Effect of Prewarming and/or Delayed Light Activation on Resin-Modified Glass Ionomer Bond Strength to Tooth Structures

INTRODUCTION: Recent research shows that the acid-base reaction and light-activated polymerization in resin-modified glass ionomers (RMGI) compete with and inhibit one another. In addition, extrinsic energy would improve some properties of RMGI. This in vitro study evaluated the effect of prewarming and/or delayed light activation on bond strength of RMGI to tooth structure. MATERIALS AND METHODS: Ninety-six flat enamel and dentin surfaces of human molars were ground with sequentially finer abrasives to 600-grit silicon carbide paper. Each surface was treated with a cavity conditioner for 10 seconds, rinsed, and gently air-dried (n=12). RMGI was applied to tooth substrates according to the following protocols: group 1) according to manufacturer's instructions; group 2) a delay of two minutes in light activation; group 3) prewarming of the encapsulated material (90 seconds, 40°C); group 4) prewarming plus a delay of two minutes in light activation. After 24 hours of storage at 37°C and 500 rounds of thermocycling, the samples were tested for shear bond strength and analyzed using two-way analysis of variance and Tukey HSD test (α=0.05). RESULTS: Significant differences were observed between study groups (p<0.05). The highest enamel bond strength was recorded in group 2. Regarding dentin groups, the highest bond strength was recorded in group 1. CONCLUSION: Within the limitations of the present study, delaying light activation might improve bond strength of RMGI to enamel; however, the standard procedure recommended by the manufacturer is the best procedure for bonding of RMGI to dentin. More investigations are necessary.