Microhardness Of Bleached Enamel Research Articles

Effect of remineralizing agent on laser and nonlaser bleached enamel surfaces subjected to erosion: An in vitro study.

Assessment of remineralizing agent's effect on laser and nonlaser bleached enamel surfaces subjected to erosion. In this study, 80 extracted human permanent anteriors were collected and divided into 4 groups with 20 teeth per sample. Enamel specimen of 3 mm × 3 mm were made using polyvinyl chloride rings and acrylic and randomly divided into four groups. Then the specimens were subjected to initial microhardness test using Vicker's hardness tester (AVK-CO, Mitutoyo, Japan). Two indentations were placed at 100 mm from one another in the center of all the samples. Bleaching with laser and without laser using hydrogen peroxide was performed followed by remineralization in the groups (Groups 1a and 2a) and then were subjected to erosion. The final hardness was measured using the above method used for initial microhardness. Microhardness in the remineralized groups showed least variation. The group in which laser bleaching was performed along with remineralization as compared with nonlaser bleaching group with remineralization showed improvement in microhardness but the data was not statistically significant. A significant difference was noted between the laser and remineralization group when compared with the groups in which no remineralization was done. After bleaching the enamel surface is more prone to erosion, so to improve the microhardness of bleached enamel a remineralizing agent should be used. A combination of diode laser bleaching and remineralizing agents leads to improved microhardness of the bleached enamel thus proving this combination to be efficacious.

Effect of Eggshell Powder and Nano-Hydroxyapatite on the Surface Roughness and Microhardness of Bleached Enamel.

The aim of the study was to evaluate the remineralizing potential of prepared solutions of eggshell powder (ESP) and nano-hydroxyapatite (nHA) on the surface roughness and microhardness of bleached enamel. Fifty bovine anterior teeth were selected and cleaned then bleached using a chemically activated in-office bleaching agent then the teeth were randomly allocated into five groups (n = 10) according to the tested remineralizing agents (10% ESP solution, 10% nHA solution, and MI Paste Plus) into; control, bleached, bleached + ESP solution, bleached + nHA solution, and bleached + MI Paste Plus groups. Then, the teeth were tested for surface roughness and microhardness of the bleached enamel, respectively. There was a statistically significant difference in the surface roughness and microhardness values of the tested groups. The highest surface roughness mean value was found in bleached enamel group, while the least mean value was found in the control group. The highest mean microhardness value was found in the bleached enamel + ESP solution group, while the least mean value was found in the bleached enamel group. The application of the tested remineralizing agents following the bleaching procedure had improved the surface roughness and microhardness of the bleached enamel. ESP and nHA present promising and potent remineralizing agents.

Comparative evaluation of surface microhardness of bleached enamel subjected to erosion after using Remin Pro and NovaMin: An in vitro study

Comparative evaluation of surface microhardness of bleached enamel subjected to erosion after using Remin Pro and NovaMin: An in vitro study

Evaluating the Effect of Diode Laser Irradiation on Microhardness of Bleached Enamel: An in Vitro Study

Aims: To investigate the effect of in-office dental bleaching techniques on the microhardness of enamel and the influence of post bleaching diode laser irradiation on the surface microhardness of bleached enamel. Materials and methods: Forty bovine teeth were prepared and then randomly allocated into two equal groups (n=20) according to bleaching technique as follows: CB: Conventional in-office bleaching technique and LB: Laser–assisted in-office bleaching technique. Each group was subdivided into two subgroups (n=10) according to laser irradiation setting as follows: C2: Conventionally bleached followed by diode laser irradiation at 2-Watt laser, C4: Conventionally bleached followed by diode laser irradiation at 4-Watt laser, L2: laser –assisted bleached followed by diode laser irradiation at 2-Watt laser and L4: Laser–assisted bleached followed by diode laser irradiation at 4-Watt laser. Vickers microhardness was assessed three times for all the specimens: before bleaching, 24 hours after bleaching and finally 24 hours after post bleaching diode laser irradiation. Paired samples t- test and independent samples t- test were utilized for statistical analysis. Results: Both bleached groups exhibited a significant decrease in micro harness after bleaching with no statistically significant differences between them. Post bleaching diode laser irradiation at 2Watt and 4Watt resulted in significant increase in microhardness with no significant difference was evident between them. Conclusions: Diode laser irradiation on bleached enamel had a positive influence on surface microhardness of enamel and it may represent a promising post bleaching treatment modality.

Impact of Bioactive Glass-Based Toothpaste on Color Properties and Surface Microhardness of Bleached Enamel

Abstract Objective The role of toothpaste used during aesthetic treatments is rarely investigated. The objective was to evaluate the effects of a bioactive glass-based toothpaste (BGT) used before or after the dental bleaching with 35% hydrogen peroxide (HP). Materials and Methods Bovine enamel blocks (4 × 4 mm; n = 12) were submitted to tooth bleaching and different treatments/storage, before or after HP, based on: (1) no toothpaste and immersion in artificial saliva (AS) after HP for 24 hours, 7 days, or 14 days (control); (2) daily BGT use and AS storage for 7 or 14 days (after HP); and (3) daily BGT use and AS storage for 7 or 14 days (prior to HP). Surface and in-depth color were determined using the CIE L*a*b* system (ΔL*, Δa*, Δb*, and ΔE) on enamel surface and underlying dentin. The surface microhardness (SMH) was evaluated using a Knoop microhardness tester. Statistical Analysis Data were submitted to analysis of variance (ANOVA) (color variables), repeated measures ANOVA (SMH), and Tukey’s test (α = 0.05). Results The color changes on the enamel or underlying dentin were not statistically different among the groups (p > 0.05). Twenty-four hours after HP presented a decrease in SMH differing from baseline (p < 0.01). This decrease did not occur in the groups previously exposed to BGT (p > 0.05). BGT use after HP for 7 days differed from group with exclusive AS storage (p < 0.05). Conclusion In-office tooth bleaching can decrease the microhardness of enamel surface; however, the use of BGT promotes the protection or enables the mineral recovery of tooth without the influence the bleaching efficacy.

Impact of Two Remineralizing Agents on Bleached Enamel Microhardness

Objective: To evaluate the influence of fluoride varnish and casein phosphopeptide-amorphous calcium phosphate (CPP-ACP) on bleached enamel microhardness. Materials and Methods: Thirty human permanent incisors were selected to preparer thirty enamel specimens. All specimens were bleached using 40% hydrogen peroxide bleaching agent (power whiting YF). The bleached enamel samples were divided into three equal groups (n = 10) according to the used remineralizing agent. Group A was treated by CPP-ACP past (GC Tooth mousse), group B was treated by Fl varnish (Biflourid 10) and group C was stored in artificial saliva. The microhardness was assessed using Vicker test (before bleaching, after bleaching and after application of different remineralizing agents). The data was collected and statistically analyze using two-way ANOVA and post hock LSD test at (P< 0.05). Results: Enamel microhardness has diminished significantly in all groups after bleaching. After application of remineralizing agents, there was a significant increase in microhardness. There was no significant difference between groups A and B, while there was significant difference between these groups and group C. Conclusions: Using Bifluoride 10 , CPP-ACP or artificial saliva improves bleached enamel microhardness.

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

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. 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. 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). 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.

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.

Effect of Remineralizing Gels on Microhardness, Color and Wear Susceptibility of Bleached Enamel.

To evaluate the effect of a remineralizing gel combining fluoride and calcium silicate/phosphate or a sodium fluoride gel on bleached enamel microhardness, color, and wear susceptibility. Two hundred forty bovine enamel-dentin samples were prepared. Baseline analysis of Knoop microhardness, color coordinates (L*a*b*), and surface profile were performed. According to the baseline microhardness values, specimens were stratified into six groups (n=40): NC (negative control)-no treatment; BL (positive control)-bleaching with 40% hydrogen peroxide gel (Opalescence Boost, Ultradent); BL/Rs-bleaching + application of calcium silicate/phosphate gel (Regenerate Serum, Unilever - Rs); Rs/BL-Rs + bleaching; Rs/BL/Rs-Rs + bleaching + Rs; and BL/F-bleaching + 2% sodium fluoride gel. After the treatment described for each group, color change (ΔE) and microhardness were evaluated again. To evaluate abrasion susceptibility, samples were randomly divided into two subgroups, according to the toothpaste used (Cp-Close Up or Rt-Regenerate), and underwent 100,000 brushing strokes. The profile of each sample was evaluated and the mean wear calculated. The data were analyzed by ANOVA and Tukey tests. All bleached groups showed a significant reduction of microhardness in relation to the negative control. The groups treated with remineralizing gels showed a significantly higher microhardness and less wear than the positive control, although nonsignificant differences were observed among them. Nonsignificant differences in ΔE were found among bleached groups. The groups brushed with Regenerate toothpaste showed significantly less wear than those brushed with Close Up toothpaste. The remineralizing gels did not interfere with bleaching efficacy. However, all the treatments minimized the surface hardness reduction caused by the bleaching procedure and enamel loss after abrasion. Regenerate toothpaste resulted in less enamel abrasion.

The Effects of Tricalcium Phosphate and Novamin Remineralizing Agents on Microhardness of Bleached Enamel with 35% Hydrogen Peroxide-An In vitro Study

Objectives: The aim of the present study was to evaluated the effects of remineralizing agents (Tricalcium phosphate and Novamin) on microhardness of bleached enamel surface with 35% hydrogen peroxide (in office).Materials and Methods: Forty human permanent maxillary premolars free from caries or enamel malformation were used. The teeth were sectioned transversally across the cemento-enamel junction, and specimens were embedded in self-cure acrylic. The labial enamel surface faced upward and then they were ground flat and polished with silicon carbide abrasive papers. A total specimen were prepared and kept in deionized water. Then the specimens were drying subjecting them for baseline microhardness testing (control). The dental bleaching treatment was performed just on the labial enamel surface of the specimens using a commercial 35% hydrogen peroxide Whitness HP bleaching gel (in-office ).It was used according to the manufacture instruction. Microhardness was tested for all specimens after bleaching. Specimens were divided into two groups according to remineralizing agent n=20, Group I: Treated by NUPRO Sensodyne with NovaMin, Group II: Treated by Clinpro™ White Varnish Tri-Calcium Phosphate. The remineralizing agent was applied for three minutes per day. Two remineralizing agents were applied for fourteen consecutive days. After each application procedure, the specimens were washed with deionized water and then kept in artificial saliva. At the end of the fourteen days the remineralized specimens were subjected to microhardness testing and values were recorded. All the data were analyzed by ANOVA and Tukey’s post hoc test. Results: Results revealed that a statistically significant decrease on mean microhardness values after enamel bleaching compared to control, followed by a significant increase on mean microhardness after the application of the both remineralizing agents. One way-ANOVA showed a statistically insignificant difference between NUPRO Sensodyne with NovaMin and Clinpro™ White Varnish at p≥0.05.Conclusions: Based on the results of this in vitro study both Tricalcium phosphate and Novamin are effective in remineralization of bleached enamel surface and no significant difference was detected in their efficacy.

Effect of Fluoride Treatments on Bleached Enamel Microhardness and Surface Morphology.

To evaluate the effect of three different fluoride treatments on the surface microhardness and morphology of human enamel exposed to two different bleaching agents. Twenty-three extracted human third molars were sectioned to obtain 90 enamel fragments, mounted on acrylic resin supports, polished and randomly divided into 9 groups (n = 10). The specimens were exposed to a combination of two bleaching agents (22% carbamide peroxide [CP] and 38% hydrogen peroxide [HP]) and three fluoride treatments (0.05% NaF daily, 0.2% NaF weekly and 5% NaF final topical fluoridation). The positive control group specimens were not exposed to bleaching agents or fluoride treatments. The negative control group specimens were exposed to the bleaching agents but none of the fluoride treatments. All specimens were stored in artificial saliva during the entire experiment, and enamel microhardness was evaluated. Surface microhardness data were statistically analysed using two-way ANOVA and Tukey's post-hoc test at a significance level of α = 0.05. Additionally, three specimens of each experimental group were examined under SEM. Two-way ANOVA revealed significant differences between the experimental groups (p < 0.05). The bleached group specimens which did not receive fluoride treatment exhibited significantly lower microhardness than those treated with fluoride (p < 0.05). Varying degrees of surface changes were observed among the experimental groups. Both bleaching agents significantly reduced enamel microhardness and the topical fluoride treatments after bleaching significantly enhanced the surface microhardness of the enamel. The surface morphology of the enamel was altered after bleaching and fluoride treatments.

Effect of three nanobiomaterials on microhardness of bleached enamel.

ObjectivesThe aim of this in vitro study was to evaluate the effect of incorporating three different nanobiomaterials into bleaching material on microhardness of bleached enamel.Materials and MethodsThe crowns of 24 extracted sound human molars were sectioned. Sixty enamel specimens (2 × 3 × 4 mm) were selected and divided into five groups (n = 12): Group 1 received no bleaching procedure (control); Group 2 underwent bleaching with a 40% hydrogen peroxide (HP) gel; Groups 3, 4, and 5 were bleached with a 40% HP gel modified by incorporation of bioactive glass (BAG), amorphous calcium phosphate (ACP) and hydroxyapatite (HA), respectively. The enamel microhardness was evaluated. The differences in Knoop microhardness data of each group were analyzed by one-way ANOVA, followed by post hoc Tukey tests.ResultsSignificant differences were observed between the study groups. The enamel microhardness changes in Groups 1, 3, 4, and 5 were significantly lower than that of Group 2 (p < 0.001).ConclusionsWithin the limitations of this study, it can be concluded that incorporation of each one of the three tested biomaterials as remineralizing agents might be effective in decreasing enamel microhardness changes subsequent to in-office bleaching.

Changes in Bleached Enamel Microhardness After Application of Casein Phosphopeptide-Amorphous Calcium Phosphate (CPP-ACP) and Diode Laser:An in vitro study

Changes in Bleached Enamel Microhardness After Application of Casein Phosphopeptide-Amorphous Calcium Phosphate (CPP-ACP) and Diode Laser:An in vitro study

Evaluation of remineralization capacity of casein phosphopeptide-amorphous calcium phosphate on the carbamide peroxide treated enamel.

Objective:The aim of this study was to evaluate the potential of casein phosphopeptide-amorphous calcium phosphate (CPP-ACP) in remineralizing the bleached enamel surface using micro-hardness.Materials and Methods:Thirty human enamel slabs were randomly divided into three groups (n = 10). Groups A and B were exposed to 20% carbamide peroxide and 35% carbamide peroxide gel, respectively. After the exposure to the bleaching agent, the slabs were kept in artificial saliva for 1-week. Group C (control group) were kept in artificial saliva for 1-week. Vickers micro-hardness test was performed by Leica VMHT-Mot micro-hardness tester. CPP-ACP (Gc Tooth Mousse, Melbourne, Australia) was then applied to specimens of Groups A and B for 3 min for 2 weeks. Micro-hardness values of postbleach Group A (Ar) and Group B (Br) were recorded and statistically analyzed by paired t-test and one-way analysis of variance at the significance level of α =0.05.Results:There was a significant decrease in micro-hardness of enamel in carbamide peroxide bleached groups. However, there was a significant increase in micro-hardness after the remineralization by CPP-ACP and the extent of remineralization is more for the Group B.Conclusions:That bleaching agents reduced enamel micro-hardness and the use of CPP-ACP after bleaching can significantly enhance the micro-hardness of bleached enamel.

The Effect of McInnes Solution on Enamel and the Effect of GC Tooth Mousse on Bleached Enamel: AnIn VitroStudy

The aim is to evaluate the effect of McInnes bleaching agent on the microhardness of enamel before and after bleaching and to evaluate the effect of G C Tooth Mousse on the bleached enamel surface for its microhardness. The materials and methods used are McInnes bleaching solution, Casein phosphopeptide-amorphous calcium phosphate CCP-ACP (G C Tooth mousse) artificial saliva (Dept. of Oral Pathology, GDC Bellary), deionized water, Vickers’ Micro Hardness tester (Zwick/ZHV, Germany), freshly extracted teeth, cold cure acrylic, Diamond disc (Horico–PFINGST New Jersey, USA, KAVO-Germany), straight handpiece (kavopecareta) and plastic moulds (6.5 × 2 mm2). The purpose of this study was to evaluate and compare microhardness of the sound enamel surface by Vickers’ Hardness Number (VHN) before and after bleaching with McInnes solution, and to evaluate the effect of casein phosphopeptide amorphous calcium phosphate (G C Tooth Mousse) on the bleached enamel surface for its microhardness. The data obtained from the test were subjected for statistical analysis and are presented as range, mean and standard deviation. P value of 0.05 or less was considered for statistical significance. The changes in microhardness at different times of assessment were analyzed using the paired ‘t’ test. The results of all the samples showed decrease in the microhardness after two cycles of bleaching, though immediately after bleaching the decrease in the microhardness was not significant (P = 0.34). However, after the second cycles, it showed a significant decrease (P<0.01) in the microhardness. After application of remineralization solution (GC Tooth mousse), the samples showed a marginal increase in the microhardness (P<0.05) after seven days and a marked increase after fourteen days (P<0.001).McInnes bleaching agent does decrease the microhardness of enamel by causing enamel demineralization and GC Tooth mousse used in the study causes an increase in the microhardness of bleached enamel by maintaining a high gradient of calcium and phosphate ions at the enamel subsurface.

The effect of a new calcium‐based agent, Pro‐Argin, on the microhardness of bleached enamel surface

This study investigated the effects of Pro-Argin application on the microhardness of bleached enamel and compared them with those of acidulated phosphate fluoride (APF) and casein phosphopeptide-amorphous calcium phosphate (CPP-ACP) applications. Forty blocks (4 × 4 × 4 mm) were prepared from the facial surfaces of 10 sound bovine incisors. The enamel surfaces were bleached with 35% hydrogen peroxide three times at 5-day intervals. The specimens were divided into five treatment regimen groups (n = 8 each): Group 1, bleaching/no surface treatment (control); Group 2, bleaching/Pro-Argin toothpaste treatment; Group 3, bleaching/Pro-Argin treatment; Group 4, bleaching/APF treatment; and Group 5, bleaching/CPP-ACP treatment. During bleaching treatments, specimens were stored in artificial saliva. Vickers microhardness measurements were performed at baseline and after treatment in all groups. Statistical analyses were performed using the paired t-test, one-way analysis of variance, and post hoc least significant difference tests. After bleaching, hardness values of enamel surfaces increased significantly in the treatment groups versus the control group (p < 0.05). However, no significant difference was found among treatment groups (p > 0.05). Through bleaching treatment, Pro-Argin application may have a positive effect on enamel surface hardness, equivalent to that of CPP-ACP or APF.

The effect of Remin Pro®on bleached enamel hardness: An in-vitro study

Remineralization as a treatment procedure has received a lot of attention both from clinicians as well as researchers. The objective of this study was to assess the effect of Remin Pro® on enamel microhardness after bleaching the teeth with McInnes bleaching agent using Vickers microhardness tester. In this study, freshly extracted ten central incisors were taken which were subjected to baseline indentation by using Vickers microhardness indenter and then McInnes bleaching solution was applied for 5 min to demineralize these teeth. Remin Pro a newer remineralizing agent was applied for 7 days, which showed an increase in microhardness at the end of 7 days. The values were subjected for statistical analysis using paired t-test. All the samples showed a decrease in the microhardness after bleaching with McInnes solution. The decrease in mean hardness from baseline to demineralization was found to be statistically significant (P < 0.001). However, remineralizing the same tooth with Remin Pro for 7 days, showed an increase in hardness, which was found to be statistically significant (P < 0.05). McInnes bleaching agent decreases the microhardness of enamel and Remin Pro® used in the study causes an increase in the microhardness of bleached enamel.

Efficacy of a Novel At-home Bleaching Technique With Carbamide Peroxides Modified by CPP-ACP and Its Effect on the Microhardness of Bleached Enamel

This study was designed to evaluate in vitro the efficacy of a novel at-home bleaching technique using 10% or 16% carbamide peroxide modified by casein phosphopeptide-amorphous calcium phosphate (CPP-ACP) and its influence on the microhardness of bleached enamel. A total of 40 bovine incisors were divided into four groups (n=10) according to the bleaching agent used: 10% carbamide peroxide only; a blend of 10% carbamide peroxide and a CPP-ACP paste; 16% carbamide peroxide only; and a blend of 16% carbamide peroxide and a CPP-ACP paste. During the 14-day bleaching regimen, the samples were stored in artificial saliva. The Vickers microhardness and color of the teeth were assessed at baseline (T0) and immediately after the bleaching regimen (T14) using a microhardness tester and a spectrophotometer, respectively. The degree of color change was determined by the Commission Internationale de l'Eclariage (CIE) L*a*b* system (ΔE, ΔL*, Δa*, and Δb*) and Vita shade guide parameters. The data were analyzed by analysis of variance and the Tukey test (p<0.05). The teeth that were bleached with a blend of peroxide (10% or 16%) and the CPP-ACP paste presented increased microhardness values at T14 compared with T0, whereas the samples that were bleached with peroxide only did not show any differences in their microhardness values. All of the bleaching agents were effective at whitening the teeth and did not show a statistically significant difference using the CIEL*a*b* system (ΔE, ΔL*, Δa*, and Δb*) or the Vita shade guide parameters. The use of a CPP-ACP paste with carbamide peroxide bleaching agents increased the bleached enamel's microhardness and did not have an influence on whitening efficacy.

A novel at-home bleaching technique modified by a CPP-ACP paste

This study was designed to evaluate in vitro the efficacy of a novel at-home bleaching technique using 10% or 16% carbamide peroxide modified by casein phosphopeptide-amorphous calcium phosphate (CPP-ACP) and its influence on the microhardness of bleached enamel. A total of 40 bovine incisors were divided into four groups (n=10) according to the bleaching agent used: 10% carbamide peroxide only; a blend of 10% carbamide peroxide and a CPP-ACP paste; 16% carbamide peroxide only; and a blend of 16% carbamide peroxide and a CPP-ACP paste. During the 14-day bleaching regimen, the samples were stored in artificial saliva. The Vickers microhardness and color of the teeth were assessed at baseline (T0) and immediately after the bleaching regimen (T14) using a microhardness tester and a spectrophotometer, respectively. The degree of color change was determined by the Commission Internationale de l'Eclariage (CIE) L*a*b* system (ΔE, ΔL*, Δa*, and Δb*) and Vita shade guide parameters. The data were analyzed by analysis of variance and the Tukey test (p<0.05). The teeth that were bleached with a blend of peroxide (10% or 16%) and the CPP-ACP paste presented increased microhardness values at T14 compared with T0, whereas the samples that were bleached with peroxide only did not show any differences in their microhardness values. All of the bleaching agents were effective at whitening the teeth and did not show a statistically significant difference using the CIEL*a*b* system (ΔE, ΔL*, Δa*, and Δb*) or the Vita shade guide parameters. The use of a CPP-ACP paste with carbamide peroxide bleaching agents increased the bleached enamel's microhardness and did not have an influence on whitening efficacy.

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.