The effect of tooth bleaching on the bond strength of an experimental primer to enamel

This study evaluated the effect of tooth bleaching on the microtensile bond strength (μTBS) of an experimental primer to enamel. Materials used were an experimental tooth manicure system (Shofu) composed of primer and light-cured flowable resin composite. Flattened enamel surfaces of bovine teeth were bleached with Nite White Excel (Discus Dental) or Hi-Lite (Shofu), with nonbleached teeth used as a control group. Each bleaching group was subdivided into three bonding modes. These were group A, application of primer for 3 s, followed by 5 s of air blowing; group B, application of primer for 10 s, followed by 5 s of air blowing; and group C, application of 20% phosphoric acid for 10 s, spraying with water for 5 s, and then air blowing for 5 s. The flowable resin paste was placed and polymerized after each enamel surface treatment. Using a low-speed diamond saw, the specimens were sectioned into beam-shaped samples with a cross-sectional area of approximately 1 mm² at the bonded interface. The samples were subjected to the μTBS test with a 1.0 mm/min crosshead speed. Data were statistically analyzed using two-way analysis of variance (ANOVA) followed by the Bonferroni/Dunn post-hoc test. The two-way ANOVA revealed significant differences in the effects of the bleaching systems and bonding mode, and significant differences were also found for the interaction between them (P < 0.01). There were no statistically significant differences in μTBS values among the specimens in groups A and B regardless of bleaching or nonbleaching (P > 0.05). In contrast, the μTBS value of group C without bleaching was significantly higher than that of all other experimental groups (P < 0.01).     

冷光牙齿漂白技术对活髓牙牙髓影响的病理观察

目的 探讨冷光牙齿漂白技术对活髓牙牙髓的影响.方法 选择因正畸需要拔除的40颗活髓牙,对照组(10颗)不做任何处理拔除,其余30颗牙采用冷光漂白后分别即刻拔除(15颗)和漂白7 d后拔除(15颗).40颗牙齿均制作病理切片,镜下观察牙髓组织形态.结果 所有活髓牙漂白前后均未发现有任何临床症状.漂白后即刻拔除组、7 d后拔除组以及对照组在镜下均表现为正常的牙髓组织结构,与对照组相比漂白后即刻拔除组及7 d后拔除组牙髓组织均无明显改变.结论 冷光牙齿漂白技术对活髓牙牙髓无明显不良影响,是一项安全可靠的漂白技术.     

Effective tooth-bleaching protocols capable of reducing H2O2 diffusion through enamel and dentine

Objectives

To evaluate the effects of experimental protocols on bleaching effectiveness and hydrogen peroxide (HP) diffusion through enamel and dentine.

Methods

Enamel/dentine discs were subjected to six bleaching sessions, consisting of 1 or 3 applications of 17.5% or 35%-HP gel for 5/15 min, or 37% carbamide peroxide (CP) gel for 10/20 min. Discs undergoing the regular protocol (35%-HP; 3 × 15 min) constituted the positive control group. Colour change (ΔE) was assessed (CIE L*a*b* system) after each session. HP diffusion was quantified (sessions 1, 3, and 6) in enamel/dentine discs adapted to artificial pulp chambers. Data were analysed by Pillai's Trace and Bonferroni test, or by one-way ANOVA and SNK/Tamhane's test (α = 5%).

Results

All tooth-bleaching protocols significantly increased the ΔE values. A reduction in HP diffusion and no significant difference in ΔE compared with the positive control were observed for the following bleaching protocols: 17.5%-HP 3 × 15 min, at the 4th session; and 35%-HP 1 × 15 and 3 × 5 min, at the 5th session. HP diffusion in the 37%-CP 3 × 20 min bleaching protocol was statistically similar to that in the positive control. The other experimental bleaching protocols significantly decreased HP diffusion through enamel/dentine discs, but the ΔE values were statistically lower than those observed in the positive control, in all sessions.

Conclusion

Shortening the contact time of a 35%-HP gel or reducing its concentration produces gradual tooth colour change and reduced HP diffusion through enamel and dentine.

Clinical significance

A reduction in HP concentration, from 35% to 17.5%, in a bleaching gel or shortening its application time on enamel provides a significant tooth-bleaching improvement associated with decreased HP diffusion across hard dental tissues. Therefore, these protocols may be an interesting alternative to be tested in the clinical situation.     

Surface alteration of human tooth enamel subjected to acidic and neutral 30% hydrogen peroxide

Objectives

To investigate the effects of acidic and neutral 30% hydrogen peroxide (HP) on human tooth enamel in terms of chemical structure, mechanical property, surface morphology and tooth colour.

Methods

Twenty-seven human dental blocks were obtained from premolars and randomly divided into three groups (n = 9): Group acidic HP (30% HP, pH ≈ 3.6), Group neutral HP (30% HP, pH ≈ 7.0) and Group DW (distilled water, pH ≈ 6.8). Attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR), Raman spectroscopy, atomic force microscopy (AFM) investigation, microhardness test and colour measurements were carried out before and after treatments. ATR-FTIR and Raman spectroscopy were analysed and then the carbonate:mineral ratio (C:M), Raman absolute intensity (RAI), Raman relative intensity (RRI), and laser-induced fluorescence intensity (FI) were obtained for evaluation.

Results

The C:M, percentage microhardness and percentage RRI of group acidic HP decreased more significantly than those of group neutral HP (P = 0.02, P = 0.001, P < 0.001, respectively) and group DW (P = 0.01, P = 0.008, P < 0.001, respectively). Whilst group neutral HP and group DW had no statistical difference in above terms (P = 0.818, P = 0.528, P = 0.158, respectively). Significant morphological alterations were observed in group acidic HP. Group acidic HP and neutral HP had no significant difference in percentage FI (P = 0.652) and ΔE (P = 0.906).

Conclusions

This study suggested that neutral 30% HP had the same efficiency in tooth bleaching and it caused less deleterious effects on enamel than acidic 30% HP.     

三种家用牙齿漂白剂对牙釉质结构及其相关力学性能的影响

目的 研究3种不同质量分数的家用牙齿漂白剂对人牙釉质结构和力学性能的影响,为评价市售家用牙齿漂白剂的安全性提供依据.方法 将60块人牙釉质样本按随机数字化表法随机分至4组:10％过氧化脲组、15％过氧化脲组、20％过氧化脲组和蒸馏水对照组,每组15块.在漂白组样本表面涂布漂白剂并将其置于37℃恒温箱中,漂白8h后去净漂白剂,再将样本保存于蒸馏水中16 h;蒸馏水对照组不做漂白处理.如此循环14 d分别用原子力显微镜、衰减全反射红外测试仪、显微拉曼光谱仪、显微硬度仪检测各组漂白前后釉质表面形貌、化学结构及硬度、断裂韧性等力学特性.结果 3个漂白组的釉质与对照组相比没有出现表面形貌、均方根表面粗糙度(P=0.774)、红外光谱中v2 CO32-∶v1 v3 PO43-(P=0.263)和显微硬度(P=0.829)的明显变化;10％、15％、20％过氧化脲组相对拉曼强度漂白后相对于漂白前的百分比分别为(105.74±11.34)％、(104.46±8.83)％和(99.52±9.32)％,与对照组[(97.62±7.46)％]相比差异均无统计学意义(P=0.062);但3个漂白组荧光背景强度漂白后相对于漂白前的百分比分别为(20.86±7.23)％、(22.14±7.34)％和(21.10±7.59)％,与对照组[(100.78±3.70)％]相比差异均有统计学意义(P＜0.001).同时,3个漂白组与对照组相比断裂韧性漂白后下降值差异亦有统计学意义(P =0.024、P=0.005、P=0.013).结论 在体外环境下,3种质量分数的家用牙齿漂白剂不会影响牙釉质中的无机物和显微硬度,但可能会造成牙釉质断裂韧性下降.     

A comparative study on component volumes from outer to inner dental enamel in relation to enamel tufts

Background and aim

Dental enamel presents marked mechanical properties gradients from outer to inner enamel, a region lacking component volumes profiles. Tufts, structures of inner enamel, have been shown to play a role in enamel resilience. We aimed at comparing component volumes from inner to outer enamel in relation to enamel tufts.

Materials and methods

Transversal ground sections from the cervical half of unerupted human third molars (n = 10) were prepared and histological points were selected along transversal lines (extending from innermost to outer enamel) traced across tufts and adjacent control areas without tufts. Component volumes were measured at each histological point.

Results

Component volumes ranges were: 70.6–98.5% (mineral), 0.02–20.78% (organic), 3.8–9.8% (total water), 3–9% (firmly bound water), and 0.02–3.3% (loosely bound water). Inner enamel presented the lowest mineral volumes and the highest non-mineral volumes. Mineral, water and organic contents differed as a function of the distance from innermost enamel but not between the tuft and control lines. Tufts presented opaqueness in polarizing microscopy (feature of fracture lines). Organic volume gradient correlated with a relatively flat profile of loosely bound water. Inner, but not outer enamel, rehydrated after air-dried enamel was heated to 50 °C and re-exposed to room conditions, as predicted by the organic/water gradient profiles.

Conclusions

Component volumes vary markedly from outer to inner enamel, but not between areas with or without tufts (that behave like fracture lines under polarizing microscopy).     

High-efficiency tooth bleaching using non-thermal atmospheric pressure plasma with low concentration of hydrogen peroxide

Light-activated tooth bleaching with a high hydrogen peroxide (HP; H₂O₂) concentration has risks and the actual role of the light source is doubtful. The use of conventional light might result in an increase in the temperature and cause thermal damage to the health of the tooth tissue.

Objective:

This study investigated the efficacy of tooth bleaching using non-thermal atmospheric pressure plasma (NAPP) with 15% carbamide peroxide (CP; CH₆N₂O₃) including 5.4% HP, as compared with conventional light sources.

Material and Methods:

Forty human teeth were randomly divided into four groups: Group I (CP+NAPP), Group II (CP+plasma arc lamp; PAC), Group III (CP+diode laser), and Group IV (CP alone). Color changes (ΔE ) of the tooth and tooth surface temperatures were measured. Data were evaluated by one-way analysis of variance (ANOVA) and post-hoc Tukey''s tests.

Results:

Group I showed the highest bleaching efficacy, with a ΔE value of 1.92-, 2.61 and 2.97-fold greater than those of Groups II, III and IV, respectively (P<0.05). The tooth surface temperature was maintained around 37ºC in Group I, but it reached 43ºC in Groups II and III.

Conclusions:

The NAPP has a greater capability for effective tooth bleaching than conventional light sources with a low concentration of HP without causing thermal damage. Tooth bleaching using NAPP can become a major technique for in-office bleaching in the near future.     

Effect of home bleaching systems on enamel nanohardness and elastic modulus

Objectives

The purpose of this study was to evaluate the nanohardness and elastic modulus of human enamel after treatment with tray and strip bleaching systems.

Methods

Fifty-five human enamel samples were exposed to five different bleaching agents. Nanoindentations were made before and after bleaching treatments following the manufacturer's directions using a Nanoindenter XP (MTS Systems Corporation, Oak Ridge, TN, USA). Nanohardness and elastic modulus measurements were obtained and the results were statistically analyzed using a repeated measures analysis of variance with a post-hoc Tukey–Kramer multiple comparison test.

Results

Nanohardness and elastic modulus measurements showed decrease of mean values for each group except the control which remained the same. There were significant differences due to time (before and after treatment) and material effects in nanohardness (P < 0.0001) and elastic modulus (P = 0.0241). Measurements after treatment showed significant decrease in nanohardness between all groups and the control group. There was a significant difference in hardness between CP and TO after treatment. Additionally, there were significant differences in elastic modulus between the control group when compared to OB and TO after treatment. While there were significant changes in the elastic modulus due to treatment for both CP and TO, there were no significant differences between any of the groups after treatment.

Conclusions

Nanohardness and elastic modulus of human enamel were significantly decreased after the application of home-bleaching systems.     

Microabrasion in tooth enamel discoloration defects: three cases with long-term follow-ups

Superficial irregularities and certain intrinsic stains on the dental enamel surfaces can be resolved by enamel microabrasion, however, treatment for such defects need to be confined to the outermost regions of the enamel surface. Dental bleaching and resin-based composite repair are also often useful for certain situations for tooth color corrections. This article presented and discussed the indications and limitations of enamel microabrasion treatment. Three case reports treated by enamel microabrasion were also presented after 11, 20 and 23 years of follow-ups.     

Efficacy and oral side effects of two highly concentrated tray-based bleaching systems

The aim of this study was to investigate the tooth-whitening efficacy and oral side effects of the two tray-based bleaching systems Visalys whitening (VW) and Opalescence PF (OP). A stratified, randomised distribution of the subjects (n = 60) to two treatment groups was performed according to baseline tooth brightness (L* values) as determined by colourimeter and to the criteria smoker/non-smoker. Tooth colour was evaluated by measuring L*a*b* values generated from standardised digital image analysis with Adobe Photoshop of the facial surfaces of the right central maxillary incisor. Tooth hypersensitivity, with intensity graded from 0 (no hypersensitivity) to 10 (high hypersensitivity), was assessed chair-side using an air syringe. After bleaching therapy, both treatment groups demonstrated significant improvements in tooth colour (p < or = 0.05). A shift towards less yellow (-Deltab*) and brighter (+DeltaL*) tooth colour was observed. Deltab* was significantly higher in the OP group in comparison to the VW group, DeltaL* showed no significant difference between the both treatment groups (p < or = 0.05). After bleaching, the intensity of tooth hypersensitivity was increased significantly compared to baseline in both groups (p < or = 0.05), with no significant difference between the both groups. Both highly concentrated bleaching systems are effective as tooth-whitening systems, with few reported side effects such as transient tooth hypersensitivity.     

Safety controversies in tooth bleaching

Tooth bleaching using peroxide-based materials is an effective procedure in dentistry. Studies provide evidence on the safety of bleaching by dental professionals. However, concerns and controversy remain regarding the safety of bleaching systems that do not involve dental professionals, especially those available at mall kiosks, salons, spas, and cruise ships. Bleaching causes tooth sensitivity and/or gingival irritation in a significant portion of patients. Bleaching requires proper examination, diagnosis, and treatment plan, which can be performed appropriately only by dental professionals; therefore, involvement of dental professionals in bleaching is necessary to maximize the efficacy and minimize potential risks.     

The influence of two home-applied bleaching agents on enamel microhardness: an in situ study

OBJECTIVE: This in situ study evaluated the influence of two home-applied bleaching agents (10% carbamide peroxide and 7.5% hydrogen peroxide) on enamel microhardness. METHODS: Ninety enamel slabs were obtained from human third molars and baseline Knoop hardness measurements were recorded under a 50 g load for 5s. The specimens were attached to intra-oral devices delivered to 10 volunteers (donor of the teeth) who used the devices 24h/day throughout the experiment. The specimens were divided in three groups, two experimental and one control; in the last group, enamel slabs were not submitted to bleaching agents, but exposed only to the action of saliva. Two custom-made trays were made for each volunteer to recover the teeth and the appliances containing the enamel slabs. The bleaching regimen was 1h/day for 21 consecutive days. Subsequently, additional hardness measurements were recorded. RESULTS: The mean values of the baseline and final microhardness were: 348 and 352.2; 346.6 and 354.5; 342 and 340.8, for control, 10% carbamide peroxide and 7.5% hydrogen peroxide groups, respectively. One-way ANOVA of the microhardness mean values revealed no statistically significant differences among groups, the specimens treated with 7.5% hydrogen peroxide has shown a tendency (p=0.056) to microhardness decrease. CONCLUSIONS: Data suggested that the tested home bleaching agents did not change the superficial enamel microhardness.     

Assessing the use of 35 percent sodium ascorbate for removal of residual hydrogen peroxide after in-office tooth bleaching

BackgroundThe authors conducted a study to quantify the amount of hydrogen peroxide remaining after in-office bleaching and to investigate the effectiveness of 35 percent sodium ascorbate (SA) on removal of the bleaching agent from dentin.MethodsThe authors sectioned 70 extracted human third molars to form 4×4×2-millimeter blocks of dentin and then categorized them into eight groups as follows: group 1, no bleaching; group 2, bleaching (35 percent hydrogen peroxide) and daily measurement; group 3, bleaching plus one application of 35 percent SA for 60 minutes; group 4, bleaching plus one application of SA for 10 minutes; group 5, bleaching plus two applications of SA for 10 minutes each; group 6, bleaching plus two applications of SA for five minutes each; group 7, bleaching plus three applications of SA for one minute each; and group 8, bleaching plus two applications of SA for one minute each. They quantified the amount of residual hydrogen peroxide by using a colorimetric assay with horseradish peroxidase and o-phenylenediamine dihydrochloride as the enzyme and substrate, respectively.ResultsThe authors analyzed the data by using the Kruskal-Wallis test (α = .05). The results showed that no hydrogen peroxide remained after 120 hours in group 2 and at their respective measurement points in groups 5, 6, 7 and 8, whereas hydrogen peroxide had been removed only partially in groups 3 and 4.ConclusionTwo applications of 35 percent SA for one minute each produced the same result—complete removal of the bleaching agent—as that observed five days after tooth bleaching with 35 percent hydrogen peroxide without any application of SA.Clinical ImplicationsIn an appropriate concentration, SA facilitates rapid elimination of residual peroxide up to two minutes after bleaching with 35 percent hydrogen peroxide. This finding suggests that clinicians can perform bonding procedures shortly after the bleaching procedure.     

活髓牙漂白引起牙齿敏感的研究进展

漂白引起的牙齿敏感(BS)是活髓牙漂白最常见的不良反应,影响了患者接受漂白治疗的舒适度和满意度,也增加了临床对活髓漂白治疗安全性的担忧.本文旨在从BS的临床特点、病因学理论、可能的影响因素和防治措施作一综述.     

Surface morphology changes in human enamel, dentin and cementum following bleaching: a scanning electron microscopy study

Abstract Extracted human premolars were cut, cleaned and divided into 6 experimental groups. Each group was treated with one of the following bleaching materials: 30% hydrogen peroxide, 10% carbamide peroxide, sodium perborate, Nu-Smile, Opalescence and DentlBright. Morphological changes in tooth surface occurred following treatment with most bleaching agents. Hydrogen peroxide and DentlBright were associated with surface changes in all dental tissues. Hydrogen peroxide, DentlBright, Nu-Smile and Opalesceilce were mainly associated will) surface changes in the cementum, which exhibited more changes than the other tissues.     

Hydrogen peroxide induces cell proliferation and apoptosis in pulp of rats after dental bleaching in vivo: Effects of the dental bleaching in pulp

ObjectiveThis study provides an in vivo evaluation of the inflammatory response, levels of cell proliferation and apoptosis, and the presence of necrosis after dental bleaching with two concentrations of hydrogen peroxide (H₂O₂).DesignWistar rats were divided into Control (placebo gel), BLUE (20% H₂O₂, 1 × 50 min), and MAXX (35% H₂O₂, 3 × 15 min) groups. At 2 and 30 days, the rats were killed (n = 10). The jaws were processed for histology analysis and PCNA and Caspase-3-cleaved immunohistochemistry, and data were submitted to the Mann-Whitney or ANOVA test (P < 0.05).ResultsAt 2 days, the MAXX group showed necrosis and the BLUE group revealed moderate inflammation on the occlusal third of the crown (P < 0.05). At 30 days, tertiary dentin had formed and there was an absence of inflammation. The level of cell proliferation was higher in the middle third of the BLUE group (P < 0.05), and cervical of MAXX at 2 days (P < 0.05), decreasing at 30 days. The apoptosis was present at 2 days, particularly in the cervical third of the crown in the bleached groups (P < 0.05), with a decrease only at 30 days in the BLUE group (P < 0.05).ConclusionsThe concentration of H₂O₂ influences effects on the pulp tissue, where a higher concentration of H₂O₂ can cause necrosis in the pulp and a prolonged effect within the apoptotic process; lower concentrations of H₂O₂ provide moderate inflammation, cell proliferation and apoptosis with a reduction of these processes over time.     

Changes in enamel surface roughness and adhesion of Streptococcus mutans to enamel after vital bleaching

Objectives. The purpose of this in vitro study was to observe the influence of vital bleaching on changes to the enamel surface and adhesion of Streptococcus mutans to tooth enamel.

Methods. The coronal part of each of 70 extracted third molars was cut in half, with either the buccal or lingual half used for experiments or controls. Experimental halves were assigned to the following conditions: (A) enamel was bleached 1, 3 or 5 times using a bleaching material with or without etching; or (B) etched condition without bleaching. All control samples were kept intact in physiological saline solution. Surface roughness (Ra; roughness center-line average: μm) of enamel was measured for 35 pairs of specimens. TS broth culture medium containing 3% glucose was inoculated with S. mutans and cultured for 72 h before adding the other 35 pairs of specimens. Under scanning electron microscopy, the number of S. mutans colonies was counted and statistically analysed.

Results. Compared to controls, bleached enamel displayed increased colonies of S. mutans. Repeated bleaching further increased bacterial adhesion and maximal colonies counts were found under conditions of five bleaching treatments plus etching (p≤0.01). Compared to controls, roughness increased after etching. However, no linear correlation was found between number of S. mutans colonies and roughness.

Conclusion. We conclude that both surface roughness and adhesion of S. mutans to the enamel surface increase after bleaching.     

Separate contribution of enamel and dentine to overall tooth colour change in tooth bleaching

Objectives

The aim of this study was to evaluate the separate contribution of enamel (E) and dentine (D) to the colour change of tooth which subjected to 10% carbamide peroxide (CP) gels using a novel recombined enamel–dentine (Recombined-ED) study model.

Methods

120 enamel–dentine (ED) samples (four homogeneous premolar ED from each patient; total = 30 × 4 ED) were involved in the present study. Two homogeneous ED samples were bleached with 10% CP and the other two ones were stored in artificial saliva for one, two or four weeks. After treatment, four kinds of layers were prepared from each four homogeneous ED samples by removing enamel or dentine part: bleached-enamel (BE), bleached-dentine (BD), control-enamel (CE) and control-dentine (CD). Initial and final colour records of samples were taken with a spectrophotometer in CIELab system. The contribution of enamel/dentine to the colour change of tooth (CTCC) was calculated by measuring the colour difference ΔE between two different enamel–dentine combinations (ΔE between BE/BD and CE/BD for enamel; ΔE between BE/BD and BE/CD for dentine). Translucency parameter (TP) was obtained by calculating the colour difference between enamel on black and white backings.

Results

ED and recombined-ED were significantly correlated in L^*a^*b^* values both for unbleached samples and bleached samples. Bleaching resulted in a significant colour change (ΔE) of E, D and ED samples. The TP of BE was significantly lower than that of CE. The CTCC of enamel was significantly higher than that of dentine all through the time points.

Conclusions

Enamel played a more important role than dentine in tooth bleaching due to the changes in translucency and colour.