The objective of this study was to assess penetration of adhesive material in enamel bleached with 35% hydrogen peroxide using optical polarized light microscopy. Extracted human teeth were randomly assigned to 5 groups, each representing a specific time interval between bleaching and the application of an adhesive material. They were designated as: (TC) the control group -restorations in unbleached teeth; (T0) comprising restorations carried out immediately after bleaching; (T7) comprising restorations 7 days after bleaching; (T14) comprising restorations 14 days after bleaching; and (T21) comprising restorations 21 days after bleaching. Length of resin tags was measured with an Axiophot photomicroscope at a ‫004ן‬ magnification, and the results subjected to an ANOVA for a comparison between groups, with a p value of Ͻ0.05. Differences between the groups were verified using a Tukey test at a confidence level of 5%. The specimens in the control group (TC) and experimental groups T7, T14 and T21 showed better penetration of adhesive material into enamel in comparison with experimental group T0. This suggests that a gap of at least 7 days should be left between bleaching enamel with 35% hydrogen peroxide and placing adhesive bonding agents and undertaking resin composite restoration work.

O objetivo desta pesquisa foi avaliar, in vitro, dentro de um período de 7 dias, os valores do pH de 4 substâncias utilizadas no clareamento intracoronário. O pH foi avaliado em cinco amostras (quatro soluções clareadoras e uma solução controle). As amostras de cada grupo foram assim constituídas: a) Grupo 1: 15ml de água destilada; b) Grupo 2: 10g de perborato de sódio (Byofórmula – Farmácia de manipulação) com 5ml de água destilada; c) Grupo 3: 10g de perborato de sódio com 5ml de peróxido de carbamida 10% (Byofórmula – Farmácia de manipulação); d) Grupo 4: 10g de perborato de sódio com 5ml de peróxido de hidrogênio 30% (Byofórmula – Farmácia de manipulação); e) Grupo 5: 15ml de peróxido de hidrogênio 30%. Os materiais foram acondicionados em frascos plásticos (FujiFilm) e o valor do pH foi estabelecido com um aparelho pH-metro (Digimed DM-20), logo após a manipulação e também após 1h, 24h e 7 dias. Os resultados mostraram que os valores do pH das associações do perborato de sódio mantiveram-se praticamente constantes, com exceção da associação com o peróxido de hidrogênio, onde ocorreu um aumento gradativo do pH no decorrer dos períodos avaliados. O pH do peróxido de hidrogênio também apresentou-se constante, mantendo-se ácido durante todo o experimento. Das quatro soluções analisadas, apenas o peróxido de hidrogênio apresentou um pH ácido, que assim se manteve em todos os períodos avaliados.

The present in vitro study evaluated the pH values of extraradicular medium after intracoronal bleaching with 30% hydrogen peroxide or 10% carbamide peroxide and different associations of sodium perborate. The study was composed of 50 extracted human premolars, randomly divided into five groups, according to the bleaching agent employed for intracoronal bleaching of these teeth: a) distilled water; b) sodium perborate with distilled water (2g/ml); c) sodium perborate with 10% carbamide peroxide (2g/ml); d) sodium perborate with 30% hydrogen peroxide (2g/ml); e) 30% hydrogen peroxide. Coronal access was performed, followed by root canal filling, confection of a cervical intermediate base with resin-modified glass ionomer cement (Vitremer-3M/ESPE) and application of the bleaching agents. The teeth were stored in plastic flasks containing distilled water, using a mechanical device. Measurement of pH of the extraradicular medium (distilled water) was performed immediately and 7 days after insertion of the bleaching agents. The pH values were analysed using the two-way ANOVA and Tukey,s test at significance level of 5%. The results of the present study confirmed the alkalinity of associations of sodium perborate and the acidity of 30% hydrogen peroxide at the immediate period. Considering the results achieved, it can be concluded that the bleaching agents employed changed the pH of the extraradicular medium at 7-day period.