Effects of adhesive temperature on the early and 6-month dentin bonding

Abstract

Objectives

The aim of this study was to test the effect of adhesive temperature on the bond strength to dentin (μTBS) and silver nitrate uptake (SNU) of an ethanol/water (Adper Single Bond 2 [SB]) and an acetone-based (Prime&Bond 2.1 [PB]) etch-and-rinse adhesive system.

Methods

The bottles of each adhesive were kept in various temperatures (5 °C, 20 °C, 37 °C and 50 °C) for 1 h previously to its application in the occlusal demineralized dentin of 40 molars. Bonded sticks (0.8 mm²) were tested in tension (0.5 mm/min) immediately (IM) or after 6 months (6 M) of water storage. Two bonded sticks from each hemi-tooth were immersed in silver nitrate and analyzed by SEM. Data were analyzed by two-way repeated measures ANOVA and Tukey's test (α = 0.05).

Results

No significant difference in μTBS was detected for both adhesives at 5 °C and 20 °C. The highest bond strength for PB was observed in the 37 °C group while for SB it was in the 50 °C. Significant reductions of bond strengths were observed for PB at 37 °C and SB at 50 °C after 6 M of water storage. Silver nitrate deposition was seen in all hybrid layers, irrespective of the group. Lower silver nitrate deposition (water trees) in the adhesive layer was seen for PB and SB at higher temperatures.

Conclusions

The heating or refrigeration of the adhesives did not improve their resin–dentin bond resistance to water degradation over time.

Introduction

The temperature of the adhesive systems can alter some properties of monomer solutions, such as viscosity and degree of conversion, which are important parameters for the bonding effectiveness.1, 2 The spreading velocity of etch-and-rinse adhesive systems,³ as well as the vapor pressures of solvent⁴ can be influenced by temperature.

Previous literature findings have already demonstrated that the immediate resin–dentin bond strengths as well as hybrid layer formation can be affected by the temperature of the adhesive.5, 6, 7, 8 Studies conducted on composites have demonstrated that composite pre-warming, around 54–60 °C, enhanced maximal polymerization rate and overall monomer conversion for resin composites.9, 10, 11 The increase in the temperature might allow free radicals and propagating polymer chains to become more flexible as a result of decreased viscosity and react to a greater extent, resulting in a more complete polymerization reaction and greater cross-linking. This increase in polymerization may lead to improved mechanical properties. Considering that adhesive systems are mainly composed of monomers, an increase in the adhesive temperature might improve the quality of the polymer formed under the hybrid layer, thereby increasing the resin–dentin bonds and the bonding interface strength to the degradation effects of water.

Therefore, the aim of this in vitro study was to evaluate the effect of different temperatures on immediate and 6-month resin–dentin bond strength and silver nitrate uptake of two-step etch-and-rinse adhesive systems. The null hypothesis to be tested is that temperature does not affect the bonding effectiveness (microtensile bond strength and silver nitrate uptake) of two-step etch-and-rinse adhesive to dentin both in the immediate and 6-month period.