In Vitro Evaluation of the Effect of Microabrasion and Resin Infiltration Materials on Enamel Microhardness and Penetration Depth

<b>Background:</b> This in vitro study aimed to evaluate the effect of microabrasion as a surface pretreatment and to compare an experimental resin infiltrant with a commercially available system (ICON) in terms of enamel surface microhardness recovery and resin penetration depth in artificially demineralized enamel lesions. <b>Methods:</b> Forty-eight caries-free human third molars were prepared to obtain standardized enamel specimens, and artificial enamel lesions were created using a pH-cycling model. Specimens were randomly allocated into four groups (<i>n</i> = 12): experimental resin with microabrasion, experimental resin without microabrasion, ICON resin with microabrasion, and ICON resin without microabrasion. When indicated, microabrasion was performed using a 6.6% hydrochloric acid paste for a total application time of 30 s, followed by standard hydrochloric acid etching as part of the infiltration protocol. Enamel surface microhardness was measured at baseline, after demineralization, and after resin infiltration. Resin penetration depth was assessed using confocal laser scanning microscopy, with six specimens per group (<i>n</i> = 6). Data were analyzed using repeated-measures mixed-effects models and one-way ANOVA (<i>p</i> < 0.05). <b>Results:</b> Resin infiltration resulted in a partial recovery of enamel surface microhardness following demineralization; however, baseline hardness values were not fully restored, and no statistically significant differences were observed among the study groups (<i>p</i> > 0.05). These findings indicate surface stabilization rather than complete mechanical or mineral restoration. The ICON resin demonstrated significantly greater penetration depth than the experimental resin. In both resin systems, microabrasion significantly increased penetration depth. <b>Conclusions:</b> Within the limitations of this in vitro study, resin infiltration primarily contributed to the stabilization of demineralized enamel surfaces rather than true remineralization or full mechanical recovery. Although microabrasion enhanced resin penetration depth, this effect should be interpreted with caution due to the potential for cumulative enamel loss. From a clinical perspective, these findings support the selective use of microabrasion to enhance resin infiltration in early enamel lesions with pronounced surface barriers, while emphasizing the need to balance penetration benefits against enamel preservation.