The Open Dentistry Journal

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Efficacy of In-office Bleaching on Microhardness of Permanent Teeth with Antioxidant Re-hardening

Esra G Çakir1, Suat Özcan2, Ibrahim Tulunoglu3, Mine B. Üçtaşli2, Ozlem Tulunoglu4, *
1 Department of Pediatric Dentistry, Faculty of Dentistry, University of Gazi, Ankara, Turkey
2 Department of Restorative Dentistry, Faculty of Dentistry, University of Gazi, Ankara, Turkey
3 Department of Comprehensive Care, CWRU School of Dental Medicine, 9601 Chester Avenue, Cleveland, OH 44106-7401, USA
4 Department of Pediatric Dentistry, CWRU, School of Dental Medicine, 9601 Chester Avenue, Cleveland, OH 44106-7401, USA



Bleaching procedures affect surface enamel structure and decrease its bonding ability to resin composite restorative materials. The application of re-hardening materials to bleached enamel surfaces may prevent this decrease in micro-hardness.


This in-vitro study aims to evaluate the surface micro hardness of human teeth enamel subjected to bleaching with Zoom Advanced Power 2 AP (Phillips, USA), and Opalescence Boost (Ultradent, USA) and compare the re-hardening effects of 10% Sodium Ascorbate, 2% acidulated phosphate fluoride gel, and a 5% Potassium nitrate 0.22% Sodium Fluoride + Calcium Nitrate gel.


Ninety human third molar teeth were used. The specimens were randomly assigned to 5 groups. After the bleaching procedure, the specimens were treated with APF, Sodium Ascorbate or Relief gel as re-hardening agents with 30 teeth in each group. Enamel micro-hardness was measured with Vickers Micro-hardness Tester. The data were evaluated with Kolmogorov-Simirnov, one-way ANOVA, Dunnett’s test, post-hoc Tukey and T-tests.


Statistical analysis revealed no significant differences among initial enamel groups’ micro-hardness values (P>.05); however, significant differences occurred between initial and after bleaching treatment group value for G3 (P< .05). After re-hardening, only the Sodium Ascorbate group showed a statistically significant increase with hardness values (P< .05) for G4 and G5.


Bleaching treatment conducted with light had no adverse effect on enamel micro-hardness. Sodium Ascorbate can be useful after bleaching to change the adverse effects of bonding on the enamel.

Keywords: Permanent teeth, In-office bleaching, Micro-hardness, Bonding, Re-hardening, Antioxidant.

Article Information

Identifiers and Pagination:

Year: 2019
Volume: 13
First Page: 436
Last Page: 442
Publisher Id: TODENTJ-13-436
DOI: 10.2174/1874210601913010436

Article History:

Received Date: 1/07/2019
Revision Received Date: 22/10/2019
Acceptance Date: 21/11/2019
Electronic publication date: 31/12/2019
Collection year: 2019

© 2019 Çakir 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 this author at the Department of Pediatric Dentistry, CWRU, School of Dental Medicine, 9601 Chester Avenue, Cleveland, OH 44106, USA; Tel: 216-7445884; E-mail:

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