Effect of Antioxidant Agents After Dental Bleaching on Color Stability and Mechanical Properties of Bonding Interface Components in Ceramic Laminate Veneer Luting.

PURPOSE: Few studies have evaluated the influence of antioxidant agents on the optical and mechanical properties of ceramic laminate veneers after dental bleaching. Thus, this in vitro study aimed to evaluate the influence of antioxidant agents on the color stability and mechanical properties, such as nanohardness (HIT), elastic modulus (Eit*), and degree of conversion (DC) of the bonding interface components after dental bleaching in ceramic laminate veneer luting. METHODS AND MATERIALS: A total of 143 bovine teeth were distributed into experimental groups, according to the procedure method (unbleached or bleached with Whiteness HP Maxx 35%), antioxidant type (control, 10% ascorbic acid, or 10% α-tocopherol), and luting period (24 hours or 14 days) (n=13). The Tetric N-Bond Universal adhesive system and Variolink Esthetic LC resin cement were used as luting agents to lute IPS e.max ceramic restorations (0.6 mm in thickness) to enamel. A UV-visible spectrophotometer was used to assess color stability before and after UV-B artificial accelerated aging for 252, 504, and 756 hours (n=8). The HIT and Eit* of the adhesive and resin cement were measured using a nanohardness tester under a load of 1000 µN, and the DC was measured using a micro-Raman spectrometer (n=5). The color stability and mechanical properties were measured and evaluated by twoway and one-way ANOVA, respectively, and Tukey test (α=0.05). RESULTS: Distinct aging periods exerted significant changes on the color stability of the restorations luted in enamel associated with ascorbic acid, bleached and unbleached, and the bleached enamel under no antioxidant agent action, for the experimental groups evaluated after 14 days (p<0.05). The use of the α-tocopherol antioxidant solution after the bleaching process for 24 hours did not alter the optical and mechanical properties of the adhesive interface of the laminate restorations compared to those of the control group (p>0.05). CONCLUSION: The use of a 10% α-tocopherol antioxidant solution produced promising results, suggesting that it could be mediately used after tooth bleaching to lute ceramic laminate veneers.

Influence of Different Dye Substances on the Effectiveness of Bleaching and H2O2 Diffusion.

This study aimed to evaluate the influence of different dye substances on the effectiveness of bleaching and hydrogen peroxide diffusion (HO). From 300 central bovine incisors, 160 enamel/dentin disks with similar E* values were selected. The specimens were distributed according to the pigment treatment. Aiming to standardize the chromatic change provided by the different pigments, the specimens from each group remained immersed in the pigment solutions for different times (32 specimens per group): DW - distilled water (Control group); BT - black tea; CO - coffee; SD - cola-based soft drink; and RW - red wine. After pigmentation and chromatic change value analysis, only 10 specimens from each group (n=10) were selected, so the chromatic alteration of all groups was similar (ΔE=8.36±0.5). The samples were subjected to bleaching treatment and diffused peroxide was quantified in a visible ultraviolet light spectrophotometer. Two more bleaching sessions were conducted to evaluate ΔE and the Whiteness Index for Dentistry (ΔWID). Concurrently, solutions were prepared with dye agents, and the same ΔE value was obtained in the teeth (ΔE=8.49±0.5). The solutions received a standardized amount of H2O2, being analyzed by a visible ultraviolet light spectrophotometer. Data analysis comprised variance and Tukey's tests (α=0.05). Higher H2O2 diffusion was observed in pigmented groups when compared with DW (p<0.05). The CO and RW groups had the highest ΔE values (p>0.05), meaning greater difficulty in responding to treatment. In relation to ΔWID, RW bleached less than the other groups after the third bleaching session (p<0.05), resembling only the SD group (p=0.467). However, 21 days after ending the bleaching treatment, only RW and CO had the lowest values (p=0.481). Analysis of the solutions revealed that only RW was altered by the peroxide (p<0.05). In conclusion, teeth pigmented with coffee and, mainly, red wine were more resistant to bleaching treatment, although all pigmentations favored increases in transenamel and transdentinal H2O2 penetration.

Does the Bleaching Gel Application Site Interfere With the Whitening Result? A Randomized Clinical Trial.

This study aimed to evaluate the effect of the bleaching gel application site on chromatic changes and postoperative sensitivity in teeth. Thirty patients were selected and allocated to three groups (n=10 per group), according to the location of the gel: GI, cervical application; GII, incisal application; and GIII, total facial. The amount and time of application of the 35% hydrogen peroxide (H2O2) gel were standardized. Color changes were analyzed by ΔE and Wid (bleaching index), using the values obtained in the readings conducted on a digital spectrophotometer in the cervical (CRs) and incisal regions (IRs) of the teeth. Spontaneous sensitivity was assessed using the questionnaire, and the stimulated sensitivity caused by the thermosensory analysis (TSA). The analysis occurred in five stages: baseline, after the first, second, and third whitening sessions (S), and 14 days after the end of the whitening, using the linear regression statistical model with mixed effects and post-test by orthogonal contrasts (p<0.05). Although the IR was momentarily favored, at the end of the treatment, the restriction of the application site provided results similar to those obtained when the gel was applied over the entire facial surface. Regarding sensitivity, only the GI showed spontaneous sensitivity. In the TSA, GIII had less influence on the threshold of the thermal sensation. It was concluded that the chromatic alteration does not depend on the gel application site. Spontaneous sensitivity is greater when the gel is concentrated in the cervical region (CR), and the teeth remain sensitized by thermal stimuli even after 14 days.

Influence of Tooth Pigmentation on H2O2 Diffusion and Its Cytotoxicity After In-office Tooth Bleaching.

CLINICAL RELEVANCE: Pigments in tooth structures affect the diffusion of H2O2 through enamel and dentin. The bleaching methodology can be impacted. SUMMARY: Objective: The aim of this study was to evaluate the influence of the presence of pigments in tooth structures on the trans-enamel and trans-dentin diffusion of hydrogen peroxide (H2O2) and its cytotoxicity after carrying out an in-office bleaching therapy.Methods and Materials: A bleaching gel with 35% H2O2 was applied for 45 minutes (three times for 15 minutes) on enamel and dentin discs (n=6), either previously submitted to the intrinsic pigmentation protocol with a concentrated solution of black tea, or not, defining the following groups: G1, unbleached untreated discs (control 1); G2, unbleached pigmented discs (control 2); G3, bleached untreated discs; G4, bleached pigmented discs. The discs were adapted to artificial pulp chambers, which were placed in wells of 24-well plates containing 1 mL culture medium (Dulbecco's modified Eagle's medium [DMEM]). After applying the bleaching gel on enamel, the extracts (DMEM + components of bleaching gel that diffused through the discs) were collected and then applied on the cultured MDPC-23 odontoblast-like cells. Cell viability (methyl tetrazolium assay and Live & Dead, Calcein AM, and ethidium homodimer-1 [EthD-1] probes), the amount of H2O2 that diffused through enamel and dentin (leuco-crystal violet product), and the H2O2-mediated oxidative cell stress (SOx) and components of degradation were assessed (analysis of variance/Tukey; α=0.05).Results: There was no significant difference between the groups G1 and G2 for all the parameters tested (p>0.05). Reduction in the trans-enamel and trans-dentin diffusion of H2O2 occurred for G4 in comparison with G3. Significantly lower cell viability associated with greater oxidative stress was observed for G3 (p<0.05). Therefore, in-office tooth bleaching therapy performed in pigmented samples caused lower cytotoxic effects compared with untreated samples submitted to the same esthetic procedure (p<0.05).Conclusion: According to the methodology used in this investigation, the authors concluded that the presence of pigments in hard tooth structures decreases the trans-enamel and trans-dentin diffusion of H2O2 and the toxicity to pulp cells of an in-office bleaching gel with 35% H2O2.

Randomized Prospective Clinical Trial of Class II Restorations Using Low-shrinkage Flowable Resin Composite.

PURPOSE: The aim of this prospective, randomized, split-mouth clinical trial was to evaluate postoperative sensitivity, clinical performance, and interproximal contacts after using different restorative systems. METHODS AND MATERIALS: Fifty-three subjects each received three class II restorations according to the restorative systems: conventional resin composite (PA: Peak Universal+Amelogen Plus, Ultradent), low-shrinkage flowable and nanoparticulate resin composites (ABF: Adper Single Bond 2+Filtek Bulk Fill Flow+Filtek Z350XT, 3M ESPE), and low-shrinkage flowable and microhybrid resin composites (XST: XP Bond+SDR+TPH3, Dentsply). Postoperative sensitivity was assessed at 24 hours, seven days, 90 days, and six months. The clinical performance and interproximal contacts were evaluated at baseline, six months, and one year. Friedman, Wilcoxon, Kruskal-Wallis, and Mann-Whitney tests were used to evaluate postoperative sensitivity and interproximal contacts. The equality test of two proportions and logistic regression analysis were used to assess the clinical performance. RESULTS: No statistically significant differences were observed among groups for postoperative sensitivity. The highest spontaneous sensitivity was reported at 24 hours. ABF was the only group that did not present a reduction in cold sensitivity. Color, marginal discoloration, and superficial staining showed differences among the groups. XST did not show superficial staining after one year. No differences were observed among groups in relation to interproximal contacts. XST resulted in the loss of interproximal contact after one year. CONCLUSIONS: Different types of restorative systems do not influence postoperative sensitivity; however, ABF maintained cold sensitivity over time. Marginal discoloration occurred for all groups but occurred earliest for PA. XST presented a reduction of interproximal contact after one year of evaluation.

A New Approach for Dental Bleaching Using Violet Light With or Without the Use of Whitening Gel: Study of Bleaching Effectiveness.

The objective of this study was to evaluate the effectiveness of violet light-emitting diodes (LEDs) in dental bleaching treatment when used in conjunction with bleaching gels containing different concentrations of hydrogen peroxide (HP). Here, 90 bovine teeth (n=15) were randomly assigned to the following groups: GI, placebo without light; GII, 35% HP without light; GIII, 17.5% HP without light; GIV, placebo with violet LED; GV, 35% HP with violet LED; and GVI, 17.5% HP with violet LEDs. Three bleaching sessions of 45 minutes were conducted; 21 cycles involving one minute of irradiation by violet LEDs with 30-second intervals were performed during each session of bleaching (GIV, GV, and GVI). Color changes (ΔE, ΔL, Δa, and Δb) were analyzed using a visible ultraviolet light spectrophotometer 7 days after each bleaching session. The mean ΔE, ΔL, Δa, and Δb values were compared between groups by analysis of variance and Tukey tests, with a significance level of 5%. The groups treated with 35% HP had higher ΔE and ΔL and lower Δb values, regardless of whether violet light was used. The group that received only violet LED differed from the control group in terms of ΔE, and the group treated with 17.5% HP and violet LED presented higher ΔE values than the group treated with 17.5% HP only. Thus, violet light did not influence bleaching efficacy when using 35% HP, but when used in conjunction with 17.5% HP, it increased the bleaching efficacy. Moreover, use of the violet LED only also prompted a bleaching effect, although it was less marked.

A clinical, randomized study on the influence of dental whitening on Streptococcus mutans population.

BACKGROUND: Dental whitening with peroxides has been popularized through the at-home technique, which employs low concentrations of peroxide applied in individual trays. However, there are few clinical trials reporting the effects of its continuous use on oral microbiota. Thus, the purpose of the present clinical, randomized study was to evaluate the influence of at-home whitening treatment on Streptococcus mutans in saliva, buccal mucosa, and subgingival and supragingival plaque. METHODS: Thirty volunteers were randomly divided into two study groups (N = 15) according to the whitening therapy: G CP, whitening using 10% carbamide peroxide 4 h daily for 21 days; and G HP, whitening using 6% hydrogen peroxide 1.5 h daily for 21 days. Samples from the predetermined locations were collected at three evaluation periods: T1, before; T2, immediately after; and T3, 30 days after the beginning of the treatment. The microbiological evaluation was made using conventional and molecular methods. RESULTS: Student's t-test demonstrated a statistically significant decrease in S. mutans population in the subgingival and supragingival plaque for HP samples between T1 and T2 no difference was found between T1 and T3 regardless of the location and the whitening product used (α = 0.05). CONCLUSIONS: Although HP reduced S. mutans during treatment, the levels returned to baseline when assessed 30 days after the treatment.

Microhardness and Roughness of Infiltrated White Spot Lesions Submitted to Different Challenges.

A white spot lesion is the first clinical sign of a caries lesion and represents mineral loss from the enamel subsurface. The purpose of this study was to evaluate the microhardness and surface roughness of white spot lesions after application of a resin infiltrant and subjection to different challenges. Caries-like lesions were induced in bovine enamel discs (n=50), and the specimens were randomly divided into five study groups (n=10): demineralized enamel (negative control, G1), infiltrated enamel (G2), infiltrated enamel submitted to brushing (G3), infiltrated enamel submitted to pH cycling (G4), and infiltrated enamel submitted to artificial aging (G5). Half of each enamel surface was used as its own positive control. Roughness data were analyzed using the Kruskal-Wallis test followed by the Dunn test. Results from microhardness were analyzed by two-way analysis of variance, followed by the Tukey test for multiple comparisons. The level of significance was set at 5%. Microhardness and roughness values obtained from the test side of the specimens were significantly lower compared with the sound enamel for all groups. Microhardness values obtained for G2, G3, and G5 were not significantly different. Values found for G1 were significantly lower compared with those for G2, G3, and G5. The lowest microhardness values were observed for G4, which was significantly different from the other groups. Surface roughness was not significantly different between G2 and G3. The resin infiltrant presented superiority over the unprotected white spot lesions, as they were more resistant to mechanical and aging challenges. However, resin infiltration was not able to reestablish the properties of sound enamel and was not resistant to a new cariogenic challenge.