Efficacy and Safety of Bleaching Gels According to Application Protocol.

OBJECTIVES: This study evaluated bleaching efficacy, enamel microhardness, and roughness of highly concentrated hydrogen peroxide (HP) gels (35%-40%) using different application protocols. Gel decomposition and pH alteration were also analyzed. METHODS AND MATERIALS: Bovine enamel/dentin specimens were divided into groups according to the bleaching gel-Pola Office Plus (POP-SDI, 37.5% HP), Opalescence Boost (OPB-Ultradent, 40% HP), Whiteness HP (WHP-FGM, 35% HP)-and application protocol-single application (SA) and multiple application (MA) during the in-office session. Deionized water was used in control group (no bleaching). Thus, seven final groups were obtained (n=15/group). Color (CIE L*a*b*), surface microhardness (SMH), and roughness (Ra) were assessed before/after treatments. The pH of gels was measured, and HP concentration was determined with potassium permanganate titration method in different times. Data were submitted to analysis of variance and Tukey tests (5%). RESULTS: All gels presented similar and clinically acceptable bleaching efficacy (ΔE>2.7) for both SA and MA, as well as no significant differences for SMH and Ra comparing the two protocols in the same gel. Peroxide decomposition significantly increased with time, but final gel concentrations were still high after 45 minutes (32.29% POP; 38.45% OPB; and 32.74% WHP). The pH decreased over time (initial - after 45 min) for WHP (6.83±0.07 - 5.81±0.06), but minimal alterations were observed for POP (8.09±0.09 - 7.88±0.07) and OPB (7.82±0.11 - 7.87±0.07). CONCLUSIONS: Peroxide decomposition was very low for all gels tested, and pH remained stable for POP and OPB gels. Bleaching protocol did not influence whitening efficacy and hazardous effects over enamel, thus potentially there was no clinical significance. Therefore, for the products tested, there is no evidence for recommending the gel change during the bleaching session.

Effect of Calcium and Fluoride Addition to Hydrogen Peroxide Bleaching Gel On Tooth Diffusion, Color, and Microhardness.

OBJECTIVES: The aim of this study was to evaluate the effect of calcium and fluoride addition to a 35% hydrogen peroxide (HP) bleaching gel with regard to its diffusion through the tooth structure, enamel microhardness, and bleaching efficacy. METHODS AND MATERIALS: Eighty specimens (6 mm in diameter and 2 mm in height; 1 mm/enamel and 1 mm/dentin) were obtained from bovine incisors that were polished and divided into four groups (n=20) according to the remineralizing agent added to the gel: Ca = 0.5% calcium gluconate; F = 0.2% sodium fluoride; Ca+F = 0.5% calcium gluconate and 0.2% sodium fluoride; and control = no agent. Initial microhardness and color were assessed. The samples were positioned over simulated pulpal chambers filled with acetate buffer solution to capture the HP. Gels were applied over enamel for 30 minutes, and HP diffusion was assessed by spectrophotometry two hours after bleaching. Microhardness was measured immediately after bleaching and then the specimens were immersed into artificial saliva for seven days for final color assessment. Data were analyzed by one-way analysis of variance followed by Tukey test. RESULTS: Bleaching reduced microhardness for all groups (p=0.0001), but the Ca+F and F groups showed lower reductions after bleaching. The addition of Ca, F, and Ca+F decreased the peroxide penetration through the tooth structure (p=0.0001), but there were no differences in color change for ΔL (p=0.357), Δa (p=0.061), Δb (p=0.823), and ΔE (p=0.581). CONCLUSION: The addition of calcium and fluoride in the gel did not affect bleaching efficacy, but it was able to reduce both the peroxide diffusion and the bleached enamel microhardness loss.

Bonding Performance of Simplified Adhesive Systems in Noncarious Cervical Lesions at 2-year Follow-up: A Double-blind Randomized Clinical Trial.

OBJECTIVES: This study aimed to evaluate the bonding performance of a universal adhesive used according to self-etching or etch-and-rinse protocols in noncarious cervical lesions (NCCLs) and to compare the two protocols with their respective gold standard techniques. METHODS AND MATERIALS: This randomized, double-blind clinical study enrolled 34 participants who met the inclusion criteria, 29 of whom returned after two years. They received 152 restorations bonded with one of the three adhesives (Scotchbond Universal Adhesive, Adper Single Bond 2, or Clearfil SE Bond) and one of the two bonding techniques tested. The NCCLs were restored with nanocomposite resin (Filtek Supreme). Final contours were done with a fine diamond rotary instrument and polished with rubber points. The restorations were evaluated using the FDI World Dental Federation criteria at baseline (seven days after the restoration procedure), 6, 12, and 24 months. Descriptive statistics, Kruskal-Wallis, Friedman analysis of variance, and least significant difference tests were performed. RESULTS: No statistically significant differences were found in esthetics or the functional and biological evaluated criteria among the adhesive systems and techniques. CONCLUSIONS: The Scotchbond Universal system behaved similarly to the conventional etch-and-rinse or self-etching systems in all the adhesion strategies in the evaluated periods.

Microleakage and Shear Bond Strength of Composite Restorations Under Cycling Conditions.

OBJECTIVES: The aim of this study was to evaluate microleakage and shear bond strength of composite restorations under different cycling conditions. METHODS AND MATERIALS: Class V cavities were prepared in the buccal and lingual surfaces of 30 human molars (n=60). A further 60 molars were used to prepare flat enamel and dentin specimens (n=60 each). Cavities and specimens were divided into six groups and pretreated with an adhesive (self-etch/Clearfil SE Bond or etch-and-rinse/Optibond FL). Composite was inserted in the cavities or adhered to the specimens' surfaces, respectively, and submitted to cycling (control: no cycling; thermal cycling: 10,000 cycles, 5°C to 55°C; thermal/erosive cycling: thermal cycling plus storage in hydrochloric acid pH 2.1, 5 minutes, 6×/day, 8 days). Microleakage was quantified by stereomicroscopy in enamel and dentin margins after immersion in silver nitrate. Specimens were submitted to shear bond strength testing. Statistical analysis was done by two-way analysis of variance and Kruskal-Wallis tests (p<0.05). RESULTS: Microleakage in enamel margins was significantly lower in the control group compared with thermal cycling or thermal/erosive cycling. Erosive conditions increased microleakage compared with thermal cycling (significant only for Clearfil SE Bond). No significant differences were observed in dentin margins. Bond strength of enamel specimens was reduced by thermal cycling and thermal/erosive cycling when Clearfil SE Bond was used and only by thermal/erosive cycling when Optibond FL was used. No differences were observed among dentin specimens. CONCLUSIONS: Thermal/erosive cycling can adversely affect microleakage and shear bond strength of composite resin bonded to enamel.

Effect of hydrogen peroxide concentration on enamel color and microhardness.

OBJECTIVES: The aim of this study was to investigate the effect of hydrogen peroxide gels with different concentrations (20%, 25%, 30%, and 35%) on enamel Knoop microhardness (KNH) as well as on changes in dental color (C). METHODS: Cylindrical specimens of enamel/dentin (3-mm diameter and 2-mm thickness) were obtained from bovine incisors and randomly divided into six groups (n=20), according to the concentration of the whitening gel (20%, 25%, 30%, 35%, control, thickener). After polishing, initial values of KNH0 and color measurement, assessed by spectrophotometry using the CIE L*a*b* system, were taken from the enamel surface. The gels were applied on the enamel surface for 30 minutes, and immediate values of KNHi were taken. After seven days of being stored in artificial saliva, new measures of KNH7 and color (L7* a7* b7*, for calculating ΔE, ΔL, and Δb) were made. Data were submitted to statistical analysis of variance, followed by Tukey test (p<0.05). RESULTS: Differences in gel concentration and time did not influence the microhardness (p=0.54 and p=0.29, respectively). In relation to color changes, ΔE data showed that the 35% gel presented a higher color alteration than the 20% gel did (p=0.006). CONCLUSION: Bleaching with 35% hydrogen peroxide gel was more effective than with the 20% gel, without promoting significant adverse effects on enamel surface microhardness.

Incremental filling technique and composite material--part I: cuspal deformation, bond strength, and physical properties.

OBJECTIVES: To evaluate the effect of composite resins (one conventional and two low-shrink composites) and filling techniques on cuspal strains (CS), microtensile bond strength (µTBS), composite ultimate tensile strength (UTS), and mechanical properties of the composites at various depths in molars with large Class II restorations. MATERIALS AND METHODS: One hundred seventeen human molars received standardized Class II mesio-oclusal-distal cavity preparations and restorations with three composites (Filtek LS [3M-ESPE]; Aelite LS [BISCO]; and Filtek Supreme [3M-ESPE]) using three filling techniques (bulk, eight increments, and 16 increments). CS was measured using strain gauges, after which the same restored teeth were used to assess µTBS and UTS. The elastic modulus (E) and Vickers hardness (VH) at different depths were determined from microhardness indentations. The CS, µTBS, UTS, E, and VH data were statistically analyzed using split-plot analysis of variance and Tukey test (p=0.05). RESULTS: The CS was higher when using 16 increments. The 'low-shrink' composites caused lower CS. The µTBS and UTS were similar for eight- and 16-increment techniques and higher when compared to the bulk filling in all composites. E and VH were constant through the depth when applied in eight or 16 increments. CONCLUSIONS: Type of composite and filling technique affected the CS, µTBS, UTS, and mechanical properties of large Class II restorations. The eight-increments filling technique resulted in generally less CS with the same µTBS and UTS than was obtained with 16 increments, without affecting E and VH through the depth of the composites.