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

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Clinical Evaluation of the Effectiveness of Different Bleaching Therapies in Vital Teeth

The aims of this in vivo study were to compare the effectiveness and color stability of at-home and in-office bleaching techniques and to evaluate whether the use of light sources can alter bleaching results. According to preestablished criteria, 40 patients were selected and randomly divided into four groups according to bleaching treatment: (1) at-home bleaching with 10% carbamide peroxide, (2) in-office bleaching with 35% hydrogen peroxide (HP) without a light source, (3) in-office bleaching with 35% HP with quartz-tungsten-halogen light, and (4) in-office bleaching with 35% HP with a light-emitting diode/laser. Tooth shade was evaluated using the VITA Classical Shade Guide before bleaching as well as after the first and third weeks of bleaching. Tooth shade was evaluated again using the same guide 1 and 6 months after the completion of treatment. The shade guide was arranged to yield scores that were used for statistical comparison. Statistical analysis using the Kruskal-Wallis test showed no significant differences among the groups for any time point (P > .01). There was no color rebound in any of the groups. The bleaching techniques tested were equally effective. Light sources are unnecessary to bleach teeth. (Int J Periodontics Restorative Dent 2012;32:303-309.)

Effect of Sodium Ascorbate on Tag Formation in Bleached Enamel

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Enamel microabrasion followed by dental bleaching for patients after orthodontic treatment - Case reports

This article reports clinical procedures used to remove residual bonded resin and enamel stains following bracket debonding at the conclusion of orthodontic treatment. A water-cooled fine-tapered diamond bur was used for resin removal, followed by enamel surface finishing using a commercially available microabrasion paste. It was noted that residual tooth coloration remained yellowish because of enamel translucency; the yellow dentin shade showed through. Additional tooth shade lightening was achieved using carbamide peroxide dental bleaching solution in custom-formed trays. This report describes a safe and effective technique that optimizes tooth appearance at the conclusion of orthodontic therapy. Mechanical resin removal, enamel microabrasion, and tooth bleaching are employed.

The influence of time interval between bleaching and enamel bonding

Objectives: the purpose of this study was to investigate the penetration of a conventional adhesive material into enamel bleached with 16% carbamide peroxide and 38% hydrogen peroxide using optical light microscopy.Methods: Extracted human teeth were randomly divided into eight experimental groups with six specimens each, according to the bleaching material and time interval after bleaching and before the bonding procedure. Groups were designated as follows: control group, restorations in unbleached teeth; restorations performed immediately after bleaching; restorations performed 7 days after bleaching; restorations performed 14 days after bleaching; and restorations performed 30 days after bleaching. The length of resin tags was measured with an Axiophot photomicroscope at 400x magnification for the calculation of the proportion of tags of study groups compared to the respective control groups. Analysis of variance was applied for comparison between groups; data were transformed into arcsine (p < 0.05).Results: the specimens of experimental groups, in which restorations were performed 7, 14, and 30 days after bleaching, showed better penetration of adhesive material into enamel than specimens restored immediately after bleaching. There was no statistically significant difference between the bleaching materials employed or in the interaction between bleaching agent and time interval.Conclusions: This suggests that a time interval of at least 7 days should be allowed between enamel bleaching and placement of adhesive bonding agents for accomplishment of composite resin restorations.

Color alteration in teeth subjected to different bleaching techniques

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Transdentinal protective role of sodium ascorbate against the cytopathic effects of H2O2 released from bleaching agents

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Ex vivo evaluation of the effectiveness of bleaching agents on the shade alteration of blood-stained teeth

Aim To evaluate ex vivo effectiveness of the three formulations of bleaching materials for intracoronal bleaching of root filled teeth using the walking bleach technique.Methodology Extracted premolar teeth were stained artificially with human blood. After biomechanical preparation, the root canals were filled and a 3-mm thick intermediate base of zinc phosphate cement was placed at the level of the cementoenamel junction. The teeth were divided into four groups (n = 12): C (control, without bleaching material), A1 (sodium perborate + distilled water), A2 (sodium perborate + 10% carbamide peroxide) and A3 (sodium perborate + 35% carbamide peroxide). The bleaching materials were changed at 7 and 14 days. Evaluation of shade was undertaken with aid of the VITA Easyshade (TM) (Delta E*ab) and was performed after tooth staining and at 7, 14 and 21 days after bleaching, based on the CIELAB system. Data were analysed by ANOVA for repeated measurements, Tukey and Dunnett tests (alpha = 0.05).Results The Tukey test revealed that group A1 (10.58 +/- 4.83 Delta E*ab) was statistically different from the others (A2, 19.57 +/- 4.72 Delta E*ab and A3, 17.58 +/- 3.33 Delta E*ab), which were not different from each other. At 7 days: A1 was significantly different from A2; at 14 and 21 days: A2 and A3 were significantly better than A1; the Dunnett test revealed that the control group was different from A1, A2 and A3 at all periods (P < 0.05).Conclusion Sodium perborate associated with both 10% and 35% carbamide peroxide was more effective than when associated with distilled water.

Effect of Sodium Ascorbate and the Time Lapse before Cementation after Internal Bleaching on Bond Strength between Dentin and Ceramic

Purpose: To evaluate the effects of the elapsed time (ET) after nonvital bleaching (NVB) and sodium ascorbate application (10%) (SAA) on the shear bond strength of dentin to ceramic.Materials and Methods: Bovine incisors were selected, internally bleached (35% carbamide peroxide) for 9 days and submitted to the following treatments (n = 10): G1, G2, G3-luting after 1, 7, and 14 days; G4, G5, and G6-luting after SAA, 1, 7, and 14 days, respectively. G7 and G8 were not bleached: G7-luting 24 hours after access cavity sealing; G8-luting 24 hours after access cavity sealing after SAA. After NVB, the vestibular dentin was exposed and flattened. The SAA was applied to the dentin (G4, G5, G6, G8) for 10 minutes, and it was then washed and dried. The dentin was etched (37% phosphoric acid), and an adhesive system (Single Bond 2) was applied. Feldspathic ceramic discs (VM7; 4-mm diameter, 3-mm thick) were luted with a dual-resin agent (RelyX ARC, 3M ESPE Dental Products, St. Paul, MN). After 24 hours, specimens were submitted to shear test on a universal testing machine. The data (MPa) were submitted to ANOVA and Dunnet's test (5%).Results: The means (+/- SD) obtained were (MPa): G1 (14 +/- 4.5), G2 (14.6 +/- 3.1), G3 (14 +/- 3.7), G4 (15.5 +/- 4.6), G5 (19.87 +/- 4.5), G6 (16.5 +/- 3.7), G7 (22.8 +/- 6.2), and G8 (18.9 +/- 5.4). SAA had a significant effect on bond strength (p = 0.0054). The effect of ET was not significant (p = 0.1519). G5 and G6 presented higher values than the other bleached groups (p < 0.05) and similar to G7 and G8 (p > 0.05).Conclusions: After NVB, adhesive luting to dentin is recommended after 7 days if sodium ascorbate has been applied prior to dentin hybridization.

Influence of surfactants on the effectiveness of bleaching gels

This study evaluated the influence of surfactants on the effectiveness of 35% hydrogen peroxide (HP) and 10% carbamide peroxide (CP) bleaching gels. One hundred and forty bovine teeth were used, which were stained by immersion in a coffee, red wine, and tobacco mixture for 7 days. At the end of this process, the color measurement at baseline was taken with the Vita Easyshade spectrophotometer. The teeth were divided into seven groups: (a) negative control (NC), (b) positive control for HP (PC-35), (c) HP + Tween 20 (T20-35), (d) HP + laurel sodium sulfate (LSS-35), (e) positive control for CP (PC-10), (f) CP + Tween 20 (T20-10), and (g) CP + laurel sodium sulfate (LSS-10). Group NC was kept in artificial saliva for 21 days. Groups PC-35, T20-35, and LSS 35 received three applications of bleaching gel for 10 min; the process was repeated after 7 days. Groups PC-10, T20-10, and LSS-10 received the gel for 8 h per day for 14 days. After the bleaching process, the final color was measured. The analysis of variance and Tukey tests showed statistically significant differences for the parameters of a dagger L, a dagger b, and a dagger E of the HP gels with surfactant and positive control group (PC-35). Within the limits of this in vitro study, the addition of surfactants to HP bleaching gel increased the bleaching effectiveness.

Effect of bleaching on the cemento-enamel junction

Purpose: To evaluate the effect of various bleaching agents on the cemento-enamel junction (CEJ) of human teeth by scanning electron microscopy (SEM) analysis. Methods: 30 intact teeth were selected and longitudinally sectioned, yielding 60 specimens. Thirty specimens served as controls; the other 30 were divided into six groups with five specimens each (n= 5) and bleached according to six protocols (Group 1: External bleaching with 10% carbamide peroxide; Group 2: External bleaching with 35% hydrogen peroxide; Group 3: External bleaching with 35% hydrogen peroxide; Group 4: Internal/external bleaching with 35% hydrogen peroxide; Group 5: Internal/external bleaching with 35% hydrogen peroxide; and Group 6: Intracoronal bleaching with a paste of sodium perborate mixed with 9% hydrogen peroxide). After treatment the specimens were prepared and examined in a scanning electron microscope. Results: the bleaching agents used in this study caused morphological changes in the CEJ and increased dentin exposure.

Effect of whitening agents on dentin bonding

Background: Several studies have shown a reduction in enamel bond strengths when the bonding procedure is carried out immediately after vital bleaching with peroxides. This reduction in bond strengths has become a concern in cosmetic dentistry with the introduction of new in-office and waiting-room bleaching techniques. The aim of this in vitro study was to evaluate the effect of three bleaching regimens: 35% hydrogen peroxide (HP), 35% carbamide peroxide (CP), and 10% CP, on dentin bond strengths. Materials and Methods: One hundred and twenty fresh bovine incisors were used in this study. The labial surface of each tooth was ground flat to expose dentin and was subsequently polished with 600-grit wet silicon carbide paper. The remaining dentin thickness was monitored and kept at an average of 2 mm. The teeth were randomly assigned to four bleaching regimens (n = 30): (A) control, no bleaching treatment; (B) 35% HP for 30 minutes; (C) 35% CP for 30 minutes; and (D) 10% CP for 6 hours. For each group, half of the specimens (n = 15) were bonded with Single Bond/Z100 immediately after the bleaching treatment, whereas the other half was bonded after the specimens were stored for 1 week in artificial saliva at 37°C. The specimens were fractured in shear using an Instron machine. Results: For the groups bonded immediately after bleaching, one-way analysis of variance (ANOVA) followed by the Duncan's post hoc test revealed a statistically significant reduction in bond strengths in a range from 71% to 76%. For the groups bonded at 1 week, one-way ANOVA showed that group B (35% HP for 30 min) resulted in the highest bond strengths, whereas 10% CP resulted in the lowest bond strengths. Student's t-test showed that delayed bonding resulted in a significant increase in bond strengths for groups B (35% HP) and C (35% CP); whereas the group bleached with 10% CP (group D) remained in the same range obtained for immediate bonding. Storage in artificial saliva also affected the control group, reducing its bond strengths to 53% of the original. ©2000 BC Decker Inc.

In vitro penetration of bleaching agents into the pulp chamber

Aim: To investigate pulp chamber penetration of bleaching agents in teeth following restorative procedures. Methodology: Bovine lateral incisors were sectioned 3 mm apical to the cemento-enamel junction and the coronal pulpal tissue was removed. Teeth were divided into six groups (n = 10): G1, G2 and G3 were not submitted to any restorative procedure, while G4, G5 and G6 were submitted to Class V preparations and restored with composite resin. Acetate buffer was placed in the pulp chamber and treatment agents were applied for 60 min at 37°C as follows: G1 and G4, immersion into distilled water; G2 and G5, 10% carbamide peroxide (CP) exposure; G3 and G6, 35% CP bleaching. The buffer solution was removed and transferred to a glass tube where leuco crystal violet and horseradish peroxidase were added, producing a blue solution. The optical density of the blue solution was determined spectrophotometrically at 596 nm. A standard curve made with known amounts of hydrogen peroxide was used to convert the optical density values of the coloured samples into microgram equivalents of hydrogen peroxide. Data were submitted to ANOVA and Tukey's test (5%). Results: Amounts of hydrogen peroxide found in the pulp chamber of G2 and G5 specimens (0.1833 ± 0.2003 μg) were significantly lower (P = 0.001) when compared to G3 and G6 specimens (0.4604 ± 0.3981 μg). Restored teeth held significantly higher (P = 0.001) hydrogen peroxide concentrations in the pulp chamber than intact teeth. Conclusion: Higher concentrations of the bleaching agent produced higher levels of hydrogen peroxide in the pulp chamber, especially in restored teeth.

Influência dos agentes clareadores na microdureza de resina composta nanoparticulada

Objective: To assess the effect of bleaching agents on the microhardness of nanoparticle resin composite. Methods: Twenty-eight cylindrical test specimens (8× 1mm) of Filtek™ Supreme XT resin (3M/ESPE) were prepared and divided into 5 groups. The initial Vickers microhardness was measured (load of 50 grams force for 30 seconds) on the top surface of the test specimens. The groups were treated and divided as follows: G1 - artificial saliva (21 days - control); G2 - 7% hydrogen peroxide gel applied for 4h/day, for 14 days; G3 - 10% carbamide peroxide for 4h/day, for 14 days: G4 - 35% hydrogen peroxide gel applied in three sessions of 30 minutes each, with an interval of one week (21 days) between the sessions; G5 - 35% carbamide peroxide, three sessions of 30 minutes each, with an interval of one week (21 days) between the sessions. The top surfaces of the test specimens received treatment and were submitted to the Vickers microhardness test. Results: The results obtained were submitted to the Analysis of Variance at a fixed criterion, at a level of significance of p=0.05. No significant differences were observed among the treatments tested (p=0.42) when compared with G1. Significant differences (Tukey test) were found when the initial microhardness values were compared with the values after experimental treatments (p<0.01). Conclusion: The application of bleaching agents did not alter the microhardness of resin composites. Therefore, there is no need to change restorations after bleaching.

Evaluating the bonding of two adhesive systems to enamel submitted to whitening dentifrices.

The aim of this study was to evaluate by micro-shear bond strength test, the bond strength of composite resin restoration to enamel submitted to whitening dentifrices. Forty bovine teeth were embedded in polystyrene resin and polished. The specimens were randomly divided into eight groups (n=5), according to the dentifrice (carbamide peroxide, hydrogen peroxide and conventional dentifrice) and the adhesive system (Prime & Bond 2.1 and Adper Single Bond 2). Dentifrice was applied for 15 minutes a day, for 21 days. Thirty minutes after the last exposure to dentifrice, the samples were submitted to a bonding procedure with the respective adhesive system. After that, four buttons of resin were bonded in each sample using transparent cylindrical molds. After 24 hours, the teeth were submitted to the micro-shear bond strength test and subsequent analysis of the fracture mode. Data were submitted to analysis of variance and Fisher's PLSD test (alpha = 0.05). The micro-shear bond strength showed no difference between adhesives systems but a significant reduction was found between the control and carbamide groups (p = 0.0145) and the control and hydrogen groups (p = 0.0370). The evaluation of the failures modes showed that adhesive failures were predominant. Cohesive failures were predominant in group IV The use of dentifrice with peroxides can decrease bonding strength in enamel.