The effect of carbamide peroxide bleaching agents on the microhardness of dental ceramics

This study examined the effect of 10% and 16% carbamide peroxide bleaching agents on the surface microhardness of micro-particulate feldspathic ceramics (VM7 and VM13, Vita Zahnfabrik). Forty specimens (8-mm diameter, 2-mm thickness) were divided into four groups (n=10): GI-VM7 + 10% Whiteness, G2-VM7 + 16% Whiteness, G3-VM13 + 10% and G4-VM13 + 16% Whiteness. The home-use bleaching agents were applied for 8 hours on 15 days, and the specimens were stored in distilled water at 37 degrees C. The Vickers hardness number (HV) was determined for each specimen. Data were analyzed by the Wilcoxon and Mann-Whitney tests (p < 0.05). The microhardness values before exposure were: g1-433 (57); g2-486 (22); g3-509 (28); g4-518 (24), and after exposure: G1-349 (32); G2-496 (95); G3-519 (38); G4-502 (81). G2 exhibited a higher and significant difference than GI in VM7 groups, and the effect of bleaching concentration was shown to be significant by the Mann-Whitney test. And for VM13, both the Wilcoxon and Mann-Whitney tests showed no significant differences. When using 10% carbamide peroxide, the microhardness of VM7 ceramic was affected, and there were no effect on the microhardness between VM7 and VM13 ceramics when 16% carbamide peroxide was used.     

Extended at-home bleaching of tetracycline-stained teeth with different concentrations of carbamide peroxide.

OBJECTIVE: The degree of color change and the dental sensitivity associated with the use of different concentrations (10%, 15%, and 20%) of carbamide peroxide every night for 6 months was evaluated in tetracycline-stained teeth. METHOD AND MATERIALS: Fifty-nine subjects were shown how to place two different concentrations of carbamide peroxide in the custom trays with reservoirs. For a period of 6 months, the patients were to insert the tray every evening before retiring. Patients returned in 1 and 2 weeks and at 1, 2, 3, 4, 5, 6, 7, 8, and 9 months for evaluation of the degree of color change by subjective shade matching and by photographic means. Sensitivity of hard or soft tissues was self-reported. RESULTS: Fifty-two subjects attended more than 90% of the recalls. A colorimeter was used to convert shade guide tabs to Commission Internationale de l'Eclairage color spaces (CIELAB). The most rapid whitening occurred in the first month. At 3 and 9 months, 91% and 85% of the subjects, respectively, were at least "a little pleased" with the results of the bleaching. In the professional evaluation, 90% of the teeth were deemed to have an excellent or satisfactory esthetic result. The higher the concentration of carbamide peroxide, the more rapidly the lightness value and color difference changed. There was no difference among the three concentrations in resulting gingival sensitivity. Patients experienced less tooth sensitivity with 10% gel than they did with 15% and 20% gels. CONCLUSION: Bleaching with 10%, 15%, and 20% carbamide peroxide is effective for removing tooth staining caused by tetracycline. The 10% concentration has the most advantages and the fewest disadvantages.     

3种浓度过氧化脲漂白剂对牙科陶瓷表面粗糙度的影响

目的评估3种浓度过氧化脲漂白剂对牙科陶瓷表面粗糙度的影响。方法 80个瓷块按随机数字表法分成4组。A、B、C组所有瓷块进行为期3周,每天8 h的漂白,A组漂白剂为质量分数10%的过氧化脲,B组为质量分数15%的过氧化脲,C组为质量分数20%的过氧化脲;D组为空白对照组,浸泡于人工唾液里。表面粗糙度仪测量所有样本初始时和漂白1 d、2 d、3 d、1周、2周、3周后的瓷块表面粗糙度,并进行统计学分析。结果 A、B、C、D 4组瓷块的初始表面粗糙度分别为（0.073±0.003）μm、（0.073±0.002）μm、（0.072±0.003）μm、（0.074±0.003）μm,3周后的粗糙度分别为（0.073±0.004）μm、（0.073±0.005）μm、（0.074±0.006）μm、（0.074±0.005）μm。7个时间点,4组组间和组内表面粗糙度差异均无统计学意义（P＆gt;0.05）。结论 3种浓度过氧化脲漂白剂对牙科陶瓷表面无明显不良影响。     

Spectrophotometric and visual evaluation of vital tooth bleaching employing different carbamide peroxide concentrations.

OBJECTIVE: The aim of the present study was to assess the hypothesis that the efficiency of vital tooth bleaching depends on the concentration of carbamide peroxide agents. METHODS: The front teeth of 30 subjects were bleached at home with 10%, 17% or 0% (control) carbamide peroxide for 1 week in a double-blind study design. Tooth shades were determined in the LCH color space employing a visual shade matching system and a spectrophotometer. Differences in lightness (Deltal), chroma (Deltac) and hue (Deltah) were measured to assess the treatment process. After 2 weeks of no treatment, tooth shades were evaluated again to assess stability of the resultant shade. RESULTS: First-time changes of shade values could be observed after 3 days in the 17% group and after 7 days in the 10% group. After 1 week, in both the 17% group (Deltal: 2.80, Deltac: -3.33, Deltah: 0.60) and the 10% group (Deltal: 2.61, Deltac: -2.54, Deltah: 0.09), values for lightness and chroma were significantly different from the control (Deltal: 0.13, Deltac: 0.14, Deltah: 0.21, p<0.05) with no difference between the test groups (p>0.05). Two weeks after treatment, a rebound of shade values could be observed in the test groups (p<0.05). SIGNIFICANCE: The study indicates that higher concentration bleaching agents might whiten teeth faster with major changes in lightness and chroma. However, by bleaching daily for 1 week, similar effects can be achieved with both a high and a low concentration agent. After treatment, a regression of the resultant shade has to be expected.     

过氧脲素漂白剂对牙釉质表面特性的影响

目的：观察１０％～３０％过氧脲素漂白剂对牙釉质表面特性的影响。方法：选用正畸拔除的健康前磨牙，经１０％、１５％、３０％过氧脲素漂白剂处理１５ｄ后，采用显微硬度测定仪、电子显微镜等手段检查。结果：１０％、１５％、３０％过氧脉素漂白剂对牙釉质表面硬度无降低作用，与对照组（ＨＶ：５８１．９±１１７．５）无明显差异；扫描电镜显示，牙釉质经漂白显现较光滑外观，无腐蚀、溶解现象。结论：１０％～３０％过氧脉素漂白剂对牙釉质表面结构无破坏作用。     

Effectiveness of different carbamide peroxide concentrations used for tooth bleaching: an in vitro study

Objectives

This in vitro study evaluated the effectiveness of three carbamide peroxide concentrations used for tooth bleaching treatments.

Material and Methods

Sixty bovine dental slabs (6x6x3 mm) were obtained, sequentially polished, submitted to artificial staining (baseline) and randomized into four groups (n=15), according to the bleaching agent concentration: distilled water (control), 10% (CP10), 16% (CP16) or 37% (CP37) carbamide peroxide. CP10 and CP16 were covered with 0.2 mL of the respective bleaching gels, which were applied on enamel surface for 4 h/day during two weeks. Samples of CP37 were covered with 0.2 mL of the bleaching gel for 20 min. The gel was light activated by two 40-s applications spaced by 10-min intervals. The gel was renewed and applied 3 times per clinical session. This cycle was repeated at 3 sessions with 5 days of interval between them. Tooth shade evaluations were done with a digital spectrophotometer at T0 (baseline), T1 (after 1-week of treatment) and T2 (1-week post-bleaching). Tooth shade means were statistically analyzed by Kruskal-Wallis and Friedman''s tests and color parameters were analyzed by two-way ANOVA and Tukey''s test (p<0.05).

Results

At T1 and T2 evaluations, tooth shade was significantly lighter than at baseline for all treatment groups, considering the color parameters ΔL*, Δa*, Δb*, ΔE* (p<0.001) or tooth shade means (p<0.001). CP37 group showed lower shade mean change than CP10 and CP16 at T1 (p<0.01), but this difference was not statistically significant at T2 (p>0.05).

Conclusions

One week after the end of the treatment, all carbamide peroxide concentrations tested produced similar tooth color improvement.     

过氧化脲漂白凝胶对牙釉质光学性质的影响

目的　探讨过氧化脲漂白凝胶对牙釉质光学性质的影响。方法　采用Opalesence10 %过氧化脲凝胶在 40颗离体前磨牙上作家庭漂白实验。漂白前测出各牙釉质的最大透光度及此时的可见光波长λ 。在漂白 2周、4周、再矿化 1周 ,分别测出可见光波长λ 时牙釉质的透光度。结果　漂白前λ =72 1nm时 ,牙釉质透光度最大 ,为 2 5 .7%。漂白前透光度 (2 5 .7% )与漂白 2周的透光度 (37.9% )及漂白 4周透光度 (39.2 % )与再矿化 1周的透光度 (4 8.4% )有极显著性差异 (P <0 .0 0 1) ,而漂白 2周与漂白 4周的透光度无显著性差异 (P >0 .0 5 )。结论过氧化脲漂白凝胶使牙釉质透光性增强 ,脱色与脱矿作用并存 ,再矿化处理能提高及稳定漂白效果。     

Effects of bleaching with carbamide peroxide gels on microhardness of restoration materials

The objective of this in vitro study was to quantitatively assess the effects of bleaching with 10 and 15% carbamide peroxide (CP) on restoration materials by performing superficial microhardness analysis. Acrylic cylindrical containers (4 x 2 mm) were filled with the following restoration products: Charisma (Heraues Kulzer, Vila Santa Catarina, S?o Paulo, Brazil), Durafill VS (Heraeus Kulzer), Vitremer (3M, Sumaré, S?o Paulo, Brazil), Dyract (Dentsply, Petrópolis, Rio de Janeiro, Brazil), and Permite C (SDI, S?o Paulo, S?o Paulo, Brazil). Sixty samples were prepared of each restoration material. Twenty samples received bleaching treatment with 10% CP, 20 samples received bleaching treatment with 15% CP, and 20 samples were kept submerged in artificial saliva, which was replaced daily. The treatment consisted of immersion of the specimens in 1 cm3 of CP at 10 and 15% for 6 hours per day during 3 weeks, whereupon the test specimens were washed, dried, and kept immersed in artificial saliva for 18 hours. Then the test and control specimens were analyzed using a microhardness gauge. The Knoop Hardness Number (KHN) was taken for each test and control specimen at five different locations by applying a 25 g force for 20 seconds. The values obtained were transformed into KHNs and the mean was calculated. The data were submitted to statistical analysis by analysis of variance and Tukey test, p < .05. The means/standard deviations were as follows: Charisma: CP 10% 38.52/4.08, CP 15% 34.31/6.13, saliva 37.36/4.48; Durafill VS: CP 10% 18.65/1.65, CP 15% 19.38/2.23, saliva 18.27/1.43; Dyract AP: CP 10% 30.26/2.81, CP 15% 28.64/5.44, saliva 33.88/3.46; Vitremer: CP 10% 28.15/3.04, CP 15% 17.40/3.11, saliva 40.93/4.18; and Permite C: CP 10% 183.50/27.09, CP 15% 159.45/5.78, saliva 215.80/26.15. A decrease in microhardness was observed for the materials Dyract AP, Vitremer, and Permite C after treatment with CP at 10 and 15%, whereas no effect on either of the two composites (Charisma and Durafill) was verified. CLINICAL SIGNIFICANCE The application of the carbamide peroxide gels at 10 and 15% did not alter the microhardness of the composite resins Charisma and Durafill. In situ and clinical studies are necessary to enable one to conclude that the reduction in microhardness of the materials effectively results in clinical harm to the restorations.     

Factors affecting mercury release from dental amalgam exposed to carbamide peroxide bleaching agent

PURPOSE: To assess, in vitro, the effects of aging and surface polishing on mercury release from dental amalgams exposed to 10% carbamide peroxide at two pH levels. METHODS: Samples of fresh and aged amalgam, polished and unpolished, were treated with 10% carbamide peroxide at pH 4.5 and at pH 6.5 for periods of 1, 4, 7, 10 and 13 days. At each time period, mercury concentrations in solution were measured using a cold-vapor atomic absorption mercury analyzer system and compared to control samples treated with phosphate buffer. RESULTS: Amalgam samples exposed to 10% carbamide peroxide released significantly more mercury in solution than samples exposed to phosphate buffer controls. Mercury release was time-dependent and significantly higher in aged amalgam than in fresh amalgam (P < 0.001). Mercury release was also pH-dependent and higher in unpolished amalgam.     

High-concentrated carbamide peroxide bleaching agents effects on enamel surface

Concern has been expressed regarding the adverse effects of peroxide-containing tooth bleaching agents on enamel surface. This study examined enamel average surface roughness before (baseline) and after an in-office bleaching protocol and investigated the influence of high concentrations of carbamide peroxide gels on its surface staining and morphology. Flat enamel surfaces were submitted to 35 and 37% carbamide peroxide or to no bleaching treatment (n = 10) and evaluated with a profilometer. Eight specimens from each group were randomly selected and immersed in a 2% methylene blue solution. Afterwards, specimens were ground into powder and prepared for the spectrophotometric analysis. Two remained specimens of each group were examined using a scanning electron microscope. Data were subjected to analysis of variance and Tukey test (P > 0.05). Baseline roughness average was statistically similar for all groups, however, 35% carbamide peroxide produced the roughest enamel surfaces. Different concentrations of carbamide peroxide produced similar staining means and enamel surface morphological alterations.     

Effects of two 10% peroxide carbamide bleaching agents on dentin microhardness at different time intervals.

OBJECTIVE: The purpose of this in vitro study was to evaluate the microhardness of human dentin exposed to two 10% carbamide peroxide agents at different bleaching times. METHOD AND MATERIALS: Opalescence 10% and Rembrandt 10% were tested. A placebo agent was used as a control group. The bleaching and placebo agents were applied to the surface of human dentin fragments for 8 hours and then stored in individual receptacles with artificial saliva for the remaining 16 hours each day. Microhardness testing was performed at baseline, after 8 hours, 7, 14, 21, 28, 35, and 42 days of treatment, and 7 and 14 days posttreatment. RESULTS: Analysis of Variance and the Tukey test revealed significant differences in microhardness values for dentin treated with the agents within each time interval. There was a decrease in the microhardness values of dentin for both bleaching agents after 8 hours of treatment. Fourteen days after the completion of treatment, the microhardness values for dentinal surfaces treated with either Opalescence or Rembrandt reached the baseline values; the dentinal surfaces treated with a placebo exhibited an increase in microhardness values posttreatment. CONCLUSION: Ten percent carbamide peroxide bleaching agents decreased dentinal microhardness over time, but after 14 days in artificial saliva storage at the completion of treatment, the baseline microhardness values were recovered.     

Higher-concentration carbamide peroxide effects on surface roughness of composites

Background: Ten percent carbamide peroxide has been used extensively within the dental profession for the purpose of bleaching teeth. Although this method has been successful, the use of higher-concentration carbamide peroxides (20–35%) for home bleaching has increased substantially in the past few years. The purpose of this study was to evaluate changes in surface roughness of a hybrid and a microfilled composite after exposure to bleaching agents containing higher concentrations of carbamide peroxide.
Materials and Methods: Sixty-eight circular, resin-based composite specimens (8 mm ± 2 mm) were prepared against a Mylar surface. Half of the specimens were fabricated from a hybrid composite material and the other half with a microfilled composite. Specimens were polished with aluminum oxide finishing disks, divided into four groups, and then exposed either to 20% carbamide peroxide for 3 hours per day for 14 days or to 35% carbamide peroxide for 1 hour per day for 14 days. The mean surface roughness (Ra) was determined for each specimen before and after exposure to bleaching agents, using mechanical profilometry. Data were analyzed by two-way analysis of variance (ANOVA) for differences between composite type, carbamide peroxide concentrations, and interaction of the two factors with respect to average surface roughness. All data analysis was performed at α= 0.05.
Results: Mean change from baseline of surface roughness (R_a) of microfilled composite and 20% carbamide peroxide was −0.03 μm ± 0.10 um; microfilled composite and 35% carbamide peroxide: 0.01 pm ± 0.02 um; hybrid composite and 20% carbamide peroxide: −0.43 um ± 0.91 um; hybrid composite and 35% carbamide peroxide: −0.19 pm ± 0.43 pm. Surface roughness of hybrid or microfilled composite did not change significantly from baseline with either concentration of carbamide peroxide ( p = .300).