Influence of Er,Cr:YSGG laser irradiation on enamel caries prevention

Abstract

The objective of this study was to evaluate the effects of chromium:yttrium-scandium-gallium-garnet (Er,Cr:YSGG) laser irradiation on the acid resistance of dental enamel. Forty human enamel samples were divided into four groups. They were manually irradiated with an Er,Cr:YSGG laser device (λ = 2.78 µm, 20 Hz, 20 s), in a scanning mode, with and without water cooling, according to the following parameters: Group 1: 0.25 W, 62.5 J/cm(2), no water cooling; group 2: 0.25 W, 62.5 J/cm(2), 5.0 ml/min; group 3: 0.5 W, 125 J/cm(2), no water cooling; group 4: 0.5 W, 125 J/cm(2), 5.0 ml/min. No airflow was used. Afterwards, the samples were submitted to an acid challenge and assessed by cross-sectional Knoop microhardness at different depths (20, 40, 60, 80, and 100 µm) from the outer enamel surface. Average values were obtained for both irradiated and control areas in each sample and they were compared to obtain a percentage of microhardness increase. Data were analyzed by analysis of variance and Fisher's exact test (α = 5%). The percentage of microhardness increase observed in group 1 (+23.58%) was similar to group 3 (+19.12%), but higher than groups 2 (+3.61%) and 4 (10.9%) (p < 0.05). The comparison of the depths showed that the Er,Cr:YSGG laser acted in the superficial layers of the dental enamel. The findings of the present study suggest that the energy densities of 62.5 and 125 J/cm(2) were capable of increasing the acid resistance of human enamel. The presence of water during irradiation makes it difficult to obtain an enamel surface more resistant to acids.

Comparative evaluation of the effect of Er:YAG laser and low level laser irradiation combined with CPP-ACPF cream on treatment of enamel caries

“…This finding corroborates the results of some previous authors (22-24) who observed no significant increase in caries resistance of the specimens irradiated with the Er:YAG or Er,Cr:YSGG lasers compared to the control group. The outcomes of this study, however, are in contrast to the studies that indicated caries inhibitive effects of erbium lasers (11-13). de Freitas et al (12) reported that the specimens submitted to the Er,Cr:YSGG laser at 8.5 J/cm2 showed 64% caries inhibition which was comparable to the cariostatic effect of the samples treated with a NaF dentifrice.…”

“…Hossain et al (26), however, indicated that Er:YAG laser without water mist was more effective in caries prevention than when it was used with water coolant. This has also been emphasized by other authors (13) who found that water, even in minimal amounts, was not favorable for the preventive effect of laser irradiation.…”

“…It has been demonstrated that the application of high power lasers such as CO2 and erbium lasers (Er:YAG and Er,Cr:YSGG) are effective in caries prevention (9-13). As these lasers are greatly absorbed by water and hy-droxyapatite of the tooth tissues, they are capable to modify the crystalline structure, acid solubility and permeability of the tooth surface and thereby increasing its resistance against demineralization.…”

The combined use of Er,Cr:YSGG laser and fluoride to prevent root dentin demineralization

“…For the acid challenge, samples were submitted to a pHcycling procedure, modified from previously described protocols 13 , 14 . The demineralization solution (pH=4.3) consisted of 2 mmol/L of Ca and 2 mmol/L of phosphate in buffer solution of acetate 0.075 mol/L, and the remineralization solution (pH=7.0) consisted of 1.5 mmol/L of Ca, 0.9 mmol/L of phosphate and 150 mmol/L of potassium chloride.…”

“…However, for caries prevention, it is important that the laser does not ablate the treated surface, but change the tissue morphologically or chemically. Therefore, to achieve the preventive effect, studies have been performed with low energy densities (sub-ablative parameters) and without water cooling 1 , 2 , 9 , 10 , 14 . It was demonstrated that the irradiation of the enamel surface with an Er,Cr:YSGG laser device, using an energy density of 8 J/cm 2 , promotes a sufficient temperature increase to change the chemical structure of enamel, turning it into a less soluble structure 9 , 10 .…”