Maria Carolina G. Erhardt

Dentin treatment with MMPs inhibitors does not alter bond strengths to caries-affected dentin

OBJECTIVES This study aimed to investigate if the use of protease inhibitors (EDTA and chlorhexidine) may influence microtensile bond strength (MTBS) of an etch-and-rinse adhesive system to caries-affected human dentin. METHODS Flat middle coronal dentin surfaces with a central region of caries-affected dentin surrounded by sound dentin were bonded with Adper Scotchbond 1 after: (1) etching with 35% H3PO4; (2) etching with 0.1M EDTA and (3) 35% H3PO4-etching followed by 5% chlorhexidine application. Resin composite build-ups were constructed incrementally and trimmed to yield hourglass specimens (0.8mm2 bonded area) that contained sound or caries-affected dentin (confirmed after debonding by microhardness measurements - KHN). Bonded specimens were tensioned at 0.5mm/min. Data were analyzed by ANOVA and multiple comparisons tests (p<0.05). Failure mode analysis was performed by scanning electron microscopy (SEM). RESULTS H(3)PO(4), EDTA and chlorhexidine pre-treatments yielded similar MTBS values, in both dentin substrates. Bond strength to sound dentin was significantly higher than that to caries-affected dentin after H3PO4-etching. Caries-affected dentin exhibited lower KHN than sound dentin. CONCLUSIONS Conditioning of caries-affected dentin with EDTA or a combined use with H3PO4 and chlorhexidine may be proposed as these protease inhibitors do not reduce MTBS to caries-affected dentin if compared to conventional H3PO4 treatment.

Increases in dentin-bond strength if doubling application time of an acetone-containing one-step adhesive.

This study investigated the microtensile bond strength (microTBS) of a one-step self-etching adhesive to human dentin and bovine enamel following different bonding treatments. Occlusal portions of human molars and labial surfaces of bovine incisors were ground flat to provide uniform dentin and enamel surfaces, respectively. Futurabond was used following five different protocols: 1) according to the manufacturers directions, 2) acid etched with 36% phosphoric acid (H3PO4) for 15 seconds, 3) 10% sodium hypochlorite (NaOCl) treated for two minutes after H3PO4-etching, 4) doubling the application time of the adhesive and 5) doubling the number of adhesive coats. Composite build-ups (6 mm in height) were constructed incrementally with Arabesk resin composite. The specimens were stored in 100% humidity for 24 hours at 37 degrees C and sectioned into beams of 1.0 mm2 cross-sectional area. Each beam was tested in tension in an Instron machine at 0.5 mm/minute, and mean microTBS data (MPa) were analyzed by one-way ANOVA and post-hoc multiple comparisons tests (alpha = 0.05). Doubling the application time of Futurabond attained the highest microTBS to dentin; whereas, no differences among all bonding application parameters evaluated could be detected when the adhesive was applied to enamel.

Adjunctive use of an anti-oxidant agent to improve resistance of hybrid layers to degradation.

OBJECTIVE To determine the role of an anti-oxidant agent (ascorbic acid-AA) on resin-dentin bonds resistance to degradation of two adhesives. METHODS Flat dentin surfaces from 48 human molars were bonded as per manufacturers instructions with: a two-step etch-and-rinse self-priming adhesive (Single Bond-SB) and a two-step self-etch adhesive (Clearfil SE Bond-CSE). Half of the specimens were bonded with the same adhesives, but after the addition of 10% AA into their formulation. Resin composite build-ups were constructed incrementally and sectioned into resin-dentin beams (1.0mm(2)) that were stored under four conditions: (1) water immersion for 24h; (2) water immersion for 1 year; (3) water immersion for 4 years; and (4) chemical challenging (immersion in 10% NaOCl for 5 h). Beams were pulled to failure in tension at 0.5mm/min. Mean microtensile bond strength (MTBS) data were analysed with ANOVA and multiple comparisons tests (P<0.05). Analysis of debonded dentin beams was performed by scanning electron microscopy (SEM). RESULTS After 24 h, SB and CSE performed equally, regardless of AA incorporation. Inclusion of AA on CSE formulation decreased MTBS following one-year water storage, but maintained SB bond strength values even after four years of water storage. NaOCl challenge diminished MTBS for both adhesives, but when AA was added to SB, this reduction was significantly lower. CONCLUSIONS The inclusion of AA on adhesives formulation exerts a protective role on resin-dentin bonds resistance to degradation when SB is used. Bonding durability of CSE may be compromised by the addition of sodium ascorbate.

One-step self-etching adhesive polymerization: Influence of a self-curing activator

OBJECTIVES The objectives of this work were to study the spatially resolved extent of photopolymerization and the final volumetric contraction of the self-etching adhesive Xeno IV (Dentsply/Caulk, Milford, DE, USA) in association with the self-curing agent Aurora (Dentsply/Caulk, Milford, DE, USA), using (1)H Stray-Field magnetic resonance imaging ((1)H STRAFI-MRI). METHODS One-dimensional (1)H STRAFI-MRI images (projections along an axis, profiles) were acquired from the adhesive with and without Aurora, before and after solvent removal. Specimens were observed after the irradiation period recommended by the manufacturers and new profiles were recorded. Extent of polymerization and volumetric contraction were obtained by subtracting the profile of the cured adhesive from the profile of the liquid; the profiles were previously normalized using an external reference signal and the highest magnetization intensity recorded from the cured adhesive, respectively. Data were obtained in the presence of oxygen. Solvent evaporation was measured by gravimetry. RESULTS High volumetric contraction was observed for Xeno IV and Xeno IV and Aurora mixture mainly related to solvent evaporation. A drying period favourably influenced the extent of photopolymerization of Xeno IV, which did not increase in the presence of Aurora. CONCLUSIONS The incorporation of Aurora reduced the extent of polymerization of the one-step adhesive, probably due to the increase in the solvent content of the mixture. It may be that enhancing solvent evaporation is important in order to reach a higher extent of polymerization during the bonding procedure.