Remineralizing Effects of 38% Silver Diamine Fluoride and 5% Sodium Fluoride Varnish on Artificial Dentin Caries Lesions in Primary Molars: An In Vitro Study

Background/Objectives: Silver diamine fluoride (SDF) is increasingly used to arrest dentin caries; however, direct laboratory comparisons with sodium fluoride (NaF) varnish in primary dentin remain limited. This study compared treatment-associated mineral and lesion-depth changes following application of 38% SDF and 5% NaF varnish to artificial dentin caries-like lesions in primary molars. Methods: Twenty-eight sound extracted or naturally exfoliated primary molars were included. Standardized 4 × 4 mm dentin windows were subjected to 14 days of pH cycling and sectioned buccolingually to produce paired treated and untreated specimens. Fourteen teeth were assigned to energy-dispersive X-ray spectroscopy (EDX) for calcium and phosphorus assessment, and 14 were assigned to polarized light microscopy (PLM) for lesion-depth measurement and qualitative evaluation. Within each analytical group, seven teeth received SDF and seven received NaF. Group differences were assessed using the Kruskal–Wallis test, followed by Dunn’s pairwise comparisons with Bonferroni adjustment. Additional lesion-depth analyses were performed using the Wilcoxon signed-rank test for treated–control comparisons and the Mann–Whitney U test for comparisons of treatment-associated lesion-depth changes between SDF and NaF. Results: Median phosphorus values were 23.13% and 44.15% in NaF-associated controls and NaF-treated specimens and 46.74% and 70.25% in SDF-associated controls and SDF-treated specimens, respectively. Corresponding calcium medians were 43.28%, 76.59%, 48.53%, and 85.00%. Mean lesion depth was 0.819 ± 0.331 mm in controls, 0.563 ± 0.418 mm after NaF, and 0.195 ± 0.074 mm after SDF. In pooled-control EDX comparisons, SDF differed from controls for phosphorus and calcium (both adjusted p < 0.001), whereas NaF differed from pooled controls for calcium (adjusted p = 0.012) but not phosphorus. For lesion depth, SDF differed from untreated controls (adjusted p = 0.003). Differences between SDF and NaF were not statistically significant (all adjusted p > 0.05). PLM showed a more continuous birefringent surface zone after SDF, whereas NaF produced more heterogeneous and predominantly superficial changes. Conclusions: Within the limitations of this in vitro study, 38% SDF was associated with significantly higher calcium and phosphorus values and reduced lesion depth compared with untreated controls in the reported analyses. Although SDF showed numerically more favorable outcomes than 5% NaF varnish, the between-treatment differences were not statistically significant.