Izabela M. Barszczewska-Rybarek

Structure–property relationships in dimethacrylate networks based on Bis-GMA, UDMA and TEGDMA

OBJECTIVES In this work the influence of structural heterogeneity of poly(dimethacrylate)s on mechanical properties was investigated. Rigid aromatic dimethacrylate (Bis-GMA), triethylene glycol dimethacrylate (TEGDMA) and flexible aliphatic urethane dimethacrylate (UDMA) have been chosen for room-temperature homopolymerizations and copolymerizations induced by a camphorquinone/N,N-dimethylaminoethyl methacrylate photoinitiating system. METHODS The following mechanical properties of poly(dimethacrylate)s were investigated: flexural modulus, flexural strength, impact strength and hardness. Atomic force microscopy (AFM) and X-ray powder diffraction (XRPD) were used to describe the morphology of polymer networks. RESULTS AFM observations showed that the heterogeneity of networks is spatially organized due to the formation of microgels and their agglomeration. Observed agglomerates are unidirectionally oriented, parallel to the direction of polymerization shrinkage. Of all the investigated mechanical properties of poly(dimethacrylate)s, the impact resistance appeared to be the least. The origin of this brittleness could be the presence of heterogeneities which were quantitatively characterized by means of XRPD. The impact resistance was shown to be related to the size of network heterogeneities which is probably influenced by intermolecular interactions, such as hydrogen bonding. SIGNIFICANCE Differences in monomer structure resulted in significantly different morphology and physical properties of the polymer networks which had been studied. The size and shape of heterogeneities affected the final mechanical properties of the polymers, especially impact resistance. In addition, the combined application of XRPD and AFM techniques can be a successful tool in the analysis of the dimethacrylate network morphology, and finally, in investigations on methacrylate-based dental materials.

Antifungal Activity of Denture Soft Lining Material Modified by Silver Nanoparticles—A Pilot Study

Soft liner materials in oral cavity environments are easily colonized both by fungi and dental plaque. These factors are the cause of mucosal infections. The microorganism that most frequently colonizes soft liner materials is Candida albicans. Colonization occurs on the surface of materials and within materials. A solution to this problem might involve modification of soft liner materials with silver nanoparticles (AgNPs). In this article, we present results showing the antifungal efficacy of silicone soft lining materials modified with AgNPs. The modification process was conducted by dissolving both material components (base and catalyst) in a colloidal solution of AgNPs and evaporating the solvent. Composites with various AgNP concentrations (10, 20, 40, 80, 120 and 200 ppm) were examined. The in vitro antifungal efficacy (AFE) of composite samples was 16.3% to 52.5%.

Sorption, solubility, bond strength and hardness of denture soft lining incorporated with silver nanoparticles.

The colonization of denture soft lining material by oral fungi can result in infections and stomatitis of oral tissues. In this study, 0 ppm to 200 ppm of silver nanoparticles was incorporated as an antimicrobial agent into composites to reduce the microbial colonization of lining materials. The effect of silver nanoparticle incorporation into a soft lining material on the sorption, solubility, hardness (on the Shore A scale) and tensile bond strength of the composites was investigated. The data were statistically analyzed using two-way ANOVA and Newman-Keuls post hoc tests or the chi-square Pearson test at the p < 0.05 level. An increase in the nanosilver concentration resulted in a decrease in hardness, an increase in sorption and solubility, a decrease in bond strength and a change in the failure type of the samples. The best combination of bond strength, sorption, solubility and hardness with antifungal efficacy was achieved for silver nanoparticle concentrations ranging from 20 ppm to 40 ppm. These composites did not show properties worse than those of the material without silver nanoparticles and exhibited enhanced in vitro antifungal efficiency.

Characterization of urethane-dimethacrylate derivatives as alternative monomers for the restorative composite matrix

OBJECTIVE The aim was accomplished by a comparative analysis of the physicochemical properties of urethane-dimethacrylate (UDMA) monomers and their homopolymers with regard to the properties of basic dimethacrylates used presently in dentistry. The homologous series of UDMA were obtained from four oligoethylene glycols monomethacrylates (HEMA, DEGMMA, TEGMMA and TTEGMMA) and six diisocyanates (HMDI, TMDI, IPDI, CHMDI, TDI and MDI). METHODS Photopolymerization was light-initiated with the camphorquinone/tertiary amine system. Monomers were tested for viscosity and density. Flexural strength, flexural modulus, hardness, water sorption and polymerization shrinkage of the polymers were studied. The glass transition temperature and the degree of conversion were also discussed. RESULTS HEMA/IPDI appeared to be the most promising alternative monomer. The monomer exhibited a lower viscosity and achieved higher degree of conversion, the polymer had lower water sorption as well as higher modulus, glass temperature and hardness than Bis-GMA. The polymer of DEGMMA/CHMDI exhibited lower polymerization shrinkage, lower water sorption and higher hardness, however it exhibited lower modulus when compared to HEMA/TMDI. The remaining monomers obtained from HEMA were solids. Monomers with longer TEGMMA and TTEGMMA units polymerized to rubbery networks with high water sorption. The viscosity of all studied UDMA monomers was too high to be used as reactive diluents. SIGNIFICANCE The systematic, comparative analysis of the homologous UDMA monomers and corresponding homopolymers along with their physico-mechanical properties are essential for optimizing the design process of new components desirable in dental formulations. Some of the studied UDMA monomers may be simple and effective alternative dimethacrylate comonomers.

Fractal analysis of heterogeneous polymer networks formed by photopolymerization of dental dimethacrylates

OBJECTIVES In this work the influence of the dimethacrylate monomer chemical structure on structural heterogeneity and physico-mechanical properties of the resulting polymer networks was investigated. Rigid aromatic dimethacrylate (Bis-GMA), triethylene glycol dimethacrylate (TEGDMA) and flexible aliphatic urethane-dimethacrylate (UDMA) were chosen for room-temperature homopolymerizations and copolymerizations induced by camphorquinone/N,N-dimethylaminoethyl methacrylate photoinitiating system. METHODS Atomic force microscopy (AFM) was used for visualizing the morphology of poly(dimethacrylate)s, which was described by: the fractal dimension (D(F)), the generalized fractal dimensions (D(q) and ΔD) as well as the modified fractal dimension (D(β)). Estimated fractal characteristics were correlated with polymer density, hardness and impact strength. RESULTS AFM images of fractured surfaces revealed the highly complex morphology of dimethacrylate polymer networks. They were found to possess the fractal character. The fractal parameters were observed to be proportional to the density, hardness and impact resistance of investigated polymers. ΔD appeared to be a good indicator of the structural heterogeneity of dimethacrylate networks. The results suggest that the fracture behavior of poly(dimethacrylate) matrix of dental materials can be controlled by the fractal morphology. SIGNIFICANCE Correlating the morphological studies with the mechanical tests would be beneficial in defining the role of morphology in the mechanical behavior of dimethacrylate networks and consequently, lead to the development of a reliable method for identifying the cause of dental material failures under stress. Thus, fractal analysis could become one of the key elements in designing and developing dental materials.

Properties of Experimental Dental Composites Containing Antibacterial Silver-Releasing Filler

Secondary caries is one of the important issues related to using dental composite restorations. Effective prevention of cariogenic bacteria survival may reduce this problem. The aim of this study was to evaluate the antibacterial activity and physical properties of composite materials with silver sodium hydrogen zirconium phosphate (SSHZP). The antibacterial filler was introduced at concentrations of 1%, 4%, 7%, 10%, 13%, and 16% (w/w) into model composite material consisting of methacrylate monomers and silanized glass and silica fillers. The in vitro reduction in the number of viable cariogenic bacteria Streptococcus mutans ATCC 33535 colonies, Vickers microhardness, compressive strength, diametral tensile strength, flexural strength, flexural modulus, sorption, solubility, degree of conversion, and color stability were investigated. An increase in antimicrobial filler concentration resulted in a statistically significant reduction in bacteria. There were no statistically significant differences caused by the introduction of the filler in compressive strength, diametral tensile strength, flexural modulus, and solubility. Statistically significant changes in degree of conversion, flexural strength, hardness (decrease), solubility (increase), and in color were registered. A favorable combination of antibacterial properties and other properties was achieved at SSHZP concentrations from 4% to 13%. These composites exhibited properties similar to the control material and enhanced in vitro antimicrobial efficiency.

Prediction of Physical Properties of Dimethacrylate Polymer Networks by a Group Contribution Approach

In this work, the correlation between experimental and theoretical values of density (ρ) and glass transition temperature (T g ) of dimethacrylate polymer networks is elaborated. The developed methodologies are based on the additive principle of the known monomer chemical structures. The predicted values of ρ differed by a maximum of 1% from the experimental values. The methodology developed for T g prediction is based on the assumption that dimethacrylate structural units are treated as main chains between ‒CH2C(CH3)‒ tri-functional volumeless cross-links. Three-quarters of the calculated T g values differed less than 20 K from the experimental ones.

Evaluation of the Length of Primary Chains in Cross-Linked Poly(methacrylate)s

Two series of cross-linked polymers were examined by equilibrium swelling: poly(methyl methacrylate) cross-linked with different amounts of triethylene glycol dimethacrylate and poly(urethane dimethacrylate)s derived from dicarbamates of oligoethylene glycols monomethacrylates and aromatic diisocyanates. The method of estimation of the length of primary chains has been proposed based on the full form of the Flory-Rehner equation. This required comparing the network parameter values obtained by swelling and those derived from some other sources. In some cases the results had no physical meaning, whereas in others they appeared to be consistent. The latter for poly(urethane dimethacrylate)s yielded the length of poly(methacrylate) primary chains in the range of two to eight, which seemed to be a reasonable result.

DMA analysis of the structure of crosslinked poly(methyl methacrylate)s

PURPOSE This paper presents the study aimed at the development of crosslinked poly(methyl methacrylate)s (X-PMMA) of varied crosslink density and the investigation of the relationships between the polymer network structure and dynamic mechanical properties. METHODS A series of model X-PMMA networks were crosslinked by the introduction of: 1, 2, 5, 10 and 20% of triethylene glycol dimethacrylate (TEGDMA). The copolymerizations led to various glass-rubber relaxation properties of the polymer networks, as revealed by dynamic-mechanical analysis (DMA). Glass temperature (Tg) and storage modulus above the Tg (Erubbery ) were a sensitive function of network architecture. DMA data were used for calculating the network parameter (Mc), crosslink density (q) and its alternative measure - the degree of crosslinking (DX). RESULTS The viscoelastic properties as well as structural parameters calculated from those showed correlation with the amount of the crosslinker. The increase in TEGDMA content resulted in the Tg, q and DX increases, whereas Mc decrease. The possible incomplete conversion of double bonds was detected in the DMA analysis, which was confirmed by the degree of conversion (DC), measured by FTIR spectroscopy. Additionally, some amount of sol fraction was found by 1H NMR experiments. CONCLUSIONS The structure-property relationships developed for the system presented in this work could be useful in tissue engineering, where X-PMMA is applied. The direct measure of storage modulus values before and above glass transition may serve as a simple and fast indicator of the X-PMMA crosslink density.