Elsevier

Journal of Dentistry

Volume 40, Issue 11, November 2012, Pages 941-948
Journal of Dentistry

Effect of laser irradiation on crystalline structure of enamel surface during whitening treatment with hydrogen peroxide

https://doi.org/10.1016/j.jdent.2012.07.015Get rights and content

Abstract

Objective

This study is to evaluate the effect of laser activation on the whitening and crystalline structure of enamel surface during whitening treatment with hydrogen peroxide.

Methods

Bovine teeth were treated with whitening gel containing 35% hydrogen peroxide. A whitening gel was applied on the enamel surface for a period of 5 min, and then irradiated using a diode laser (740 nm) during whitening treatment for 0, 30, 60, 120 and 180 s for the GL0-W, GL30-W, GL60-W, GL120-W and GL180-W groups, respectively. The total whitening application time was 30 min for all groups.

Results

Laser-irradiated enamel groups showed a similar lightness compared to the GL0-W group. The thickness of porous layer observed on the enamel surface of GL0-W group was decreased by increasing the laser irradiation time. While the Ca and P contents of the GL0-W group were lower than those of the non-whitening treated group (GL0-C), the Ca and P contents of the GL180-W group were similar to those of the GL180-C group. The enamel crystallinity was dramatically decreased by whitening treatment without laser irradiation. However, the decrease of crystallinity was protected by laser irradiation during whitening treatment. Raman measurement verified that laser irradiation could prevent the loss of mineral compositions on enamel and maintain its crystalline structure.

Significance

The professional whitening treatment with hydrogen peroxide and diode laser activation improves not only the whitening effect but also protects the change of enamel structure compared to the treatment with only gel.

Introduction

Tooth whitening is a cosmetic treatment which can be performed on non-vital and vital teeth using various concentrations of hydrogen peroxide (3–38%) and carbamide peroxide (10–30%). Tooth whitening can be categorized into two types: self (at home) whitening and professional (in-office) whitening. Professional whitening treatment is performed by using a high concentration of hydrogen peroxide (35–38%), while activating agents such as heat, light or laser increase the efficacy of the whitening treatment.1, 2, 3, 4, 5

The first example of professional bleaching of stained teeth was that accomplished by M’Quillen in 1867.6 In 1937, Ames applied a heat source to 35% hydrogen peroxide.1 In 1989 tooth whitening became largely used with the introduction of a whitening gel by Haywood and Heymann7. Since the early 1980s, a heated spatula or a heat lamp has been used as a heat source to accelerate the bleaching process of concentrated hydrogen peroxide. As bleaching techniques developed, several different types of irradiation sources such as light, LED or laser have been used to accelerate the professional bleaching procedure.2, 3, 4 Among irradiation sources, laser tooth bleaching began in 1996, with the approval of the argon laser (480 nm) and the CO2 laser (10.6 μm).5 The advantages of professional bleaching over home bleaching include dentist control, avoidance of soft-tissue exposure and reduced total treatment time.

Generally, dental bleaching is accompanied by increased tooth or gingival sensitivity.8 Also, some evaluations have reported that the microhardness value and calcium content of enamel decrease and its surface micromorphology changes after exposure to peroxide based formulations.9, 10, 11, 12, 13 As mentioned above, many studies have evaluated the effects of peroxide-based products on the physical and chemical properties of tooth enamel.11, 13, 14 If additional laser irradiation during whitening-gel treatment improves tooth bleaching, the morphology and/or the crystalline structure of enamels could be different between laser-treated and non-treated teeth. However, there are insufficient studies about how enamel crystalline structures are affected by laser irradiation during whitening gel treatment. In this study, therefore, the effect of laser activation on the whitening and crystalline structure of enamel surface during whitening treatment with hydrogen peroxide was investigated.

Section snippets

Tooth preparation

Twenty bovine teeth were used for this study. Bovine tooth is convenient to evaluate the characteristics enamel surface because they have a relatively large flatness and uniform compositions.15 The extracted teeth were cleaned and stored in an aqueous solution of 0.1% thymol for over 24 h. After the teeth were washed with distilled water, the crown was separated from the root using diamond precision cutting system (Exakt, DE/300CL/CP, USA) with water. In order to decrease the thickness of teeth

Results

Fig. 2 shows the discrepancy between the lightness (ΔL*) on teeth before and after the whitening treatments. The results indicate a significant improvement in brightness through the whitening treatment. While the mean value of changes in lightness for whitening-treated teeth combined with laser irradiations were higher than that for the only gel-treated tooth, but it was not significant.

Fig. 3 shows the XRD patterns for the control group and whitening treated sample groups. All XRD peaks were

Discussion

The recent development of laser-assisted tooth whitening procedures offers patients an easier, faster, non-invasive, and affordable way to have whiter teeth.16, 17, 18 The objective of laser bleaching is to achieve the ultimate power bleaching process using the most effective energy source, while avoiding any adverse effect.19 A laser beam can activate high concentration hydrogen peroxide (35%) extremely quickly and thus help to achieve satisfactory whitening of teeth and diode lasers have a

Conclusion

Bovine teeth were treated with whitening gel containing 35% hydrogen peroxide combined with diode laser irradiation. Teeth brightness was increased by laser-assisted whitening. Cracks and pores observed in the enamel of the group treated only with whitening gel (GL0-W) were decreased by increasing the laser irradiation time. While the GL0-W group had low Ca and P contents compared with the non-whitening treated group (GL0-C), the Ca and P contents of the GL180-W group were similar to those of

Acknowledgements

This study was supported by the National Research Foundation of Korea (NRF) grants funded by the Korea government (MEST) (No. 2011-0010666 and 2011-0030762).

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