Enamel diffusion modulated by Er:YAG laser (Part 1)--FRAP.

UNLABELLED: Several studies have demonstrated the caries protective effect of lasers by strengthening enamel crystalline structure. However, the effect of laser on enamel diffusion (ED) remains unclear. OBJECTIVES: This study aimed to quantify the laser-induced alteration of diffusion coefficients (DC) in enamel using fluorescence recovery after photobleaching (FRAP). METHODS: Eleven caries-free enamel sections were characterized morphologically using stereomicroscopy, polarized light microscopy and scanning electron microscopy, before and after laser treatment with Er:YAG laser 50 mJ x 5 s x 5 Hz. With 20 microM fluorescein, DCs were measured (n=11) by FRAP coupled with confocal microscopy. RESULTS: The DCs measured were 2.89+/-0.61 x 10(-7)cm(2)/s and 4.076+/-0.73 x 10(-7)cm(2)/s, at the lased and unlased areas, respectively (p=0.001). CONCLUSIONS: This study has confirmed the reduction of ED as a potential mechanism involved in laser-induced caries prevention. FRAP was demonstrated to be a promising technique for evaluating diffusion-related phenomenon in enamel.

Enamel diffusion modulated by Er:YAG laser (Part 2). Organic matrix.

UNLABELLED: Organic matrix (OM) has been hypothesized as a key player in the laser-induced retardation of enamel diffusion (LRED). OBJECTIVES: Therefore, this study was aimed to quantify the contribution of OM in LRED. METHODS: Four groups of enamel sections (n=10) were assigned to 'normal', 'laser treated', 'OM extracted' and 'laser+OM extraction' groups for measurement of diffusion coefficient (DC) using fluorescence recovery after photobleaching (FRAP) and fluorophores transport study (FTS). Er:YAG laser treatment and OM extraction were performed on respective groups. Sections were characterized with stereomicroscopy and polarized light microscopy. Treatment effects were statistically assessed with a factorial ANOVA. RESULTS: DC measured by FRAP and FTS coupled with confocal microscopy revealed the significant effect of OM (p=0.001) and laser treatment (p<0.01). After OM extraction, the laser effect on diffusion decreased about 34-75%, confirming the significant role of OM in LRED. CONCLUSION: Both FRAP and FTS may be promising tools to quantify enamel DC.