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

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.

Human premolars were extracted and randomly divided into four groups. The occlusal enamel was then removed to expose a flat superficial dentin surface. Cavities 3.5mm long and 3.5mm wide were prepared to a depth 3mm 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 24h storage at 37 degrees C in water, all the teeth were sectioned to obtain bar-shaped specimens with a bonded surface area of approximately 0.9 mm x 0.9 mm. Dentin micro-tensile bond strength was measured at a crosshead speed of 0.5mm/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).

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.

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.