Demineralization Effects of 2 Bleaching Procedures on Enamel Surfaces With and Without Post-treatment Fluoride Application

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.

Effectiveness and Safety of Over-the-Counter Tooth-Whitening Agents Compared to Hydrogen Peroxide In Vitro

(1) This study investigated the whitening effect, cytotoxicity and enamel surface alterations induced by different over-the-counter (OTC) bleaching agents in comparison to hydrogen peroxide. (2) Human teeth (n = 60) were randomly assigned into 6 groups (n = 10), stained with coffee solution for 7 d, followed by a whitening period of 7 d with either placebo, bromelain, sodium bicarbonate, sodium chlorite, PAP or hydrogen peroxide. Color measurements were performed with a spectrophotometer. Scanning electron micrographs (SEM) were taken to assess the enamel structure. Cytotoxicity of the tested substances was assessed based on the cell viability of primary human fibroblasts. (3) The application of all whitening gels resulted in a greater color difference of the enamel (ΔE) in comparison to the negative control. Hydrogen peroxide caused the greatest color difference. Bromelain and PAP treatment showed no enamel surface changes, in contrast to hydrogen peroxide treatment, which showed very mild interprismatic dissolution. Bromelain was the only non-cytotoxic agent. (4) The maximum effect achieved by all OTC bleaching agents was the removal of stains, whereas hydrogen peroxide was capable of further whitening the teeth. Bromelain treatment was neither cytotoxic, nor resulted in enamel surface alterations, and its whitening effect was less, yet still effective, compared to hydrogen peroxide.

The micro-shear bond strength of resin cements to aged laser bleached enamel after using different desensitizing agents

OBJECTIVES

To evaluate the micro-shear bond strength of two resin cements to aged laser bleached enamel after the application of three different desensitizing agents.

MATERIALS AND METHODS

Forty extracted human central and lateral incisors were prepared and bleached using laser activation bleaching protocol. The teeth were assigned randomly into four groups for desensitization; G1: No post-bleaching treatment, G2: GC MI Paste Plus, G3: Hydroxyapatite nanoparticles (n-HAP) and G4: Flor-Opal. Specimens were subjected to aging for 6 months. All groups were subdivided into two subgroups according to the resin cements used (dual-curing resin cement and light-curing resin cement).

RESULTS

Flor-Opal groups showed the highest statistically significant micro-shear bond strength (MSBS), followed by GC MI Paste Plus and n-HAP groups with no statistically significant difference between them. The light-curing resin cement had statistically higher MSBS than dual-curing resin cement in case of no-post bleaching treatment and n-HAP groups, and no statistical difference in case of GC MI Paste Plus and Flor-Opal groups.

CONCLUSION

Usage of desensitizing agents containing, CPP-ACP, n-HAP or fluoride after laser bleaching can enhance the bond strength of the resin cements to enamel.

CLINICAL SIGNIFICANCE

The composition of the desensitizing agents applied after laser bleaching could interfere in bond strength values.

Development of Controlled-Release Carbamide Peroxide Loaded Nanoemulgel for Tooth Bleaching: In Vitro and Ex Vivo Studies

Burst release of carbamide peroxide (CP) from traditional hydrogels causes severe inflammation to periodontal tissues. The present study explores the development of a novel CP nanoemulgel (CP-NG), an oil-in-water nanoemulsion-based gel in which CP was loaded with a view to controlling CP release. CP solid dispersions were prepared, using white soft paraffin or polyvinylpyrrolidone-white soft paraffin mixture as a carrier, prior to formulating nanoemulsions. It was found that carrier type and the ratio of CP to carrier affected drug crystallinity. Nanoemulsions formulated from the optimized CP solid dispersions were used to prepare CP-NG. It was found that the ratio of drug to carrier in CP solid dispersions affected the particle size and zeta potential of the nanoemulsions as well as drug release behavior and tooth bleaching efficacy of CP-NG. Drug release from CP-NG followed a first-order kinetic reaction and the release mechanism was an anomalous transport. Drug release rate decreased with an increase in solid dispersion carriers. CP-NG obtained from the solid dispersion with a 1:1 ratio of CP to the polymer mixture is suitable for sustaining drug release with high tooth bleaching efficacy and without reduction of enamel microhardness. The developed CP-NG is a promising potential tooth bleaching formulation.

Remineralization potential of grape seed extract hydrogels on bleached enamel compared to fluoride gel: An in vitro study

Background

Remineralizing of bleached enamel is a common procedure that aims to compensate enamel mineral lose. This study aimed to evaluate the remineralization effectiveness of experimentally prepared grape seed extract hydrogels (GSE) compared to fluoride gel on bleached enamel.

Material and Methods

Thirty extracted maxillary incisor were bleached using white smile bleaching agent. Bleached specimens were divided into three groups (10/group) according to the remineralizing agents tested: [GSE 6%, GSE 10%, or fluoride gel]. After bleaching and remineralization procedure, the specimens were stored in artificial saliva at 37°C. Micro-hardness and Energy-Dispersive X-ray and ultra-morphological evaluation were tested at baseline, after bleaching and after remineralization.

Results

Statistical significant decrease on mean micro-hardness values had resulted after bleaching procedure compared to baseline, followed by a significant increase in GSE (10%) and fluoride groups. GSE (6%) application showed the least statistical significant mean micro-hardness, which was statistically insignificant different compared to bleaching procedure. Elemental analysis results revealed a statistical significant decrease on Ca, and Ca/P ratios (At%) values after bleaching compared to baseline, followed by a significant increase after treatment with all tested remineralizing gels. SEM photomicrograph of sound enamel shows smooth uniform appearance with few pores. Bleached enamel showed irregular pitted disorganized enamel surface. Bleached enamel exposed to GSE and fluoride gel showed occlusion of enamel surface porosities and precipitates of different sizes.

Conclusions

The specially prepared GSE hydrogels has positive effects on the remineralization process of bleached enamel making it an effective natural agent with remineralizing potential.

Key words:Remineralization, bleaching, grape seed extract, fluoride, enamel.

Dental bleaching efficacy and impact on demineralization susceptibility of simulated stained-remineralized caries lesions

OBJECTIVES

To evaluate the efficacy of different bleaching systems on artificially created stained-remineralized caries lesions; and to assess the susceptibility of the bleached lesions to further demineralization.

METHODS

Human enamel specimens were sectioned, polished, demineralized, and randomly divided into six groups (n = 21) to create stained-remineralized lesions, either non-metallic (non-Met: G1, G2 and G3) or metallic (Met: G4, G5 and G6). G1 and G4 received no bleaching treatment, while G2 and G5 were treated with 15% carbamide peroxide (at-home bleaching protocol; 4 h/d×7), and G3 and G6 with 40% hydrogen peroxide (in-office bleaching protocol; 20min × 3). Susceptibility to further demineralization was tested after bleaching treatment. Lesion mineral loss and depth were measured by transversal microradiography, and color change by spectrophotometry. Outcomes were analyzed using ANOVA models followed by Fisher's PLSD tests (α = 0.05).

RESULTS

Metallic-stained lesions were significantly darker (all p < 0.001) and more resistant to bleaching (p < 0.005) than non-Met ones. For both stain types, the at-home bleaching protocol was more effective than the in-office (p < 0.005); however, it also increased the lesion susceptibility to demineralization (p < 0.05) [ΔΔZ mean ± SD ranging from 205 ± 73 to 313 ± 188 (at home) vs. 132 ± 45 to 206 ± 98 (in office); p < 0.05]. After bleaching, non-Met lesions were significantly more susceptible to demineralization (p < 0.05), with the ΔΔZ ranging from 206 ± 98 to 313 ± 188 compared to Met lesions ranging from 132 ± 45 to 205 ± 73.

CONCLUSIONS

At-home bleaching protocol presented greater bleaching efficacy compared to in-office bleaching protocol. After bleaching, metallic-stained lesions were more resistant to subsequent demineralization compared to non-metallic stained lesions.

CLINICAL SIGNIFICANCE

Bleaching stained-arrested caries lesions may improve aesthetics but also increase susceptibility to demineralization, depending on the type of stain involved and bleaching system used.

Effect of low-level laser therapy combined with 5000 parts per million fluoride dentifrice on postbleaching sensitivity: A clinical, randomized, and double-blind study

OBJECTIVE

The aim of this double-blind, randomized, controlled clinical study was to assess the efficacy of low-level laser therapy (LLLT) combined with 5000 ppm fluoride dentifrice on postbleaching sensitivity in teeth exposed to 35% hydrogen peroxide for four weeks.

MATERIALS AND METHODS

Twenty-five volunteers were evaluated using the split-mouth model in which the right and left maxillary/mandibular quadrants were randomized and allocated to one of two groups: GPLACEBO, in which the laser tip was positioned without the emission of light (placebo effect) + 5000 ppm sodium fluoride, or GLASER, which comprised LLLT + 5000 ppm sodium fluoride. For both groups, LLLT and placebo were used before bleaching, whereas fluoride was applied after bleaching. LLLT was applied at two points: on the central cervical and medial regions of the incisors, canines, and premolars in the corresponding hemi-arch. At each point, 60 J/cm² was applied for 16 seconds with an irradiance of 3.75 W/cm² using the therapeutic infrared device. To assess tooth sensitivity, a modified visual analogue scale was used after an evaporative stimulus, and a daily pain questionnaire was also applied.

RESULTS

The Wilcoxon and Friedman tests demonstrated a significant difference in the incidence of sensitivity pain between GPLACEBO and GLASER (P ≤ .05), with different evaluation times.

CONCLUSION

Teeth treated with laser therapy in combination with the topical use of sodium fluoride at each bleaching session demonstrated less sensitivity compared with the application of sodium fluoride only.

CLINICAL SIGNIFICANCE

The use of a low-level laser therapy in combination with topical use of sodium fluoride improves symptoms of dentin sensitivity at each bleaching session.

Effect of sodium fluoride pretreatment on the efficacy of an in-office bleaching agent: An in vitro study

This in vitro study evaluated the effect of sodium fluoride (NaF) on the bleaching efficacy using an artificial discolored bovine tooth model. Twenty specimens were prepared from bovine teeth by staining with black tea extract and were divided into two groups (n = 10). In control group, specimens were immersed in distilled water for 30 min. In NaF group, specimens were applied with 0.2% NaF for 30 min. Then, the specimens in each group were bleached by an in-office bleaching material (Shofu Hi-Lite, Shofu, Kyoto, Japan). The CIE L*a*b* values were measured by a dental colorimeter before and after 10 consecutive bleaching treatments, and the color difference (ΔE) was calculated. Brightness and color difference (ΔE) increased in both groups per bleaching cycle. There were no statistical differences in ΔE values between both groups (p > 0.05). It was concluded that the application of NaF before bleaching did not interfere with the bleaching effect.

Effectiveness of a new non-hydrogen peroxide bleaching agent after single use - a double-blind placebo-controlled short-term study

Tooth whitening represents perhaps the most common aesthetic procedure in dentistry worldwide. The efficacy of bleaching depends on three aspects: bleaching agent, bleaching method, and tooth color.

Chemical Composition and Microhardness of Human Enamel Treated with Fluoridated Whintening Agents. A Study in Situ

Background:

Dental whitening has been increasingly sought out to improve dental aesthetics, but may cause chemical and morphological changes in dental enamel surfaces.

Objective:

Assess in situ the effects of high-concentration hydrogen peroxide with and without fluoride on human dental enamel using the ion chromatography test (IC) and the Knoop hardness test (KHN).

Material and Methods:

Nineteen enamel specimens were prepared using third human molars. These specimens were fixed on molars of volunteers and were divided into groups: OP38-Opalescence Boost PF38%, PO37-Pola Office 37.5% and CO-Control group. For chemical analysis (n= 3), the dentin layer was removed, keeping only the enamel, which was subjected to acidic digestion by microwave radiation. It was necessary to perform sample dilutions for the elements fluorine (F), calcium (Ca) and phosphorus (P) for quantification using the IC test. The KHN (n= 5) was performed before and after the treatments. Five indentations were made, separated by 100 µm, for each specimen using a load of 25 gf for 5 seconds in the microdurometer. The data were analyzed using ANOVA with a 5% significance level.

Results:

The OP38 group had the largest concentrations of F, Ca and P ions. The PO37 group showed the lowest concentrations of F and Ca ions. The average KHN was not significantly different between the OP38 and PO37 groups.

Conclusion:

Enamel whitened with hydrogen peroxide containing fluoride had greater concentrations of F, Ca and P ions. The presence of fluoride in the whitening agent did not influence the enamel microhardness.

After bleaching enamel remineralization using a bioactive glass-ceramic (BioSilicate®)

Tooth bleaching agents may weaken the tooth structure, therefore, it is important to minimize any risks of enamel and dentine damage caused by them. In this way, different materials have been used to avoid or minimize the tooth damage during bleaching. Recently, bioactive glasses have been demonstrated to be effective in mineralization of dental structures. Therefore, this study evaluated the effect of BioSilicate® (a polycrystalline bioactive glass-ceramic) after bleaching by Laser-induced breakdown spectroscopy (LIBS) technique. Bovine dental blocks with 4 × 4 × 3 mm were obtained (n = 20), sequentially embedded in epoxy resin and then polished. Bleaching was performed using 35% hydrogen peroxide (Whiteness HP). Calcium (Ca) and phosphate (P) intensity values by LIBSwere obtained before the treatment (T0, baseline – control Group), after bleaching (T1), and after BioSilicate® application (T2). The use of BioSilicate® after bleaching showed to be an optimal way to remineralize enamel surface making BioSilicate® application a promising adjunct step to avoid or minimize the mineral loss on enamel surface after bleaching.

Role of fluoridated carbamide peroxide whitening gel in the remineralization of demineralized enamel: An in vitro study

Introduction:

The use of self-administered carbamide peroxide bleaching gels has become increasingly popular for whitening of discolored vital teeth. Studies have reported that its use may induce increased levels of sensitivity and surface roughness of the tooth due to demineralization. This study evaluates the effect of fluoride addition to the bleaching agent – its remineralizing capacity and alterations in the whitening properties.

Materials and Methods:

Twenty-four extracted lower third molar teeth, with the pretreatment shade determined, were taken up in the study. Each tooth was sectioned into four and labeled as groups A, B, C, and D. The tooth quadrants in group A-C were demineralized; groups A and B were treated with 10% carbamide peroxide gel (group-A without fluoride and group-B with 0.463% fluoride addition) (no further treatment was carried out for group c) group-D remained as the control. The post-treatment shade was determined. The tooth samples were sectioned (approximately 200 μm) for evaluation under a light microscope. The depth of demineralization was analyzed at five different equidistant points. Statistical analysis was carried out with t-tests, accepting ≤0.05 as significant.

Results and Conclusion:

Addition of fluoride caused remineralization of demineralized enamel. The tooth whitening system showed that the remineralization properties did not affect the whitening properties.

Does post-bleaching fluoridation affect the further demineralization of bleached enamel? An in vitro study

BACKGROUND

Topical fluoride agents have been shown to be the most effective method in treating demineralized enamel after in-office bleaching treatments. Thus, this study aimed to examine the effects of two different post-bleaching fluoridation agents: 1.5% titanium tetrafluoride (TiF(4)) (9200 ppm) and 2.1% sodium fluoride (NaF) (9500 ppm), on the calcium loss of enamel after an acidic challenge.

METHODS

Ten maxillary premolars were sectioned into four pieces and then divided into the following four groups: Group 1: Control, kept in artificial saliva, no treatment; Group 2: 38% hydrogen peroxide (HP); Group 3: 38% HP followed by 1.5% TiF(4); Group 4: 38% HP followed by 2.1% NaF solution. The specimens were subjected to demineralization for 16 days, refreshing the solution every 4 days; that is, on the 4th, 8th, 12th, and 16th days. Calcium ion (Ca(2+)) concentration was determined by an atomic absorption spectrophotometer. Data were analyzed using Friedman and Wilcoxon tests (p = 0.05).

RESULTS

The loss of Ca(2+) in each of the test groups was compared with that of the control group, depicting that there was a statistically significant difference among the groups after 4, 8, 12, and 16 days and in total (p < 0.05). The calcium released from the fluoride-applied groups was lower when compared with the 38% HP and control group. At the end of the 16th day, the total amount of calcium released from the TiF(4-)treated samples (9.12 mg/mL) was less than from the NaF-treated samples (13.67 mg/mL) (p < 0.05).

CONCLUSIONS

Regarding the results of our in vitro study, the risk of further demineralization was significantly reduced with the use of TiF(4) and NaF after bleaching with 38% HP. TiF(4) was found to be more effective in preventing Ca2+ release owing to acid attack when compared with NaF. In the case of an intra-oral acidic exposure, the use of topical 1.5% TiF(4) and 2.1% NaF agents might be beneficial after bleaching with 38% HP.

Acid demineralization susceptibility of dental enamel submitted to different bleaching techniques and fluoridation regimens

The aim of the current study was to assess the acid demineralization susceptibility of bleached dental enamel submitted to different fluoride regimens. One hundred bovine enamel blocks (6×6×3 mm) were randomly divided into 10 groups (n=10). Groups 1 and 2 received no bleaching. Groups 3 to 6 were submitted to an at-home bleaching technique using 6% hydrogen peroxide (HP; G3 and G4) or 10% carbamide peroxide (CP; G5 and G6). Groups 7 to 10 were submitted to an in-office bleaching technique using 35% HP (G7 and G8) or 35% CP (G9 and G10). During bleaching, a daily fluoridation regimen of 0.05% sodium fluoride (NaF) solution was performed on groups 3, 5, 7, and 9, while weekly fluoridation with a 2% NaF gel was performed on groups 4, 6, 8, and 10. The samples in groups 2 to 10 were pH cycled for 14 consecutive days. The samples from all groups were then assessed by cross-sectional Knoop microhardness at different depths from the outer enamel surface. The average Knoop hardness numbers (KHNs) were compared using one-way analysis of variance and Tukey tests (α=0.05). The comparison between groups 1 and 2 showed that the demineralization method was effective. The comparison among groups 2 to 6 showed the same susceptibility to acid demineralization, regardless of the fluoridation method used. However, the samples from groups 8 and 10 showed more susceptibility to acid demineralization when compared with group 2 (p<0.05). Groups 7 and 9 provided similar results to group 2, but the results of those groups were different when compared with groups 8 and 10. The use of 6% HP and 10% CP associated with daily or weekly fluoridation regimens did not increase the susceptibility of enamel to acid demineralization. However, the use of 35% HP and 35% CP must be associated with a daily fluoridation regimen, otherwise the in-office bleaching makes the bleached enamel more susceptible to acid demineralization.

Effect of incorporation of remineralizing agents into bleaching gels on the microhardness of bovine enamel in situ

AIM

This study evaluated the effect of adding calcium or fluoride to 35% hydrogen peroxide (HP) bleaching gel and the effect of human saliva on the microhardness of sound and demineralized enamel, using an in situ model.

MATERIALS AND METHODS

Cylindrical bovine enamel specimens (3 × 2 mm) were divided into two groups (n = 30): sound enamel (SE) and demineralized enamel (DE). Each group was divided into three subgroups, according to the bleaching gel: 35% HP; 35% HP + calcium; 35% HP + fluoride. After bleaching therapy, the specimens were fixed to intraoral devices worn by 10 volunteers for 7 days. Surface enamel microhardness (SMH) was measured before and after bleaching procedures, and after 1 and 7 days of saliva exposure. Data were analyzed by Repeated Measures ANOVA (5%).

RESULTS

The variable time resulted in significant differences for SE and DE groups (p = 0.001). For SE, significantly lower SMH was detected for control at post-bleaching period in comparison to the baseline and after 7 days. For DE, the lowest mean values were obtained before bleaching, and the addition of calcium to the peroxide significantly increased enamel SMH. The exposure to human saliva resulted in increased SMH.

CONCLUSION

The addition of potential remineralizing agents into bleaching gels might play an important role in maintaining the microhardness of sound enamel and in inducing remineralization of artificially demineralized enamel right after bleaching, and the remineralizing action of human saliva might minimize the deleterious effects of bleaching gels on enamel. Clinical significance: The incorporation of calcium into HP bleaching gel might be beneficial for the initial phases of the bleaching procedure.

Impact of remineralizing agents on enamel microhardness recovery after in-office tooth bleaching therapies

OBJECTIVE

It has been shown that bleaching with 35/38% hydrogen peroxides may alter both enamel morphology and mineral content. This study aimed to analyze the morphology and microhardness of enamel bleached with in-office hydrogen peroxides and exposed toremineralizing agents.

MATERIALS AND METHODS

After recording initial enamel morphology and microhardness, 60 bovine incisors were bleached using either a calcium-containing 35% hydrogen peroxide (Whiteness HP Blue) or a calcium-free 35% hydrogen peroxide (Whitegold Office) (n = 30). Then, the teeth were subjected to one of three post-bleaching remineralizing treatments (n = 10): storage in artificial saliva only, application of a sodium fluoride gel or application of a nanohydroxyapatite-based agent (Nano-P). After 24 h and 14 days of post-bleaching treatments, the enamel morphology and microhardness were re-evaluated. The microhardness data were analyzed by means of two-way ANOVA with repeated measurements and Tukey tests (p < 0.05), while the enamel morphology was analyzed descriptively.

RESULTS

Samples exposed to Nano-P presented statistically the highest microhardness 24 h after its application in comparison with other remineralizing agents. The microhardness recovery did not occur in any of the groups 14 days after treatment. The morphology of all samples 14 days after the application of all remineralizing agents presented a higher number of irregularities.

CONCLUSION

Although some remineralizing products provided microhardness recovery and a positive effect on enamel morphology at 24 h post-bleaching, none of them were able to maintain microhardness and enamel morphology at 14 days post-bleaching.

Effect of delaying toothbrushing during bleaching on enamel surface roughness: an in vitro study

This study aimed to evaluate the effect of toothbrushing on enamel surface roughness at three different intervals after daily bleaching treatment. Eighty enamel slabs were initially evaluated for surface roughness and then randomly divided into four groups. The bleaching procedure was carried out for 21 days, six hours daily. In the control group (group 1), the specimens were not brushed after bleaching, but in groups 2-4, they were brushed with toothpaste immediately, one hour, or two hours after bleaching, respectively. Then the specimens were stored in artificial saliva. Enamel surface roughness was reevaluated at the end of the period. Kruskal-Wallis and Mann-Whitney U tests showed statistically significant differences in the means of surface roughness values between the immediately brushed group and the three other groups (p<0.001). Daily toothbrushing immediately after bleaching increased enamel surface roughness; however, postponing the procedure for one or two hours after daily bleaching and exposing the specimens to artificial saliva during the study period resulted in enamel surface roughness comparable to that of the control group.

In vitro evaluation of the microhardness of bovine enamel exposed to acid solutions after bleaching

Acid erosion is a superficial loss of enamel caused by chemical processes that do not involve bacteria. Intrinsic and extrinsic factors, such as the presence of acid substances in the oral cavity, may cause a pH reduction, thus potentially increasing acid erosion. The aim of this study was to evaluate the microhardness of bleached and unbleached bovine enamel after immersion in a soda beverage, artificial powder juice and hydrochloric acid. The results obtained for the variables of exposure time, acid solution and substrate condition (bleached or unbleached enamel) were statistically analyzed by the ANOVA and Tukey tests. It was concluded that a decrease in microhardness renders dental structures more susceptible to erosion and mineral loss, and that teeth left unbleached show higher values of microhardness compared to bleached teeth.

Effect of bleaching on sound enamel and with early artificial caries lesions using confocal laser microscopy

The aim of this study was to evaluate effect of bleaching agents on sound enamel (SE) and enamel with early artificial caries lesions (CL) using confocal laser scanning microscopy (CLSM). Eighty blocks (4 x 5 x 5 mm) of bovine enamel were used and half of them were submitted to a pH cycling model to induce CL. Eight experimental groups were obtained from the treatments and mineralization level of the enamel (SE or CL) (n=10). SE groups: G1 - unbleached (control); G2 - 4% hydrogen peroxide (4 HP); G3 - 4 HP containing 0.05% Ca (Ca); G4 - 7.5% hydrogen peroxide (7.5 HP) containing amorphous calcium phosphate (ACP). CL groups: G5 - unbleached; G6 - 4 HP; G7 - 4 HP containing Ca; G8 - 7.5 HP ACP. G2, G3, G6, G7 were treated with the bleaching agents for 8 h/day during 14 days, while G4 and G8 were exposed to the bleaching agents for 30 min twice a day during 14 days. The enamel blocks were stained with 0.1 mM rhodamine B solution and the demineralization was quantified using fluorescence intensity detected by CLSM. Data were analyzed using ANOVA and Fisher’s tests (α=0.05). For the SE groups, the bleaching treatments increased significantly the demineralization area when compared with the unbleached group. In the CL groups, no statistically significant difference was observed (p>0.05).The addition of ACP or Ca in the composition of the whitening products did not overcome the effects caused by bleaching treatments on SE and neither was able to promote remineralization of CL.

In vitro evaluation of the effect of delaying toothbrushing with toothpaste on enamel microhardness subsequent to bleaching the teeth with 15% carbamide peroxide

Changes in enamel surface microhardness as a result of bleaching with carbamide peroxide in various in vitro conditions have been reported. The present study evaluated the effect of oral hygiene procedures on enamel microhardness at three time intervals following bleaching with 15% carbamide peroxide. Although this was an in vitro study, the purpose was to address whether or not a patient's toothbrushing following at-home bleaching might affect surface changes in tooth enamel. Eighty enamel slabs were prepared from impacted human third molars that had been extracted surgically. Subsequent to placing the specimens in acrylic resin, their surfaces were smoothed, and they were randomly divided into four equal groups. The specimens were initially evaluated for microhardness by Vickers test. The bleaching procedure was carried out for 21 days for 6 hours daily. In each group, the surfaces of specimens were brushed with toothpaste immediately, 1 hour, and 2 hours after bleaching except for the control group. The specimens were stored in artificial saliva. Enamel microhardness was again measured at the end of the bleaching period. Then the differences in enamel microhardness between the two periods were calculated. Data were analyzed with a nonparametric Kruskal-Wallis test at a significance level of p<0.05. The differences in the microhardness values before and after intervention between the groups were not significant (p=0.59). Daily oral hygiene procedures either immediately or 1 or 2 hours after daily bleaching procedures and exposing the specimens to artificial saliva during the study period produced no significant differences in enamel microhardness values.

Susceptibility of enamel treated with bleaching agents to mineral loss after cariogenic challenge

Objectives. Controversial reports exist whether bleaching agents cause a susceptibility to demineralization. The aim of this study was to compare the calcium loss of enamel treated with different bleaching agents and activation methods. Method and Materials. The specimens obtained from human premolars were treated in accordance with manufacturer protocols; 10% carbamide peroxide, 38% hydrogen peroxide light-activated, 38% hydrogen peroxide laser-activated, and no treatment (control). After cariogenic challenge calcium concentrations were determined by Inductively Coupled Plasma Mass Spectrometry. Results. No differences were found between the calcium loss of the laser-activated group and 10% carbamide peroxide group (p > 0.05). However, the differences between laser-activated and control groups were statistically significant (p < 0.05). The differences between 10% carbamide peroxide and the control group were not significant (p > 0.05). On the other hand, the light-activated group showed a significantly higher calcium loss compared with the other groups (p < 0.05). Conclusions. The results show that bleaching agents may cause calcium loss but it seems to be a negligible quantity for clinical aspects.

Microhardness of intracoronal dentin exposed to bleaching and fluoride treatment

OBJECTIVES

The aim of this study was to assess the surface microhardness (SMH) of intracoronal dentin exposed to 38% hydrogen peroxide (HP) light-activated or not and to 2% sodium fluoride gel (F2%) or 5% varnish (F5%).

STUDY DESIGN

Intracoronal dentin specimens were exposed to bleaching (B), bleaching and light activation (BL), or no bleaching (NB), followed by F2%, F5%, or no exposure (NF). SMH test was performed. Four specimens of each group were analyzed by scanning electron microscopy (SEM).

RESULTS

Analysis of variance and Tukey test (α = 5%) showed higher SMH of NB than BL or B. Specimens exposed to F5% presented the highest SMH and differed from F2% and NF. BL + NF yielded inferior SMH and was similar to B + NF, BL + F2%, B + F2%, BL + F5%, and NB + NF. NB + F5% showed superior values and did not differ from NB + F2%, B + F5%, and NB + NF.

CONCLUSIONS

Bleaching with 38% HP, light-activated or not, reduced the SMH of intracoronal dentin. F5% provided SMH to the level of unbleached specimens.

The effect of fluoride therapies on the morphology of bleached human dental enamel

The aim of this in vitro study was to evaluate qualitatively the surface morphology of enamel bleached with 35% hydrogen peroxide (HP) followed by application of fluoridated agents. Forty intact pre molars were randomly distributed into four groups (n = 10), treated as follows: Group I (control group) remained stored in artificial saliva at 37 °C, Group II - 35% HP; Group III - 35% HP + acidulated fluoride (1.23%) and Group IV - 35% HP + neutral fluoride (2%). The experimental groups received three applications of bleaching gel and after the last application all specimens were polished. This procedure was repeated after 7 and 14 days, and during the intervals of applications, the specimens were stored in artificial saliva at 37°C. Scanning electron microscopy (SEM) analysis showed superficial irregularities and porosities to varying degrees in bleached enamel compared to control group. Sample evaluation was made by attributing scores, and data were statistically analyzed using Kruskal-Wallis and Dunn tests (P < 0.05). SEM qualitative investigation demonstrated that 35% hydrogen peroxide affected human dental enamel morphology, producing porosities, depressions, and superficial irregularities at various degrees. These morphological changes were higher after the application of 1.23% acidulated fluoride gel.

FT-Raman and energy dispersive X-ray fluorescence spectrometric analyses of enamel submitted to 38% hydrogen peroxide bleaching, an acidic beverage, and simulated brushing

OBJECTIVE

This study aimed to investigate the effects on enamel surface treated with hydrogen peroxide bleaching and acidic soft drink immersion and/or brushing with whitening dentifrices.

MATERIALS AND METHODS

Fifty-six standardized enamel slabs obtained from labial surfaces of bovine incisors were used. Enamel slabs were ground flat, polished, and randomly assigned to one of seven treatment groups: (1) control, in which no treatment was performed, (2) soft drink immersion, (3) 38% hydrogen peroxide bleaching, (4) simulated toothbrushing with whitening dentifrice, (5) soft drink immersion and bleaching, (6) soft drink immersion, bleaching, and toothbrushing, and (7) bleaching and toothbrushing. The mineral concentration of enamel surfaces was determined before and after treatments by means of Fourier transform (FT)-Raman spectroscopy and energy dispersive x-ray fluorescence spectrometry (EDXRF). Data were statistically analyzed by ANOVA and Tukey test (p < 0.05).

RESULTS

Raman spectroscopy results indicated that enamel mineral content decreased after all treatments except in group 1, whereas EDXRF results exhibited mineral decrease in groups 3, 4, 5, and 7.

CONCLUSION

Bleaching alone or in combination with soft drink immersion and brushing decreases enamel mineral content.

Influence of remineralizing gels on bleached enamel microhardness in different time intervals

This study evaluated the influence of bleaching gel pH, the effect of applying remineralizing gels after bleaching and the effect of artificial saliva on enamel microhardness. Seventy bovine incisors were divided into three groups: Group 1 (n=10) received no bleaching procedure (control); Group 2 was bleached with a 35% hydrogen peroxide neutral gel (n=30) and Group 3 was bleached with a 35% hydrogen peroxide acid gel (n=30). Each experimental group was subdivided into three groups (n=10) according to the post-bleaching treatment: storage in artificial saliva, application of a fluoride gel and application of a combination of calcium and fluoride gel. The specimens were stored in artificial saliva for 7, 15 and 30 days and enamel microhardness was evaluated. The Vickers microhardness data were analyzed by three-way RM ANOVA, which revealed a significant difference only for treatment factor. The Tukey's test showed that the groups bleached followed by no additional treatment exhibited microhardness means significantly lower than the bleached groups treated with remineralizing gels. The Dunnet's test showed a significant difference only for the group bleached with acid gel without remineralizing treatment compared to the control group measured immediately after bleaching. It was concluded that acid bleaching gel significantly reduced enamel microhardness and that use of remineralizing gels after bleaching can significantly enhance the microhardness of bleached enamel.

Influence of Potentially Remineralizing Agents on Bleached Enamel Microhardness

Dentists should be aware of the enamel demineralization potential of 35% hydrogen peroxide. The addition of fluoride and calcium can enhance remineralization of surface and subsurface bleached enamel.

Effect of fluoridated bleaching gels on the remineralization of predemineralized bovine enamel in vitro

OBJECTIVES

This study evaluated possible differences regarding the remineralization of predemineralized enamel after exposure to fluoridated or non-fluoridated bleaching gels.

METHODS

120 enamel specimens were prepared from sixty bovine incisors; before and after demineralization (37 degrees C; pH 4.95; 10d), one-quarter of each specimen's surface was covered with nail varnish (control sound/demineralized). Subsequently, the specimens were stored for 16h daily in a remineralizing solution (pH 7.0; 14d), while for the remaining time (8h) various bleaching gels were applied: (1) no treatment (control), (2) Opalescence regular (O, Ultradent), (3) Opalescence PF (O-PF), (4) Nite White ACP (NW-ACP, Discus Dental) and (5) Nite White ACPF (NW-ACPF). Following, half of the bleached parts were nail-varnished and stored for another 3-weeks period in a remineralizing solution. Differences in mineral losses (DeltaDeltaZ) and lesion depths (DeltaLD) before and after treatment/remineralization period were evaluated from microradiographs. DeltaDeltaZ(surface) values (mineral loss of the outer 18microm of the lesion) were calculated.

RESULTS

After 2 and 5 weeks DeltaDeltaZ/DeltaLD values of the bleaching groups did not differ significantly from the controls. Treatment with NW-ACPF for 2 weeks resulted in significantly lower DeltaDeltaZ values compared to NW-ACP (p=0.032) and NW-ACPF in higher values than Opalescence regular (p=0.006). Two weeks treatment with O and O-PF resulted in decreased DeltaDeltaZ(surface) values compared to control (p<0.0005), whereas with NW-ACPF no significant differences could be observed (p=0.062). Application of NW-ACP induced significantly increased DeltaDeltaZ(surface) values compared to control (p=0.001).

CONCLUSIONS

No supporting influence of fluoride-containing bleaching gels on remineralization could be observed.

Effect of fluoride containing bleaching agents on enamel surface properties

OBJECTIVES

To evaluate the effects of fluoridated bleaching agents and post-bleaching fluoridation treatment on the whitening efficiency and microhardness of bovine enamel.

METHODS

Twenty five freshly extracted bovine incisors were cut into halves, embedded and then divided into the following five groups: Group 1, untreated controls; Group 2, treatment with 10% carbamide peroxide (CP) bleaching agent; Group 3, treatment with 10% CP followed by a 0.9% sodium fluoride gel application, Group 4, treatment with 10% CP containing 0.11% fluoride; Group 5, treatment with an experimental bleaching agent consisting of 10% CP and 0.37% fluoride. Groups 2-5 were treated 8h per day for 14 days then immersed in saliva for 2 weeks. Enamel morphology changes were evaluated under SEM on Day 14. Changes in enamel color and microhardness were evaluated on Days 7 and 14, and compared with the baseline data. Additionally, microhardness was determined on post-bleaching Days 21 and 28.

RESULTS

After 2 weeks, an erosion pattern was noted on the specimens in Groups 2 and 3. Groups 4 and 5 showed a milder demineralized pattern. All the bleached enamel specimens revealed increased whiteness and overall color value. Groups 2 and 3 showed significantly decreased enamel microhardness compared to their baseline data. The specimens treated with fluoridated bleaching agents showed relatively less reduction in enamel microhardness than those treated with nonfluoridated agents during the bleaching treatment.

CONCLUSIONS

The fluoridated bleaching agents produced less demineralization of surface morphology and microhardness. The addition of fluoride did not impede the whitening effect.

Effects of New Formulas of Bleaching Gel and Fluoride Application on Enamel Microhardness: An In Vitro Study

The results of this study suggest that tooth bleaching may lead to a reduction in enamel micro-hardness. Nonetheless, the application of a high concentration fluoride post-bleaching treatment may increase enamel microhardness and may restore enamel hardness to a level similar to non-bleached enamel, if the bleaching formula contains fluoride, potassium or ACP.