Aim:The purpose of the present randomized clinical trial was to evaluate the color change, rebound effect and sensitivity of at-home bleaching with 15% carbamide peroxide and power bleaching using 38% hydrogen peroxide.Materials and Methods:For bleaching techniques, 20 subjects were randomized in a split mouth design (at-home and power bleaching): In maxillary and mandibular anterior teeth (n = 20). Color was recorded before bleaching, immediately after bleaching, at 2 weeks, 1, 3 and 6 month intervals. Tooth sensitivity was recorded using the visual analog scale. The Mann-Whitney test was used to compare both groups regarding bleaching effectiveness (ΔE1), rebound effect (ΔE2) and color difference between the rebounded tooth color and unbleached teeth (ΔE3) while the Wilcoxon compared ΔE within each group. Distribution of sensitivity was evaluated using the Chi-square test (α =0.05).Results:There was no significant difference between groups regarding ΔE1 and ΔE3 (P > 0.05). Even though, ΔE2 showed no significant difference between groups after bleaching as well as at 2 week, 1 month and 3 month follow-up periods (P > 0.05). Although, significant difference was found in ΔE2 (P < 0.05 Mann-Whitney) between two methods after 6 months and a high degree of rebound effect was obtained with power bleaching. Within each group, there was no significant difference between ΔE1 and ΔE3 (P < 0.05 Wilcoxon). The distribution of sensitivity was identical with both techniques (P > 0.05).Conclusion:Bleaching techniques resulted in identical tooth whitening and post-operative sensitivity using both techniques, but faster color regression was found with power bleaching even though color regression to the baseline of the teeth in both groups was the same after 6 months.
The findings of this study support the selection of silorane-based composite for the restoration of maxillary premolars with standardized Class II cavity preparations in order to strengthen the resistance to fracture to the same extent as do dimethacrylate composites using cavity liners or without them.
Aim: This study evaluated the influence of mechanical loading and thermocycling on microleakage of class V resin-based composite restorations with and without enamel bevel. Methods and Materials: Sixty class V cavity preparations measuring 3.0 mm wide (mesiogingivally) x 2.0 mm high (occluso-gingivally) x 1.5 mm deep with the occlusal margin in enamel and the gingival margin in cementum were prepared on the buccal surfaces of human premolars using a #12 diamond round bur (Drendel & Zweiling Diamant GmbH, Lemgo, Germany) in a high-speed, water-cooled handpiece. The specimens were then divided into two groups of 30 specimens each, based on the type of enamel cavosurface margin configuration as beveled or nonbeveled (butt joint). After restoring the preparations with a flowable resin-based composite (Tetric Flow, Ivoclar Vivadent-AG, Schaan, Liechtenstein) and finishing and polishing with sequential discs (Sof-Lex Pop-on, 3M-ESPE, St. Paul, MN, USA), the teeth were stored at 37°C and 100 percent humidity. Twenty-four hours later, half of the specimens in each group (nonbeveled "N" or beveled "B") were exposed to a cycling loading for 250,000 cycles to simulate occlusal loading and assigned to two subgroups (NL+ or BL+), while the remainder of the specimens in each group were only maintained in a 100-percent-humidity environment, without any cyclical loading, until tested (NL-or BL-). The specimens were sealed with sticky wax (Kemdent, Associated Dental Products, Swindon, UK) and nail polish. The apical foramen of each tooth was sealed with sticky wax and the rest of the tooth was covered with nail varnish, except for an area within 1.0 mm around the composite restoration. To detect marginal leakage, all of the samples were stored in a 0.5 percent basic fuchsine solution for 24 hours. The specimens were then sectioned longitudinally using a low-speed diamond blade (IsoMet, Buehler Ltd., Lake Bluff, IL, USA), machined, and evaluated under 25X magnification using a stereomicroscope (M9, Wild Heerbrugg, Switzerland). The specimens were scored on a scale from 1 to 4 on the degree of dye penetration. The qualitative data were analyzed by the Mann-Whitney U test at a 5 percent significance level (p<0.05). The null hypothesis of this study was
Aim:To evaluate the effect of dental bleaching with carbamide peroxide at different exposure times on the microleakage of resin composite and resin-modified glass ionomer restorations after placement in extracted human teeth.Methods and Materials: 120 Class V cavity preparations were placed at the cementoenamel junction (CEJ) of human teeth. Half of the cavities were restored with Filtek P60 resin composite(C) and the other half were restored with Fuji II LC resin-modified glass ionomer (G). Each group was randomly divided into four subgroups (n=15). Groups C1 and G1 were not bleached and stored in artificial saliva at 37°C to serve as control groups, while in Groups C2 and G2, C3 and G3, and C4 and G4 specimens were exposed to a 15% carbamide peroxide gel for one day, one week, and two weeks, respectively, following the placement of restorations. Microleakage was assessed using the dye penetration method. Data were analyzed using the Kruskal-Wallis and Wilcoxon tests (p=0.05). Results:The Kruskal-Wallis test showed no significant difference among all groups of composite or glass ionomer restorations with either enamel or dentinal margins with regard to microleakage (p>0.05). The Wilcoxon test revealed more marginal leakage in the enamel/ glass ionomer margins than the enamel/ composite margins (p<0.05). In comparisons within each group, the Wilcoxon test showed there was more microleakage in dentinal margins of composite restorations than in the enamel margins in the test groups (p<0.05). The dentinal margins of the glass ionomer in control groups showed more leakage than the enamel margins, but after the bleaching procedure all experimental groups showed statistically similar microleakage in both the enamel and dentinal margins (p>0.05). Conclusions:Postoperative bleaching with carbamide peroxide could increase microleakage in the dentinal margins of composite and the enamel margins of resin-modified glass ionomer restorations.Clinical Significance: Rebonding of resin composite restorations should be considered following bleaching with 15% carbamide peroxide in order to reseal the margins. Resin-modified glass ionomer is not suitable as a filling material before bleaching because of its susceptibility to increased microleakage. Citation: Moosavi H, Ghavamnasiri M, Manari V. Effect of Postoperative Bleaching on Marginal Leakage of Resin Composite and Resin-Modified Glass Ionomer Restorations at Different Delayed Periods of Exposure to Carbamide Peroxide.
Aim The aim of this in vitro study was to evaluate the effect of 20% carbamide peroxide (CP) on the flexural strength (FS) of bovine enamel and dentin complex. Methods and Materials One hundred sound bovine teeth were selected for use. Blocks (2×3×8 mm) from the middle portion of the facial surfaces of each crown were sectioned from the teeth. The specimens were randomly divided into five groups (n=20) based on the time period of vital bleaching. Group 1 comprised the control group kept in artificial saliva. The experimental groups subjected to immersion in 20% CP, Opalescence, for four, six and eight weeks, respectively (eight hours daily). Mechanical testing was performed 24 hours after the last treatment using an Instron Universal Testing Machine with a crosshead speed of 0.5 mm/min. The results were analyzed by one-way analysis of variance (ANOVA) and Tukey's test (α=0.05). Results Mean values for FS were 141.27, 103.06, 120.71, 130.23, and 117.90 (Mpa), respectively. Statistically significant differences in FS were noted among the groups. A statistically significant difference was observed between Group 2 (two week bleach) and the control. Conclusion Application of 20% CP bleach for two weeks provided significant decreases in FS of bovine enamel and dentin complex. Similar decreases were not observed among the other groups. Citation Ghavamnasiri M, Abedini S, Tazangi AM. Effect of Different Time Periods of Vital Bleaching on Flexural Strength of Bovine Enamel and Dentin Complex. J Contemp Dent Pract 2007 March;(8)3:021-028.
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