Evaluation of new compositions of 10% hydrogen peroxide-based bleaching agents containing trimetaphosphate and fluoride on enamel demineralization

This study evaluated the effect on enamel demineralization of 10% hydrogen peroxide (H₂ O₂ ) gels containing different concentrations of sodium trimetaphosphate (TMP) and sodium fluoride (NaF) combined with the daily use of fluoridated or placebo dentifrice. Bovine enamel blocks were selected by surface hardness (n = 72) and randomly assigned to one of the following experimental treatments: 10% H₂ O₂ ; 10% H₂ O₂  + 3% TMP + 0.1% NaF; and 10% H₂ O₂  + 0.3% TMP + 0.05% NaF, each with or without fluoridated dentifrice. H₂ O₂ -based gels were applied for 30 min d^-1 followed by treatment with dentifrice (1 min). Enamels blocks were stored in artificial saliva at 37°C between sessions during the 14 days of experiment. Percentage of surface hardness loss (%SH) was calculated, and the blocks were cut into halves to analyze cross-sectional hardness (ΔKHN). Polarized light microscopy images were obtained of the longitudinal sections of the samples. Enamel treated with fluoridated dentifrice presented lower hardness loss than those treated with placebo dentifrice (%SH and ΔKHN). Use of TMP- and NaF-based gels, regardless of concentration, led to the lowest %SH values. Specimens treated with 10% H₂ O₂ gel had the highest %SH and ΔKHN values. Gels with 10% H₂ O₂  + 3% TMP + 0.1% NaF showed the lowest ΔKHN values. Microscopy images clearly showed that the addition of TMP and NaF to the H₂ O₂ -based gels was effective in reducing the loss of hardness, and the fluoridated dentifrice helped minimize it in all treatments.

Fluoride-containing adhesive: durability on dentin bonding

OBJECTIVES

To evaluate (1) the influence of fluoride-containing adhesive on microtensile bond strength (microTBS) and (2) in vitro secondary caries inhibition at the resin-dentin interface after 24 h and 3 months water-storage and (3) the degree of conversion of different adhesives after 24h 1 month.

METHODS

Flat surfaces of human teeth were ground and randomly assigned to six groups: (SBMP-24) Scotchbond Multi-Purpose control [SBMP], 24 h; (SE-24) SBMP etch and primer+Clearfil SE Bond adhesive [SE], 24h; (PB-24) SBMP etch and primer+Clearfil Protect Bond adhesive [PB], 24h; (SBMP-3) SBMP, 3 months; (SE-3) SBMP+SE, 3 months; and (PB-3) SBMP+PB, 3 months. To evaluate the effect of the adhesive resin alone, all teeth were etched with 35% phosphoric acid and primed with SBMP primer prior to applying the adhesive resin. Bonded assemblies were prepared for microTBS and stored in distilled water at 37 degrees C for 24h and 3 months. Sections of restored teeth of each group were exposed to an acid challenge. The specimens were sectioned, polished, and then observed with polarized light microscopy (PLM). Also, the degree of conversion (DC) of the adhesives was measured using Fourier Transform-Infrared spectroscopy (FTIR) at 24 h and 1 month, after polymerization.

RESULTS

microTBS values obtained in MPa (24h/3m) were: (MP) 61.5+/-10.5/52.9+/-8.9, (SE) 55.5+/-11.8/55.6+/-13, and (PB) 50.3+/-9.9/61.0+/-13.6. For interface analysis by PLM, an inhibition zone (IZ) adjacent to the hybrid layer was created only when the fluoride-containing adhesive (PB) was used. The DC in percentage (24 h, 1 month) were: (MP) 60.5+/-2.8/61.3+/-0.6, (SE) 69.6+/-1.3/70.7+/-0.05, and (PB) 53.1+/-0.4/58.3+/-1.6.

SIGNIFICANCE

The fluoride-containing adhesive demonstrated significant increase of bond strength values after water-storage. This material was also able to create an acid inhibition zone in dentin. There was a significant increase of degree of conversion after 1 month only for PB.

Effect of long-term water storage on etch-and-rinse and self-etching resin-dentin bond strengths

This study sought to evaluate the long-term bond strength of etch-and-rinse and self-etch adhesive systems to dentin after one year of water storage. Crown fragments from the buccal surface of extracted bovine incisors were ground flat to expose dentin surfaces. Four etch-and-rinse and two self-etch bonding agents were used according to manufacturers' instructions. Bonded specimens were stored in water for either 24 hours or one year at 37 delete C. After elapsed storage times, specimens were tested for shear bond strength (SBS) at 0.5 mm/min. Data were analyzed by ANOVA and Tukey's tests (p < 0.05). Both evaluated factors (adhesive system and storage time) and their interactions were statistically significant. Single Bond produced the highest SBS regardless of the water degradation period. One-year water storage reduced the SBS of Prime & Bond NT and One-Up Bond F significantly; the other adhesives performed similarly. Long-term bond strengths of etch-and-rinse and self-etch adhesive systems are susceptible to hygroscopic and hydrolytic effects to varying extents, depending on their chemistry and structure. The presence of monomers with different properties might induce preferential degradation of specific adhesive polymer systems.

In vitro microleakage of composite restorations after nonvital bleaching

OBJECTIVE

After bleaching treatment, esthetic restorations often need to be replaced due to color changes. Some papers have shown alterations in the bond of adhesive restorations to bleached teeth. The purpose of this study was to evaluate tooth and resin composite adhesion when submitted to nonvital dental bleaching.

METHOD AND MATERIALS

One hundred and twenty bovine teeth were assigned to 3 groups (n = 40); paste of sodium perborate and water; 37% carbamide peroxide gel; and no bleaching (control). After 3 weeks of continuous bleaching treatment, standardized Class V cavities were prepared at the cementoenamel junction and restored with Single Bond adhesive system and Z100 resin composite. The samples were thermocycled 1,500 times (5 +/- 1/55 +/- 1 degrees C) with a 1-minute dwell time. Then, they were immersed in a 2% methylene blue solution (pH 7) for 4 hours, sectioned, and analyzed by stereomicroscopy. Microleakage analyses were done, using scores from 0 to 4, considering leakage on the incisal wall (enamel) and the cervical wall (dentin). Data were analyzed by Kruskal-Wallis and Mann-Whitney tests (alpha = 0.05).

RESULTS

The results showed that sodium perborate and carbamide peroxide gel significantly increase the microleakage in Class V resin composite restorations to dentin but not to enamel margins.

CONCLUSION

The risk of microleakage in dentin margins is increased soon after bleaching treatment.