Effect of carbamide peroxide-based bleaching agents containing fluoride or calcium on tensile strength of human enamel

Altered physical-chemical properties of home bleaching gels after an accelerated stability study and their effects on tooth enamel

OBJECTIVES

To investigate the physical-chemical properties of home bleaching gels based on Carbamide Peroxide (CP) and Hydrogen Peroxide (HP) after accelerated stability (AS) and its effects on enamel.

MATERIALS AND METHODS

A total of 360 bovine teeth blocks were divided (n = 12): Control, CP10%-Whiteness Perfect, CP10%-Pola Night, HP7.5%-Pola Day, and HP7.5%-White Class Calcium. Microhardness (KHN), roughness (Ra), color (ΔE and ΔE₀₀), hardness, compressibility, elasticity, cohesiveness, adhesiveness, weight, pH, and calcium (Ca) quantification in enamel were analyzed without storage of the bleaching gels and after AS at 1 and 3 months. Data of Ca, KHN, and Ra were analyzed through mixed models for repeated measurements and the Tukey-Kramer test. Values of weight, hardness, compressibility, and elasticity were analyzed with two-way ANOVA and Tukey's test. ΔE/ΔE₀₀ data, cohesiveness, and adhesiveness were analyzed with Kruskal-Wallis and Dunn tests (α = 0.05).

RESULTS

Groups subject to AS had lower ΔE and ΔE₀₀ compared to those without storage. Lower KHN and higher Ra values were found after bleaching treatment in all groups compared to controls. Higher amounts of Ca were found on the first day of evaluation in the gels subject to AS for 3 months, regardless of the bleaching agent used.

CONCLUSIONS

Incorrectly stored bleaching gel accentuates adverse effects on enamel. Temperature and humidity interfere directly with the chemical stability of bleaching agents, reducing their properties.

CLINICAL RELEVANCE

HP is an unstable oxidizing agent when stored at high temperatures. Therefore, pH becomes more acidic and potentiates the demineralizing effect on enamel.

EVALUATION OF MINERAL CONTENT OF TOOTH ENAMEL AFTER APPLICATION VIOLET LED ASSOCIATED WITH 35% HYDROGEN PEROXIDE

BACKGROUND

The aim of this study was to evaluate the microhardness and quantify the presence of minerals (Calcium and Phosphorous) of tooth enamel submitted to bleaching with violet LED light, either associated with 35% hydrogen peroxide gel, or not.

METHODS

Bovine incisors were selected and divided into 4 Groups according to the bleaching technique used: C- Without bleaching (Control); VL- violet LED; HP- 35% Hydrogen Peroxide; HP+VL- 35% Hydrogen Peroxide + violet LED. The response variables were surface microhardness (n=12), Energy Dispersive Spectroscopy (EDS) (n=6) and scanning electron microscopy (SEM) (n=3).

RESULTS

The 2-way ANOVA test with repeated measures showed that there was difference in the microhardness values of enamel in the specimens in all of the Groups when the values measured in the initial and final time intervals were compared, however, without significant differences between the values of the different treatments in both time intervals. The results with reference to EDS were analyzed with the 1-way ANOVA test. There was difference among the Groups only in the Ca%, with Group HP obtaining the lowest values, with significant difference from those of the C Group. SEM images showed a smooth, homogeneous enamel surface and similarity among the Groups, irrespective of the treatment performed.

CONCLUSIONS

Therefore, it was concluded that the changes caused in enamel by the use of violet LED Light, either associated with 35% hydrogen peroxide, or not, did not differ from those of non-bleached tooth enamel, showing absence of harm to the mineral content of tooth enamel resulting from the use of violet LED.

Influence of Prolonged Dental Bleaching on the Adhesive Bond Strength to Enamel Surfaces

The objective of this in vitro study was to assess the influence of prolonged bleaching pre- and postrestoration on the bond strength (microshear) to enamel using 4% hydrogen peroxide (PH4). In the postrestorative bleached specimens evaluation, the composite cylinders were assembled after bleaching, while in the prebleached specimens, the cylinders were assembled before. Therefore, in the postbleached specimens, 60 bovine teeth were randomly assigned as follows: G1: control; G2: 14 days bleaching before bond strength (BS) testing; G3: 21 days; and G4: 28 days. In prebleached specimens, 180 bovine teeth were randomly assigned as follows: G1: control; G5: 14 days bleaching, storage in artificial saliva (AS) for 24 h before BS testing; G6: 14 days beaching, AS storage for 7 days before BS testing; G7: 21 days bleaching, AS storage for 24  h before BS testing; G8: 21 days bleaching, AS storage for 7 days before BS testing; G9: 28 days bleaching, AS storage for 24 hours before BS testing; and G10 : 28 days bleaching, AS storage for 7 days before BS testing. The results were submitted to ANOVA one-way (postrestoration bleaching) and two-way (prerestoration bleaching) and Tukey's post hoc test (p ≤ 0.05). In the postrestoration bleaching, no statistical difference between times was found. However, when bleached groups were compared to the control (G1), an expressive difference was detected (p ≤ 0.0001). For prerestoration bleaching, all experimental groups were statistically different from G1 (p ≤ 0.05), except G6 (p ≥ 0.01), and for G5 and G6, statistical differences were found (p ≤ 0.01). There were no significant differences between G7 and G8 and between G9 and G10, regardless of the AS storage times (p ≥ 0.05). It was concluded that prolonged bleaching with PH4 decreased adhesion resistance regardless of the moment of the bleaching (post- and prerestoration bleaching).

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.

Influence of Time Intervals between Bleaching Procedures on Enamel Microhardness and Surface Roughness

BACKGROUND

Dental bleaching has been increasingly sought out to improve dental aesthetics, but it may cause changes in dental enamel.

OBJECTIVE

To assess the influence of different time intervals on bleaching gel applications with regard to the Microhardness (MH) and Surface Roughness (SR) on dental enamel.

MATERIAL AND METHODS

Forty bovine incisors were randomly divided into two groups (G1 and G2) and both were bleached with 35% Hydrogen Peroxide (HP35) (n=20; G1: seven-day interval and G2: two-day interval). The MH and SR tests were performed before bleaching (T0) and after the first (T1), second (T2), and third (T3) bleaching gel applications. The specimens were stored in artificial saliva between each application (37°C). The data were analyzed using the student's t-test (p ≤ 0.05) for dependent samples.

RESULTS

The reduced time interval (two days) led to a significant reduction in MH, while MH was not affected during the seven-day interval. The SR results increased regardless of the bleaching gel application time interval.

CONCLUSION

The decreased time interval of two days between bleaching gel applications caused changes in MH but did not influence the SR of dental enamel.

Penetration Capacity, Color Alteration and Biological Response of Two In-office Bleaching Protocols

Hydrogen peroxide (H2O2) penetrates into the dental hard tissues causing color alteration but also alterations in pulpal tissues. Hard-tissue penetration, color alteration and the pulp response alterations were evaluated for two in-office bleaching protocols with H2O2. For trans-enamel/dentin penetration and color alteration, discs of bovine teeth were attached to an artificial pulp chamber and bleached according to the groups: BLU (20% H2O2 - 1x50 min, Whiteness HP Blue); MAX (35% H2O2 - 3x15 min, Whiteness HP Maxx); Control (1x50 min, placebo). Trans-enamel/dentin penetration was quantified based on the reaction of H2O2 with leucocrystal violet and the color analyzed by CIELab System. Twenty Wistar rats were divided into two groups (BLU and MAX) and their maxillary right molars were treated according to the same protocols of the in vitro study; the maxillary left molars were used as controls. After 2 days, the animals were killed and their maxillae were examined by light microscopy. The inflammation of pulp tissue was scored according to the inflammatory infiltrate (1, absent; 2, mild; 3, moderate; 4, severe/necrosis). Data were analyzed by statistical tests (α=0.05). MAX showed higher trans-enamel/dentinal penetration of H2O2 (p<0.05). The color alteration was similar for both groups (p>0.05), and different when compared to Control group (p<0.05). MAX showed severe inflammation in the upper thirds of the coronal pulp, and BLU showed moderate inflammation (p<0.05). In-office bleaching protocols using lower concentrations of hydrogen peroxide should be preferred due to their reduced trans-enamel/dentinal penetration since they cause less pulp damage and provide same bleaching efficiency.

An In Vitro Evaluation of Human Enamel Surfaces Subjected to Erosive Challenge After Bleaching

OBJECTIVES

This study aimed to evaluate whether tooth enamel bleached with hydrogen peroxide (H₂ O₂ ) is more susceptible to erosion when compared with unbleached tooth enamel; and whether the presence of calcium (Ca) in the bleaching gel influenced this process.

MATERIALS AND METHODS

Enamel blocks were prepared from human molars, and submitted to surface microhardness analysis (baseline). Blocks were prepared and randomly divided into four treatment groups (n = 20): G1 and G2-bleached with 7.5% H₂ O₂ , with and without Ca, respectively; G3 and G4-bleached with 35% H₂ O₂ , with and without Ca, respectively. After bleaching, these groups were submitted to an erosive challenge with 1% citric acid. G5 and G6 (n = 20, each) were the negative (without bleaching) and positive controls (without bleaching, but with erosion), respectively. The percentage of surface hardness loss (%SHL), the 3D non-contact profilometry and Scanning Electron Microscopy (SEM) analyses were performed.

RESULTS

G2 showed the highest %SHL after bleaching. G1 presented the lowest %SHL in comparison with G2, G3, G4, and G6 after erosion (p < 0.05), which was confirmed only by the SEM analysis.

CONCLUSION

It is suggested that low concentration of H₂ O₂ with calcium can be recommended for at-home bleaching agents, which may avoid the mineral loss of bleached enamel after an erosive challenge.

CLINICAL SIGNIFICANCE

Low concentration of H₂ 0₂ with calcium can be recommended for at-home bleaching agents, which may avoid the mineral loss of bleached enamel after an erosive challenge. (J Esthet Restor Dent 29:128-136, 2017).

An In Situ Study of the Influence of Staining Beverages on Color Alteration of Bleached Teeth

The aim of this study was to evaluate overall color change in bovine tooth fragments submitted to dental bleaching treatment performed simultaneously with the ingestion of beverages containing dyes. For this purpose, tooth fragments assembled into intraoral devices were submitted to at-home dental bleaching using 10% carbamide peroxide (CP) for 14 days and to immersion in staining beverages for 10 minutes daily. The specimens were divided into the following study groups according to bleaching treatment and staining substance (n=12): G I (negative control): no bleaching + distilled water; G II (positive control): bleaching + distilled water; G III: bleaching + coffee; and G IV: bleaching + grape juice. Twelve volunteers used the device continually, except during meals, oral hygiene, dental bleaching, and pigment challenge. Color readings were performed using a spectrophotometer both before the bleaching treatment and after each treatment week. The results were submitted to the normality test. The data obtained were submitted to analysis of variance and the Tukey or Kruskal-Wallis and Dunn tests (α=0.05). All bleached groups showed similar ΔE results at the end of treatment. Staining beverages generated negative ΔL mean values, and the lowest result was obtained in the treatment with coffee after 14 days. The Δa values in the groups that received treatment with staining beverages were higher when compared to the control groups. Dental bleaching associated with the consumption of staining substances may not affect overall tooth color change by the end of the treatment, although the consumption of staining substances did influence the different color dimensions.

Influence of bleaching and desensitizing gel on bond strength of orthodontic brackets

OBJECTIVE

The objective of this study was to assess, in vitro, the influence of bleaching gel and the use of desensitizing agent over bond strength of ceramic brackets bonded to bovine enamel.

METHODS

One hundred bovine incisors were selected and randomly divided into five groups (n = 20): Group 1, control group (without bleaching); Group 2, bleached with 35% hydrogen peroxide; Group 3, bleached with 35% hydrogen peroxide (three applications, 15 minutes each) and desensitizing agent applied for 10 minutes; Group 4, bleached with 35% hydrogen peroxide for 40 minutes; Group 5, bleached with 35% hydrogen peroxide for 40 minutes with desensitizing agent applied for 10 minutes. Brackets were bonded 7 days after bleaching and submitted to shear bond strength test after 24 hours at a compression rate of 1 mm/minute. After fracture, the adhesive remnant index (ARI) was assessed under stereoscopic at 40 x magnification. Shear strength data (MPa) were submitted to one-way ANOVA and Tukey's test with significance level set at 5%.

RESULTS

Group 5 (29.33 MPa) showed significantly higher bond strength than Group 1 (19.19 MPa), Group 2 (20.59 MPa) and Group 4 (23.25 MPa), but with no difference in comparison to Group 3. There was no significant difference among the other groups. The adhesive remnant index showed predominance of score 3, that is, all resin remained adhered to enamel for all groups.

CONCLUSION

Bleaching with 35% hydrogen peroxide with calcium associated with desensitizing agent application produced higher bond strength values of brackets bonded to bovine enamel.

Do different bleaching protocols affect the enamel microhardness?

Objective:

Tooth bleaching tends to increase enamel roughness and porosity, in addition to reducing surface microhardness. The aim of this in vitro study was to evaluate the effects of bleaching treatments using different hydrogen peroxide (HP) concentrations, with and without light activation on bovine enamel microhardness.

Materials and Methods:

The buccal surfaces of sixty bovine incisors were flattened and polished and the enamel specimens were divided into six groups: G1 : c0 ontrol, exposed to artificial saliva; G2: 35% HP applied in two sessions (45’ each); G3: 35% HP applied in two sessions (3 × 15’ each); G4: 35% HP applied in one session (3 × 7’30”) plus hybrid light (HL); G5: 25% HP applied in one session (3 × 7’30”) plus HL; and G6: 15% HP applied in one session (3 × 7’30”) plus HL. After the treatment, the enamel specimens were stored in artificial saliva. The surface microhardness (Knoop) was measured at the baseline, 24 h and 7 days after bleaching. The data was analyzed using the ANOVA test, followed by the Tukey–Krummer test (P < 0.05).

Results:

All bleaching procedures lead to a decrease in surface microhardness when compared with the control group after 24 h. The lowest change in surface microhardness was found in the specimens treated with 15% HP plus HL. However, 35% HP plus HL induced the highest decrease in surface microhardness. After 7 days of remineralization, the surface microhardness returned to normal levels for all bleached specimens.

Conclusion:

Therefore, it can be concluded that the bleaching protocols caused a slight enamel surface alteration. However, the remineralization process minimized these effects.

Effect of fluoride gels on microhardness and surface roughness of bleached enamel

The effect of bleaching treatments containing added calcium and combined with neutral or acidic fluoride gels on tooth enamel was investigated in vitro through Knoop microhardness (KHN) and surface roughness (SR) measurements. A total of 60 bovine incisors were tested, including 30 for SR measurements and 30 for KHN measurements. The specimens were divided into 12 groups and subjected to a bleaching agent with hydrogen peroxide 35% (Whiteness HP 35% Maxx, FGM) or hydrogen peroxide 35% with calcium (Whiteness HP 35% Blue Calcium, FGM) and a fluoride treatment flugel acidulated phosphate fluoride (APF) or flugel neutral fluoride (NF). Control specimens were submitted to bleaching treatments without fluoride. Microhardness tests were performed using a Knoop indentor. Roughness measurements were obtained using a roughness analyzer. Measurements were obtained before and after treatment. The specimens were stored in distilled water at 37 °C between treatments. The results were analyzed using descriptive and inferential statistics. Treatments using APF combined with 35% HP caused a decrease in microhardness, while NF combined with HP 35% Ca increased the enamel hardness. Fluoride gels did not alter the SR of the bleached enamel.

Effects of a bleaching agent with calcium on bovine enamel

Objective:

This in vitro study analyzed the effects of a bleaching treatment containing 35% hydrogen peroxide (HP) with or without calcium on bovine enamel, using the Knoop hardness number (KHN), tristimulus colorimetry (TC), and scanning electron microscopy.

Materials and Methods:

Forty-five specimens were randomly divided into groups (n = 5), which included artificial saliva (negative control [NC]), 35% HP (positive control [PC]), and 35% HP Blue Calcium (HP Blue). The specimens were subjected to three bleaching sessions. During the sessions, the specimens were immersed in artificial saliva at 37°C. Before and after bleaching, KHN tests were conducted using a force of 25 gf for 5 s. TC was performed using the CIE-L*a*b* system and readouts were obtained at the following 4 time points: Before the bleaching treatment; after the first session, the second session, and the third session. The specimens were dehydrated and coated with gold, and the photomicrographs were analyzed in a double-blind manner with a LEO microscope.

Results:

Using one-way analysis of variance and Tukey's test (P < 0.05), a statistically significant difference was identified between the initial and final mean KHNs of the NC and PC groups, while the initial and final mean KHNs were not significantly different in the HP Blue group. The final mean values of ΔE, ΔL, and Δb of the PC and HP Blue groups were significantly higher than the initial values (P < 0.01 for both). The photomicrographs revealed no differences among the groups.

Conclusions:

Therefore, treatment with HP Blue prevented changes in the KHN without reducing the efficacy of bleaching.

Color alteration, hydrogen peroxide diffusion, and cytotoxicity caused by in-office bleaching protocols

OBJECTIVES

This study evaluated the color alteration, cytotoxicity, and hydrogen peroxide (HP) diffusion associated with different in-office bleaching protocols.

MATERIALS AND METHODS

Bovine enamel/dentin disks were subjected to three bleaching sessions with 35 % HP (three 15-min applications), 35 % HP (one 45-min application), or 20 % HP (one 45-min application). The control group was not bleached. Before bleaching, the disks were adapted to artificial pulp chambers positioned in compartments containing 1 ml of acetate buffer or medium, so that the dentin remained in contact with these substances. Immediately after bleaching, the HP that diffused through the disks was stabilized by acetate buffer and was quantified (two-way repeated measures ANOVA/Fisher's protected least significant difference (PLSD) test; α = 5 %). Cells of mouse dental papilla cell-23 (MDPC-23) were incubated in this culture media for 1 h, followed by analysis of cellular metabolism (methyl tetrazolium assay) (one-way ANOVA/Tukey test; α = 5 %) and morphology (scanning electron microscopy). The specimen color alteration (ΔE) was analyzed by reflection spectrophotometry (two-way repeated measures ANOVA/Fisher's PLSD test; α = 5 %).

RESULTS

All protocols showed equal effectiveness at the end of the treatment. HP diffusion was significantly higher in the groups bleached with 35 % HP. Reapplication of 35 % HP resulted in increased diffusion only in the first session; however, the decrease in cell metabolism was similar for all studied protocols.

CONCLUSION

Despite greater peroxide diffusion in the groups treated with 35 % HP, all protocols showed the same effectiveness and were cytotoxic to MDPC-23 cells.

CLINICAL RELEVANCE

Bleaching protocols using high HP concentrations should be avoided because they exert aggressive actions on odontoblast-like cells.

Changes in the stiffness of demineralized dentin following application of tooth whitening agents

OBJECTIVE

The purpose of this study was to evaluate the effect of the bleaching agents on the elastic modulus of bovine demineralized dentin matrix (EMDM).

MATERIALS AND METHODS

Eighty-five slices were obtained from 17 bovine teeth. The slices were divided randomly into five experimental groups (n = 17): unbleached control group (CG), 4% hydrogen peroxide (HP4), 4% hydrogen peroxide + 0.05% Ca (HP4 + Ca), 7.5% hydrogen peroxide + ACP (HP7.5) and 10% carbamide peroxide (CP10). The HP4, HP4 + Ca and CP10 groups were treated with the bleaching agents for 8 h/day (14 days), while the samples of HP7.5 group were exposed to bleaching agent for 30 min twice a day (14 days). The CG was kept in 100% humidity. After bleaching treatments, the enamel of the samples was removed and 85 dentin beams (0.5 × 1.7 × 7.0 mm) were prepared. Afterwards, the beams were immersed in 10% phosphoric acid solution (5 h) and rinsed with water (10 min). The beams were tested after 24 h, 7 and 14 days of storage in distilled water, using three-point bend method. Data were statistically analyzed using ANOVA and Fisher's test.

RESULTS

All bleaching treatments reduced the EMDM. After 14 days post-bleaching, the EMDM increased for HP4 and HP4+Ca groups.

CONCLUSIONS

The use of bleaching agents promoted a decrease in EMDM, which indicates that the bleaching treatment interacts with the dentin organic matrix. The EMDM measurement for the specimens of the 7.5% hydrogen peroxide group that were immersed in water at 14 days post-bleaching did not recover the EMDM values when compared to the control group.

Effects of the addition of fluoride and calcium to low-concentrated carbamide peroxide agents on the enamel surface and subsurface

OBJECTIVE

The present study aimed to determine if the addition of fluoride (F) and calcium (Ca) to home-applied 10% carbamide peroxide (CP) bleaching agents reduces mineral loss on the enamel surface and subsurface.

BACKGROUND

Home-applied 10% carbamide peroxide effectively whitens teeth. However, bleaching possibly promotes adverse side effects such as tooth hypersensitivity and morphological and chemical alterations, such reductions in calcium and fluoride, that affect the enamel surface.

METHODS

Sixty human enamel slabs were selected based on evaluation of their surface microhardness (n = 10) and submitted to the application of either a placebo agent, Whiteness™, Opalescence™, Pola Night,™ or one of two experimental carbamide peroxide gels: the first with 0.2% fluoride added and the second with 0.2% calcium added. The gel was applied for 6 h/day for 14 days. Samples were submitted to FT-Raman spectroscopy to evaluate surface mineral content before and after treatment. Additionally, cross-sectional microhardness and polarized light microscopy were carried out, to determine enamel subsurface inorganic loss and lesion depth.

RESULTS

A significant decrease in mineral content was observed after carbamide peroxide treatment, which resulted in increased lesion depth (p < 0.05). Cross-sectional microhardness assessment and polarized light microscopy demonstrated that all groups (except the placebo) exhibited enamel subsurface mineral loss; however, the inorganic deficit could be effectively controlled by the addition of F and Ca to the experimental bleaching agents.

CONCLUSIONS

The addition of F and Ca to home-applied bleaching agents may reduce enamel mineral loss.

Influence of prolonged light-curing time on the shear bonding strength of resin to bleached enamel

This study evaluated the effect of prolonged light-curing time using a light-emitting diode unit (LED) on the shear bond strength of a resin composite to enamel immediately after bleaching. The enamel surfaces of human molars were divided into four groups: one control and three bleaching groups. One bleaching group (CP) was exposed to a 10% carbamide peroxide bleaching agent and bonded after 24 hours. The other two bleaching groups (HP) were bleached with a 38% hydrogen peroxide bleaching agent, then bonded either within one hour (HPA) or after 24 hours (HPB). All groups were subdivided into two subgroups and cured for two different times (20 or 40 seconds) with an LED unit. Shear bond strength (SBS) was tested with a universal-testing machine and the data were analyzed by ANOVA and post-hoc tests. Scanning electron micrographs of representative specimens were taken. A significant difference was seen between the control and HPA groups for both curing times (p = 0.000). However, neither the CP nor HPB groups showed any significant differences compared with the control groups (p > 0.05). Two-way ANOVA showed that a significant effect of the curing time factor was recorded for all groups (p = 0.000). Prolonged curing time, using an LED unit with a light intensity of 500 mW/cm2, increased resin-enamel bonding strengths for the control and bleached groups when bonding was performed after 24 hours of immersion in deionized water. However, the SBS was still compromised when bonding was performed immediately to enamel bleached with 38% HP.