Effect of Bleaching Agents on the Nanohardness of Tooth Enamel, Composite Resin, and the Tooth-Restoration Interface.

This in vitro study aimed to evaluate the nanohardness of tooth enamel, composite resin, dental adhesive, and enamel hybrid layer exposed to 35% hydrogen peroxide-based bleaching agents and analyze the tooth-restoration interface using scanning electron microscopy (SEM). This study used 40 crowns of bovine incisors, which were embedded in epoxy resin. A 2 × 2 × 2-mm cavity was prepared in the medial third of the flattened buccal surface of each tooth and restored (two-step etch-and-rinse Adper Single Bond 2 + nanocomposite resin Filtek Z350 XT). The specimens were polished and divided into four groups (n=10), corresponding to each bleaching agent used (TB: Total Blanc Office, pH=7.22-6.33; HPB: Whiteness HP Blue, pH=8.89-8.85; HP: Whiteness HP, pH=6.65-6.04; PO: Pola Office, pH=3.56-3.8), applied in accordance with manufacturer protocols. The nanohardness of the substrates was measured before and immediately after the bleaching procedure and after 7-day storage in artificial saliva with an Ultra-Microhardness Tester (DUH-211S, Shimadzu). Loads used were 100 mN for tooth enamel and composite resin and 10 mN for adhesive and enamel hybrid layer. For SEM analysis, epoxy replicas were prepared through high-precision impressions of the specimens. For nanohardness, the statistical tests two-way analysis of variance and Tukey (p<0.05) revealed that the agent with the lowest pH value (PO) was the only one to decrease the nanohardness of enamel and the enamel hybrid layer immediately after its application; however, after 7-day storage in artificial saliva, the nanohardness levels of these substrates returned to their original values. SEM analysis revealed small gaps between tooth enamel and adhesive after the exposure to all bleaching agents; however, the most evident gap in the tooth-restoration interface was observed immediately after application of agent PO. No bleaching agent used changed the nanohardness of the composite resin and adhesive layer.

Effect of a CO2 Laser on the Inhibition of Root Surface Caries Adjacent to Restorations of Glass Ionomer Cement or Composite Resin: An In Vitro Study.

This study investigated the effect of CO2 laser irradiation on the inhibition of secondary caries on root surfaces adjacent to glass ionomer cement (GIC) or composite resin (CR) restorations. 40 dental blocks were divided into 4 groups: G1 (negative control): cavity preparation + adhesive restoration with CR; G2: (positive control) cavity preparation + GIC restoration; G3: equal to group 1 + CO2 laser with 6 J/cm(2); G4: equal to group 2 + CO2 laser. The blocks were submitted to thermal and pH cycling. Dental demineralization around restorations was quantified using microhardness analyses and Light-Induced Fluorescence (QLF). The groups showed no significant differences in mineral loss at depths between 20 µm and 40 µm. At 60 µm, G2 and G3 ≠ G1, but G4 = G1, G2 and G3. At 80 µm, G4 ≠ G1, and at 100 µm, G4 = G2 = G1. At 140 and 220 µm, G2, G3, and G4 = G1. The averages obtained using QFL in groups 1, 2, 3, and 4 were 0.637, 0.162, 0.095, and 0.048, respectively. QLF and microhardness analyses showed that CO2 laser irradiation reduced mineral loss around the CR restorations but that it did not increase the anticariogenic effect of GIC restorations.

Effect of enamel preparation method on in vitro marginal microleakage of a flowable composite used as pit and fissure sealant.

OBJECTIVES: The aim of this in vitro study was to evaluate the microleakage in occlusal surfaces, after preparation with Er:YAG laser and compared to the diamond-bur conventional technique. METHODS: Thirty premolars were divided into three groups: I - high-speed handpiece + 37% phosphoric acid; II - Er:YAG laser (350 mJ, 4 Hz and 112 J/cm(2)) + 37% phosphoric acid; and III - Er:YAG laser (350 mJ, 4 Hz and 112 J/cm(2)) + Er:YAG laser (80 mJ, 4 Hz, and 25 mJ/cm(2)). All cavities received the same adhesive system and were restored with flowable composite according to manufacturer's instructions. Teeth were submitted to thermal cycling and immersed in 50% silver nitrate solutions for 8 h in total darkness. Specimens were sectioned longitudinally in the bucco-lingual direction, in slices of 1 mm thick. Each slice was immersed into photo developing solution and was photographed, and microleakage was scored from 0 to 7, by three calibrated examiners. RESULTS: A statistically significant difference (P < 0.0001) was observed between Er:YAG laser prepared and etched specimens and those in the other groups. CONCLUSIONS: It can be concluded that no significant difference was noted between the two types of enamel preparation when etching was performed. Preparing and treating the enamel surface exclusively by Er:YAG laser resulted in the highest degree of leakage.

[Bond strength to dentin of resin composites associated with filled and unfilled adhesive systems]. / Resistência de união à dentina de resinas compostas associadas a sistemas adesivos com e sem carga.

This study analyzed in vitro two brands of one-step adhesive systems of fourth generation (Optisolo--Kerr, filled; and Single Bond--3M, unfilled) and two composite resins (Prodigy--Kerr and Z100--3M), aiming at evaluating their bond strength to dentin. Eighty human extracted molars were embedded in acrylic resin and grounded until dentin was exposed in longitudinal direction. The specimens were divided in 4 groups. Composite resin cones were bonded to the specimens using the mentioned adhesive systems, following the instructions of the manufacturers. The test-specimens were submitted to tensile tests using a 4442 Universal Mini-Instron Machine with the speed of 0.5 mm/min. The results were converted into MPa, according to the area of adhesion, and submitted to statistical analysis with ANOVA. There was significant statistical difference (p < 0.01) between the adhesive systems (F = 7.24). Optisolo (m = 11.03 +/- 4.23) showed better bond strength than Single Bond (m = 8.37 +/- 4.54). There was no significant statistical difference (p > 0.05) between the composites (F = 0.43).

Nd:YAG laser effects on the microleakage of composite resin restorations.

OBJECTIVE: This study evaluated microleakage of composite restorations submitted to marginal treatment with Nd:YAG laser and surface sealant. BACKGROUND DATA: Previous studies have demonstrated that Nd:YAG-lased enamel melted and became recrystallized with a morphologic appearance similar to lava, and has been used clinically in the sealing of enamel pits and fissures. METHODS: Class V cavities in enamel of human premolars were restored with composite resin (Z100, 3M) and randomly divided in six groups: G1, control; G2, surface sealant marginal treatment; G3 to G6, were treated with pulsed Nd:YAG laser (1.064 microm) marginal treatment, contact fiberoptic (300 microm), air cooling, for 30 seconds, powers of 1.2-2 W, repetition rates of 20-30 Hz, energies of 40-100 mJ. Teeth were impermeabilized, immersed in a rhodamine dye, sectioned, and evaluated under stereomicroscope microscopy with scores. RESULTS: There were significant differences between marginal treatments; there were no differences between groups 1, 2, and 4, and 3,5, and 6; lower values of microleakage were at groups 3, 5, and 6 (Kruskal-Wallis,p = 0.05). CONCLUSION: Nd:YAG laser showed improved marginal sealing and decreased microleakage of composite resins restorations.