Previous studies have shown that argon laser irradiation of enamel and root surfaces (at 488 nm wavelength) increases hardness and confers resistance to cariogenic and erosive attack. This protective effect is enhanced greatly when topically applied fluoride gel is combined with laser irradiation. Objectives: This study investigated whether a laser-activated fluoride (LAF) effect occurs with other major visible laser wavelengths, using an erosive challenge to dental enamel in vitro. Methods: Slabs of sound human enamel were prepared from extracted sound molar and premolar teeth, divided to give matched test and control sides, and the surfaces polished with 1200 grit silicon carbide paper prior to treatment with 1.23% neutral sodium fluoride gel followed immediately by laser irradiation. KTP (532 nm), InGaAsP (633 nm), and argon ion lasers (488 or 514 nm) were used in continuous mode at identical irradiation parameters (spot size 5 mm; energy density 15 J/cm-2). Vicker’s hardness (VHN) was determined using a mini-load hardness tester before either laser/fluoride or sham treatment, and again after exposure to 1.0M hydrochloric acid for 5 minutes. Results: Following acid challenge, the median VHN of the control side reduced significantly by 54.5 (P<0.0001, N=40). In all four laser treatment groups, the VHN of the test side increased significantly (P=0.001, N=10 per group): by 41.5 for 488 nm, by 72 for 514 nm, and by 113 for both the 532 and 633 nm wavelengths, respectively. Conclusion: From these in-vitro results, we conclude that the action spectrum of laser activation of fluoride is relatively wide, and includes several visible laser wavelengths commonly used in dental practice.
Supported in part by ADRF.