The effect of fluoride varnish on the color stability and surface microhardness of bioactive restorative materials: An in vitro study

The aim of the study is to evaluate the effect of fluoride varnishes on both the color stability and surface microhardness of different fluoride-releasing restorative materials exposed to beverages commonly consumed by children . This study was conducted as an in vitro experimental study design. Three different restorative materials (Dyract XP, Beautifil II, and Cention N) and a colorless fluoride varnish were used. The solutions in which the samples were immersed were selected as beverages commonly preferred by children: cherry juice, chocolate milk, and cola. Color changes of the samples were measured using a spectrophotometer at 1, 7, 14, and 28 days and calculated according to the CIEDE2000 total color difference formula. Surface microhardness values were measured using a digital microhardness testing device at 1 and 28 days. To assess the effects of variables and their interactions in repeated observation designs, generalized linear models and generalized linear mixed models were fitted. Following model estimation, Tukey's-adjusted estimated marginal means were computed to identify significant pairwise differences. Fluoride-releasing restorative materials exhibited varying degrees of color change and decrease in surface microhardness when immersed in different staining solutions. Among the tested materials, Cention N demonstrated the greatest color stability (ΔE=1.01 for fluoride applied group, ΔE=1.45 for the group without fluoride application) and least reduction in surface microhardness. Fluoride application initially caused a slight discoloration immediately after application. However, following immersion in different solutions, fluoride application appeared to enhance color stability (ΔE=1.59 in the varnish-applied group, ΔE=2.21 in the group without varnish application), but did not have a statistically significant effect on the surface microhardness. A negative correlation was observed between color change and surface microhardness; as the surface microhardness decreased, the extent of color change increased. This study highlights the prominent role of intraoral environmental factors in influencing the durability and aesthetic properties of fluoride-releasing restorative materials. Topical fluoride application has a beneficial effect on the color stability with a more pronounced effect observed with Cention N.