Influence of enamel border and regional variability on durability of resin–dentin bonds

Objectives To evaluate the influence of enamel border on regional resin–dentin microtensile bond strength (μTBS) over time. Methods Thirty human third molars had a flat dentine surface exposed. Two adhesive systems (Single Bond [SB] and ScotchBond Multi Purpose Plus [SBMP]) were applied and composite resin crowns (Filtek Z250) were constructed. Teeth were divided into three groups (n = 5). Group A, specimens were sectioned to obtain sticks to be tested in tension (0.5 mm/min) immediately. Group B specimens were stored without outer enamel in water for 6 months, before sectioning and testing. Group C, specimens were stored with outer enamel in water for 6 months, before sectioning and testing. In all groups, the origin of the sticks, periphery and inner regions was controlled. The data for each adhesive were subjected to a two-way repeated measure ANOVA (location versus storage conditions) and Tukeyʹs test. Results No significant degradation in μTBS was observed for SBMU in all conditions. For SB, a significant reduction on μTBS was observed in the specimens without enamel border (group B). The degradation was more pronounced in the specimens from the periphery. Conclusions The three-step etch-and-rinse system is less susceptible to water degradation effects; stable resin–dentin bonds can be achieved with two-step etch-and-rinse systems as long as there is a bonded enamel border.