effect of repeated preheating on color stability of three types of composite resins and a giomer: an in vitro study

Background. this study assessed the effect of repeated preheating of three types of composite resins and a giomer on their color stability. methods. in this in vitro study, 128 composite resin and giomer specimens with a 10-mm diameter and a 2-mm height were evaluated in eight groups (n=16) of heliomolar microfilled, brilliant enamel microhybrid, and tetric n-ceram nanohybrid composite resins, and beautifil ii giomer used at room temperature and also after preheating of the tube in a water bath at 55‒60 °c for 40 times. after preparing the specimens, their color parameters were measured by a spectrophotometer. the specimens were immersed in a tea solution for 3 hours/day for 40 days and underwent spectrophotometric color assessment again. the color change (∆e) was calculated and analyzed by two-way anova (α=0.05). results. the effects of composite resin type (p<0.001) and preheating (p<0.001) and their interaction effect (p<0.001) were significant on ∆e. immersion in a tea solution caused a significantly greater color change in giomer (p<0.05). the ∆e of the microfilled composite resin was significantly higher than that of nanohybrid (p=0.003) and microhybrid composite resin (p=0.004). conclusion. repeated preheating of giomer, microhybrid, and nanohybrid composite resin specimens to 55‒60 °c for 40 times adversely affected their color stability in the tea solution. the color change was significantly greater for giomer.