Influence of hydrogen peroxide-based bleaching agents on the bond strength of resin–enamel/dentin interfaces

This study evaluated the effect of different bleaching techniques on the bond strength of pre-existing adhesive restorations in enamel and dentin. Hydrogen peroxide-based bleaching gels with different concentrations (7.5% and 35%) were used on composite restorations of Adper Single Bond 2 (3M/ESPE, St. Paul, USA) and Filtek Z250 (3M/ESPE, St. Paul, USA). Twenty human third molars were randomly divided into 8 groups: GE—enamel control; GE7.5—bleaching using 7.5% hydrogen peroxide; GE35—bleaching using 35% hydrogen peroxide; GE 7.5+35—bleaching using 7.5% and 35% hydrogen peroxide; GD—dentin control; GD7.5—7.5% hydrogen peroxide; GD35—35% hydrogen peroxide; and GD 7.5+35—7.5% and 35% hydrogen peroxide. Bleaching was performed using long clinical application-time to low concentration gel, and short clinical application-time to high concentration gel. Unbleached specimens were stored in artificial saliva for 14 days. Specimens subject to micro-shear testing and data were analyzed by Analysis of Variance and Tukey's test (p=0.05). Enamel micro-shear bond strength was reduced after 7.5% hydrogen peroxide and after association of 7.5% and 35% hydrogen peroxide. Bleaching treatment altered dentin bond strength only when using 7.5% hydrogen peroxide. The results suggest that the bond strength of the restorations was influenced by the clinical extent of bleaching-gel application time and was not dependent on bleaching-gel concentration.     

A new experimental adhesive system containing G-IEMA – physicochemical properties

The ultimate goal of this study was the development of a new Bis-GMA-free dental adhesive system with improved adhesive properties. Instead of Bis-GMA, a dendritic macromer (G-IEMA), derived from 2-isocyanatoethyl methacrylate (IEMA), was used and its physicochemical properties were investigated. G-IEMA was synthesized and subsequently incorporated into an experimental adhesive (AE2) formulated without Bis-GMA. Double bond conversion (DBC), polymerization shrinkage (PS), water sorption (WS) and solubility (SL) were evaluated and results were compared with three other adhesives: – an experimental adhesive formulated with Bis-GMA (AE1); Scotchbond? (SBU); and, Futurabond M+^? (FUT). Comparisons between adhesives for DBC, PS, WS and SL properties were performed using One-Way ANOVA and the Kruskal-Wallis test, at the 5% significance level. Statistical analysis of DBC data, using one-way ANOVA, revealed significant differences between adhesives (p < .001). AE2 presented a significantly higher DBC than SBU (p < .001) and FUT (p = .004); no significant differences were observed between AE2 and AE1 (p = .403) with 60?s of light-curing. Kruskal-Wallis test revealed no significant differences between adhesives (p = .094) for PS. One-Way ANOVA showed no significant differences among adhesives for WS (p = .213) and SL (p = .175). In conclusion, G-IEMA-based adhesive AE2 presented comparable DBC, PS, WS and SL when compared to Bis-GMA-based adhesive AE1. The results obtained so far are promising, revealing that G-IEMA macromer might be a good substitute monomer to prepare Bis-GMA-free adhesive systems.     

Pervaporation for Drying and Dewatering

Dewatering denotes moisture removal from materials and it is a more general term than drying. In dehydration and drying technology, a growing role of modern techniques used either separately or in hybrid solutions is observed. Membrane techniques find many industrial applications in this field. Based on available literature, examples of dehydration on membranes, important from the viewpoint of energy saving, environmental protection, and recoverable energy sources, are presented in this study. Special attention is given to the process of pervaporation as the most modern and promising technique for azeotropic mixture separation to be used in dehydration of solvents, including alcohols, and removal of volatile organic compounds from sewage, concentration of aromas, and separation of multicomponent systems.     

Interactions between a collagen-binding adhesive and dental substrate

The adhesion between polymer adhesives and dentin involves the removal of minerals, by acid etching the dentin surface, to allow for monomer infiltration among collagen fibrils. However, instability within this hybrid layer has been observed, which may partially be attributed to a slow degradation of the collagen not protected by the adhesive. The objective of this work was to improve the stability of the hybrid layer by increasing the interactions between adhesives and collagen through the incorporation of a monomer that behaves reactively toward collagen in the adhesive. In this work, a control adhesive was prepared based on a chemical formulation containing Bis-GMA and HEMA, and was modified by incorporating different concentrations (5, 10, and 20%) of NSA (N-acryloxysuccinimide), which contains an ester group capable of interacting with primary amine. These experimental adhesives were applied to bovine dentin for the in vitro production of the interfacial layer, which was analyzed by Raman spectroscopy and scanning electron microscopy. The obtained results showed that it was possible to incorporate the NSA monomer into the adhesive up to a maximum concentration of 10%. The presence of amide bonds in the Raman spectra, as well as the presence of a large amount of experimental adhesive within the interfacial layer, as indicated in the scanning electron microscopy images, may suggest the occurrence of chemical interactions between polymers and dentin collagen fibrils. These interfacial chemical interactions involving dental adhesives and dentin can be an important tool in protecting the hybrid layer from degradation.     

Influence of chlorhexidine in cavities prepared with ultrasonic or diamond tips on microtensile bond strength

This study evaluated the effect of chlorhexidine (CLX) in cavities prepared with either ultrasound-mounted CVDentUS diamond tips or conventional diamond burs on dentin bond strength after 24 h and 180 days. Forty-eight dentin surfaces from sound third molars were flattened and divided into four groups (n = 12), according to the type of cavity preparation (CVDentUS ultrasound tip or conventional diamond) and with or without 2% CLX (Consepsis) treatment. After application of the adhesive system (Clearfil SE Bond), microhybrid composite resin blocks (Charisma) were made on the dentin surface in increments. After 24 h, the specimens were sectioned into stick-shaped samples with an adhesive interface of approximately 1 mm². From each tooth, half of the sticks were evaluated after 24 h of storage in distilled water and the other half after 180 days, using a universal testing machine. Three-way analysis of variance showed no significant triple interactions (p = 0.722) or double interactions between factors. Higher bond strength values were observed with the use of ultrasonic tips (p = 0.019), irrespective of whether or not CLX was applied in either time period. No difference in bond strength values was observed in terms of CLX application (p = 0.581). No significant difference in bond strength values was shown after storage for 24 h or 180 days (p = 0.302). In conclusion, the ultrasonic tips promoted greater bond strength to dentin, irrespective of whether or not CLX was applied, and storage time.     

One-year bonding performance of one-bottle etch-and-rinse adhesives to dentin at different moisture conditions

Abstract

This study aimed to investigate the one-year bond strengths to dentin of one-bottle etch-and-rinse adhesive systems applied under different moisture conditions. Class V cavities were prepared in bovine incisors and randomly allocated (n?=?8) according to the type of adhesive system used – SB (Adper? Single Bond 2); PB (Prime & Bond 2.1); and XPB (XP Bond) – and the moisture condition kept in the cavity – moist, over-wet, and over-dry. Filtek? Z250 was used for teeth restoration. Specimens for microtensile bond strength (µTBS) test were obtained and stored in water for 24?h or 1?year, and submitted to mechanical testing. Data were analyzed using t-tests, ANOVA and the Holm–Sidak post hoc test (α?=?0.05). Weibull analysis was used to verify the reliability of specimens. The type of adhesive and the moisture condition of the substrate affected the µTBS. At 24?h, SB performed better under the moist and over-wet conditions. At 1?year, SB, PB, and XPB showed the greatest percentage reduction at the moist (～38%), over-wet (100%), and over-dry (100%) conditions, respectively. The reliability of adhesives was affected by the variable factors tested. In conclusion, the solvent composition of adhesives and the moisture condition of the substrate play an important role in the bond strength and bonding stability of resin-based restorations, as well as on the reliability of the adhesive interfaces over time.