Acid erosion is a superficial loss of enamel caused by chemical processes that do not involve bacteria. Intrinsic and extrinsic factors, such as the presence of acid substances in the oral cavity, may cause a pH reduction, thus potentially increasing acid erosion. The aim of this study was to evaluate the microhardness of bleached and unbleached bovine enamel after immersion in a soda beverage, artificial powder juice and hydrochloric acid. The results obtained for the variables of exposure time, acid solution and substrate condition (bleached or unbleached enamel) were statistically analyzed by the ANOVA and Tukey tests. It was concluded that a decrease in microhardness renders dental structures more susceptible to erosion and mineral loss, and that teeth left unbleached show higher values of microhardness compared to bleached teeth.

Este estudo propôs avaliar, através da microscopia eletrônica de varredura (MEV), a capacidade de limpeza e remoção de "smear layer" e debris das paredes de canais radiculares preparados e irrigados com soluções de hipoclorito de sódio (NaOCl) a 2,5%, gluconato de clorexidina (CLX) a 2,0% e soro fisiológico (controle). Utilizaram-se 50 dentes unirradiculares extraídos com um único canal. Cortaram-se as coroas no limite cervical e os canais foram preparados até o instrumento 45. Durante o preparo foram feitas irrigações com as soluções a serem avaliadas: Grupo 1: NaOCl a 2,5% (10 raízes); Grupo 2: NaOCl a 2,5% seguido de irrigação com EDTA a 17% por 2 minutos (10 raízes); Grupo 3: CLX a 2,0% (10 raízes); Grupo 4: CLX a 2,0% e EDTA a 17% por 2 minutos (10 raízes); Grupo 5: soro fisiológico (5 raízes); Grupo 6: soro fisiológico e EDTA a 17% por 2 minutos (5 raízes). Após o preparo, os canais foram irrigados com as soluções em teste, e as raízes cortadas no sentido V-L para avaliação por MEV, nos terços cervical, médio e apical, verificando-se a presença de "smear layer" e debris. Os dados relativos aos escores atribuídos foram avaliados pelo teste Kruskal-Wallis com p = 5%. Os resultados mostraram que o uso do EDTA diminuiu significativamente (p < 0,05) a "smear layer" para todas as soluções avaliadas em todos os terços. Quando não se utilizou o EDTA, somente para o grupo do NaOCl, verificou-se quantidade significativamente maior de "smear layer" no terço apical. Exceto para a CLX, o uso de EDTA diminuiu significativamente a quantidade de debris. Concluiu-se, que após o preparo, faz-se necessária a utilização do EDTA a fim de promover melhor limpeza das paredes dos canais radiculares.

The purpose of this study was to carry out a scanning electron microscopic (SEM) analysis of the cleaning qualities and smear layer removal from root canal walls, instrumented and irrigated with 2.5% NaOCl, 2.0% chlorhexidine and saline solutions. Fifty extracted teeth were used in this study. All teeth were radiographed to determine the existence of a single canal. The crowns were cut at the cervical limit and the root canals were instrumented with K-type files up to size 45. During root canal preparation, irrigations were made with the different solutions being evaluated: Group 1: 2.5% NaOCl (10 roots); Group 2: 2.5% NaOCl and 17% EDTA for 2 minute (10 roots); Group 3: 2.0% chlorhexidine (10 roots); Group 4: 2.0% chlorhexidine and 17% EDTA for 2 minutes (10 roots); Group 5: saline solution (5 roots); Group 6: saline solution and 17% EDTA for 2 minutes (5 roots). After instrumentation, the canals were irrigated with each one of the solutions and the roots were cut in the buccolingual direction for SEM analysis, at the cervical, middle and apical thirds, to ascertain the presence or absence of smear layer and debris. SEM analysis was performed by three calibrated examiners and scores were submitted to Kruskal-Wallis test at the significance level of p = 5%. Results showed that the use of 17% EDTA decreased the smear layer significantly (p < 0.05) for all evaluated solutions in all thirds. When EDTA was not used, a significantly higher quantity of smear layer on the apical third was observed only in the NaOCl groups. The use of 17% EDTA was significant for debris removal except for the chlorhexidine groups. The following conclusion could be drawn: the use of 17% EDTA was necessary to enhance cleanness of the root canals.