Correction to: The use of clays for chlorhexidine controlled release as a new perspective for longer durability of dentin adhesion.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

The use of clays for chlorhexidine controlled release as a new perspective for longer durability of dentin adhesion.

The adhesive systems have the function to establish the connection between the restorative material and dental tissue, therefore it is of fundamental importance, because failures in the adhesive interface can reduce the life of a dental restoration. This study investigated the possibility of using the adhesive layer as a chlorhexidine modified release system evaluating their impact on the properties of these systems as well as evaluating the impact of these systems on immediate and post-aging dentin adhesion. Were used a matrix with BisGMA, UDMA, HEMA and TEGDMA copolymer and clay particles (Dellite 67G); associated with a chlorhexidine and a camphorquinone photoinitiator system. The properties of these systems were evaluated by the XRD, FTIR spectrophotometer, flexural strength, elasticity modulus, drug release, enzymatic inhibition and dentin adhesion resistance. The presence of the clay can raise the mechanical properties of the adhesive systems engendering a more resistant hybrid layer and led to a more sustained release of chlorhexidine in the systems, allowing a longer effective period of MMP-2 inhibition. The hypothesis that the addition of clays as release modulators could increase the effectiveness of these drugs in inhibiting the dentin's MPPs and consequently enhancing the adhesive durability was confirmed. These results indicate that the controlled release of chlorhexidine is able to reduce the process of loss of adhesion presenting itself as a promising system to increase the longevity of dental restorations.

Effect of Nanofiller Loading on Cure Efficiency and Potential Color Change of Model Composites.

OBJECTIVES: To evaluate the effect of nanofiller loading on cure efficiency and potential color change of experimental composites. MATERIALS AND METHODS: Four different polymeric materials were produced using the same organic matrix blend. To this matrix, different amounts of 0.05 µm fumed silica filler were added: no filler, 13, 52, and 65wt%. Fourier transform infrared spectroscopy was used to evaluate the degree of conversion (DC) for each composite using near-IR analysis, and spectrophotometry according to CIELab chromatic space was used to evaluate the color change.To induce color change, composites were artificially aged with exposure to cycles of UV-B light for 300 hours. Trasmission electron microscopy was used to illustrate nanoffiler aglomeration in the resin matrix. Data were analyzed using correlation analysis (α = 0.05). RESULTS: There was an excellent inverse linear correlation between filler wt% and either DC or color change. Greater changes to red (+Δa) and yellow (+Δb) were observed as the filler wt% increased. CONCLUSIONS: A higher percentage of nano-sized filler particles in dental resin composites directly affects their cure efficiency and potential for color change. CLINICAL SIGNIFICANCE: The increase in filler particle loading negatively affected monomer conversion and color stability of resin-based composites. As reduced filler loading results in poorer mechanical properties, to enhance color stability, resin-based composites should be formulated by making the refractive index of the polymeric matrix more closely match that of the filler throughout the polymerization process. (J Esthet Restor Dent, 2016).

In vitro characterization of a biocompatible composite based on poly(3-hydroxybutyrate)/hydroxyapatite nanoparticles as a potential scaffold for tissue engineering.

The use of regeneration scaffolds has been a promising strategy in the bone tissue engineering area. Among the materials available for this purpose the poly(3-hydroxybutyrate) - PHB stands out for its adequate biocompatibility and osteoinduction capacity. Hydroxyapatite, in turn, has as its main characteristics its ability to increase bioactivity and cell proliferation. Thus, the objective of the present study was to obtain PHB composites with nanohydroxyapatite (Hap) (0.05%, 0.20%, and 0.50%) and evaluate the microstructure, thermal and mechanical properties and molecular dynamics. Besides that, in vitro biological properties such as wettability, cell viability and adhesion of L929 fibroblasts cells, enzymatic degradation and radiographic contrast were evaluated. The results indicate a weak interaction between Hap and PHB, however, the dispersion states of the nanoparticles can influence crystallization and thermal stability. Through the evaluation of the mechanical behavior was verified a harder behavior with the Hap addition. The wettability of the systems showed a tendency to increase with the addition of nanoparticles. All systems presented high values of viability and cell adhesion, the latter being more pronounced for systems containing Hap. The nanoparticles acted as a barrier slowing the rate of enzymatic degradation and contributed to the increase in radiographic contrast. The results obtained indicate that the systems are promising for application in tissue engineering.

The use of an elastomeric methacrylate monomer (Exothane 24) to reduce the polymerization shrinkage stress and improve the two-body wear resistance of bulk fill composites.

OBJECTIVES: Characterize the chemical structure of an elastomeric monomer (Exothane 24) and evaluate the degree of conversion (DC), polymerization shrinkage stress (PSS), rate of polymerization (Rp), flexural strength (FStrenght), flexural modulus (FModulus), Vickers hardness (VHardness) and two-body wear resistance of dental bulk fill composites (BFCs) containing Exothane 24. METHODS: The Exothane 24 was characterized using mass spectroscopy, elemental analysis, 13C- and 1H NMR. BFCs were formulated containing Exothane 24 (E10, E25, and E50). Similar BFCs containing regular UDMA (U10, U25, and U50), commercial conventional, and BFCs were used as control groups. ATR-FTIR spectroscopy was used to measure DC and the Rp of the composites. The PSS was measured using the universal testing machine method. Specimen bars were used to assess the FStrenght, FModulus, and VHardness. RBCs were submitted to a two-body wear test using a chewing simulator machine; the rate and volumetric wear loss were evaluated using an optical scanner. Data were analyzed statistically with α = 0.05 and ß = 0.2. RESULTS: Exothane 24 is a urethane isophorone tetramethyl methacrylate monomer with polymerization stress-relieving properties. No differences were found in the DC up to 4 mm in depth for E25. All BFCs had similar FStrenght, except for E50. E25 had the lowest volumetric wear loss and wear rate. E25 had approximately 30% lower PSS and slower Rp than commercial BFCs with similar wear resistance to conventional commercial composites. SIGNIFICANCE: The Exothane 24 reduced the PSS and increased the wear resistance of BFCs; however, the formulation is important to optimize the properties of the BFCs.

Production and Characterization of Poly (Lactic Acid)/Nanostructured Carboapatite for 3D Printing of Bioactive Scaffolds for Bone Tissue Engineering.

Biocompatible scaffolds are porous matrices that are bone substitutes with great potential in tissue regeneration. For this, these scaffolds need to have bioactivity and biodegradability. From this perspective, 3D printing presents itself as one of the techniques with the greatest potential for scaffold manufacturing with porosity and established structure, based on 3D digital modeling. Thus, the objective of the present work was to produce 3D scaffolds from the poly (lactic acid) (PLA) and the nanostructured hydroxyapatite doped with carbonate ions (CHA). For this purpose, filaments were produced via fusion for the fused-filament 3D printing and used to produce scaffolds with 50% porosity in the cubic shape and 0/90°configuration. The dispersive energy spectroscopy and Fourier transform infrared spectroscopy (FTIR) analysis demonstrated the presence of CHA in the polymeric matrix, confirming the presence and incorporation into the composite. The thermogravimetric analysis made it possible to determine that the filler concentration incorporated in the matrix was very similar to the proposed percentage, indicating that there were no major losses in the process of obtaining the filaments. It can be assumed that the influence of CHA as a filler presents better mechanical properties up to a certain amount. The biological results point to a great potential for the application of PLA/CHA scaffolds in bone tissue engineering with effective cell adhesion, proliferation, biocompatibility, and no cytotoxicity effects.

Effect of monomer type on the CC degree of conversion, water sorption and solubility, and color stability of model dental composites.

OBJECTIVE: This study has investigated the influence of BisGMA, BisEMA, BisEMA 30, and two UDMA-based monomers (UDMA and Fit 852), with TEGDMA as co-monomer, on the degree of conversion, water sorption, water solubility, and optical properties of experimental dental composites. METHODS: Materials were formulated at 70/30 molar rations using BisGMA, BisEMA, BisEMA 30, UDMA or FIT 852, as base monomers, combined with TEGDMA. 60wt% of silanated-glass particles was added. Degree of conversion (DC) and polymerization kinetics were monitored using Fourier-transformed infrared spectroscopy in the near-IR range. Water sorption (Wsp) and solubility (Wsl) were assessed using mass variation after 60days water storage. Color was evaluated using a digital spectrophotometer, applying the CIELab parameters 24h after dry storage and 60days after water immersion to calculate ΔE values. All data were analyzed using ANOVA and Tukey's test (pre-set alpha=0.05). RESULTS: The BisGMA-based co-monomer mixture presented the lowest DC (62±1%), whereas BisEMA 30 had the highest DC value (95±2%). The highest Wsp was observed for BisEMA 30 (12.2±0.8%), and the lowest for BisEMA (0.4±0.1%). BisEMA has shown the lowest Wsl (0.03±0.01%) and BisEMA 30 the highest one (0.97±0.1%). The ΔE values showed that BisEMA 30 (7.3 color units) and Fit 852 (3.8 color units) altered the color stability providing ΔE>3.3, which is considered clinically unacceptable. CONCLUSIONS: The chemical composition and structure of the base monomer influenced the degree of conversion, water sorption, water solubility, and color stability. Considering the overall results, it is possible to state that the base monomer BisEMA mixed with the co-monomer TEGDMA presented the best performance in terms of all the parameters tested. SIGNIFICANCE: The resin matrix composition might influence physical property degradation processes and color stability of dental resin composites. Formulations based on BisEMA seem most promising for materials' development.