Home bleaching technique has been a popular treatment for discolored teeth [
Furthermore, it has been discovered that, by reducing the particle size down to nanorange, the remineralization process would be amplified [
On the other hand, tricalcium phosphate (TCP) is a transitional phase in hydroxyapatite conversion. This complex consists of some structural sites that can be activated by various organic molecules, leading to very good remineralization [
Application of bioactive glass or n-HAP in conjunction with carbamide peroxide bleaching has been investigated in very few recent studies [
Rod-like hydroxyapatite particles (diameter < 100 nm, aspect ratio 2-3) were purchased from Nanoshel Co. (Panchkula, India). Meanwhile, plate-like
Forty caries-free bovine incisors were selected and after cleaning with aqueous slurry of pumice, they were stored in 1% thymol solution. The roots of the teeth were embedded in arch form silicon blocks. Subsequently, a plastic cover was fabricated for the crowns of the teeth using a vacuum forming machine. Finally, a digital photograph was taken in a standard method for determining the color of each tooth.
All the digital photographs were taken under a standard condition in a complete dark chamber while the distance of the camera (Canon EOS D40) was fixed. In order to work in a constant environment, the background was black while the samples were put in a silicon box. For exposure metering, a circular punch of the gray card with a reflectance value of 18% was put near each sample and the same manual exposure mode was selected for the whole samples [
Carbamide peroxide 20% gel (Opalescence, Ultradent, USA) was inserted in each plastic cover and the crowns of the teeth were exposed to one daily application of the bleaching agents for two hours for fourteen consecutive days. Finally, another digital photograph was taken for recording the color. In order to mimic the oral condition during bleaching, the specimens were stored in 100% relative humidity at 37°C. After each daily treatment, the specimens were thoroughly rinsed with air/water spray and stored in distilled water until the next day.
Following the bleaching process, all the specimens were randomly divided into five groups containing eight teeth.
Five 30 × 100 mm glass boxes were prepared and the specimens were immersed in the boxes as follows. The control group specimens (the first group) were daily immersed for 10 minutes in a standard tea solution (boiling 1 gr of tea in 100 mL of water for 2 minutes and then passing the solution through gauze in order to remove the tea leaves), [ The second group specimens were daily immersed in 10% TCP for 3 minutes prior to receiving the treatments similar to the control group. The third group specimens were daily immersed in 5% TCP for 3 minutes prior to receiving the treatments similar to the control group. The fourth group specimens were daily immersed in 10% HAP for 3 minutes prior to receiving the treatments similar to the control group. The fifth group specimens were daily immersed in 5% HAP prior to receiving the treatments similar to the control group.
All these treatments were repeated for five days and finally a new photograph was taken for recording the color. Afterward, the photographs were analyzed.
The Adobe Photoshop software (CS5) was used to analyze the photographs. First, the global color cast of the images was eliminated according to the piece of gray card in the pictures. In order to compare the color, we incorporated the Commission Internationale de l’Eclairage (CIE) system in the form of
One sample of each group was observed to evaluate the changes in the surface morphology after five days of treatment. The samples were mounted on the aluminum stub using carbon-coated double sided adhesive tape and then coated with gold using a sputter coater. Subsequently, the superficial microstructure of the specimens was analyzed using scanning electron microscopy (SEM) (TESCAN, VEGAII, XMU, Czech Republic).
After exploring the normal distribution, Wilcoxon test was used to compare the baseline color parameters with the results of after bleaching. Meanwhile, the data regarding the specimens receiving mineralizing agents were analyzed using one-way ANOVA and post hoc Bonferroni test. Statistical significance was defined at
Color parameters of the teeth before and after bleaching (
The absolute mean values ± standard deviations of color parameters of the teeth before and after bleaching.
As it is summarized in Table
Bleached and final (after treatment by experimental solutions) values of
Groups |
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Baseline | Bleached | Final | Baseline | Bleached | Final | Baseline | Bleached | Final | ||
No treatment | 67.14 ± 3.14 | 69.37 ± 2.81 | 61.21 ± 4.39 | −1.69 ± 0.49 | −1.00 ± 0.47 | −4.12 ± 0.95 | −5.48 ± 1.21 | −4.20 ± 1.40 | −9.92 ± 1.78 | 12.65 ± 2.38a |
|
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n-TCP 10% | 66.98 ± 3.93 | 68.76 ± 3.14 | 64.51 ± 2.92 | −2.22 ± 1.10 | −1.23 ± 0.71 | −3.28 ± 1.44 | −5.63 ± 2.59 | −4.66 ± 1.93 | −6.75 ± 1.95 | 7.44 ± 1.69b,c |
n-TCP 5% | 66.15 ± 4.08 | 69.30 ± 3.88 | 62.37 ± 2.86 | −2.19 ± 0.93 | −1.48 ± 0.78 | −3.91 ± 1.62 | −7.36 ± 2.89 | −6.26 ± 2.89 | −10.24 ± 2.74 | 11.70 ± 4.07a,c |
|
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n-HAP 10% | 64.59 ± 7.26 | 66.63 ± 4.80 | 62.02 ± 3.93 | −2.71 ± 3.36 | −1.70 ± 1.70 | −4.38 ± 1.09 | −5.33 ± 0.91 | −4.31 ± 0.98 | −10.24 ± 3.7 | 10.25 ± 2.88a,c |
n-HAP 5% | 63.66 ± 1.90 | 66.56 ± 2.33 | 60.78 ± 2.97 | −2.64 ± 0.82 | −1.46 ± 0.46 | −3.96 ± 1.02 | −7.51 ± 2.72 | −6.14 ± 2.00 | −9.80 ± 3.16 | 10.60 ± 4.05a,c |
Values were mean ± standard deviation.
a,b,cSame letters were not significant by Bonferroni multiple comparison of
Although the experimental and control samples had quite similar color immediately after bleaching (a and b), the experimental sample that was treated by 10% nano-tricalcium phosphate and restained by tea solution (c) showed more color stability than the control sample (d) that was restained by tea solution without receiving any treatment.
As Figure
SEM micrographs of the enamel surfaces in different groups (×4000). (a) Control, (b) 10% n-TCP (nano-tricalcium phosphate), (c) 5% n-TCP, (d) 10% n-HAP (nanohydroxyl apatite), and (e) 5% n-HAP. All the experimental group showed smoother surface compared to the control except for the 5% n-HAP.
The results of the current study showed that application of n-HAP or n-TCP on tooth surface after bleaching protocol would decrease the restaining of enamel. However, only the 10% n-TCP had a significant effect.
The results of the present study are consistent with previous reports incorporating other agents such as fluoride, nanocarbonate apatite, or CCP-ACP after bleaching [
Resembling our study, Pedreira de Freitas et al. compared the effect of 2% neutral sodium fluoride and nano-HAP after bleaching treatment and reported that the surface gloss increased only in the nano-HAP group [
One of the most interesting outcomes of the current research was the stronger effect of n-TCP compared to n-HAP. This finding is in agreement with researchers who studied the soluble compound of calcium and phosphate (amorphous ACP) [
However, our results demonstrated a dose-dependent effect for n-TCP because it was not meaningfully effective at 5% but a significant restaining inhibition occurred at 10%. Similarly, in published literatures, dose dependency has been reported frequently for remineralizing agents [
Moreover, the SEM micrographs showed noticeably smoother surface in the groups receiving remineralizing treatment (except for n-HAP 5%) compared to the control. Accordingly, it has been reported that n-HAP may be deposited onto the enamel surface [
Although our SEM micrograph showed signs of remineralization in n-HAP groups, our color analysis did not demonstrate significant restaining prevention for n-HAP groups. This finding is consistent with some investigators while it is against some other ones [
Overwhelmingly, as it is shown in Table
After bleaching, all the experimental solutions prevented the restaining of enamel to some extent. However, only the 10% n-TCP could significantly maintain the resultant color compared to the control, indicating the recovery of the damaged enamel surface by the calcium phosphate compound.
The authors declare that there is no conflict of interests regarding the publication of this paper.
The authors acknowledge with gratitude the Dental Research Center of Shahed Dental School, Tehran, Iran, for financial support of the study.