Evaluation of the aesthetic effect, enamel microhardness and trans-amelodentinal cytotoxicity of a new bleaching agent for professional use containing trimetaphosphate and fluoride

Inorganic Phosphate Effect in a Hydrogen Peroxide-based Bleaching Agent: Physicochemical, Mechanical, and Morphological Properties of Dental Enamel

OBJECTIVES

This in vitro study aimed to assess the impact of incorporating calcium glycerophosphate (CaGP) and sodium fluoride (NaF) in addition to 35% hydrogen peroxide concerning the enamel mechanical and morphological properties.

METHODS

Specimens of bovine enamel were chosen based on their initial surface hardness (SHi) and subsequently divided into five gel groups (n=12): 1) 35% Hydrogen Peroxide (HP) Gel; 2) HP + 0.1% NaF Gel (HP/NaF); 3) HP + 0.25% CaGP Gel (HP/CaGP); 4) HP + 0.1% NaF + 0.25% CaGP Gel (HP/NaF/CaGP) and 5) HP Blue 35% Gel (HP Blue). The bleaching gels were applied thrice, for 40 min, at intervals of 7 days each. After 21 days, the final surface hardness (SHf), integrated hardness (IH), Polydispersity Index (PdI) and Zeta Potential (Zp), surface roughness (Ra, after and before), and surface/structural analysis by Scanning Electron Microscopy (SEM) were determined. The data were submitted to ANOVA (one-way and two-way) followed by the Student-Newman-Keuls test (α=0.05).

RESULTS

The addition of NaF to HP reduced demineralization by 11.5% in relation to HP (p<0.05). The NaF/CaGP association reduction is 22.8 and 20% higher in comparison to HP/NaF/CaGP and HP Blue, respectively. The IH when the PH/NaF/CaGP bleaching gel was applied, was 14% higher compared to HP and HP Blue groups.

CONCLUSIONS

It can be concluded that the association of NaF and CaGP with the 35% hydrogen peroxide gel (HP/NaF/CaGP) significantly changed tooth enamel demineralization in terms of surface, depth, roughness, and enamel morphology.

Influence of coating dental enamel with a TiF4-loaded polymeric primer on the adverse effects caused by a bleaching gel with 35% H2O2

OBJECTIVE

To evaluate whether coating enamel with a polymeric primer (PPol) containing titanium tetrafluoride (TiF4) before applying a bleaching gel with 35% H2O2 (35% BG) increases esthetic efficacy, prevents changes in morphology and hardness of enamel, as well as reduces the cytotoxicity from conventional in-office bleaching.

MATERIALS AND METHODS

Standardized enamel/dentin discs were stained and bleached for 45 min (one session) with 35% BG. Groups 2TiF4, 6TiF4, and 10TiF4 received the gel on the enamel previously coated with PPol containing 2 mg/mL, 6 mg/mL, or 10 mg/mL, respectively. No treatment or application of 35% BG directly on enamel were used as negative control (NC), and positive control (PC), respectively. UV-reflectance spectrophotometry (CIE L*a*b* system, ΔE00, and ΔWI, n = 8) determined the bleaching efficacy of treatments. Enamel microhardness (Knoop, n = 8), morphology, and composition (SEM/EDS, n = 4) were also evaluated. Enamel/dentin discs adapted to artificial pulp chambers (n = 8) were used for trans-amelodentinal cytotoxicity tests. Following the treatments, the extracts (culture medium + bleaching gel components diffused through the discs) were collected and applied to odontoblast-like MDPC-23 cells, which were assessed concerning their viability (alamarBlue, n = 8; Live/Dead, n = 4), oxidative stress (n = 8), and morphology (SEM). The amount of H2O2 in the extracts was also determined (leuco crystal violet/peroxidase, n = 8). The numerical data underwent one-criterion variance analysis (one-way ANOVA), followed by Tukey's test, at a 5% significance level.

RESULTS

Regarding the ΔE00, no difference was observed among groups 2TiF4, 6TiF4, and PC (p > 0.05). The ΔWI was similar between groups 2TiF4 and PC (p > 0.05). The ΔWI of group 6TiF4 was superior to PC (p < 0.05), and group 10TiF4 achieved the highest ΔE00 and ΔWI values (p < 0.05). Besides limiting enamel microstructural changes compared to PC, group 10TiF4 significantly increased the hardness of this mineralized dental tissue. The highest cellular viability occurred in 10TiF4 compared to the other bleached groups (p < 0.05). Trans-amelodentinal H2O2 diffusion decreased in groups 2TiF4, 6TiF4, and 10TiF4 in comparison with PC (p < 0.05).

CONCLUSION

Coating enamel with a PPol containing TiF4 before applying a 35% BG may increase enamel microhardness and esthetic efficacy and reduce the trans-amelodentinal cytotoxicity of conventional in-office tooth bleaching. The PPol containing 10 mg/mL of TiF4 promoted the best outcomes.

In-office Bleaching Activated With Violet LED: Effect on Pulpal and Tooth Temperature and Pulp Viability

OBJECTIVES

This study evaluated the influence of hydrogen peroxide (HP) with or without titanium dioxide nanotubes (TiO2) associated with violet LED (VL) regarding: a) the temperature change in the pulp chamber and facial surface; b) the decomposition of HP; and c) the cytotoxicity of the gels on pulp cells.

METHODS AND MATERIALS

The experimental groups were: HP35 (35% HP/Whiteness HP, FGM); HP35+VL; HP35T (HP35+TiO2); HP35T+VL; HP7 (7.5% HP/White Class 7.5%, FGM); HP7+VL; HP7T (HP7+TiO2); and HP7T+VL. TiO2 was incorporated into the bleaching gels at 1%. Eighty bovine incisors were evaluated to determine temperature change in 8 experimental groups (n=10/group). A k-type thermocouple was used to evaluate the temperatures of the facial surface and in the pulp chamber, achieved by enabling endodontic access to the palatal surface, throughout the 30-minute session. HP decomposition (n=3) of gels was evaluated by using an automatic potentiometric titrator at the initial and 30-minute time points. Trans-enamel and trans-dentinal cell viability were assessed with a pulp chamber device as well as enamel and dentin discs (n=6), and the treatment extracts (culture medium + diffused components) were collected and applied to MDPC-23 odontoblast cells to evaluate cell viability according to the MTT test.

RESULTS

A temperature increase in the pulp chamber was observed in the presence of VL at 30 minutes (p<0.05) (Mann-Whitney test). Also at 30 minutes, HP35 showed greater decomposition in the presence of VL rather than in its absence (p<0.05) (mixed linear models and the Tukey-Kramer test). HP7 provided greater cell viability than the groups treated with HP35 (p<0.05) (generalized linear models test). Cell viability was significantly lower for HP7 in the presence of VL (p<0.05).

CONCLUSION

Pulpal temperature increased with VL (maximum of 1.9°C), but did not exceed the critical limit to cause pulp damage. Less concentrated HP resulted in higher cell viability, even when associated with VL.

In vitro assessment of dental erosion caused by clear aligners

The primary objective of this in vitro study was to investigate the erosive potential of enamel under the use of clear aligners (CA), by simulating in vivo conditions experienced by patients who do not remove their CA during the consumption of acidic beverages. In addition, the difference in erosion protection conferred by artificial and human saliva was also evaluated. Sound-extracted human premolars (n = 20) had half of their surfaces protected with acid-resistant nail polish and were randomly distributed into two experimental groups (n = 10): teeth immersed in human saliva or artificial saliva. All teeth had half of their lingual surfaces enclosed by a CA device. The erosive challenges consisted of individual immersion of each sample in citrus acid three times a day, intermediated by immersion in human saliva or artificial saliva for 2 h, during ten days of the erosive protocol. The enamel mineral content was analyzed by high-resolution microtomography. The differential mineral concentration profiles were obtained by subtracting the profile of the mineral concentration of the exposed area and enamel under the CA area from the respective sound area (control). In addition, enamel wear and enamel volume loss were measured. Scanning electron microscopy (SEM) was also performed to analyze the enamel surface. Data were analyzed by two-way ANOVA, followed by the Student-Newman-Keuls test. The enamel wear was higher in teeth immersed in artificial saliva, when compared to human saliva (p < 0.001). The volume loss of the exposed enamel area was lower for tooth immersed in human saliva than in artificial saliva (p < 0.001), during the acid challenge protocol. The use of CA during acid challenges promoted wear and mineral loss of dental enamel, being these changes more pronounced on the enamel surface under the CA. These results open a new path for the development of further studies adopting clinical protocols that promote more accurate responses in the clinical practice during orthodontic treatment.

Enzymatically Driven Mineralization of a Calcium-Polyphosphate Bleaching Gel

To examined alkaline phosphatase enzyme (ALP) activity and the effects of incorporating it in the thickener solution of a hydrogen-peroxide-based bleaching gel containing calcium-polyphosphate (CaPP) on the orthophosphate (PO43-) levels, bleaching effectiveness, and enamel microhardness. ALP activity was assessed at different pH levels and H2O2 concentrations, and in H2O- and Tris-based thickeners. Circular dichroism (CD) was used to examine the ALP secondary structure in water-, Tris-, or H2O2-based mediums. The PO43- levels were evaluated in thickeners with and without ALP. Enamel/dentin specimens were allocated into the following groups: control (without bleaching); commercial (Whiteness-HP-Maxx); Exp-H (H2O-based); CaPP-H; ALP-H (CaPP+ALP); Exp-T (Tris-based); CaPP-T; and ALP-T (CaPP+ALP). Color changes (ΔE/ΔE00) and the bleaching index (ΔWID) were calculated, and surface (SMH) and cross-sectional microhardness (CSMH) were assessed. The two-way ANOVA and Tukey's post-hoc tests were used to compare ALP and PO43- levels; generalized linear models were used to examine: ΔE/ΔE00/SMH/CSMH; and Kruskal-Wallis and Dunn's tests were used for ΔWID (α = 5%). The ALP activity was higher at pH 9, lower in H2O2-based mediums, and similar in both thickeners. The CD-spectra indicated denaturation of the enzyme upon contact with H2O2. The PO43- levels were higher after incorporating ALP, and the ΔE/ΔE00/ΔWID were comparable among bleached groups. SMH was lower after bleaching in Exp-H, while CSMH was highest in ALP-T.

Influence of bleaching gels formulated with nano-sized sodium trimetaphosphate and fluoride on the physicochemical, mechanical, and morphological properties of dental enamel

OBJECTIVES

To evaluate in vitro the effects of sodium fluoride (F) and nano-sized sodium trimetaphosphate (TMPnano) added to a 35% hydrogen peroxide (H2O2) bleaching gel on the color alteration, enamel mechanical and morphological properties, and H2O2 transamelodentinal diffusion.

MATERIALS AND METHODS

Bovine enamel/dentin discs (n = 180) were divided according to the bleaching gel: 35% H2O2 (HP); 35% H2O2 + 0.1% F (HP/F); 35% H2O2 + 1% TMPnano (HP/TMPnano); 35% H2O2 + 0.1% F + 1% TMPnano (HP/F/TMPnano) and 35% H2O2 + 2% calcium gluconate (HP/Ca). The gels were applied 3 times by 40 min; once each 7-day. The Commission Internationale de l'Eclairage (CIE) L*a*b* total color alteration (ΔE), color alteration by CIEDE2000 (ΔE00), whitening index (ΔWID), surface (SH) and cross-sectional hardness (ΔKHN), surface roughness (Ra), and transamelodentinal diffusion were determined. Enamel surfaces were evaluated by Scanning Electron Microscopy (SEM) and X-ray Dispersive Energy (EDX). Data were submitted to ANOVA, followed by the Student-Newman-Keuls test (p <0.05).

RESULTS

ΔE, ΔE00, and ΔWID were similar among the gels that promoted a bleaching effect after treatment (p <0.001). Mineral loss (SH and ΔKHN), Ra, and H2O2 diffusion were lower for HP/F/TMPnano; the HP and HP/Ca groups presented the highest values (p <0.001). For SEM/EDX, surface changes were observed in all bleached groups, but less intense with TMPnano.

CONCLUSIONS

Gels containing F/TMPnano do not interfere with the bleaching effect and reduce enamel demineralization, roughness, H2O2 diffusion, and morphological changes.

CLINICAL RELEVANCE

Whitening gels containing F/TMPnano can be used as a new strategy to increase safety and maintain clinical performance.

Effect of an In-Office Bleaching Agent with Surface Pre-Reacted Glass-Ionomer Filler on the Enamel Surface: A In-Vitro Study

In-office bleaching with high concentrations of hydrogen peroxide (H₂O₂) agents causes undesirable alterations in the enamel. Surface pre-reacted glass-ionomer (S-PRG) filler is a functional material known for its acid-neutralizing and demineralization-inhibition properties. This study evaluates the effect of S-PRG filler incorporation in H₂O₂-based bleaching on the enamel surface. Bovine enamel surfaces were bleached using a bleaching paste formulated with a liquid (35% H₂O₂) and a powder containing 5% or 10% S-PRG filler. The surface roughness and the Vickers microhardness of the treated enamel surfaces were evaluated. The enamel surfaces were observed under a scanning electron microscope (SEM) and analyzed using energy dispersive X-ray (EDX) technology. The surfaces were challenged by citric acid and observed by SEM. The specimens bleached with the paste containing the S-PRG filler showed lower enamel surface roughness and higher microhardness values than did those bleached with the plain paste (0% S-PRG filler); meanwhile, there were no significant differences between the 5% or 10% S-PRG filler groups. The S-PRG filler groups showed enamel surface morphologies similar to those of the non-bleached enamel, according to SEM observation, and EDX analysis detected the presence of fluoride and strontium ions. The S-PRG filler groups showed a higher resistance to erosion. The S-PRG filler mitigated the detrimental effects of bleaching agents on the enamel surface and provided resistance to erosion.

Fluoride and trimetaphosphate association as a novel approach for remineralization and antiproteolytic activity in dentin tissue

OBJECTIVE

The study evaluated the effect of solutions containing fluoride (F) and/or sodium trimetaphosphate (TMP) and F/TMP on the inhibition of MMP-2 and MMP-9, and on dentin remineralization in vitro.

DESIGN

Bovine root dentin blocks were prepared, and caries-like lesions were induced in two thirds of the surface. Blocks were then randomly divided into 13 groups/solutions (n = 10): Placebo; 0.3 %, 1 % and 3 % NaOH-hydrolyzed TMP; 0.3 %, 1 % and 3 % TMP; 250, 500 and 1100 ppm F; 250 ppm F + 0.3 % TMP; 500 ppm F + 1 % TMP and 1100 ppm F + 3 % TMP. One third of each specimen was treated with the respective solutions in pH-cycling. The mineral concentration (g_HAp × cm^-3 × µm) was determined by computed X-ray microtomography, and data submitted to ANOVA and Student-Newman-Keuls' test (p < 0.05). The ability of the solutions to inhibit MMP-2 and MMP-9 activity was assessed by zymography.

RESULTS

F/TMP association led to less mineral loss in the deeper region of the lesion and reduced the depth of lesions when compared to its counterpart without TMP (p < 0.001). 3 % TMP (hydrolyzed or not), 500 ppm F and 1100 ppm F completely inhibited MMP-2 activity, while for MMP-9 such effects were only achieved by treatment with 1100 ppm F + 3 % TMP.

CONCLUSION

Treatment with 1100 ppm F + 3 % TMP fully inhibits the gelatinolytic activity of MMPs-2 and - 9 and shows greater remineralizing capacity in artificial caries lesions in dentin. However, hydrolyzing TMP does not improve its anti-proteolytic activity and its remineralizing capacity.

Evaluation of bleaching efficacy, microhardness, and trans-amelodentinal diffusion of a novel bleaching agent for an in-office technique containing hexametaphosphate and fluoride

OBJECTIVE

This study evaluated in vitro the effects of calcium gluconate (CaGlu), sodium fluoride (NaF), sodium hexametaphosphate (HMP), and NaF/TMP added to a 35% hydrogen peroxide (H₂O₂) bleaching gel on the color change, enamel hardness, and trans-amelodentinal diffusion.

MATERIALS AND METHODS

Enamel discs/bovine dentin (n = 150) were divided according to the bleaching gel: 35% H₂O₂ (H₂O₂); 35% H₂O₂ + 0.1% NaF (H₂O₂/NaF); 35% H₂O₂ + 1% HMP (H₂O₂/HMP); 35% H₂O₂ + 0.1% NaF + 1% HMP (H₂O₂/NaF/HMP), and 35% H₂O₂ + 2% CaGlu (H₂O₂/Caglu). The bleaching gels were applied three times (40 min/session) at 7-day intervals between each application. Then, color alteration (ΔE), whitening index (ΔWI_D), percentage of surface hardness loss (% SH), cross-sectional hardness (ΔKHN), and trans-amelodentinal diffusion were determined. Data were submitted for analysis of variance (ANOVA), followed by the Student-Newman-Keuls test (p < 0.05).

RESULTS

All bleaching gels showed significant color changes after treatment (p < 0.001). ΔE and ΔWI_D were similar among the evaluated gels. Mineral loss (% SH and ΔKHN) and trans-amelodentinal diffusion of hydrogen peroxide were lower for H₂O₂/NaF/HMP; the H₂O₂/CaGlu group presented the highest values about the other groups (p < 0.001).

CONCLUSION

It is possible to conclude that the addition of NaF/HMP to the in-office bleaching agent did not interfere with the bleaching efficacy and reduced enamel demineralization and H₂O₂ diffusion.

CLINICAL SIGNIFICANCE

The association of NaF/HMP to the bleaching gel can be used as a novel approach for minimizing the adverse effects of H₂O₂ by-products and with similar clinical efficacy.