Fracture resistance and bonding performance after antioxidants pre-treatment in non-vital and bleached teeth.

The purpose of this study was to evaluate the effect of vitamin C containing sodium ascorbate prepared solution on dentin bond strength of resin composite to non-vital bleached tooth and on fracture resistance of restored non-vital bleached tooth. Sixty (30 pairs, left and right) extracted sound human maxillary premolar teeth were collected from 30 patients. All teeth were endodontically treated and each pair was randomized assigned into microtensile bond strength and fracture resistance tests. The teeth were divided into 3 groups for each test which were 1) non-bleach tooth, 2) bleached with 35% hydrogen peroxide and immediately restored with resin composite, and 3) bleached with 35% hydrogen peroxide, followed by application of 10% vitamin C prepared solution and immediately restored with resin composite. Samples of microtensile bond strength test were cut to obtain stick-shaped specimens and tested with a universal testing machine. Samples of fracture resistance test were embedded in acrylic resin with simulated periodontal ligament before subjecting to an axial compression test in the universal testing machine. Results showed that the bleached tooth followed by 10% vitamin C solution application group had the highest microtensile bond strength (55.566 ± 3.514 MPa) while the bleached group had the significant lowest bond strength (36.571± 2.609 MPa). The non-bleached group showed the highest fracture strength (1053.44 ± 183.65 N) and the bleached group had significant less strength (616.98 ± 97.07 N). There was no significant difference between the non-bleached group and vitamin C solution application group in both microtensile bond strength and fracture strength tests (p>0.05). The most failure mode in the microtensile bond strength test for all groups was adhesive failure and was favorable failure in the fracture resistance test. The microtensile bond strength was positively correlated to the fracture resistance (r=0.639, p<0.001). In conclusion, the use of 10% vitamin C containing sodium ascorbate prepared solution could increase the microtensile bond strength and fracture strength of non–vital bleached tooth comparable to non-bleached tooth.

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. 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%). 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). After NVB, adhesive luting to dentin is recommended after 7 days if sodium ascorbate has been applied prior to dentin hybridization.

ObjectivesSome antioxidants are believed to restore dentin bond strength after dental bleaching. This study was done to evaluate the influence of antioxidants on the bond strength of bleached bovine dentin.Materials and MethodsThirty incisors were randomly assigned to 10 groups (two unbleached control and eight bleached groups: immediate bonding IB, 4 wk delayed bonding DB, 10% sodium ascorbate treated SA, 10% α-tocopherol treated TP groups). Teeth in half of groups were subjected to thermal stress, whereas the remaining groups were not. Resin-dentin rods with a cross-sectional area of 2.25 mm2 were obtained and microtensile bond strength was determined at a crosshead speed of 1 mm/min. Fifteen specimens were prepared for SEM to compare the surface characteristics of each group. The change in dentin bond strength from thermal stress and antioxidant treatment was evaluated using two-way analysis of variance (ANOVA) and Sheffe's post hoc test at a significance level of 95%.ResultsThe control group exhibited the highest bond strength values, whereas IB group showed the lowest value before and after thermocycling. The DB group recovered its bond strength similar to that of the control group. The SA and TP groups exhibited similar bond strength values with those of the control and DB groups before thermocycling. However, The TP group did not maintain bond strength with thermal stress, whereas the SA group did.ConclusionsApplying a 10% sodium ascorbate solution rather than 10% α-tocopherol solution for 60 sec is recommended to maintain dentin bond strength when restoring non-vitally bleached teeth.

The purpose of this study was to analyze the influence of 10% sodium ascorbate (SA) on the hybrid layer, resin tag length, and bond strength to dentin after bleaching. Six groups were tested: G C, control; G SA, sodium ascorbate (SA) + restoration; G CP, bleaching with carbamide peroxide (CP) + restoration; G CP+SA, bleaching with CP + SA+ restoration; G HP, bleaching with 35% hydrogen peroxide (HP) + restoration; and G HP+SA, HP + SA + restoration. After dental bleaching, the dentin was exposed and the antioxidant solution was applied to groups G SA, G CP+SA, and G HP+SA, before bonding procedures. The teeth were sectioned in the mesiodistal direction. One section was decalcified, and the specimens were embedded in paraffin and sectioned in the longitudinal direction with a thickness of 6 μm. Fifteen slices of each specimen were selected according to a systematic sample of slices with an interval proportional to the total number of slices obtained for each tooth. The specimens were stained using the Brown & Brenn method, and an optic microscope was used to analyze the hybrid layer thickness and resin tag length. The remaining tooth segment was sectioned into stick-shaped specimens and used for microtensile bond strength testing (0.5 mm/min). Statistical analysis was performed using two-way analysis of variance and Fisher test. The results for hybrid layer + tag formation (in micrometers) were G C, 13.27 Aa; G SA, 11.85 Ba; G CP, 6.84 Bb; G CP+SA, 9.02 Ab; G HP, 7.28 Bb; and G HP+SA, 9.22 Ab; bond strength results (in MPa) were G C, 49.5 Aa; G SA, 51.7 Aa; G CP, 37.16 Bb; G CP+SA, 47.69 Aa; G HP, 32.39 Ab; and G HP+SA, 39.67 Ab. Tooth bleaching with CP or HP impairs the formation of the hybrid layer and resin tags and reduces the microtensile bond strength. Statistically, the use of SA significantly increases the hybrid layer thickness and resin tag length. The microtensile bond strength values for carbamide peroxide increased, but the microtensile bond strength for hydrogen peroxide was not affected.

This study evaluated the effect of different concentrations of alpha-tocopherol in gel form on fracture strength, hybrid layer formation, and microtensile bond strength of endodontically treated teeth bleached with 40% hydrogen peroxide (H2 O2 ). Sixty bovine incisors were randomized into one of six groups (n=10 incisors per group) defined by the interventions carried out after endodontic treatment. In the control group, no additional intervention was carried out, while all teeth in the five intervention groups were bleached with 40% H2 O2 and subsequently treated with alpha-tocopherol at concentrations of 15% (15AT), 20% (20AT), or 25% (25AT), with 10% sodium ascorbate (10SA), or with nothing (40HP). Fracture strength was evaluated in a mechanical testing machine, hybrid layer formation was assessed using scanning electron microscopy, and bond strength was determined using microtensile bond-strength testing. Data were analyzed using Kruskal-Wallis and Dunn's tests. No statistically significant difference regarding fracture strength was observed among groups. Hybrid layer formation was greater in the 15AT group than in groups 40HP and 10SA. Teeth in groups 15AT, 20AT, and 25AT demonstrated higher bond strength than teeth in groups 40HP and 10SA. Alpha-tocopherol, preferably at 15%, effectively reverses the deleterious effects, of bleaching, on hybrid layer formation and bond strength to dentin.

PURPOSE: This study evaluated the effect of 10% sodium ascorbate (10SA), in gel (10SAg) or aqueous solution (10SAs) formulations, on fracture resistance of endodontically treated tooth submitted to dental bleaching procedures with 15% hydrogen peroxide associated with titanium dioxide (15HP-TiO2) nanoparticles and photoactivated by LED-laser. MATERIAL AND METHODS: Forty maxillary premolars were endodontically-treated and embedded in acrylic resin up to the cement-enamel junction. The specimens were divided into four groups (n=10): G1 (negative control): no bleaching, coronal access restored with composite resin; G2 (positive control): three dental bleaching sessions using 15HP-TiO2 and LED-laser photoactivation and restored with composite resin (positive control); G3 (10SAg): similar procedures to G2, but applied 10SA, in gel formulation, for 24 hours before restoration; G4 (10SAs): similar procedures to G3, but applied 10SA, in aqueous solution formulation. The 15HP-TiO2 was applied on buccal and lingual surfaces of the crown tooth and inside the pulp chamber and photoactivated by LED-laser. Between each bleaching session, the teeth were maintained in artificial saliva, at 37oC, for 7 days. In sequence, the teeth were submitted to fracture resistance testing using an eletromechanical machine test. The data was analyzed using Kruskal Wallis test (p = 0.05) RESULTS: There are no differences significant among the groups in relation to fracture resistance of endodontically treated teeth (p&gt;0.05). CONCLUSIONS: The use of 10% sodium ascorbate, in gel or aqueous solution formulations, did not interfered on the fracture resistance teeth after dental bleaching using 15HP-TiO2 and LED-laser photoactivation.

Effect of 35% Sodium Ascorbate Treatment on Microtensile Bond Strength after Nonvital Bleaching

BackgroundMany orthodontic patients request dental bleaching during orthodontic treatment to achieve a faster aesthetic resolution, however, no attention has been paid to the inflammatory processes that can occur when both therapies are indicated together. So, this clinical trial evaluated the inflammatory parameters and color alterations associated with dental bleaching in patients wearing a fixed orthodontic appliance.MethodsThirty individuals aged between 18 and 40 years were equally and randomly allocated into three groups: FOA (fixed orthodontic appliance), BLE (dental bleaching), and FOA + BLE (fixed orthodontic appliance + dental bleaching). The orthodontic appliances and the bleaching procedures were performed in the maxillary premolars and molars. For dental bleaching a 35% hydrogen peroxide was used. The gingival crevicular fluid (GCF) and nitric oxide (NO-) levels were evaluated at different time-points. Color evaluation was performed using an Easyshade spectrophotometer at baseline (FOA, FOA + BLE, BLE), one month after (FOA + BLE) and 21 days after appliance removing (FOA + BLE and FOA groups), in each tooth bleached. The ANOVA and Tukey’s tests, with a significance level of 5%, were used for statistical analysis.ResultsThe GCF volume in the FOA + BLE and FOA groups significantly increased at the time points evaluated (p < 0.001); however, this did not occur in the BLE group (p > 0.05). On the other hand, NO- levels significantly decreased during dental bleaching with or without fixed orthodontic appliances (FOA + BLE and BLE groups; p < 0.05), while no significant changes were observed in the FOA group (p > 0.05). Significant changes in color were observed in the FOA + BLE and BLE groups compared to in the FOA group (p < 0.01). However, the presence of fixed orthodontic appliance (FOA + BLE) negatively affected the bleaching efficacy compared to BLE group (p < 0.01).ConclusionsDental bleaching did not increase the inflammatory parameters in patients wearing fixed orthodontic appliance. However, in the presence of orthodontic appliances, the bleaching efficacy was lower than that of bleaching teeth without orthodontic appliances.Trial registrationRBR-3sqsh8 (first trial registration: 09/07/2018).

Antioxidant effect on shear bond strength of orthodontic brackets after tooth bleaching: A scoping review of in vitro studies

Reduction in bond strength when bonding was done immediately after intracoronal bleaching procedure has been recognized. The purpose of this study is to assess the effect of antioxidants (10% sodium ascorbate (SA), 0.1M thiourea and7% sodium bicarbonate (SB)) on reversing bonding strength of composite resin to bleached dentin. Materials and method: Sixty upper 1st premolar teeth, were selected, the crowns of the teeth were embedded in acrylic resin blocks exposing a flat dentin from the buccal surface, then divided into 6 groups (10 samples each). Bleaching for the experimental groups was performed using 35% hydrogen peroxide bleaching gel (pola-office).Group A (Negative control group; dentin samples immediately bonded with composite without bleaching)Group B (Positive control group; dentin samples bleached and immediately bonded with composite). Group C (Dentin samples bleached and stored for 14 days in DDW then bonded with composite). Group D (Dentin samples bleached and treated with 10% (SA) then immediately bonded with composite). Group E (Dentin samples bleached and treated with 0.1M thiourea then immediately bonded with composite). Group F (Dentin samples bleached and treated with 7% SB then immediately bonded with composite).The shear bond strength was determine using instron testing machine. Results: Bleaching the dentin with 35 % hydrogen peroxide gel for 24 minutes resulted in reduction in bond strength of the bleached teeth when bonding was performed immediately after bleaching. Delayed bonding of composite to the bleached dentin for 14 days will result in a highly significant increase in the shear bond strength. Conclusion: Treating the bleached dentin with 10% (SA) in water base showed a highly significant increase in the shear bond strength of the composite to dentin and reversing the bond strength value to the level of the unbleached dentin. Treating the bleached dentin with 0.1M thiourea significantly increased the shear bond strength of the composite to dentin.

Effect of sodium ascorbate on dentin bond strength after treatment with oxidizing root canal irrigants

Introduction. Dental bleaching is the first choice to improve smile esthetics, but, in some cases, it needs to be associated with resin composite restoration to obtain a satisfactory result. Unfortunately, the bonding of resin-based materials can be impaired due to residual oxygen molecules, which can decrease the durability of the restoration. Objectives. To evaluate the effect of the antioxidant application on the bond strength of bleached enamel after 24 hr and 3 years of water storage. Methods. In total, 84 bovine teeth were used in this study. Of these, 77 were bleached with 35% hydrogen peroxide in a single session for three cycles of 15 min. Then, the specimens were divided into groups (n = 7 each): control (without bleaching), without antioxidant (WA) use; application of 10% sodium ascorbate (SA) gel, grape seed (GS) extract, and aloe vera (AV). The restorative procedure was performed immediately after bleaching, 7 and 14 days after bleaching. Specimens were sectioned and evaluated using microtensile bond strength (μTBS). Half of the resin-enamel sticks were tested after 24 hr, and the remaining half after 3 years of water storage. µTBS data were analyzed using a three-way analysis of variance, Tukey’s test, and Dunnett’s test. Results. The lowest µTBS values were observed when the restoration was performed immediately after bleaching in the AV, GS, and WA groups when compared with the SA group ( p &lt; 0.005 ). However, no significant differences were observed among all groups after 3 years of water storage ( p &lt; 0.001 ). Conclusions. SA at 10% was the most effective antioxidant agent for improving the immediate bond strength. However, independent of the antioxidant agent used, the bond strength values were maintained or recovered after 3 years of water storage. SA at 10% could be used to avoid delayed bonding procedures after in-office whitening without compromising bond strength over time. Clinical Significance. The use of antioxidants after dental bleaching can be effective in improving the bonding durability of the adhesive restorations.

Whitening of teeth is a popular choice among dental clinicians and patients. However, the changes in enamel structure and composition induced by the bleaching agents cause a decrease in the shear bond strength of brackets leading to premature bracket debonding. Among several methods to overcome this, the most common is delaying bonding by 2-4 weeks. This waiting period can be eliminated by applying an antioxidant (sodium ascorbate) which causes a reversal in the reduction of bond strength. This study aims to compare the efficacy of a naturally occurring antioxidant (gooseberry) and sodium ascorbate in normalizing the bond strength of enamel to prebleached levels. Seventy-two extracted premolars were divided into 4 equal groups; 1st group - control group - unbleached teeth, bonded directly, 2nd group - bleached with 16% carbamide peroxide (8 h for 1 week), then bonded. 3rd and 4th group - similarly bleached, followed by application of 10% sodium ascorbate and gooseberry extract (3 h respectively), then bonded. Bond strength was checked using Instron Universal Testing Machine. The bond strength of the control group was the highest and that of the carbamide group was drastically reduced. Considerable increase in the bond strength was seen after treatment with sodium ascorbate with negligible difference between sodium ascorbate and control group (P > 0.05). Treatment with gooseberry extract did improve the bond strength but was not as effective as sodium ascorbate postbleaching.

The effect of hybrid layer thickness on bond strength: demineralized dentin zone of the hybrid layer

Introduction Due to an increase in patient awareness and search for aesthetic treatments, dental bleaching is a frequent and safe procedure in clinical practice for the removal of stains [1]. Bleaching agents are known to adversely affect the bond strength between resin composite and tooth surface, when adhesive procedures are performed immediately after tooth bleaching [2]. The reduction in bond strength is related to the presence of residual oxygen, a sub product of hydrogen peroxide that remains on the tooth surface and which may interfere with infiltration of the resin in the dentine tubules and inhibit the polymerisation of resin monomers [3]. Antioxidant agents like sodium ascorbate, grape seed extract and green tea may be used as an alternative to delay the restorative procedure due to their potential as reversers of these adverse effects [2]. This study aims to assess the influence of different antioxidant agents on the bond strength of restored bleached teeth. Materials and methods The present study was approved by the Ethics Committee of Instituto Universitário Egas Moniz. Fifteen human permanent molars were sectioned into identical halves that were randomly distributed between five groups (n = 6): unbleached control group (CG), bleaching + resin composite bonded immediately (G1), bleaching + sodium ascorbate (G2), bleaching + grape seed extract (G3) and bleaching + green tea (G4). G1, G2, G3 and G4 were bleached for 4 h/day for a 7-day period. After bleaching, G1 samples were immediately restored with an adhesive system and a resin composite, in G2 samples a 10% sodium ascorbate gel was applied, in G3 a 5% grape seed extract and in G4 a 5% green tea, all applied for 15 min. After these antioxidants, G2, G3 and G4 were immediately restored. After 24 h, samples were sectioned in order to obtain 1.0 (± 0.3) mm2 microspecimens. The microspecimens were tested in a universal testing machine at a speed of 0.5 mm/min. Data were analysed by using a two-way ANOVA, at a significance level of 5%. Results G1 group (bleaching only) recorded the lowest mean bond strength value (9.5 (± 1.2) MPa) and it was significantly lower than the control group (CG) (19.3 (± 2.7) MPa) (p = .001). Groups in which sodium ascorbate (G2) (19.2 (± 1.3) MPa), grape seed extract (G3) (16.5 (± 0.8) MPa) and green tea (G4) (16.7 (± 2.0) MPa) were applied presented significantly higher bond strength values when compared to bleaching only (G1) (p < .001). When comparing the antioxidant agents, G2 (10% sodium ascorbate) exhibited significantly higher mean bond strength values when compared to G3 (5% grape seed extract) (p = .016). Discussion and conclusions Treatment of the enamel surface with antioxidant agents such as sodium ascorbate, grape seed extract and green tea following the bleaching procedure and immediately before the restorative procedure can reverse the compromised bond strength. These alternative strategies are effective and may be used instead of delaying the procedure.