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Low-level laser therapy has been investigated as a possible stimulus for enhancement of proliferation and differentiation of various cell types, but few reports relate undifferentiated mouse pulp cells (OD-21) response to irradiation in in vitro models. The aim of this study was to analyze the influence of low-level laser therapy (λ=660 nm), with three different irradiation times, on the behavior of OD-21 cell line. The cells were cultivated and divided into three groups: non-irradiated/control (group I); irradiated with 88 s (group II); irradiated with 177 s (group III) and irradiated with 265 s (group IV). Cell growth and viability were assessed after 7 and 10 days. Data were analyzed by Kruskal-Wallis and Mann-Whitney tests (α=.05). At day 7, there was a higher cell growth in groups I and II, as compared to group IV (p<.01). At the 10th day, group I showed a higher cell growth as compared to group II (p<.05). Cell viability in group IV was significantly lower at the 7th day, as compared to groups I (p<.001), II (p<.01) and III (p<.001). Cell viability in all the groups was over 80%, except in group IV at day 7. Irradiation time of group I influenced positively the proliferation and viability of OD-21 cells in late cell culture period. Keywords: Low-Level Laser Therapy. Cell Culture. Stem Cells. ResumoA terapia a laser de baixa intensidade tem sido investigada como possível estímulo para aumento da proliferação e diferenciação de vários tipos de células, mas poucos relatos relacionam a resposta de células indiferenciadas da polpa dentária de camundongos (OD-21) à irradiação em modelos in vitro. O objetivo deste estudo foi analisar a influência do laser de baixa intensidade (λ=660 nm), com três períodos de irradiação diferentes, no comportamento das células da linhagem OD-21. As células foram cultivadas e distribuídas em três grupos: não irradiado / controle (grupo I); irradiado com 88 s (grupo II); irradiado com 177 s (grupo III) e irradiado com 265 s (grupo IV). O crescimento e a viabilidade celular foram avaliados após 7 e 10 dias. Os dados foram analisados pelos testes de Kruskal-Wallis e Mann-Whitney (α = 0,05). No dia 7, houve crescimento celular maior nos grupos I e II, em comparação ao grupo IV (p <0,01). No décimo dia, o grupo I apresentou crescimento celular superior ao grupo II (p <0,05). A viabilidade celular no grupo IV foi significativamente menor no sétimo dia, em comparação aos grupos I (p <0,001), II (p <0,01) e III (p <0,001). A viabilidade celular em todos os grupos foi superior a 80%, exceto no grupo IV no dia 7. O tempo de irradiação do grupo I influenciou positivamente a proliferação e a viabilidade das células OD-21 no período mais tardio da cultura celular. Palavras-chave: Laserterapia de Baixa Intensidade. Cultura Celular. Células Tronco.

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The aim of this study was to assess the surface and the substrate/glass ionomer cement (GIC) interface after Er:YAG laser irradiation by means of scanning electron microcopy. Material and methods: Thirty human third molars were selected and had their roots removed. Crowns were sectioned to obtain discs that were randomly assigned to three groups according to the surface pretreatment: 40% polyacrylic acid (control); Er:YAG laser irradiation (80mJ/2Hz) or Er:YAG laser followed by 40% polyacrylic acid. Two discs of each group were put aside to the surface analysis and the others were bisected. One half received Ketac-Fil and the other received Fuji II LC. Specimens were prepared for SEM and were analyzed under different magnifications. Results: Er:YAG laser group showed no adhesive interface for both enamel and dentin, but strongly damaged the interface build-up for dentin/Fuji II LC. The application of laser irradiation followed by the polyacrylic acid exhibited gaps and irregularities for both substrates. Conclusion:Er:YAG laser irradiation combined or not with 40% polyacrylic acid produced a surface unfavorable for GIC interaction, especially for the resin-modified ones.