Thesis & Dissertations

Aim: the objective of this study was to evaluate the effect of etching capacity of three universal adhesives having different pH on bonding effectiveness to dentin using two etching strategies. Methods: Eighty-four extracted sound premolar teeth were selected for the study. The coronal part was sectioned to reveal a flat dentinal surface. The teeth were ultra-sonically cleaned for 15 minutes and stored at room temperature in demineralized water. The polished specimens were randomly divided into three main groups: moderate (pH range 1-2), mild (pH range 2-2.5), and ultra-mild (pH range >2.5). Each group was further divided into two sub-groups (n=14) according to etching strategy (ER) or (SE). Hollow cylinders of 0.75 mm internal diameter and 4.0 mm in height were cut from micro-borne rubber tubing and placed over the treated dentin surface and a nanohybrid resin composite was packed into the cylinders using a suitable diameter applicator and polymerized using a light-curing unit. After storage in demineralized water at 37 C for 24 hours half of the groups were assigned for immediate testing while the other half were assigned for 15000 thermocycling. The specimens were examined under scanning electron microscope to examine the bonding surface and characterize the failure mode. The μSBS values and mode of failure were recorded and statistically analyzed using three-way ANOVA test. Results: etching capacity, etching strategy and thermocycling had a statistically significant effect on mean μSBS. The interaction between the three variables had no statistically significant effect on mean μSBS; therefore the variables are independent from each other. Regardless of etching strategy and thermocycling, moderate group showed the statistically significantly highest mean μSBS. Mild group showed statistically significantly lower mean value. Ultra-mild group showed the statistically significantly lowest mean μSBS. Regardless of etching capacity group and thermocycling, ER showed statistically significantly higher mean μSBS than SE. Regardless of etching capacity and etching strategy, there was a statistically significantly decrease in mean μSBS after thermocycling. For mode of failure, with ER strategy, either immediately or after thermocycling, all specimens showed cohesive failure thus, no comparisons were done. With SE strategy, either immediately or after thermocycling, all specimens showed cohesive and adhesive failures, so there was no statistically significant difference in mode of failure among the three groups. Conclusion: Within the limitations of this study: 1. The etching capacity of universal adhesives and the etching strategy may influence bonding effectiveness to dentin. 2. The intermediate pH (range 1-2) seems to have better bond quality to dentin than mild and ultra-mild pH (range 2-2.5, pH > 2.5 respectively). 3. The μSBS of universal adhesives could be improved with the use of ER strategy. 4. Thermal aging appears to influence the μSBS of universal adhesives.. 5. Bonding performance of universal adhesives used in this study is material dependent.