Effect of home-bleaching gels modified by calcium and/or fluoride and the application of nano-hydroxyapatite paste on in vitro enamel erosion susceptibility

Protective role of calcium-based agents in dental bleaching gels: insights from a systematic review and meta-analysis of clinical and laboratory evidence

OBJECTIVES

This systematic review and meta-analysis (SRM) evaluated the effect of incorporating calcium-based bioactive agents in bleaching gels on dental structure preservation and whitening efficacy.

METHODS

A comprehensive search was conducted across databases up to November 2024. Two independent reviewers screened and selected clinical trials and in vitro studies evaluating the effects of calcium-based bioactive agents in bleaching gels, following predefined PICO criteria. Data extraction and quality assessments were performed using the Cochrane Collaboration tool and Joanna Briggs Institute Critical Appraisal Tools. Meta-analyses were conducted with RevMan software, using the mean difference as the effect measure.

RESULTS

Out of 4,289 articles identified, 56 met the inclusion criteria, consisting of 50 in vitro studies and 6 clinical trials. The agents evaluated included calcium ions, calcium gluconate, amorphous calcium phosphate, CPP-ACP, and calcium polyphosphate. Overall, all agents reduced the adverse effects associated with bleaching therapy, such as minimizing changes in the mechanical and morphological properties of enamel, reducing transamelodentinal diffusion, and clinically decreasing tooth sensitivity. None of the calcium-based agents interfered with the bleaching effect. In short, the studies demonstrated a low risk of bias.

CONCLUSIONS

Calcium-based agents incorporated into bleaching gels reduced bleaching-induced changes in dental tissues and demonstrated clinical aesthetic results comparable to conventional gels. However, further clinical trials are needed to optimize formulations, application protocols, and confirm the findings of this study.

CLINICAL RELEVANCE

This SRM provides evidence that these agents offer additional benefits by enhancing the biocompatibility and safety of whitening therapy over conventional treatments, guiding clinicians in material selection for whitening procedures.

Effect of whitening products on sound enamel and on artificial caries lesions during a cariogenic challenge

OBJECTIVE

To investigate the effect of fluoride-containing whitening products on sound enamel and on artificial caries lesions during a cariogenic challenge.

MATERIALS AND METHODS

Bovine enamel specimens (n = 120) with three areas [non-treated sound enamel (NSE), treated sound enamel (TSE), and treated artificial caries lesion (TACL)] were randomly assigned to the four groups: whitening mouthrinse (WM: 2.5% hydrogen peroxide-100 ppm F-), placebo mouthrinse (PM: 0% hydrogen peroxide-100 ppm F-), whitening gel (WG: 10% carbamide peroxide-1130 ppm F-), and deionized water (negative control; NC). The treatments (2 min for WM, PM, and NC, and 2 h for WG) were carried out during a 28-day pH-cycling model (6 × 60 min demineralization/day). Relative surface reflection intensity (rSRI) and transversal microradiography (TMR) analyses were performed. Fluoride uptake (surface and subsurface) was measured in additional enamel specimens.

RESULTS

For TSE, a higher value of rSRI was observed in WM (89.99% ± 6.94), and a greater decrease in rSRI was observed for WG and NC, and no sign of mineral loss was verified for all groups (p > 0.05). For TACL, rSRI significantly decreased after pH-cycling for all experimental groups with no difference between them (p < 0.05). Higher amounts of fluoride were found in WG. WG and WM exhibited intermediate values of mineral loss, similar to PM.

CONCLUSIONS

The whitening products did not potentialize the enamel demineralization under a severe cariogenic challenge, and they did not exacerbate mineral loss of the artificial caries lesions.

CLINICAL RELEVANCE

Low concentrated hydrogen peroxide whitening gel and mouthrinse containing fluoride do not intensify the progression of caries lesions.

Excessive Dental Bleaching with 22% Carbamide Peroxide Combined with Erosive and Abrasive Challenges: New Insights into the Morphology and Surface Properties of Enamel

This study aimed to evaluate the effects of 22% carbamide peroxide combined with an erosive challenge and simulated brushing on enamel. Bovine incisor teeth were divided into G1, tooth bleaching; G2, tooth bleaching + erosive challenge; and G3, tooth bleaching + erosive challenge + simulated brushing, and evaluated at T0, before any intervention; T1, 14 days after the proposed treatments; and T2, 28 days after the proposed treatments. Tooth bleaching was performed daily for 1 h for 28 days. The microhardness, surface roughness, mass variation, and ultrastructure were analyzed at T0, T1, and T2. Two-way analysis of variance for repeated measures was performed and Tukey's post hoc test (α = 5%) was used. The surface roughness increased in groups G2 and G3 as a function of time, whereas microhardness and mass measurements demonstrated a significant reduction for groups associated with challenges. Ultrastructural evaluation indicated a loss of the aprismatic layer and exposure of the enamel prisms in all groups after 14 days of bleaching, with more pronounced results in G2 and G3 after 28 days. In conclusion, abrasive and erosive challenges potentiated the deleterious effects of tooth whitening on microhardness, ultramorphology, and mass, without affecting the roughness of dental enamel.

Is prolonged bleaching more harmful to dental enamel than daily dietary and hygienic oral habits?

The ultrastructural and mechanical properties of enamel surface were evaluated after prolonged bleaching treatments with 10% carbamide peroxide in the presence or absence of orange juice (erosive challenge) and toothbrushing (abrasive challenge). In total, 145 incisor bovine teeth were used in this study. Twenty-five samples were prepared for the ultrastructural evaluations, and 120 samples were prepared for microhardness and roughness tests. These 120 samples were divided into eight experimental groups (n = 15): G1- artificial saliva; G2- abrasion; G3- erosion; G4- dental bleaching; G5- erosion + abrasion; G6- bleaching + abrasion; G7- bleaching + erosion; and G8- bleaching + erosion + abrasion. All groups were tested at T0 (before treatment), T1 (14 days), T2 (21 days), and T3 (28 days). Two-way analysis of variance for repeated measures and the post hoc Sidak tests (p ≤ 0.05) were used. The roughness evaluation demonstrated an increase in damage for all experimental groups with an increase in the time period. For microhardness, the groups exposed to artificial saliva (AS) and abrasive challenge did not show any differences at any time points, while the other groups showed a decrease in microhardness from T0 to T3. Ultrastructural evaluation showed different surface alterations in response to the treatments. Despite prolonged bleaching periods, the procedure caused lesser enamel surface alterations than exposure to orange juice alone or in combination with brushing.

One-year follow-up comparing at-home bleaching systems outcomes and the impact on patient's satisfaction: Randomized clinical trial

OBJECTIVE

To compare at-home systems with reduced daily time of use (10% hydrogen peroxide [HP] gel with prefilled (PT) or customized trays (CT), and 10% carbamide peroxide [CP] gel), with the conventional nightguard vital bleaching (10% CP). Bleaching efficacy, adverse effects, and patient's satisfaction were evaluated.

METHODS

Sixty participants were randomly divided into treatments (14 days): Opalescence GO (OGO)-10%HP PT-30 min, White Class-10%HP CT-30 min, Opalescence PF-10%CP CT-2 h, and Opalescence PF-10%CP CT-8 h. Color difference (visual and spectrophotometer), tooth sensitivity (visual analogue scale), gingival condition (Löe index), enamel mineralization (laser fluorescence), and patients' satisfaction (questionnaire) were assessed. Statistical tests were applied (5%).

RESULTS

After 1 year, color difference was similar for the groups (p > 0.05). All groups showed similar sensitivity risk (p > 0.05). The intensity of sensitivity and gingival irritation was mild for all gels, but higher for OGO. Fluorescence after bleaching remained similar to those of sound enamel. All participants were satisfied with treatments.

CONCLUSIONS

All systems produced similar bleaching efficacy, which was maintained after 1 year. Patients were satisfied with bleaching outcomes. Tooth sensitivity occurred in all groups, but with overall mild intensity. No relevant gingival irritation and enamel demineralization was observed.

CLINICAL SIGNIFICANCE

Bleaching with 10% HP gels in prefilled and CTs represent efficacious alternative for tooth color change, with patients' acceptance similar to conventional 10% CP. Patients must be warned about the mild sensitivity and gingival irritation potential, mainly with PTs.

A Comparative Evaluation of Nanohydroxyapatite-Enriched Hydrogen Peroxide Home Bleaching System on Color, Hardness and Microstructure of Dental Enamel

This study aimed to evaluate two hydrogen peroxide (HP)-based at-home bleaching systems in order to analyze whether nano-hydroxyapatite (nHA) addition may represent a reliable and safe solution for tooth whitening without altering dental microstructure and hardness. Human third molars (N = 15) were treated with two bleaching agents, one containing 6%HP (6HP) and the other 6% HP nHA-enriched (6HP-nHA) with average particle diameter ranging from 5-20 nm. Their effects on enamel were assessed using a spectrophotometer, Vickers microhardness (VMH) test and Scanning Electron Microscopy (SEM), comparing the treated groups with the non-treated control group (CTR). Color analysis revealed improvement in whiteness in both groups compared to CTR. VMH test results showed no differences among the groups. SEM analysis highlighted no evident changes in the enamel microstructure of tested groups compared to CTR. At high magnification, in 6HP group, a slight increase in irregularities of enamel surface morphology was observed, while 6HP-nHA group displayed removal of the aprismatic layer but preservation of the intact prismatic structure. These results suggest that the 6HP-nHA agent may be recommended to provide reliable whitening treatment, without damaging the enamel micromorphology and hardness.

Enhancing the Anti-Erosive Properties of Fluoride and Stannous with the Polymer Carbopol

This in vitro study investigated whether Carbopol 980 polymer could potentiate the anti-erosive effect of solutions containing sodium fluoride (F) and sodium fluoride associated with stannous chloride (FS). The dissolution of hydroxyapatite treated with the experimental solutions (F [500 ppm F-], F + Carbopol [0.1%], FS [500 ppm F- + 800 ppm Sn2+], FS + Carbopol) was evaluated. Deionized water was the negative control, and a commercial mouth rinse (AmF/NaF/SnCl2; 500 ppm F + 800 ppm Sn2+; Elmex® Erosion Protection) was the positive control. The solutions were also evaluated in an erosion-rehardening protocol, with two treatments per day, using bovine enamel specimens (n = 15) and human saliva. The acid challenge was performed using 0.3% citric acid (pH 2.6) for 2 min. Microhardness was measured at different times: baseline, after the first erosive challenge, after treatment, and after the second erosive challenge. Based on microhardness values, the demineralization, rehardening, and protective potentials were calculated. The alkali-soluble fluoride on enamel surfaces was also measured. Data were analyzed using ANOVA and Tukey tests (α = 0.05). Groups treated with FS + Carbopol showed the lowest hydroxyapatite dissolution and the highest rehardening and protective potentials. The measurement of alkali-soluble fluoride on enamel surfaces was also higher in the FS + Carbopol group. Carbopol was able to significantly increase the protective effect of the fluoridated solutions in addition to optimizing the adsorption of fluoride on the enamel surface.

Randomized in situ trial on the efficacy of Carbopol in enhancing fluoride / stannous anti-erosive properties

OBJECTIVE

To evaluate if the bioadhesive polymer (Carbopol 980) could potentiate the protective effect of sodium fluoride with stannous chloride (FS) solution on the control of enamel erosive wear.

METHODS

Cylindrical bovine enamel specimens were polished and randomly allocated into three groups (n = 60): FS (500 ppm F^- +800 ppm Sn²⁺ - positive control), FS + Carbopol (0.1% Carbopol), and ultrapure water (negative control). A randomized double-blind cross-over in situ model with three phases was used. In each phase, volunteers (n = 15) used a palatal appliance containing 4 specimens: two were submitted to an erosion model (2 h of pellicle formation; immersion in 1% citric acid, pH 2.3, for 5 min, 4x/day; 1 h intervals of saliva exposure; and treatment with the test solutions for 1 min, 2x/day). Besides erosion, the other two specimens were also subjected to abrasion (2x/day, 15 s) with active electric toothbrush, before the treatment with the solutions. After 5 days, enamel surface loss (μm) was evaluated by profilometry. Data were analyzed by two-way RM-ANOVA and Tukey tests (5%).

RESULTS

There were significant differences for both challenge and treatment factors. Erosion/abrasion challenge resulted in significantly higher enamel loss than erosion only (p < 0.05). The surface loss values for the erosion/remineralization model were (means ± SL): C = 14.7 ± 5.8b; FS = 9.0 ± 7.5ab; FS + Carbopol = 5.9 ± 3.8a; and for erosion/abrasion: C = 26.6 ± 10.1c; FS = 15.0 ± 8.8b; FS + Carbopol = 12.3 ± 7.9ab.

CONCLUSION

The association of Carbopol to the FS solution significantly protected the enamel against erosive wear, but it was not significantly superior to FS only.

CLINICAL SIGNIFICANCE

Under highly erosive and abrasive conditions, rinsing with solutions containing sodium fluoride plus stannous chloride, associated or not with the Carbopol polymer, is an effective approach to control enamel erosive wear.

Effect of Indigenously Developed Nano-Hydroxyapatite Crystals from Chicken Egg Shell on the Surface Hardness of Bleached Human Enamel: An In Vitro Study

Objective:

The objective was to evaluate the effect of nano-hydroxyapatite (nHA) derived from chicken eggshell on bleached human enamel in comparison with commercial casein phophopeptide-amorphous calcium phosphate (CPP-ACP) paste using Vickers microhardness test.

Materials and Methods:

nHA powder was prepared from chicken eggshell using combustion method. nHA slurry was prepared by mixing 1.8 g of nHA powder with 0.3 ml of distilled water. Forty intact maxillary anterior teeth were collected and decoronated, and the crowns were embedded in acrylic mold with the labial enamel surfaces exposed. Baseline microhardness evaluation was done (T₀). The specimens were randomly divided into the following four groups (n = 10) based on the surface treatment of enamel: Group 1: no bleaching treatment; Group 2: bleaching with 30% hydrogen peroxide (HP) solution; Group 3: bleaching followed by the application of CPP-ACP; and Group 4: bleaching followed by the application of nHA. The specimens were stored in artificial saliva at 37°C for 2 weeks, after which they were subjected to Vickers microhardness test (T₁₄). One-way ANOVA and Tukey's post hoc multiple comparison tests were used for statistical analysis (P < 0.05).

Results:

Bleaching with HP significantly decreased the enamel microhardness. CPP-ACP and nHA derived from chicken eggshell increased the enamel microhardness significantly. There was no significant difference in microhardness values among the CPP-ACP and nHA groups.

Conclusion:

Nano-hydroxyapatite sourced from chicken eggshell was as effective as CPP-ACP in remineralizing and restoring the lost microhardness of bleached enamel.

Comparison of Bleaching Products With Up to 6% and With More Than 6% Hydrogen Peroxide: Whitening Efficacy Using BI and WI D and Side Effects - An in vitro Study

The aim of this study was to evaluate the effect of bleaching agents containing different concentrations of hydrogen peroxide (HP) on color-change and on enamel-surface in bovine teeth. Furthermore the influence on cell viability and proliferation was investigated. Two hundred and forty teeth were randomly assigned into four groups (home bleaching ≤6%, in-office bleaching ≤6%, in-office bleaching > 6% HP, and control group). Bleaching was performed after artificial staining and the bleached index (BI) as well as the whiteness index (WI_D) was measured at several time points. Chemical analysis for HP concentrations and the pH of the bleaching products was done. Furthermore, enamel surfaces of randomly selected specimens were analyzed using scanning electron microscopy (SEM) and cytotoxicity of the tested bleaching products was evaluated in vitro using dental pulp cells (DPCs) and L929 cells. A statistically significant whitening effect was observed in almost all products. As expected all investigated products resulted in decreased cell viability, however, with different values of LC50 (median lethal concentration). SEM analysis showed an analog of enamel alterations with decreasing pH, increasing exposure time, and increasing HP concentration. Bleaching agents containing a low HP concentration are considered to be effective and to have less damaging effects on enamel and tested cells.

Effect of Calcium and Fluoride Addition to Hydrogen Peroxide Bleaching Gel On Tooth Diffusion, Color, and Microhardness

Objectives:

The aim of this study was to evaluate the effect of calcium and fluoride addition to a 35% hydrogen peroxide (HP) bleaching gel with regard to its diffusion through the tooth structure, enamel microhardness, and bleaching efficacy.

Methods and Materials:

Eighty specimens (6 mm in diameter and 2 mm in height; 1 mm/enamel and 1 mm/dentin) were obtained from bovine incisors that were polished and divided into four groups (n=20) according to the remineralizing agent added to the gel: Ca = 0.5% calcium gluconate; F = 0.2% sodium fluoride; Ca+F = 0.5% calcium gluconate and 0.2% sodium fluoride; and control = no agent. Initial microhardness and color were assessed. The samples were positioned over simulated pulpal chambers filled with acetate buffer solution to capture the HP. Gels were applied over enamel for 30 minutes, and HP diffusion was assessed by spectrophotometry two hours after bleaching. Microhardness was measured immediately after bleaching and then the specimens were immersed into artificial saliva for seven days for final color assessment. Data were analyzed by one-way analysis of variance followed by Tukey test.

Results:

Bleaching reduced microhardness for all groups (p=0.0001), but the Ca+F and F groups showed lower reductions after bleaching. The addition of Ca, F, and Ca+F decreased the peroxide penetration through the tooth structure (p=0.0001), but there were no differences in color change for ΔL (p=0.357), Δa (p=0.061), Δb (p=0.823), and ΔE (p=0.581).

Conclusion:

The addition of calcium and fluoride in the gel did not affect bleaching efficacy, but it was able to reduce both the peroxide diffusion and the bleached enamel microhardness loss.

Effects of experimental bleaching agents on the mineral content of sound and demineralized enamels

High concentrations of hydrogen peroxide can cause adverse effects on composition and structure of teeth. However, the addition of calcium and fluoride in bleaching agents may reduce enamel demineralization.

Enamel Mineral Content Changes After Bleaching With High and Low Hydrogen Peroxide Concentrations: Colorimetric Spectrophotometry and Total Reflection X-ray Fluorescence Analyses

The purpose of this study was to evaluate the calcium (Ca) and phosphorous (P) content in enamel bleached with high and low concentrations of hydrogen peroxide (HP) using Total Reflection X-Ray Fluorescence (TXRF) and colorimetric spectrophotometry (SPEC). Forty-eight sound human third molars were used. Their roots were embedded in polystyrene resin and immersed for seven days in an artificial saliva solution. Then they were distributed into six groups to receive the bleaching treatments. The agents of high HP concentration (for in-office use) evaluated were Whiteness HP Maxx/FGM (35% HP), Whiteness HP Blue/FGM (35% HP, 2% calcium gluconate), Pola Office+/SDI (37.5% HP, 5% potassium nitrate), and Opalescence Boost/Ultradent (38% HP, 1.1% ion fluoride, 3% potassium nitrate); these agents were applied to enamel in three sessions. The agents of low HP concentration (for home use) evaluated were Pola Day/SDI (9.5% HP) and White Class 10%/FGM (10% HP, potassium nitrate, calcium, fluoride), and these agents were applied for 14 days. Enamel microbiopsies were evaluated by TXRF and SPEC analysis before the bleaching treatment (baseline), during the treatment, and 14 days after the end of the treatment. For TXRF, the Kruskal-Wallis test showed that Ca and P were not influenced by agent (p>0.05). For SPEC, Pola Office+, Opalescence Boost, Pola Day, and White Class 10% caused a decrease of Ca over time; there was a significant decrease of P over time to Pola Office+ and White Class 10%. The Spearman test showed no correlation between the Ca (p=0.987; r²=-0.020) and P (p=0.728, r²=0.038) obtained by SPEC and TXRF. For TXRF and SPEC, changes in Ca and P during bleaching occurred independently of the HP concentration used.

The effects of fractional CO2 laser, Nano-hydroxyapatite and MI paste on mechanical properties of bovine enamel after bleaching

Background

This study investigated the effect of post bleaching treatments to the change of enamel elastic modulus and microhardness after dental bleaching in- vitro.

Material and Methods

Fifty bovine incisor slab were randomly assigned into five groups (n=10). The samples were bleached for three times; 20 minutes each time, by 40% hydrogen peroxide. Next it was applied fractional CO2 laser for two minutes, Nano- hydroxy apatite (N-HA) and MI-paste for 7 days and 2 minutes per day. The sound enamel and bleached teeth without post treatment remained as control groups. The elastic modulus and microhardness were measured at three times; 24 hours, 1 and 2 months. Data were statistically analyzed by two-way analysis of variance with 95% confidence level.

Results

Different methods of enamel treatment caused a significant increase in elastic modulus compared to bleached group (P<0.05). Modulus was significantly increased in 1 and 2 months (P<0/001: bleach, P= 0/015: laser, P= 0/008: NHA, P=0/010: MI paste) but there were no significantly difference between 1 and 2 months (P>0.05). There was any significance difference for hardness among treated and control groups, but hardness increased significantly by increasing storage time (P<0.05).

Conclusions

The use of the protective tested agents can be useful in clinical practice to reduce negative changes of enamel surface after whitening procedures.

Key words:Bleaching enamel, CO2 laser, MI pastes, Nano-hydroxy apatite, Microhardness, Elastic modulus.

Influence of bioadhesive polymers on the protective effect of fluoride against erosion

OBJECTIVE

This study investigated if the incorporation of the bioadhesive polymers Carbopol 980, Carboxymethyl cellulose (CMC), and Aristoflex AVC in a fluoridated solution (NaF-900ppm) would increase the solution's protective effect against enamel erosion.

METHODS

Enamel specimens were submitted to a 5-day de-remineralization cycling model, consisting of 2min immersions in 0.3% citric acid (6x/day), 1min treatments with the polymers (associated or not with fluoride), and 60min storage in artificial saliva. Ultrapure water was used as the negative control and a 900ppm fluoride solution as positive control. The initial Knoop microhardness (KHN1) was used to randomize the samples into groups. Another two microhardness assessments were performed after the first (KHN2) and second (KHN3) acid immersions, to determine initial erosion in the first day. The formula: %KHN_alt=[(KHN3-KHN2)/KHN2]*100 was used to define the protective effect of the treatments. After the 5-day cycling, surface loss (SL, in μm) was evaluated with profilometry. Data were analyzed with 2-way ANOVA and Tukey's tests (p<0.05).

RESULTS

For %KHN_alt, the polymers alone did not reduce enamel demineralization when compared to the negative control, but Carbopol associated with NaF significantly improved its protective effect. The profilometric analysis showed that Carbopol, associated or not with NaF, exhibited the lowest SL, while CMC and Aristoflex did not exhibit a protective effect, nor were they able to improve the protection of NaF.

CONCLUSIONS

It is concluded that Carbopol enhanced NaF's protection against initial erosion. Carbopol alone or associated with NaF was able to reduce SL after several erosive challenges.

CLINICAL SIGNIFICANCE

Carbopol by itself was able to reduce the erosive wear magnitude to the same extent as the sodium fluoride, therefore, is a promising agent to prevent or control enamel erosion.