dentin). Clinician B obt ained much higher (p < 0.001) and more uniform bond strengths with One-Step (56 +/- 13 MPa in superficial dentin and 57 +/- 12 MPa in deep dentin). Wi th MacBond, there were no zero bonds and hence less variation, with a mean of 41 +/- 13 MPa in superficial dentin and 27 +/- 12 MPa ((x) over bar +/- SD) in deep dentin. When pairs of Z100 resin composite cylinders were bonde d together with One-Step and then sectioned into an array, there was little variation in regional bond strength (37 +/- 1 MPa). Dividing bonded resin composite buildups into an array of 20 to 30 1 x 1 x 8 mm beams allows for the evaluation of uniformity of resin-dentin bonds. The method used in this study detected local regional differences in resin-dentin bond strengths. The largest differences were shown to be related to technique rather than t o material. The results indicate that resin-dentin bonds may not be as homo genous as was previously thought.