Influence of Time Intervals between Bleaching Procedures on Enamel Microhardness and Surface Roughness

Roberta Pimentel de Oliveira*, Juliana Costa Pereira Baia, Mara Eliane Soares Ribeiro, Mario Honorato da Silva e Souza Junior, Sandro Cordeiro Loretto
Faculty of Dentistry, Federal University of Para, Augusto Corrêa Street, number 1. Guamá, Belém, Para, Brazil

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Creative Commons License
© 2018 Pimentel de Oliveira et al.

open-access license: This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 International Public License (CC-BY 4.0), a copy of which is available at: ( This license permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

* Address correspondence to the author at the Faculty of Dentistry, Federal University of Para, Augusto Corrêa Street, number 1. Guamá, Belém, Para, Brazil; Tel: +55 (91) 98097-2222; E-mail:



Dental bleaching has been increasingly sought out to improve dental aesthetics, but it may cause changes in dental enamel.


To assess the influence of different time intervals on bleaching gel applications with regard to the Microhardness (MH) and Surface Roughness (SR) on dental enamel.

Material and Methods:

Forty bovine incisors were randomly divided into two groups (G1 and G2) and both were bleached with 35% Hydrogen Peroxide (HP35) (n=20; G1: seven-day interval and G2: two-day interval). The MH and SR tests were performed before bleaching (T0) and after the first (T1), second (T2), and third (T3) bleaching gel applications. The specimens were stored in artificial saliva between each application (37°C). The data were analyzed using the student’s t-test (p ≤ 0.05) for dependent samples.


The reduced time interval (two days) led to a significant reduction in MH, while MH was not affected during the seven-day interval. The SR results increased regardless of the bleaching gel application time interval.


The decreased time interval of two days between bleaching gel applications caused changes in MH but did not influence the SR of dental enamel.

Keywords: Dental bleaching, Bleaching agents, Peroxides, Hydrogen peroxide, Dental enamel, Hardness tests.