An in-vitro microtensile test of Scotchbond Multi-Purpose adhesive applied at different priming times

Adhesive bonding to dentin can fail if the dentin is too wet during application of the bonding resin. This study compared the in vitro 24-hour microtensile bond strength of teeth restored at four different priming times at the gingival cavity wall of Class II resin composite restorations. After IRB approval, six pairs of extracted third molars (yielding 12 teeth) received a proximal Class II prep/restoration in each tooth. Each pair was from the same patient. Four treatment groups were randomly assigned for each pair. The treatment groups were: TM-primer applied and dried according to manufacturer's directions; T30-primer allowed to dry for an additional 30 seconds; T60-primer dried for an additional 60 seconds; T120-primer dried for an additional 120 seconds. The teeth were restored with 3M ESPE Scotchbond Multi-Purpose Dental Adhesive and 3M ESPE Z100 Restorative. Manufacturers' directions were followed except for the additional primer dwelling times. The teeth were sectioned to obtain rectangular specimens with a surface area of approximately 0.5 mm2. Samples were tested on the Instron at 1.0 mm/minute until failure. The results in megapaschals were TM (n=15) 25.5+/-12.2; T30 (n=14) 22.7+/-13.6; T60 (n=15) 28.1+/-14.7; T120 (n=20) 27.7+/-15.2. Samples that debonded during the preparation phase and could not be tested from each group were TM=5, T30=6, T60=5, T120=1. A one-way ANOVA found no statistically significant difference between groups. Ninety percent of the samples broke through the adhesive layer as observed under the scanning electron microscope at 2000x. A chi square analysis found no difference in the number of debonds between groups. Increasing the primer drying time did not increase the microtensile bond strength of adhesive bonded to the dentin gingival wall.