Abstract Background Initial enamel lesions represent a reversible stage of dental caries, yet conventional remineralization methods often face challenges in acid resistance. This study aimed to evaluate the synergistic effect of Er, Cr: YSGG laser and nano-hydroxyapatite (nano-HA) on the remineralization of initial enamel lesions and their sustainability against subsequent acid challenges. Methods One hundred bovine incisors were used to create artificial white spot lesions. Specimens were randomly assigned to five groups ( n = 20): G1 (CPP-ACP + F), G2 (Nano-HA), G3 (Er, Cr: YSGG laser), G4 (Laser + Nano-HA), and G5 (Nano-HA + Laser). After treatment, specimens underwent a 10-day pH-cycling protocol (6 h demineralization/18 h artificial saliva). Surface microhardness (Vickers), surface roughness (Ra), and surface morphology (SEM) were evaluated at three stages: post-demineralization, post-remineralization, and post-pH-cycling. Data were analyzed using Two-way and Repeated Measures ANOVA with Tukey HSD post-hoc tests ( p < 0.05). Results Laser-assisted groups (G3, G4, and G5) exhibited significantly higher microhardness values compared to G1 and G2 across all stages ( p < 0.05). Following pH-cycling, G4 (Laser + Nano-HA) showed significantly higher hardness preservation compared to G5 (Nano-HA + Laser) ( p < 0.05). While laser application significantly increased surface roughness in all measurement stages ( p < 0.05), the application of nano-HA in G4 and G5 partially masked these irregularities. SEM analysis confirmed that G4 provided a more compact and homogeneous mineral layer, with fewer longitudinal cracks after acid challenge compared to other groups. Conclusions The combination of Er, Cr: YSGG laser and nano-HA, particularly when the laser is applied first, significantly enhances the remineralization efficacy and acid resistance of enamel. This synergistic approach offers a promising clinical alternative for the long-term management of initial caries lesions.
KAPLAN et al. (Tue,) studied this question.