In vitro Microtensile Test of Scotchbond Multipurpose at Different Priming Times

Adhesive bonding to dentin can fail if the dentin is too wet during application of the bonding resin (Tay et al, 1996). Objective: To compare 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. Methods: After IRB approval six pairs of extracted third molars (yielding 12 teeth) received a class II prep/restoration in the proximal of 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 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. Teeth were restored with 3M^TMEspe^TMScotchbond^TM Multi-Purpose Dental Adhesive and 3M^TMEspe^TMZ100^TM Restorative. Manufacturer's directions were followed except for the additional primer drying 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/min till failure. 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. 90% 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. Conclusion: Increasing the primer drying time did not increase the microtensile bond strength of adhesive bonded to the dentin gingival wall. Supported in part by USPHS Grant DE07294 and DE09696. purkj@umkc.edu