Effects of layering techniques on the micro-tensile bond strength to dentin in resin composite restorations

Abstract

Objectives The purpose of this work was to investigate the effects of layering techniques in resin composite restorations on the micro-tensile bond strength to the dentin of the occlusal cavity. Methods Human premolars were extracted and randomly divided into four groups. The occlusal enamel was then removed to expose a flat superficial dentin surface. Cavities 3.5 mm long and 3.5 mm wide were prepared to a depth 3 mm below the dentin surface. The adhesive Single Bond was applied according to the manufacturer's instructions. The teeth were then restored with Z100 resin composite as follows: Group 1 was restored in horizontal increments (three layers). Groups 2 and 3 were restored in different oblique increments (three layers). Group 4 was restored in oblique increments (four layers). After 24 h storage at 37 °C in water, all the teeth were sectioned to obtain bar-shaped specimens with a bonded surface area of approximately 0.9 mm × 0.9 mm. Dentin micro-tensile bond strength was measured at a crosshead speed of 0.5 mm/min. The results obtained were statistically analyzed using one-way ANOVA and SNK test at a significance level of P = 0.05. All fractures were then observed under a scanning electron microscope (SEM). Results The results showed that there is a significant difference between the strength of the micro-tensile bonds to the dentin of occlusal cavities depending on which of the four layering restorative techniques was used ( P < 0.01). SEM observation showed that failure patterns were most evidently interfacial cohesive failure. Significance Layering techniques in resin composite restorations affected the micro-tensile bond strength between the resin composite and the dentin. But the outcomes related to only Single Bond, as the same using other adhesives might have different outcomes.