Evaluation of In-Office Bleaching on Enamel and Dentine: An FTIR Study

AYCA DOGAN1, KURTULUS GOKDUMAN2, SUKRAN BOLAY3, FERIDE SEVERCAN4

1 Department of Cosmetic Technology, Kocaeli University, Izmit, TURKEY

2 Department of Biotechnology , Middle East Technical University, Ankara, TURKEY

3 Department of Restorative Dentistry, Hacettepe University, Ankara, TURKEY

4 Department of Biology , Middle East Technical University, Ankara, TURKEY

Abstract: In recent years bleaching of vital teeth has become popular among both dentist and patients. Different bleaching agents were used for this purposes. They are either applied professionally at high dose (office bleaching) or by patient at lower dose (home bleaching). However the effects of bleaching on teeth is still unclear and controversial. In the present work we studied the effect of a high concentration bleaching agent (35% hydrogen peroxide) which is called as office bleaching, on human enamel and dentine using Fourier Transform Infrared (FTIR) Spectroscopic Technique. The results revealed differences in the signal intensity/area values and peak positions of some bands in between the treated and control tissues. In addition, the OH stretching band of hydroxyapatite at 3566 cm-1 appeared in the spectra of enamel tissue which was absent in dentin. The relative amount of carbonate and phosphate changed for the treated groups. In conclusion office bleaching caused some alterations in the structure and concentrations of enamel. However, these changes was not significant in dentin tissue.

Key-Words: Office bleaching; Tooth whitening; Hydrogen peroxide; Enamel; Dentine; FTIR Spectroscopy

1 Introduction

The technique of bleaching or whitening teeth was first described in 1877[1]. Since then bleaching of teeth has been in use, with little changes in science or technique during that time[2]. For example in 1937, Ames described a technique for treating mottled enamel by using a combination of hydrogen peroxide, ether, and heat [3]. However current in-office bleaching technique is basically the same as the technique developed between 1880-1916, which uses 35% hydrogen peroxide with rubber dam isolation[2].

The history of “modern day” tooth bleaching, however, began in 1989. In 1989 Haywood and Heyman introduced the nightguard vital bleaching method[4]. When home ‘nightguard’ bleaching using carbamide peroxide was introduced in 1989, it appeared that the in-office approach would become less popular. However, at the present time there has been a recent resurgence in-office bleaching, primarily due to aggressive marketing of various ‘high tech’ light sources such as lasers and plasma arc lights, coupled with claims of reducing bleaching time, even to a single office visit.

In-office bleaching product contains 30-35% hydrogen peroxide[2]. The mechanism of the action of bleaching agents is thought to be due to the ability of hydrogen peroxide to form oxygen free radicals that interact with adsorbed colored organic molecules and oxidize these macromolecules and pigment stains, producing dental discoloration into smaller and lighter molecules.[5]

In the present work we aimed to study the effect of a high concentration bleaching agent (35% hydrogen peroxide) which is called as office bleaching, on human enamel and dentine composition using Fourier Transform Infrared (FTIR) Spectroscopic Technique. We used FTIR spectroscopy because with this technique biological systems can be observed atmolecular level without any damage in structural components[8-11].

2 Materials and Methods

Fourteen human premolars newly extracted for periodontal reasons were used. They were randomly divided into control and treatment groups of seven specimens. The specimens of experimental groups were exposed to 35% hydrogen peroxide. The control and experimental groups were stored in distilled water for 7 days. The roots of each tooth were sealed with nail varnish to prevent the penetration of bleaching agent. The roots were sectioned to obtain flat buccal and lingual enamel surfaces from half of the crown. The specimens were sectioned with a high-speed diamond rotary instrument using water and air spray. Enamel and dentine specimens were ground in liquid nitrogine and then, were investigated in the form of KBr pellets by using FTIR spectroscopic technique. A Perkin-Elmer spectrometer was used with 4 cm-1 resolution for this purpose.

3 Results and Discussion

The tooth mainly composed of enamel, dentine, dentine-enamel junction and pulp. Enamel is the hardest tissue found in the human body. Mature enamel is highly mineralized [12]. It contains 96% inorganic material, 1% organic material and 3% water by weight. The inorganic component is mainly calcium phosphate in the form of hydroxyapatite crystals. Other elements present are small amounts of carbonate, magnesium, potassium, sodium and fluoride. Dentine is softer than enamel. The composition of dentine is approximately 70% inorganic material, 20% organic material and 10% water by weight. The main inorganic component is hydroxyapatite, and the main organic component is Type I collagen[13].

Figure 1 shows the representative FTIR spectra for control groups in the 4000-1000 cm-¹ region for enamelThe bands are labelled on the figure and their band assignments are given in Table I.

Figure 2 shows normalized A) treated and untreated enamel and B) treated and untreated dentin IR spectra in 3900-2000 cm-¹ region. Figure 3 demonstrates normalized A) treated and untreated enamel and B) treated and untreated dentin IR spectra in the 1900-450 cm-¹ region. As seen from the figures dramatic changes are observed for enamel.

Figure1. The representative FTIR spectra of A) enamel and B) dentin of control group in 4000-1000 cm-¹ region

Table 1. Major absorptions in IR spectra of control enamel.

Band # / Enamel
Frequency
(cm-1) / Dentine
Frequency
(cm-1) / Definitions of the spectral assignment
1 / 3567 / _ / OH stretching
2 / 3369 / 3363 / O-H and N-H group stretching vibration: polysaccharides, protein
3 / 1637 / 1652 / H2O and organic material-enamel-
Amide I (protein C=O stretch)-dentin-
4 / 1544 / 1547 / Amide II (protein N-H bend, C-N stretch)
5-7 / 1200-900 / 1200-900 / ۷1۷3 PO4 stretching (mineral)
8 / 890-850 / 890-850 / ν2 CO3-2 (mineral) type B
9-10 / 700-450 / 700-450 / ۷4 PO4 bending (mineral)


Figure 2. The average normalized A) treated and untreated enamel and B) treated and untreated dentine IR spectra in the 3900-2000 cm-¹

Mineral matrixes of the enamel and tisues are composed in its majority of crystals of carbonated hydroxyapatite and the absorbed components in the infrared region are the hydroxyl (OH-), carbonate (CO3-2) and phosphate radical (PO4-3). [14]. In the spectra of enamel samples, the hydroxyl stretching vibration is seen as a shoulder at 3566 cm-¹ which has a high degree of crystallinity, because this vibration assigned to the OH groups which located within the crystalline channels of calcium hydroxyapatite. [15]. The broad band at 3400 cm-¹ corresponds to NH stretching vibrations of Amide A and intermolecular OH bonding as seen from Fig 2. The frequency of this band shifted to lower values in treated enamel which indicates that NH groups were involved in a new set of hydrogen bonds of weaker strength[16,17].

Figure 3. The averaged normalized A) treated and untreated enamel and B) treated and untreated dentine IR spectra in the 1900-450 cm-¹ region.

Dentine is mainly composed of type I collagen as the organic material. Type I collagen constitues around 90% of the dentin protein fraction. Therefore the amide I absorbance of proteins mainly due to collagen and it is observed at 1655 cm-1 .Carbonate bands overlaps the amide II bands at around 1545 cm-1 . Therefore, in the present study the amide II band of the protein matrix were not taken into consideration[14,15].

The ۷2 carbonate (870-880 cm-¹) bands and ۷1۷3 phosphate (900-1200 cm-1 ), ۷4 phosphate (520-650 cm-1) in the enamel spectrum and 560-605 cm-¹ in the dentin spectrum) stretching bands which arise from mineral components are observed. (14)

Investigations of mineral crystallinity focused essentially on the ۷1۷3 phosphate band between 1200-900 cm-1 [16-18]. As seen from figure 3, there is a decrease in the intensity of ۷1۷3 phosphate band indicates a decrease in mineral components in the treated enamel and dentine tissue. However, these changes are more dramatic for enamel samples. Moreover, similar decrease is observed in the ۷4 phosphate band for treated enamel and dentine samples.

After deconvolution, ۷1۷3 PO4 band is divided into a high and low freguency domain. The 1020 cm-1 component is characteristic of poorly crystalline apatites and the 1030 cm-1 component of the more crystalline ones.

Carbonate plays an important role in affecting crysttallinity and solubility of the mineral matrix as seen from figure 3 The intensity of carbonate band at 870-880 cm-¹ was seen to decreased implying that there is a decrease in carbonate content in treated enamel samples[16-18]. This decrease in CO3-2 content may disturb or disorganize the apatite lattice. However, this decrease are not great for dentine tissues.

The mineral to matrix ratio is indicative of the relative quantity of mineral present in calcified tissues[19]. The intensity of ۷1۷3 phosphate stretching and the amide I bands were evaluated to determine the relative ratio of mineral and protein matrix. Intensity of the mineral to matrix ratio decreased from 56, 218 to 15,455 after the treatment of Hydrogen Peroxide for enamel tissue. However, this ratio was not dramatically decreased after the treatment of Hydrogen Peroxide for dentine tissue. These changes can be ccclearly seen seen from Fig3. .

4 CONCLUSION I

In the present study it was determined that bleaching treatment led to a significant loss of calcium and phosphate in treated enamel tissue by using FTIR spectroscopic method. Loss of mineral components observed from the PO4 bands indicates that demineralization took place in the enamel samples. This fact led to decrease in hardness of enamel samples [13]. Furthermore, the decrease in total carbonate content was associated with lower mineral crystallinity. Hydrogen peroxide bleaching treatment gave no statistically significant changes in dentine tissues.

The adverse effects of hydrogen peroxide on enamel were evident in specimens bleached in vitro but presence of saliva could prevent the demineralizing effect of bleaching agents in clinical conditions. It might be proposed that remineralization of bleached enamel is improved by application of highly concentrated fluorides. It was found that the frequent use of fluoride dentifrice resulted in greater benefit in enamel surface rehardening, with a similar effect on fluoride uptake, when compared with its combination with a single fluoride varnish application. These studies are under investigation in our laboratory.

This study was supported by METU research found: BAP-2004 07 02 -00-131.

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