Enhancement of Fluoride Retention in Human Enamel Using Low-Energy Blue Diode Laser (445 nm): An Ex Vivo Study

This ex vivo study aimed to evaluate the effect of low-energy 445 nm diode laser irradiation on permanent fluoride retention in human enamel.

Eighty caries-free extracted permanent human teeth were used to prepare 480 enamel discs (2 × 2 mm). Baseline fluoride content in untreated enamel specimens (control group E) was measured using particle-induced gamma-ray emission (PIGE). All specimens then received a topical application of acidulated phosphate fluoride for 5 min, followed by rinsing with double-distilled water for 1 min. Fluoride quantification was subsequently repeated. Specimens were randomly allocated into two groups: fluoridated only (EF; n = 240) and fluoridated plus laser-treated (EFL; n = 240). Each group was further subdivided based on storage conditions: either in air or in double-distilled water at 36 °C for 7 days. Laser irradiation was performed using a 445 nm diode laser in continuous-wave mode at 350 mW for 30 s, with a beam diameter of 10 mm, an energy density of 13.375 J/cm², and a power density of 0.445 W/cm².

At baseline, mean fluoride content across all specimens was 702.23 ± 201 ppm. Immediately after fluoridation, fluoride levels increased to 11,059 ± 386 ppm in the EF group and 10,842 ± 234 ppm in the EFL group, with no significant difference between groups. After 7 days of storage in air, fluoride retention decreased to 5714 ± 1162 ppm in EF and 5973 ± 861 ppm in EFL, again without significant difference. However, after 7 days of immersion in double-distilled water, the EF group exhibited complete loss of acquired fluoride, with values falling below baseline (337 ± 150 ppm). In contrast, the EFL group retained a substantial portion of the fluoride acquired during fluoridation (total 1533 ± 163 ppm), indicating that laser irradiation significantly prevented fluoride loss (p < 0.001).

Low-energy 445 nm diode laser irradiation of fluoridated enamel significantly enhances fluoride retention under aqueous conditions simulating osmotic processes. Laser treatment preserved a substantial portion of fluoride acquired during fluoridation, whereas fluoridated but unlased enamel lost nearly all fluoride, with levels dropping below baseline. This approach may offer clinical benefits for improving enamel fluoride enrichment, thereby increasing resistance to acid challenge and reducing caries risk.