The Effect of Different White Spot Lesion Treatments on the Enamel Microhardness—An In Vitro Pilot Study

<b>Background/Objectives:</b> Dental caries, one of the most common oral diseases worldwide, represents a major public health concern. Contemporary dentistry has established several non-invasive approaches and resin infiltration, as a micro-invasive path, in the treatment of white spot lesions (WSLs). This study aimed to evaluate the effect of different WSL treatments on enamel surface microhardness. <b>Materials and Methods:</b> Seventy-five intact human premolars extracted upon orthodontic indication and the demineralizing solution composed of acetic acid, monopotassium phosphate and calcium chloride with pH = 4.4 and exposure time 96 h were used. The samples were randomly divided into five groups (n = 15): I-intact enamel (control group); II-artificial white spot lesion; III-artificial WSL treated with fluoride varnish; IV-artificial WSL treated with casein phosphopeptide-amorphous calcium phosphate (CPP-ACP) paste; V-resin-infiltrated artificial WSL. The surface microhardness was determined using the Oliver-Pharr method and a spherical indenter (Shimadzu Indenter, Kyoto, Japan). One-way analysis of variance (ANOVA) followed by a Post Hoc test (Bonferroni) was used with a level of significance set at <i>p</i> < 0.05. <b>Results:</b> Resin-infiltrated white spot lesions showed comparable microhardness mean value as the control group: 68.23 (±21.45) and 63.57 (±18.89), respectively (<i>p</i> > 0.05). Also, resin infiltration increased enamel microhardness compared to WSL values, with a statistically significant difference (<i>p</i> < 0.05). Fluoride varnish and CPP-ACP treatment resulted in equivalent values (50.84 ± 14.35 and 50.99 ± 15.31, respectively). <b>Conclusions:</b> Different WSL treatments (fluoride varnish, CPP-ACP and resin infiltration) produced comparable enamel microhardness values. Among the tested agents, resin infiltration resulted in higher microhardness values, while fluoride varnish and CPP-ACP demonstrated equivalent outcomes.