In vitro evaluation of enamel demineralization after several overlapping CO2 laser applications.

This study aimed to evaluate the effects of repeated CO2 laser applications on the inhibition of enamel demineralization. Sixty-five human dental enamel slabs were randomly assigned to the following groups (n = 13): control (C), one application of the CO2 laser (L1), two applications of the CO2 laser (L2), three applications of the CO2 laser (L3), and four applications of the CO2 laser (L4). Enamel slabs were irradiated by a 10.6-µm CO2 laser operating at 5 J/cm(2). The slabs were subjected to a pH-cycling regimen and then analyzed by FT-Raman spectroscopy, energy-dispersive X-ray fluorescence spectrometry (EDXRF), cross-sectional micro-hardness, and scanning electron microscopy (SEM). Statistical analysis was performed using ANOVA and Tukey tests (p < 0.05). FT-Raman spectroscopy showed a reduced carbonate content for L1, L3, and L4 groups when compared to C (p < 0.05). The EDXRF data showed no statistical differences between the control and irradiated groups for calcium and phosphorus components (p > 0.05). Cross-sectional micro-hardness data showed a statistically significant difference between the control and all irradiated groups (p < 0.05), but no difference was found among the irradiated groups (p > 0.05) up to 30-µm depth. A tendency of lower demineralization occurred in deeper depths for L3 and L4 groups. The SEM results showed that with repeated applications of the CO2 laser, a progressive melting and recrystallization of the enamel surface occurred. Repeated irradiations of dental enamel may enhance the inhibition of enamel demineralization.

The effect of soft-start polymerization by second generation LEDs on the degree of conversion of resin composite.

Fourier-Transform (FT)--Raman spectroscopy was used to evaluate in vitro the degree of conversion (DC) of Charisma dental composite cured by three different light curing units (LCUs) using soft-start and normal protocols. Eighty circular blocks of resin (7 mm in diameter x 2.5 mm thick) were prepared and cured using the following sources: halogen light (Degulux soft-start, n = 20, G1-G2), low power light emitting diode (LED) with transparent polymer tip (LD13, n = 20, G3-G4) and fiber optic tip (LD13, n = 20, G5-G6) and, finally, high power LED (Radii, n = 20, G7-G8). The top and bottom surfaces of the blocks were analyzed by FT-Raman spectroscopy. The respective DCs were estimated calculating the peak height ratio of the aliphatic C=C (1640 cm(-1)) and aromatic C=C (1610 cm(-1)) Raman modes. The DC at the surfaces ranged between 50% and 60% for the top and 46% and 58% for the bottom. The halogen light and high power LED LCUs with the soft-start and normal protocols produced the highest DC values of dental composite at both surfaces (p < 0.001). Curing by low power LED in the soft-start protocol did not produce adequate DC at the depth of 2.5 mm. The type of LCU light guide tip did not present a significant statistical difference in the final DC of the dental composite (p > 0.05).

Combined effects of carbon dioxide laser and fluoride on demineralized primary enamel: an in vitro study.

This in vitro study aimed at evaluating the efficacy of a CO(2) laser (10.6 microm) alone or combined with acidulated phosphate fluoride (APF) on the inhibition of lesion progression in primary enamel. The specimens were treated with/without CO(2) laser and/or APF and submitted to pH cycling. Microhardness analysis was performed and the enamel mineral loss values were obtained. The groups treated with laser and/or APF presented lower mineral loss when compared to the control group (p < 0.05). Laser irradiation alone or combined with APF decreased lesion progression in primary enamel. However, the combined treatment did not show any significant additional effect.