Effect of conventional and power office bleaching with diode laser and led light on enamel microhardness

Aim: The present study aimed to asses enamel microhardness after office bleaching with diode laser and LED light compared to the conventional bleaching procedure. Methods: Thirty-nine human premolar teeth were collected and randomly divided into three groups regarding of the bleaching technique. Group 1: Snow O bleaching gel with LED light-curing unit; Group 2: Snow L bleaching gel with diode laser irradiation; and Group 3: Opalescence Boost bleaching gel with no light source in group 3. Enamel surface changes were evaluated in one tooth in each study group and one intact tooth as a reference under a scanning electron microscope (SEM). In the remaining samples (n=12), enamel microhardness was determined by Vickers microhardness test before and after bleaching. Data were analyzed with repeated-measures ANOVA to compare microhardness changes, followed by post hoc Tukey tests at the 0.05 significance level. Results: Enamel microhardness decreased in all the groups after bleaching, with the maximum decrease in microhardness in the Snow O bleaching group with LED light, which was significantly higher than the other groups (P=0.002). The two other groups did not exhibit any significant difference in microhardness decrease (P>0.05). Conclusion:Based on the limitations of this study, it can be concluded power bleaching with 980nm diode laser was less time-consuming compare to conventional bleaching procedure and yielded better outcomes in terms of enamel surface microhardness compared to the use of an LED light-curing unit

Effect of cement type on microleakage of cast post-and-core systems under cyclic loading / Efeito do tipo de cimento na microinfiltração de núcleos metálicos fundidos submetidos à fadiga cíclica

Objective: The purpose of this study was to compare the microleakage of four cements in cast post-andcoresystems under cyclic loading. Materials and methods: Sixty-four human premolars were sectionedat the cement-enamel junction, endodontically treated, and divided into four groups (n = 16). Cast postsand cores were fabricated for root segments and were cemented with zinc phosphate cement (Harvard),resin-modified glass ionomer (Fuji PLUS), dual-cured phosphate methacrylate resin cement (Panavia F),or a dual-cured resin cement (Variolink II). All specimens underwent thermal cycling for 1.500 cycleswith 5 °C and 55 °C, with a dwelling time of 12 seconds. Half of the specimens of each group were subjectedto cycling loading with 50 N at 1.2 Hz for 750,000 cycles. Specimens were then immersed in 5%basic fuchsin solution for 24 hours. Specimens were sectioned, visualized by stereomicroscope under40x magnification and scored for dye penetration. The ratio between the length of the interface and thelength of dye penetration was also determined. Microleakage differences between the four cements were analyzed by Kruskal-Wallis test, and the effect of fatigue was analyzed with Mann-Whitney nonparametrictest (α =.05). Results: No failures occurred during fatigue testing. The zinc phosphate cement showedsignificantly higher microleakage values compared to other cements under both unloaded and loadedconditions (p = .007 and p = .006). Fatigue significantly increased the microleakage in all groups (p < .05).Conclusions: The microleakage values for the resin cements and the resin-modified glass ionomer weresimilar and significantly less than those of zinc phosphate, irrespective of loading. Fatigue loading increasedthe microleakage values for all the cements.

Objetivo: O objetivo deste estudo foi comparar a microinfiltração de pinos e núcleos de preenchimento metálicoscimentados com quatro diferentes materiais. Materiais e Métodos: 64 pré-molares humanos foram seccionadosna junção cemento-esmalte, tratados endodonticamente e divididos em quatro grupos (n = 16). Pinos enúcleos metálicos fundidos foram fabricados e cimentados com cimento de fosfato de zinco (Harvard), cimentode ionômero de vidro modificado (Fuji Plus), cimento resinoso dual de metacrilato fosfato (Panavia F) e cimentoresinoso dual (Variolink II). Todos os espécimes foram submetidos à ciclagem térmica (1.500 ciclos a 5-55 °C, 12segundos de banho). Metade dos espécimes de cada grupo foi submetida a uma carga cíclica de 50 N a 1,2 Hz emum total de 750.000 ciclos. Após a ciclagem, os espécimes foram imersos em solução de fucsina básica 5% por24 horas, seccionados, visualizados sob aumento de 40x e ranqueados quanto à penetração do corante. A proporçãoentre o comprimento da interface e o comprimento da penetração do corante foi também determinada.As diferenças de infiltração entre os quatro cimentos foram analisadas por teste de Kruskal-Wallis e o efeito dafadiga foi analisado por teste não paramétrico de Mann-Whitney (α = 0,05). Resultados: Não ocorreram falhasdurante o teste de fadiga. O cimento de fosfato de zinco mostrou valores de infiltração significativamente maiorescomparados aos demais cimentos na ausência ou presença da fadiga (p = 0,007 e p = 0,006). A fadiga elevousignificativamente a microinfiltração em todos os grupos (p < 0,05). Conclusões: Os valores de microinfiltraçãopara os cimentos resinosos e para o cimento de ionômero de vidro modificado foram similares e inferiores àquelesdo cimento de fosfato de zinco, independente da aplicação do teste de fadiga. A fadiga elevou os valores de microinfiltraçãopara todos os cimentos.