Monomer Dimethacrylate Research Articles

The designing of degradable unsaturated polyester based on selective cleavage activated hydrolysis and its application in recyclable carbon fiber composites

In recent years, the extensive application of unsaturated polyester resins (UPRs) and their composites has resulted in an increasing environmental problem and it is necessary to find a simple and efficient recycling method especially for the high-value reinforced fibers. Here a self-polymerizable dimethacrylate monomer containing a cleavable unit, β-carbonyl hindered urethano, was designed for a degradable UPR which has a good flexible strength of 79 MPa and Tg of 119.7 °C. Moreover, through the hydrolysis of ester that was previously activated by selective cleavage of hindered C–O bond in urethano, the resin could be directly degraded in an aqueous solution (4/1 M ratio of hydrazine and NaOH and 0.04 mol/mL of total concentration) at 80 °C in 4 h, and the degraded products could be simply separated by solubility. Furthermore, its carbon fiber composite was degraded in only 2.5 h and the recycled carbon fiber fabrics well maintained their original woven structure, surface chemical composition, graphitized structure and mechanical strength. This work provides a new method for efficient degradation and recycling of fiber reinforced thermosetting resin composites.

Bio-based Non-estrogenic Dimethacrylate Dental Composite from Cloves

Bisphenol A (BPA), as an endocrine disruptor derived from petroleum-based chemicals, has been prohibited by several regulatory agencies for use in a wide variety of consumer products. For the sake of reducing human exposure to BPA derivatives and in the context of sustainability, it is far-reaching to develop high-performance and low-toxic materials from bountiful biomass sources. The objective of this work was to synthesize 2 bio-based dimethacrylate monomers, 2,2′-dially-4,4′-dimethoxy-5,5′-diglycerolate acrylatediphenylmethane (BEF-EA) and 2,2′-dially-4,4′-dimethoxy-5,5′-diglycerolate methacrylatediphenylmethane (BEF-GMA), using eugenol as the raw material. The estrogenic activity of bio-based bisphenol 2,2′-dially-4,4′-dimethoxy-5,5′-dihydroxydiphenylmethane (BEF) was evaluated and compared with estrogen and commercial bisphenols. After photopolymerization of the di(meth)acrylates diluted with tri(ethyleneglycol) dimethacrylate (TEGDMA), bio-based visible light-curing materials were prepared, and their properties were systematically investigated. Notably, di(meth)acrylates BEF-GMA and BEF-EA derived from these nonestrogenic bio-based phenols exhibited improved biocompatibility and low viscosity (down to 220–280 Pa.s). BEF-GMA and BEF-EA resin matrix exhibits lower volumetric polymerization shrinkage (about 8.5%), high photopolymerization reactivity (>50% in 60 s), and mechanical properties (fracture energy >5.5 N mm; flexural strength of 87–91 MPa, etc), which were comparable or superior to commercial Bis-GMA. The respective bio-based composites still exhibit adequate properties. Therefore, introducing eugenol-based visible light-curable dimethacrylate monomers into dental materials is a potential strategy to establish green sustainability and biocompatible dental materials without BPA.

Effects of ionic liquids and dual curing on vat photopolymerization process and properties of 3d-printed ionogels

Ionic liquids (ILs) can facilitate photopolymerization reactions involved in the fabrication of ionogels (IGs). In this study, ILs were immobilized by 3D printing through polymerization of vinyl-monomers in their medium. The effect of ILs on the vat photopolymerization (VP) process was studied. Multiple IL-compatible photopolymer formulations were developed by using EmimBF4, BmimBF4, OmimBF4, and EmimTFSI ionic liquids and photocurable N-vinylpyrrolidone (NVP) and triethylene glycol dimethacrylate (TEGDMA) monomers. The photoinduced radical copolymerization of NVP with TEGDMA was studied using a combination of photo-DSC, Jacobs working curves and FTIR methods. The analysis revealed a dichotomy of IL-based VP as the addition of ILs led to a significant acceleration of polymerization and an increase in the critical exposure energy due to a higher conversion degree necessary for the gelation. Moreover, the Jacobs working curves showed that penetration depth dramatically changed with IL type. Based on these results, overcuring time was calculated and applied in the VP process to ensure that enough monomers were converted in each 3d-printed layer to prevent interlayer cracking. Furthermore, the dual curing approach was applied to achieve the highest possible conversion by adding a thermal initiator (AIBN). Dual curing increased the mechanical properties of ionogels but led to a reduced ionic conductivity due to an inhibition of IL’s mobility. In addition, this study found IL compositions for ionogels demonstrating no shrinkage after photopolymerization and post-curing. We suggest that the outcomes of the present study created a platform for fabricating high-resolution 3d-printed nonvolatile and nonflammable ionogels.

Preparation and characterization of silica based nanoclusters as reinforcement for dental applications

AbstractAs composite resins become the most extensively utilized material in the field of cosmetic and restorative dentistry, several strategies to overcome dental composites' challenges such as long‐term mechanical failure and secondary caries are continuously being developed. Among them, the design of suitable fillers to optimize their clinical performance has been given priority in addressing those shortcomings. In this study, silica‐based nanoclusters were synthesized and used as fillers to prepare UV curable dental composites was assessed. Nanoclusters were prepared by prepolymerization followed by pulverization and sieving of commercial silica nanoparticles with triethylene glycol dimethacrylate monomer. The composites were then made by filling 55:25:20 weight ratio of urethane dimethacrylate, bisphenol A glycidyl methacrylate, and triethylene glycol dimethacrylate, respectively with varying concentration of nanoclusters. The clusters and composites were characterized by SEM, TGA, and FTIR analyzes. The results have shown a significant improvement of physical and mechanical properties in composites containing nanoclusters. Increasing nanocluster concentration caused a reduction in composite polymerization shrinkage, water absorption and solubility as well as limited rise of flexural strength. At 50% filler load, nanoclusters doped composites exhibited higher flexural strength than nanoparticles doped composites. Furthermore, the blending of nanoclusters with nanoparticles as fillers produced the composites having the lowest polymerization shrinkage (2.2%) and the highest flexural strength (113.91 MPa). Overall, the synthesized nanoclusters have shown greater performance in comparison with the current available silica nanoparticles.

Effects of Sr/F-Bioactive Glass Nanoparticles and Calcium Phosphate on Monomer Conversion, Biaxial Flexural Strength, Surface Microhardness, Mass/Volume Changes, and Color Stability of Dual-Cured Dental Composites for Core Build-Up Materials.

This study prepared composites for core build-up containing Sr/F bioactive glass nanoparticles (Sr/F-BGNPs) and monocalcium phosphate monohydrate (MCPM) to prevent dental caries. The effect of the additives on the physical/mechanical properties of the materials was examined. Dual-cured resin composites were prepared using dimethacrylate monomers with added Sr/F-BGNPs (5 or 10 wt%) and MCPM (3 or 6 wt%). The additives reduced the light-activated monomer conversion by ~10%, but their effect on the conversion upon self-curing was negligible. The conversions of light-curing or self-curing polymerization of the experimental materials were greater than that of the commercial material. The additives reduced biaxial flexural strength (191 to 155 MPa), modulus (4.4 to 3.3), and surface microhardness (53 to 45 VHN). These values were comparable to that of the commercial material or within the acceptable range of the standard. The changes in the experimental composites’ mass and volume (~1%) were similar to that of the commercial comparison. The color change of the commercial material (1.0) was lower than that of the experimental composites (1.5–5.8). The addition of Sr/F-BGNPs and MCPM negatively affected the physical/mechanical properties of the composites, but the results were satisfactory except for color stability.

Swelling behavior and tensile strength of additively manufactured and commercial O-rings in the presence of linear, branched, cyclic, and aromatic compounds and alcohols

O-rings were manufactured using vat photopolymerization additive manufacturing (AM) processes using acrylate and dimethacrylate monomers. Preliminary tests using Flexible 80A and Elastic 50A resin with various printing orientations show that Flexible 80A in the “optimal” orientation is best for printing. Exposure of these O-rings and those from commercial sources to linear, branched, cyclic, and aromatic compounds and alcohols for 24 h causes swelling and changes in the ultimate tensile strength. AM O-rings swell less than the commercially manufactured acrylate O-rings, and their greatest swellings occur with aromatic compounds and the least swellings with linear alkanes. The swelling behavior of commercial O-rings is consistent with reported Hansen solubility parameters. The AM O-ring swelling patterns as a function of Hansen solubility parameters are similar to those of commercial acrylate O-rings. The tensile strength of the unexposed AM O-rings is less than the commercial O-rings and has greater variability. Swelling reduces the ultimate tensile strength of the acrylate O-rings. After evaporation, the tensile strengths of most of the O-rings return to their unexposed values. One major exception is AM O-rings exposed to toluene, where structural damage caused much lower tensile strengths.

Nondestructive x-ray reflectivity analysis of Al distributions of ultraviolet-cured spin-coated resist films hybridized with trimethylaluminum

Ultraviolet (UV)-cured spin-coated resist films of 100 nm and thinner thicknesses made with bisphenol A-based dimethacrylate monomers on silicon substrates were hybridized by multiple-pulsed vapor infiltration of sequential trimethylaluminum (TMA) doses and a final H2O dose. Nondestructive x-ray reflectivity measurements without film shrinkage enabled characterization of the internal layer structures of the UV-cured films unmodified before hybridization and hybridized by TMA infiltration and chemical fixing. It was possible to determine the thickness, density, and interface roughness of each layer in the unmodified and hybridized UV-cured films. The TMA infiltration and chemical fixing resulted in the formation of the highest-density Al-rich layer near the film surface. The presence of the highest-density layer arising from the most abundant component, Al, was confirmed through energy-dispersive x-ray spectroscopy and time-of-flight secondary ion mass spectrometry. The increase in the cycle number of TMA dose from 100 to 150 and 200 cycles had little effect on organic–inorganic hybridization of the 100 nm-thick UV-cured films. The thickness of the outermost Al-rich layer near the film surface was approximately 30 nm, which was unchanged when the film thicknesses of 100, 75, and 50 nm were changed. The outermost skin layer suppressed the infiltration of TMA into the UV-cured films. The infiltration of TMA into the UV-cured films progressed as the film thicknesses decreased.

A novel shape memory polymer composites with grafted hydroxyapatite nanoparticles for high strength and stiffness applications

AbstractShape memory polymer (SMP) composites have evolved uniquely, employing nanoscale fillers, which add multifunctionality to the basic resin. In this work, the effect of inorganic, grafted hydroxyapatite (g‐HAp) nanoparticles on the dynamic (mechanical), thermo‐mechanical and microstructural properties of copolymer, based on diurethane dimethacrylate (DUDMA), (t‐butyl acrylate (tBA), and crosslinker poly(ethylene glycol) dimethacrylate (PEGDMA), has been investigated. The agglomeration of nanofillers is limited by using PEG dimethacrylate monomer to graft HAp nanoparticles. Importantly, it is observed that mixing DUDMA in (tBA + PEGDMA) has improved the Young's Modulus of SMP composite to 5.4 GPa at RT (comparable to aircraft grade resin) with a glass transition temperature (Tg) of 55°C. Tensile stress is high as 51.46 MPa with improved strain at failure from 0.07% to 0.05%. The elongation strains of 4–8% are achieved, which provide the required strain compatibility to develop aerospace SMPs as well as SMP composites for structural and bio‐medical applications.

An approach for the scalable production of macroporous polymer beads

A tubular co-flow reactor to produce macroporous polymer beads by polymerization of medium and high internal phase emulsion (M/HIPE) templates was developed. This reactor allows for improved production rates compared to tubing based microfluidic devices. Water-in-oil (W/O) M/HIPEs, containing methyl methacrylate (MMA) and ethylene glycol dimethacrylate (EGDMA) monomers in the continuous phase, were injected into a re-circulating carrier phase. The continuous phase of the emulsion droplets was UV polymerized in situ, resulting in polyM/HIPE beads. The emulsion composition was adjusted to produce poly(MMA-co-EGDMA) porous polymer beads with a protective crust and an interconnected internal pore structure. HCl loaded beads were produced by adding the active ingredient into the dispersed emulsion phase, leading to HCl encapsulation in the porous structure of the beads after polymerization. Even after exposure to ambient conditions for 24 h, 60% of the HCl remained in the beads, indicating good encapsulation efficiencies. Thus, it is possible to use such macroporous beads as delivery vehicles.

Properties of A Model Self-Healing Microcapsule-Based Dental Composite Reinforced with Silica Nanoparticles.

Aim: The purpose of this study was to evaluate the mechanical properties of an experimental self-healing dental composite model (SHDC) composed of SiO2 nanoparticles with varying percentages of triethylene glycol dimethacrylate (TEGDMA) monomer and N,N-dihydroxyethyl-p-toluidine (DHEPT) amine microcapsules. Materials and methods: Microcapsules were prepared by in-situ polymerisation of PUF shells, as explained in our previous work. The model SHDC included bisphenol A glycidyl dimethacrylate (Bis-GMA:TEGDMA) (1:1), 1 wt% phenyl bis(2,4,6-trimethylbenzoyl) phosphine oxide (BAPO), 0.5 wt% benzoyl peroxide (BPO) catalyst, 20 wt% silanised silica dioxide (SiO2) (15 nm) and (0, 2.5, 5, 7.5, 10 wt%) of microcapsules (120 ± 45 μm). Light transmission, hardness, degree of conversion (DC), flexural strength and elastic modulus of the SHDC model were measured. Results: The degree of conversion of the SHDC ranged from 73 to 76% 24 h after polymerisation. Hardness measurements ranged from 22 to 26 VHN (p > 0.05); however, the flexural strength was adversely affected from 80 to 55 MPa with increasing microcapsules of up to 10 wt% in the composites (p < 0.05). Conclusion: Only flexural strength decreased drastically ~30% with increasing microcapsules (>10 wt%) in the composites. All other measured properties were not significantly affected. Accordingly, we recommend a stronger composite material that could be created by increasing the filler content distribution in order to achieve a hybrid self-healing composite with enhanced mechanical properties.

Degradable and Recyclable Unsaturated Polyester Resin Based on the Selective Cleavage of a Hindered C–O Bond

The extensive use of unsaturated polyester resins and their composites has resulted in an increasingly aggravating problem of waste materials which are difficult to remold or degrade endowed by their highly crosslinked network. A simple and facile recovery method to fully degrade resins remains challenging so far. Here, a hindered C–O bond with a carbonyl group in the β-position of steric ester was introduced into the design and preparation of a dimethacrylate monomer and its self-polymerized unsaturated polyester resin. The obtained resin with good thermal, mechanical, and solvent-resistance properties could be efficiently degraded within 3.5 h at 90 °C at an 80% concentration of aqueous hydrazine hydrate. Selective cleavage of the hindered bond due to steric and electronic effects was activated by the prior addition of the introduced carbonyl group. Degradation products rich in benzene and carboxyl/carboxylate groups respectively could be separated readily according to the water solubility, being expected to be reused as a flocculant and other functional additives. This work provides a promising strategy for the facile recycling of unsaturated polyester resins.

Influence of Dimethacrylate Monomer on the Polymerization Efficacy of Resin-Based Dental Cements—FTIR Analysis

The degree of polymerization for dimethacrylate resin-based materials (BisGMA, TEGDMA, UDMA, HEMA) ranges from 55 to 75%. Literature data indicate that polymerization efficacy depends, among other factors, on the type of methacrylate resin comprising the material. The aim of this study was to evaluate the polymerization efficacy of four dental cement materials characterized by different polymerization mechanisms using FTIR analysis. In the present study, the FTIR method was adopted to analyze the degree of polymerization efficacy of four resin-based dental cement materials, two of which were self-cured and two were dual-cured cements. The IR spectral analysis was performed 24 h after the polymerization of the cementitious material. RelyX ARC cement exhibits the lowest polymerization efficacy (61.3%), while that of Variolink II (85.8%) and Maxcem Elite is the highest (90.1%). Although the efficacy of self-cured cements appears to be superior, the difference is not statistically significant (p = 0.280). Polymerization efficacy largely depends on the chemical structure of the material in terms of the presence of a particular methacrylate resin and less on the polymerization mechanism itself, i.e., whether it is a self-cured or dually cured dental cement. Thus, in clinical practice, cementitious materials with a higher proportion of TEGDMA compared with BisGMA are recommended.

Preparation and evaluation of novel bio-based Bis-GMA-free dental composites with low estrogenic activity

ObjectiveAlthough bisphenol Aglycidyl methacrylate (Bis-GMA) are widely used in the dental composite, its raw materials include the petroleum-based product bisphenol A (BPA) with high estrogenic activity (EA). In this study, two new BPA-free dimethacrylate monomers from bio-based material creosol were synthesized and evaluated. MethodsThe renewable bisphenol monomer 5, 5'-methylenedicreosol (BCF) was prepared from bio-based material creosol. By the human breast cancer cells (MCF-7 cells) proliferation assay, a risk assessment of BCF was performed to determine if BCF possessed reduced EA in comparison to BPA. Then, the novel monomers 5, 5'-methylenedicreosol diglycidyl ether diacrylate (BCF-EA) and 5, 5'-methylenedicreosol diglycidyl ether dimethacrylate (BCF-GMA) were synthesized from BCF with epichlorohydrin and (meth)acrylate. All products were investigated by 1H NMR and FT-IR spectra. The control resin was a mixture based on Bis-GMA and tri(ethyleneglycol) dimethacrylate (TEGDMA) with a weight ratio of 5:5 (5B5T). Similarly, experimental resin matrix was a mixture based on BCF-EA/TEGDMA (5E5T) and BCF-GMA/TEGDMA (5G5T). And their corresponding composites were then prepared with corresponding resin matrices and hybrid SiO2 (5E5TC, 5G5TC and 5B5TC). The properties of these composites were investigated according to the standard or referenced methods. Each sample was evaluated for double bond conversion (DC), shrinkage stress (SS) and volumetric polymerization shrinkage (VS). Water sorption (WS), water solubility (SL), mechanical properties and cytotoxicity were also measured. Results1H NMR and FT-IR spectra confirmed the chemical structure of each monomer. EA test revealed that bio-based bisphenol monomer BCF as the precursor of BCF-EA and BCF-GMA showed lower EA than BPA. Cured resin matrix: Both 5E5T and 5G5T had nearly the same DC (p < 0.05), which was higher than 5B5T (p < 0.05); 5E5T and 5G5T had lower VS, SL and cytotoxicity than 5B5T (p < 0.05); mechanical properties of 5E5T and 5G5T were all better than those of 5B5T (p < 0.05). Cured composite: There was no significant difference in conversion (p < 0.05); 5E5TC and 5G5TC had significantly lower VS (p < 0.05); WS of 5E5TC and 5G5TC were similar (p < 0.05), but higher compared to 5B5TC (p < 0.05); 5E5TC and 5G5TC had the deeper depth of cure (p > 0.05); before water immersion, there was no significant difference in flexural strength between 5E5TC and 5G5TC (p > 0.05), and higher than 5B5TC (p < 0.05); 5E5TC and 5G5TC showed less cytotoxicity than 5B5TC (p < 0.05). SignificanceThe new BPA-free di(meth)acrylates are promising photocurable dental monomers owning to bio-based raw material, high degree of conversion coupled with low curing shrinkage and good mechanical properties. Therefore, BCF-EA and BCF-GMA has a potential to be used as the substitution for Bis-GMA to prepare Bis-GMA-free dental composite.

Synthesis of uniform submicron poly(lactic acid)-based particles/capsules by radical precipitation polymerization

Poly(l-lactic acid) (PLLA) is a well-known biopolymer, usually synthesized via step-growth or ring-opening polymerization from lactic acid or a lactide monomer, respectively. PLLA microspherical particles are produced by dispersion polymerization with a ring-opening lactide monomer using a particular copolymer chain as a stabilizer. This is not easy to achieve when dehydration is needed. Here, a robust and simple synthesis of a nearly monodisperse, submicron PLLA-based particle/capsule was proposed via radical precipitation polymerization without the use of surfactant. A commercial PLLA was first glycolyzed with ethylene glycol to obtain a low molecular weight glycolyzed PLLA (GPLLA). Then, the GPLLA was copolymerized with methacrylic acid and ethylene glycol dimethacrylate monomers using a benzoyl peroxide initiator. Active sites on the GPLLA backbone were generated by hydrogen abstraction of benzoyloxy radicals that further copolymerized before self-assembly to form the polymer particles. Uniform particle size of about 580 nm with a low polydispersity index (PDI) of 0.012 was obtained. This method was also implemented to produce nearly monodisperse capsules containing linalool. The particle size of PLLA-based capsules was about 280 nm with narrow particle size distribution (PDI of 0.120). The PLLA-based capsules effectively inhibited microbial growth of Staphylococcus aureus, Escherichia coli and Candida albicans and were not toxic to human cells.

Mechanical Properties of Experimental Composites with Different Photoinitiator.

Objective The effect of different photoinitiators on mechanical properties of experimental composites was evaluated. Materials and Methods Resin composites were formulated by using a blend of bisphenol A-glycidyl and triethylene glycol (50/50 wt%) dimethacrylate monomers, and 65 wt% of barium aluminium silicate and silica filler particles. Photoinitiators used were 0.2% camphorquinone (CQ) and 0.8% co-initiator (DMAEMA); 0.2% phenyl-propanedione and 0.8% DMAEMA; 0.1% CQ + 0.1% phenyl propanedione and 0.8% DMAEMA; 0.42% mono(acyl)phosphine oxide (MAPO); and 0.5% bis(acyl)phosphine oxide (BAPO). Specimens ( n = 10) were light cured by using a multiple-emission peak light-emitting diode for 20 seconds at 1,200 mW/cm 2 of irradiance and Knoop hardness and plasticization, depth of cure, flexural strength, and elastic modulus were evaluated. Data were statiscally analyzed at significance level of α = 5%. Results Experimental composites containing MAPO and BAPO photoinitiators showed the highest values of flexural strength, elastic modulus, top surface hardness, and lower hardness reduction caused by alcohol compared with CQ. Composites containing CQ and PPD showed similar results, except for depth of cure and hardness of bottom surface. Conclusion BAPO and MAPO showed higher flexural strength, elastic modulus, hardness on top surface, and lower polymer plasticization to CQ.

Raman spectroscopic study of gamma radiation‐initiated polymerization of diethylene glycol dimethacrylate in different solvents

AbstractIn this work, the degree of conversion and polymerization kinetics of diethylene glycol dimethacrylate (DEGDMA) monomer in different solvents upon gamma irradiation with different doses have been studied by Raman spectroscopy and mass difference measurements. Density functional theory calculations were performed on the monomer and the crosslinked structure to obtain the assignment of Raman peaks to specific bonds. The evolution of the bonding configuration of the structure with dose and the composition of the monomer mixture was investigated. The dependence of the polymerization rate on the solvent type was explained by the mechanism of the polymerization affected by the relative solubility of the components of the monomer mixture. Raman measurements revealed also that there are not fully crosslinked monomer molecules in the polymer matrix.

Effect of Incorporating a Dimethacrylate Monomer on the Shear Bond Strength of Two Adhesive Resin Cements to Zirconia Ceramic.

Self-assembled nano-layering resulting from interaction of the phosphate functional group of adhesive monomers with zirconia ceramic surface has been proposed. The purpose of this study was to investigate the bond strengths of two adhesive resin cements (Panavia F 2.0 and BisCem) containing phosphate monomers added with various concentrations (0.0, 1.0, 3.0, and 5.0 wt%) of triethylene glycol dimethacrylate (TEGDMA) to air-abraded zirconia ceramic. The polished/air-abraded zirconia plates (KaVo Everest® ZS-Ronde) were imaged using atomic force microscopy and the average surface roughness (Ra) values were calculated (n = 5). The surface energy parameters of the zirconia plates and the resin cements were calculated based on the extended Fowkes theory. All resin-bonded (diameter: 2.38 mm) zirconia specimens were stored in water at 37 °C for 24 h and then half of them additionally thermocycled 10,000 times before the shear bond strength (SBS) test (n = 10). Air-abrasion of zirconia surface significantly increased the γhS (hydrogen bonding component) value (p < 0.001), as well as greatly increasing the surface area (p < 0.001). For both resin cements, the γhS (dipole-dipole component) gradually increased with increasing incorporated TEGDMA concentrations, whereas the γhS gradually decreased. Overall, the addition of 3.0 wt% of TEGDMA consistently resulted in higher SBS values even after thermocycling. Under the tested condition, reducing the concentration of the adhesive monomers with phosphate functional group by adding the dimethacrylate monomer (up to 3.0 wt%) increased the bond strength between the resin cements and zirconia ceramic.

Development of di-methacrylate quaternary ammonium monomers with antibacterial activity

Nine antibacterial di-methacrylate monomers based on bis-quaternary ammonium salts (bis-QAMs) were synthesized and structurally characterized. The biological activity of the bis-QAMs was tested in terms of minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) on different bacterial strains achieving promising results and, in most cases, a complete bactericidal effect using a bis-QAM concentration lower than 1 mg/mL. Two of the structures showed comparable and superior activity against S. mutans than the commercial monomer 12-methacryloyloxydodecyl pyridinium bromide (MDBP). All the bis-QAMs here described were able to inhibit S. mutans biofilm formation at a concentration equal to the MIC value. From the analysis of the obtained data, some correlation regarding the structure and the antibacterial activity of the bis-QAMs could be drawn: a flexible alkyl C12 spacer between the two quaternary ammonium moieties increased the monomer antibacterial effect in comparison to the aromatic ones; the equilibrium between hydrophobic and hydrophilic moieties was directly correlated to the bactericidal range of action; the increase of the steric hindrance of the ammonium side groups might be both advantageous or disadvantageous to the antibacterial efficacy depending on the whole monomer chemical structure. Even though the possible correlation between the monomer structures and their bacteriostatic or bactericidal effect is under investigation, the monomers exhibited low cytotoxicity on human dental pulp stem cells, confirming their promising potential in the dental materials' field. Statement of significanceThe use of dental resins with antibacterial monomers might prevent the formation of secondary caries at the restoration margins. For this purpose, a series of di-methacrylate bis-quaternary ammonium monomers (QAMs) was developed. Unlike antibacterial mono-methacrylate monomers already described in the literature, the synthesized di-methacrylate monomers have the potential of acting as cross-linkers stabilizing the polymeric network and bear two quaternary ammonium groups that increase their antibacterial ability.The QAMs exert bactericidal activity on both Gram(+) and Gram(−) bacterial strains maintaining at the same time good biocompatibility with the oral environment.Some structural elements of the monomers were clearly related to high antibacterial properties, and this can help design new active structures and better understand their mechanism of action.

Surface Integrity of Dimethacrylate Composite Resins with Low Shrinkage Comonomers.

The goal of current research was to investigate the influence of adding low shrinkage “Phene” like comonomers hexaethylene glycol bis(carbamate-isoproply-α-methylstyrene) (HE-Phene) and triethylene glycol bis(carbamate-isoproply-α-methylstyrene) (TE-Phene) on the surface and color characteristics of composite resin. A range of weight fractions (0, 10, 20, 30, 40 wt.%) of HE/TE-Phene monomers were mixed with bisphenol A glycidyl methacrylate (GMA)/triethylene glycol dimethacrylate (TEGDMA) monomer. Experimental composite resins were made by mixing 71 wt.% of silica fillers to 29 wt.% of the resin matrix. A Vickers indenter and glossmeter were used for testing surface hardness (SH) and gloss (SG) at 60°. A chewing-simulator was used to evaluate the surface wear after 15,000 cycles. Color change (∆E) and translucency parameter (TP) were measured using a spectrophotometer. Data showed that HE/TE-Phene monomer had no negative impact (p > 0.05) on surface gloss, wear, color change and translucency of experimental composite resins. Surface hardness was in a reducing direction with the increas in HE/TE-Phene weight fraction (p < 0.05). The study results suggested that incorporating HE/TE-Phene monomers up to 30 wt.% with Bis-GMA/TEGDMA resin did not negatively influence the surface integrity of composite resins except for SH.

TEGDMA (Triethylene Glycol Dimethacrylate) Induces Both Caspase-Dependent and Caspase-Independent Apoptotic Pathways in Pulp Cells.

Monomers leached from resin-based composites (RBCs) may reach intrapulpal concentrations of the millimolar (mM) range, which could contribute to inflammation. The aim of this investigation was to assess the cytotoxicity of triethylene glycol dimethacrylate (TEGDMA) monomers on pulp cells as well as to identify molecular mechanisms leading to apoptosis. Pulp cells were harvested from molars extracted for orthodontic reasons and cultured through an explant method. To assess cytotoxicity, cells underwent a 5-day exposure to 0.75, 1.5, and 3 mM TEGDMA and were subject to cell counting and WST-1 staining. Based on the findings, cells were subsequently exposed to 0.1, 0.2, 0.75, 1.5, and 3 mM TEGDMA for 24 h to uncover the details of apoptosis. Changes in the production or cleavage of the apoptosis-specific proteins caspase-8, caspase-9, caspase-3, caspase-12, and Apoptosis-Inducing Factor (AIF) were measured by Western blot. The 5-day study showed concentration- and time-dependent cytotoxicity. Significant cell death was detected after 24 h with TEGDMA concentrations of 1.5 and 3 mM. One-day exposure to TEGDMA led to the activation of caspase-8, -9, -3, and -12 and an increased AIF production. Results suggest that relevant concentrations of TEGDMA monomers, leached from RBCs, induce apoptosis in pulp cells through both caspase-dependent as well as caspase-independent mechanisms. Endoplasmic reticulum stress and the activation of caspase-independent apoptotic pathways may be further mechanisms by which monomers induce apoptosis in pulp cells.