The use of erbium lasers to prevent caries in enamel has shown positive results. However, it is not known if Er,Cr:YSGG laser can also be used to increase acid resistance of root dentine, which is another dental tissue susceptible to the action of cariogenic bacteria. Objective: To analyze the effects of the Er,Cr:YSGG laser (λ=2.78 μm, 20 Hz) irradiation associated with 2% neutral sodium fluoride (NaF) to prevent root dentin demineralization. Material and Methods: One hundred human root dentin samples were divided into 10 groups (G) and treated as follows: G1: no treatment; G2: NaF; G3: laser (4.64 J/cm2) with water cooling (WC=5.4 mL/min); G4: laser (4.64 J/cm2) without WC; G5: laser (8.92 J/cm2) with WC; G6: laser (8.92 J/cm2) without WC; G7: laser (4.64 J/cm2) with WC and NaF; G8: laser (4.64 J/cm2) without WC and NaF; G9: laser (8.92 J/cm2) with WC and NaF; G10: laser (8.92 J/cm2) without WC and NaF. The NaF gel was applied alone or after 4 min of irradiation. After 14 days of acid challenge, the samples were sectioned and the Knoop microhardness (KHN) test was done at different depths (30, 60, 90 and 120 μm) from the outer dentin surface. Data were analyzed by one-way ANOVA and Fisher’s test (α=5%). Results: The results showed that G8 and G10 presented higher KHN than the G1 for the depths of 30 and 60 μm, indicating an increase of the acid resistance of the dentin in up to 35% (p<0.05). Conclusions: The use of Er,Cr:YSGG laser irradiation at 4.64 J/ cm2 and 8.92 J/cm2 without water cooling and associated with 2% NaF can increase the acid resistance of human root dentin.

A maioria dos estudos que utilizam o laser Nd:YAG com ação preventiva são em dentes permanentes, e são escassos os estudos em dentes decíduos. Desta forma, o objetivo do presente estudo foi avaliar in vitro o efeito do laser Nd: YAG combinado ou não com flúor na resistência ácida do esmalte decíduo após a indução de cárie artificial, através da avaliação de microdureza longitudinal e profundidade da desmineralização. Para tanto, foram selecionados 60 fragmentos de esmalte obtidos a partir da superfície bucal / lingual de molares decíduos irrompidos, os quais foram isolados com esmalte de unha e cera, deixando uma área exposta de 9 mm² na superfície do esmalte. Os espécimes foram divididos aleatoriamente em 6 grupos (n = 10) de acordo com o tipo de tratamento: C- Controle: sem tratamento; APF: aplicação de gel flúor fosfato acidulado 1,23%; FV: aplicação de verniz fluoretado 5%; L: aplicação do Laser Nd:YAG 0,5 W/10 Hz no modo contato; APFL: aplicação de gel flúor fosfato acidulado + Laser Nd:YAG; FVL: aplicação de verniz fluoretado 5% + Laser Nd:YAG. Após os tratamentos, os espécimes foram submetidos a um ciclo de desremineralização para a indução de lesão de cárie artificial. Os dados de microdureza longitudinal (%LMC) foram avaliados pelo teste de Kruskal-Wallis e os dados de profundidade da desmineralização foram avaliados pelos testes ANOVA e Fisher’s LSD (α=5%). Observou-se que os grupos APFL e APF apresentaram menor percentual de perda de dureza (p<0,05). A profundidade de desmineralização foi menor em todos os grupos tratados em comparação com o controle. Em conclusão, o laser Nd: YAG associado ou não com flúor/verniz não foi mais efetivo do que o flúor sozinho para prevenir a desmineralização do esmalte durante o período experimental.

Most studies dealing with the caries preventive action of Nd:YAG laser have been done in permanent teeth and studies on primary teeth are still lacking. The aim of this study was to evaluate in vitro the effect of Nd:YAG laser combined or not with fluoride sources on the acid resistance of primary tooth enamel after artificial caries induction by assessing longitudinal microhardness and demineralization depth. Sixty enamel blocks obtained from the buccal/lingual surface of exfoliated human primary molars were coated with nail polish/wax, leaving only a 9 mm² area exposed on the outer enamel surface, and randomly assigned to 6 groups (n=10) according to the type of treatment: C-control (no treatment); APF: 1.23% acidulated phosphate fluoride gel; FV: 5% fluoride varnish; L: Nd:YAG laser 0.5 W/10 Hz in contact mode; APFL: fluoride gel + laser; FVL: fluoride varnish + laser. After treatment, the specimens were subjected to a des-remineralization cycle for induction of artificial caries lesions. Longitudinal microhardness data (%LMC) were analyzed by the Kruskal-Wallis test and demineralization depth data were analyzed by oneway ANOVA and Fisher’s LSD test (á=0.05). APFL and APF groups presented the lowest percentage of microhardness change (p<0.05). Demineralization depth was smaller in all treated groups compared with the untreated control. In conclusion, Nd:YAG laser combined or not with fluoride gel/varnish was not more effective than fluoride alone to prevent enamel demineralization within the experimental period.