Development of an antibacterial and anti-metalloproteinase dental adhesive for long-lasting resin composite restorations.

Despite all the advances in adhesive dentistry, dental bonds are still fragile due to degradation events that start during application of adhesive agents and the inherent hydrolysis of resin-dentin bonds. Here, we combined two outstanding processing methods (electrospinning and cryomilling) to obtain bioactive (antimicrobial and anti-metalloproteinase) fiber-based fillers containing a potent matrix metalloproteinase (MMP) inhibitor (doxycycline, DOX). Poly(ε)caprolactone solutions containing different DOX amounts (0, 5, 25, and 50 wt%) were processed via electrospinning, resulting in non-toxic submicron fibers with antimicrobial activity against Streptococcus mutans and Lactobacillus. The fibers were embedded in a resin blend, light-cured, and cryomilled for the preparation of fiber-containing fillers, which were investigated with antibacterial and in situ gelatin zymography analyzes. The fillers containing 0, 25, and 50 wt% DOX-releasing fibers were added to aliquots of a two-step, etch-and-rinse dental adhesive system. Mechanical strength, hardness, degree of conversion (DC), water sorption and solubility, bond strength to dentin, and nanoleakage analyses were performed to characterize the physico-mechanical, biological, and bonding properties of the modified adhesives. Statistical analyses (ANOVA; Kruskal-Wallis) were used when appropriate to analyze the data (α = 0.05). DOX-releasing fibers were successfully obtained, showing proper morphological architecture, cytocompatibility, drug release ability, slow degradation profile, and antibacterial activity. Reduced metalloproteinases (MMP-2 and MMP-9) activity was observed only for the DOX-containing fillers, which have also demonstrated antibacterial properties against tested bacteria. Adhesive resins modified with DOX-containing fillers demonstrated greater DC and similar mechanical properties as compared to the fiber-free adhesive (unfilled control). Concerning bonding performance to dentin, the experimental adhesives showed similar immediate bond strengths to the control. After 12 months of water storage, the fiber-modified adhesives (except the group consisting of 50 wt% DOX-loaded fillers) demonstrated stable bonds to dentin. Nanoleakage was similar among all groups investigated. DOX-releasing fibers showed promising application in developing novel dentin adhesives with potential therapeutic properties and MMP inhibition ability; antibacterial activity against relevant oral pathogens, without jeopardizing the physico-mechanical characteristics; and bonding performance of the adhesive.

Acrylamides and methacrylamides as alternative monomers for dental adhesives.

OBJECTIVE: Synthesize and characterize a methacrylamide monomer for adhesive system and evaluate the physicochemical properties of the adhesive resin. METHODS: The liquid methacrylamide monomer N,N',N″-(nitrilotris(ethane-2,1-dyil)tris(2-methylacrylamide) (TMA) was prepared by reaction of methacrylic anhydride and tris(2-aminoethyl)amine with 60% yields. The TMA structure was analyzed by 1H NMR, 13C NMR, ATR-FTIR and UHPLC-QTOF-MS. Experimental adhesive resin containing bisphenol-A glycidyl methacrylate (BISGMA), 2-hydroxyethylacrylamide (HEAA), 2-hydroxyethylmethacrylate (HEMA) and TMA were formulated. Polymerization kinetics of neat TMA and experimental adhesive resin (TMA33%/HEAA66%, TMA50%/HEAA50%, TMA66%/HEAA33%, TMA50%/HEMA50%, BisGMA/HEAA/TMA and BisGMA/HEMA) were evaluated using Differential Scanning Calorimetry. Physiochemical properties for BisGMA/HEAA/TMA and BisGMA/HEMA adhesives were evaluated by cytotoxicity, ultimate tensile strength (UTS), softening in solvent (ΔKHN), contact angle (θ), microtensile bond strength (µTBS) and failure analysis. A primer was also formulated with H2O/HEAA/AMPS (2-acrylamido-2-methylpropane sulfonic acid) and the pH value was verified and compared to commercial primer. RESULTS: Adhesive resin with only HEAA and TMA (TMA33%/HEAA66%, TMA50%/HEAA50%, TMA66%/HEAA33%) showed lower conversion and polymerization rate after 40s of light activation. Conversion up to 60% was found for BisGMA/HEAA/TMA and BisGMA/HEMA adhesive resin without significant difference between groups, p>0.05. Cytotoxicity, UTS, µTBS, ΔKHN and θ showed no statistical difference, p>0.05, between BisGMA/HEAA/TMA and BisGMA/HEMA adhesive resin. SIGNIFICANCE: In this study, the proposed synthetic route resulted in a tris(methacrylamide). A new primer composed without acrylates or methacrylates was formulated for 3-step etch-and-rinse adhesive system without the presence of HEMA monomer. Physicochemical properties and cell viability of BisGMA/HEAA/TMA adhesive resin represents an alternative adhesive resin without HEMA monomer.

Effect of nanostructured zirconium dioxide incorporation in an experimental adhesive resin.

OBJECTIVES: The aim of this study was to evaluate the influence of nanostructured zirconium dioxide incorporation in an experimental adhesive resin. METHODS: ZrO2 particles were characterized by X-ray diffraction (XRD), micro-Raman spectroscopy and Brunauer-Emmett-Teller (B.E.T). Experimental adhesive resins were formulated with 0, 0.5, 1, 4.8, and 9.1% ZrO2 in weight. The adhesives were evaluated based on degree of conversion (DC), radiopacity, softening in solvent and microtensile bond strength (µTBS) 24 h and after 1 year of aging. Mineral deposition at the hybrid layer was assessed with micro-Raman spectroscopy at the baseline and after 14 days. RESULTS: XRD showed monoclinic and tetragonal phases of ZrO2.particles. B.E.T data revealed a surface area of 37.41 m2/g, and typical chemical groups were shown on the Raman spectra. The addition of ZrO2 did not influence the radiopacity. The addition of 4.8% and 9.1 wt.% ZrO2 showed higher initial hardness with increased softening in solvent (P < 0.05) and promoted mineral deposition at the dentin interface. DC was significantly increased in the group with 1% ZrO2 (P < 0.05). The µTBS test showed difference on the group with 9.1 wt.% of ZrO2, with a significant reduction after aging. CONCLUSION: The incorporation of ZrO2 promoted mineral deposition on the adhesive interface and the addition of 1 wt.% caused a significant increase on the DC without compromising the other physicochemical characteristics, which may prove promising for the development of new dental adhesive systems. CLINICAL RELEVANCE: The mineral deposition on the hybrid layer can result in a longer stability of the adhesive, thus delaying the hydrolytic degradation.

The influence of calcium chloride on the setting time, solubility, disintegration, and pH of mineral trioxide aggregate and white Portland cement with a radiopacifier.

This study evaluated the influence of addition of 10% calcium chloride (CaCl(2)) on the setting time, solubility, disintegration, and pH of white MTA (WMTA) and white Portland cement (WPC). A test of the setting time was performed following the #57 ADA specifications and a test of the final setting time according to the ASTM. For the solubility tests disintegration and pH, Teflon rings were filled with the cements and weighed after setting. After 24 h in a desiccator, they were once again weighed. Thereafter, they were immersed in MiliQ water for 24 and 72 h and 7, 14, and 28 days, with maintenance in the desiccator and weighing between periods. The pH of water in which the rings were immersed was measured immediately after contact with them and in the other periods. The addition of CaCl(2) provided a significant reduction (50%) in the initial setting time of cements. The final setting time of WMTA was reduced in 35.5% and the final setting time of WPC in 68.5%. The WMTA with CaCl(2) absorbed water and gained weight with time, except for in the 24-h period. The addition of CaCl(2) to the WPC reduced its solubility. The addition of CaCl(2) increased the pH of WMTA in the immediate period and at 24 and 72 h and for WPC in the immediate period and at 24 h. The addition of CaCl(2) to WMTA and WPC reduced the setting times and solubility of both and increased the pH of cements in the initial periods.