Effects of in-office and at-home bleaching on human enamel and dentin: an in vitro application of Fourier transform infrared study

Differences of Enamel Microhardness Post External Bleaching After Application with Casein Phosphopeptide Amorphous Phosphate (CPP-ACP) and 5% Sodium Fluoride (NAF)

Background:

Bleaching is an effort to lighten the color of teeth through the application of chemicals. One of the side effects of bleaching is that it causes demineralization so that the hardness of the enamel will decrease. The hardness of the enamel can be returned back through the mineral laying process, namely remineralization.

Objective:

The purpose of this study was to determine whether there were differences in post-bleaching enamel hardness after Casein Phosphopeptide Amorphous Phosphate (CPP-ACP) or 5% sodium fluoride (NaF) application.

Methods:

In this in-vitro research, bleaching was applied to 30 lower premolars that were divided into three groups, the first group without remineralization, the second group remineralization with CPP-ACP, and the third group remineralization with NAF. Enamel microhardness was measured using Vickers Hardness Tester Machine before bleaching, immediately after bleaching, after application of remineralization pastes, and after 7 days. The teeth were bleached with 40% hydrogen peroxide and underwent remineralization for 7 days.

Results:

The results showed differences in enamel microhardness after using CPP-ACP or 5% sodium fluoride (NaF) application, and the highest post-bleaching enamel hardness was after 5% NaF application. The data were analyzed and tested using ANOVA to measure the differences in hardness between more than 2 groups, and using the post hoc student t-test to measure the differences in violence between the 2 groups. Natural remineralization can occur with saliva but not optimally; therefore, additional remineralizing agents are needed.

Conclusion:

The conclusion of this study was that 5% NaF used as a remineralization agent after in-vitro bleaching could increase enamel microhardness more than CPP-ACP after 7 days of application.

Effects of incorporating 45S5 bioactive glass into 30% hydrogen peroxide solution on whitening efficacy and enamel surface properties

OBJECTIVES

This study aimed to evaluate the effects of 30% hydrogen peroxide (HP) solution containing various contents of 45S5 bioactive glass (BAG) on whitening efficacy and enamel surface properties after simulating the clinical bleaching procedure.

MATERIALS AND METHODS

A total of 60 bovine enamel specimens discolored with black tea were divided into five groups treated with distilled water (DW), HP, 0.01 wt.% BAG + HP, 1.0 wt.% BAG + HP, and 20.0 wt.% BAG + HP (n = 12). The pH change was observed for 20 min immediately after mixing the experimental solutions, which were applied for 20 min/week, at 37 °C over 21 days. Color, gloss, roughness, microhardness, and micromorphology measurements were conducted before and after bleaching treatment.

RESULTS

All groups containing BAG experienced an increase in pH from 3.5 to 5.5 in less than 1 min, and the final pH increased as the BAG content increased. The ΔE of all experimental groups was significantly higher than that of the DW group (p < 0.05), but there were no significant differences between different BAG contents (p > 0.05). Gloss significantly decreased in all experimental groups compared to the DW group, and the increased BAG content had significantly affected the decrease in gloss (p < 0.05). There was no statistical difference in surface roughness (p > 0.05), but hardness increased significantly with BAG content after bleaching treatment (p < 0.05).

CONCLUSIONS

HP containing 45S5 BAG showed efficacy in tooth whitening. Also, the pH value of the HP remained acidic near 3.5 for 20 min, while the HP containing the 45S5 BAG showed an increase in pH, which inhibited the demineralization of the enamel surface, and maintained the surface morphology.

CLINICAL RELEVANCE

These novel materials are promising candidates to minimize enamel surface damage caused by HP during bleaching procedure in dental clinic.

Assessment of the effect of experimental bleaching agent with nano-bioactive material on postoperative sensitivity: A randomized, triple blind clinical trial

OBJECTIVES

This clinical study aimed to evaluate the effect of incorporating bioactive nanoparticles (n-Bm) inside an in-office bleaching gel on the risk and intensity of tooth sensitivity (TS) and on bleaching effectiveness.

MATERIALS AND METHODS

Sixty-six participants were selected and randomly assigned into two groups: control-only in-office gel and experimental-in-office gel with n-Bm. Teeth were bleached in two sessions (3 × 15-min). TS was recorded using a VAS and NRS. The color change was evaluated by subjective (VITA Classical and VITA Bleachedguide) and objective (Easyshade spectrophotometer) methods at baseline and 30 days after the end of treatment. The TS was evaluated by McNemar, Wilcoxon Signed Rank, and paired t test. The color changes between groups were compared using paired t test (α = 0.05).

RESULTS

No significant differences between the groups were observed in the risk (control = 27% [95%IC 18-39]; experimental = 21% [95%IC 13-32]) and intensity of TS, as well as in the color change (p >0.05) for any color measurement.

CONCLUSION

The inclusion of n-Bm into the bleaching agents did not affect the whitening effectiveness, as well as the risk and intensity of TS between groups. However, the results of the absolute risk of TS were low for both in-office gels used.

CLINICAL SIGNIFICANCE

Despite no significant differences between groups, both experimental bleaching agents present suitable results with low values for TS.

Neurosensory analysis of tooth sensitivity during at-home dental bleaching: a randomized clinical trial

Objective The objective of this study was to evaluate dental sensitivity using visual analogue scale, a Computerized Visual Analogue Scale (CoVAS) and a neurosensory analyzer (TSA II) during at-home bleaching with 10% carbamide peroxide, with and without potassium oxalate. Materials and Methods Power Bleaching 10% containing potassium oxalate was used on one maxillary hemi-arch of the 25 volunteers, and Opalescence 10% was used on the opposite hemi-arch. Bleaching agents were used daily for 3 weeks. Analysis was performed before treatment, 24 hours later, 7, 14, and 21 days after the start of the treatment, and 7 days after its conclusion. The spontaneous tooth sensitivity was evaluated using the visual analogue scale and the sensitivity caused by a continuous 0°C stimulus was analyzed using CoVAS. The cold sensation threshold was also analyzed using the TSA II. The temperatures obtained were statistically analyzed using ANOVA and Tukey's test (α=5%). Results The data obtained with the other methods were also analyzed. 24 hours, 7 and 14 days before the beginning of the treatment, over 20% of the teeth presented spontaneous sensitivity, the normal condition was restored after the end of the treatment. Regarding the cold sensation temperatures, both products sensitized the teeth (p<0.05) and no differences were detected between the products in each period (p>0.05). In addition, when they were compared using CoVAS, Power Bleaching caused the highest levels of sensitivity in all study periods, with the exception of the 14th day of treatment. Conclusion We concluded that the bleaching treatment sensitized the teeth and the product with potassium oxalate was not able to modulate tooth sensitivity.

Effects of in-office bleaching on human enamel and dentin. Morphological and mineral changes

BACKGROUND

The effects of HP-based products upon dental enamel and dentin are inconclusive.

AIM

To evaluate changes in micromorphology and composition of calcium (Ca) and phosphate (P) in enamel and dentin after the application of 37.5% hydrogen peroxide (HP) and 35% carbamide peroxide (CP) METHODS: Crowns of 20 human teeth were divided in two halves. One half was used as control specimen and the other as experimental specimen. The control specimens were kept in artificial saliva, and the experimental specimens were divided into four groups (n=5 each): group 1 (enamel HP for 45min); group 2 (dentin HP for 45min); group 3 (enamel CP for 90min); and group 4 (dentin CP for 90min). The morphological changes were evaluated using confocal laser scanning microscopy (CLSM), while the changes in the composition of Ca and P were assessed using environmental scanning electron microscopy combined with a microanalysis system (ESEM+EDX). The results within each group and between groups were compared using the Wilcoxon test and Mann-Whitney U-test, respectively (p<0.05).

RESULTS

Similar morphological changes in the enamel and no changes in dentin were assessed with both products. Ca and P decreased in enamel and dentin, without significant differences between them or with respect to their control specimens (p>0.05).

CONCLUSIONS

When bleaching products with a neutral pH are used in clinical practice, both, the concentration and the application time should be taken into account in order to avoid possible structural and mineral changes in enamel and dentin.

Effect of three nanobiomaterials on microhardness of bleached enamel

OBJECTIVES

The aim of this in vitro study was to evaluate the effect of incorporating three different nanobiomaterials into bleaching material on microhardness of bleached enamel.

MATERIALS AND METHODS

The crowns of 24 extracted sound human molars were sectioned. Sixty enamel specimens (2 × 3 × 4 mm) were selected and divided into five groups (n = 12): Group 1 received no bleaching procedure (control); Group 2 underwent bleaching with a 40% hydrogen peroxide (HP) gel; Groups 3, 4, and 5 were bleached with a 40% HP gel modified by incorporation of bioactive glass (BAG), amorphous calcium phosphate (ACP) and hydroxyapatite (HA), respectively. The enamel microhardness was evaluated. The differences in Knoop microhardness data of each group were analyzed by one-way ANOVA, followed by post hoc Tukey tests.

RESULTS

Significant differences were observed between the study groups. The enamel microhardness changes in Groups 1, 3, 4, and 5 were significantly lower than that of Group 2 (p < 0.001).

CONCLUSIONS

Within the limitations of this study, it can be concluded that incorporation of each one of the three tested biomaterials as remineralizing agents might be effective in decreasing enamel microhardness changes subsequent to in-office bleaching.

Effects of 45S5 bioglass on surface properties of dental enamel subjected to 35% hydrogen peroxide

Tooth bleaching agents may weaken the tooth structure. Therefore, it is important to minimize any risks of tooth hard tissue damage caused by bleaching agents. The aim of this study was to evaluate the effects of applying 45S5 bioglass (BG) before, after, and during 35% hydrogen peroxide (HP) bleaching on whitening efficacy, physicochemical properties and microstructures of bovine enamel. Seventy-two bovine enamel blocks were prepared and randomly divided into six groups: distilled deionized water (DDW), BG, HP, BG before HP, BG after HP and BG during HP. Colorimetric and microhardness tests were performed before and after the treatment procedure. Representative specimens from each group were selected for morphology investigation after the final tests. A significant color change was observed in group HP, BG before HP, BG after HP and BG during HP. The microhardness loss was in the following order: group HP>BG before HP, BG after HP>BG during HP>DDW, BG. The most obvious morphological alteration of was observed on enamel surfaces in group HP, and a slight morphological alteration was also detected in group BG before HP and BG after HP. Our findings suggest that the combination use of BG and HP could not impede the tooth whitening efficacy. Using BG during HP brought better protective effect than pre/post-bleaching use of BG, as it could more effectively reduce the mineral loss as well as retain the surface integrity of enamel. BG may serve as a promising biomimetic adjunct for bleaching therapy to prevent/restore the enamel damage induced by bleaching agents.

Hydrogen Peroxide Diffusion Dynamics in Dental Tissues

The aim of this study was to investigate the diffusion dynamics of 25% hydrogen peroxide (H2O2) through enamel-dentin layers and to correlate it with dentin’s structural alterations. Micro-Raman Spectroscopy (MRS) and Fourier Transform Infrared Photoacoustic Spectroscopy (FTIR-PAS) were used to measure the spectra of specimens before and during the bleaching procedure. H2O2 was applied to the outer surface of human enamel specimens for 60 minutes. MRS measurements were performed on the inner surface of enamel or on the subsurface dentin. In addition, H2O2 diffusion dynamics from outer enamel to dentin, passing through the dentin-enamel junction (DEJ) was obtained with Raman transverse scans. FTIR-PAS spectra were collected on the outer dentin. MRS findings revealed that H2O2 (O-O stretching µ-Raman band) crossed enamel, had a more marked concentration at DEJ, and accumulated in dentin. FTIR-PAS analysis showed that H2O2 modified dentin’s organic compounds, observed by the decrease in amides I, II, and III absorption band intensities. In conclusion, H2O2 penetration was demonstrated to be not merely a physical passage through enamel interprismatic spaces into the dentinal tubules. H2O2 diffusion dynamics presented a concentration gradient determined by the chemical affinity of the H2O2 with each specific dental tissue.

The effect of cold-light-activated bleaching treatment on enamel surfaces in vitro

This in vitro study aims to evaluate the crystal and surface microstructure of dental enamel after cold-light bleaching treatment. Twelve sound human premolars were cross-split into four specimens, namely, mesio-buccal (Group LP), disto-buccal (Group P), mesio-lingual (Group NP) and disto-lingual (Group L) specimens. These four groups were treated using the standard cold-light bleaching procedure, a bleaching agent, a peroxide-free bleaching agent and cold-light, respectively. Before and after treatment, all specimens were analyzed by high-resolution, micro-area X-ray diffraction and scanning electron microscopy. Using a spectrometer, tooth color of all specimens was measured before and after treatment. The phase of the enamel crystals was identified as hydroxyapatite and carbonated hydroxyapatite. After treatment, specimens in Groups LP and P showed significantly weaker X-ray diffraction peaks, significant reduction in crystal size and crystallinity, significant increase in L* but decrease in a* and b*, and obvious alterations in the surface morphology. However, specimens in Groups NP and L did not show any significant changes. The cold-light bleaching treatment leads to demineralization in the enamel surface. The acidic peroxide-containing bleaching agent was the major cause of demineralization, whereas cold-light did not exhibit significant increase or decrease effect on this demineralization.

FTIR and SEM analysis of CO2 laser irradiated human enamel

OBJECTIVES

Considering the enamel chemical structure, especially carbonate band, which has a major role in the caries prevention, the objective of the present study was to assess the chemical alterations on the enamel irradiated with CO(2) laser by means of FTIR spectroscopy and SEM analysis.

DESIGN

The enamel surfaces were analysed on a spectrometer for acquisition of the absorption spectrum relative to the chemical composition of the control sample. The irradiation was conducted with a 10.6-μm CO(2) laser (0.55W, 660W/cm(2)). The carbonate absorption band at 1600-1291cm(-1) as well as the water absorption band at 3793-2652cm(-1) was measured in each sample after the irradiation. The water band was measured again 24-h after the irradiation. The band area of each chemical compound was delimited, the background was subtracted, and the area under each band was integrated. Each area was normalized by the phosphate band (1190-702cm(-1)).

RESULTS

There was a statistically significant decrease (p<0.05) in the water content after irradiation (control: 0.184±0.04; irradiated: 0.078±0.026), which increased again after rehydration (0.145±0.038). The carbonate/phosphate ratio was measured initially (0.112±0.029) and its reduction after irradiation indicated the carbonate loss (0.088±0.014) (p<0.05).

CONCLUSION

The 10.6-μm CO(2) laser irradiation diminishes the carbonate and water contents in the enamel after irradiation.

Influence of activated bleaching on various adhesive restorative systems

STATEMENT OF THE PROBLEM

  When adhesive restorations are used in combination with bleaching in clinical applications, it is generally recommended to wait for a period of time between the two procedures. However, it is not clear if a time interval is necessary between applying the bleaching treatments and the silorane-based restorative system.

PURPOSE

  The purpose of this in vitro study was to determine if activated bleaching affects the bond strength of silorane-based restorative, a newly developed restorative that uses a polymerization system that has been reported to be insensitive to oxygen.

METHODS

  A gel consisting of 38% hydrogen peroxide was applied to ground labial enamel surfaces and activated using a diode laser to bleach the teeth. Then, without waiting for any period of time, four different restorative materials were applied to the bleached enamel surfaces, and these sets were compared with nonbleached control samples. The shear bond strength of the restorative systems to enamel was tested, and data was evaluated using two-way analysis of variance and Tukey HSD tests.

RESULTS

  Significant differences (p<0.05) in shear bond strengths were found among bleached and nonbleached enamel surfaces.

CONCLUSION

  It may be more beneficial to allow a time interval of 2 to 3 weeks between activated hydrogen peroxide bleaching and applying silorane-based composite restoratives or methacrylate-based composites than just applying restorative agents immediately after bleaching. However, further studies are needed to examine the structural effects of activated hydrogen peroxide on enamel.

CLINICAL SIGNIFICANCE

A time interval should be allowed between the application of silorane-based or methacrylate-based restorations and activated hydrogen peroxide bleaching systems.

Determination of simvastatin-induced changes in bone composition and structure by Fourier transform infrared spectroscopy in rat animal model

Simvastatin is a hypolipidemic drug which is used to control hypercholesterolemia and to prevent cardiovascular disease. In the current study, the effects of high and low doses of simvastatin treatment on tibia of healthy rats were investigated. Wistar rats were used for the control, 20mg and 50mg simvastatin-treated groups. Molecular investigations were performed using Fourier transform infrared spectroscopy. In the bones of the two groups of simvastatin-treated rats, the relative mineral/matrix ratio (p<0.001), relative carbonate content (p<0.001), carbonate/amide I ratio (p<0.001) and crystallinity (p<0.001) decreased significantly compared to the control group. Low dose of simvastatin treatment is more effective in reducing the relative carbonate content indicating the amount of carbonate substitution for phosphate in the mineral crystal. The olefinic band almost disappeared in the high dose of simvastatin-treated group which implies a decrease in unsaturation and an increase in lipid peroxidation. The higher frequency value and the bandwidth of CH(2) asymmetric stretching band for the 50mg treated group imply more disordered (p<0.001) and fluid (p<0.001) membrane structure. Low dose of simvastatin is more effective in strengthening the bone than high dose simvastatin treatment. High dose simvastatin treatment induces lipid peroxidation and changes the lipid composition and concentration, which are known to affect membrane physical properties.

Low dose simvastatin induces compositional, structural and dynamic changes in rat skeletal extensor digitorum longus muscle tissue

Statins are commonly used drugs in the treatment of hypercholesterolaemia. There are many adverse effects of statins on skeletal muscle, but the underlying mechanisms remain unclear. In the present study, the effects of low dose (20 mg/kg) simvastatin, a lipophilic statin, on rat EDL muscle (extensor digitorum longus muscle) were investigated at the molecular level using FTIR (Fourier-transform infrared) spectroscopy. FTIR spectroscopy allows us rapid and sensitive determination of functional groups belonging to proteins, lipids, carbohydrates and nucleic acids simultaneously. The results revealed that simvastatin treatment induces a significant decrease in lipid, nucleic acid, protein and glycogen content. A significant increase in the lipid/protein and nucleic acid/protein ratios was also obtained with simvastatin treatment. Furthermore, an increase in lipid order and membrane fluidity was detected. A decrease in the bandwidth of the amide I band and shifting of the position of this band to higher frequency values in treated muscle indicates structural changes in proteins. Detailed secondary structure analysis of the amide I band revealed a significant increase in antiparallel and aggregated beta-sheet, random coil structure and a significant decrease in beta-sheet structure, which indicates protein denaturation.