Biomedical subjects

Joseph M Antonucci

Publications and source records attributed to Joseph M Antonucci.

11 recordsLinked to original sources

PubMed2007

Interphase effects in dental nanocomposites investigated by small-angle neutron scattering.

Small-angle and ultrasmall-angle neutron scattering (SANS and USANS) were used to characterize silica nanoparticle dispersion morphologies and the interphase in thermoset dimethacrylate polymer nanocomposites. Silica nanoparticle fillers were silanized with varying mass ratios of 3-methacryloxypropyltrimethoxysilane (MPTMS), a silane that interacts with the matrix through covalent and H-bonding, and n-octyltrimethoxysilane (OTMS), a silane that interacts through weak dispersion forces. Interphases with high OTMS mass fractions were found to be fractally rough with fractal dimensions, D(s), between 2.19 and 2.49. This roughness was associated with poor interfacial adhesion and inferior mechanical properties. Mean interparticle distances calculated for composites containing 10 mass % and 25 mass % silica suggest that the nanoparticles treated with more MPTMS than OTMS may be better dispersed than OTMS-rich nanoparticles. The results indicate that the covalent bonding and H-bonding of MPTMS-rich nanoparticles with the matrix are necessary for preparing well-dispersed nanocomposites. In addition, interphases containing equal masses of MPTMS and OTMS may yield composites with overall optimal properties. Finally, the combined SANS/USANS data could distinguish the differences, as a function of silane chemistry, in the nanoparticle/silane and silane/matrix interfaces that affect the overall mechanical properties of the composites.

Dental Materials↗

PubMed2005

Interphase structure-property relationships in thermoset dimethacrylate nanocomposites.

OBJECTIVES: The aim of this research was to better understand the relationships between interphase composition and the resultant mechanical properties of thermoset methacrylate nanocomposites, ultimately for the purpose of improving the properties of dental restorative materials through manipulation of the interphase. METHODS: Silica nanoparticles were silanized with three different silanes and blends of those silanes to generate six different interphase compositions. The silanes varied in their relative polarity, flexibility, and reactivity towards photo-polymerization. Composites containing 60% by mass of the silanized fillers were prepared and analyzed for uncured paste handling characteristics, vinyl conversion, biaxial flexure strength (BFS), modulus, and Knoop hardness. RESULTS: Dual silanization of the fillers improved the handling characteristics of the uncured composite pastes compared to those containing fillers silanized with 3-methacryloxypropyltrimethoxysilane. To obtain high BFS, functional groups reactive in free radical polymerization were needed in the composite interphase, but a high concentration of those groups was not necessary. Moduli were highest for composites with interphases that contained styrylethyltrimethoxysilane, a reactive aromatic silane. The hardness values of the composites with reactive interphases were all comparable. Methacrylate conversion was only modestly influenced by silane interphase composition. SIGNIFICANCE: This study suggests that dual silanization is a practical method for improving the handling characteristics of uncured dental restorative nanocomposites while maintaining or improving the mechanical properties of the cured composites.

Chemical Phenomena↗

PubMed2005

Ethoxylated bisphenol dimethacrylate-based amorphous calcium phosphate composites.

Improving the anti-demineralizing/remineralizing and mechanical properties of amorphous calcium phosphate (ACP) composites has been the focus of our recent research. In this study, an ethoxylated bisphenol A dimethacrylate (EBPADMA) was blended with triethylene glycol dimethacrylate (TEGDMA), 2-hydroxyethyl methacrylate (HEMA) and methacryloxyethyl phthalate (MEP) to form experimental resins with different EBPADMA/TEGDMA molar ratios (0.50, 0.85 and 1.35) and a constant HEMA/MEP molar ratio (8.26). Composites were prepared by admixture of either unmilled or milled zirconia-ACP filler (40% by mass) and photo-activated resin (60% by mass). One aim was to test if improved ion release can be achieved by elevating the EBPADMA/TEGDMA ratio while lowering the level of surface active methacryloxyethyl phthalate in the resin without adversely affecting the biaxial flexure strength (BFS), degree of vinyl conversion (DC) and water sorption (WS) of composites. A second aim was to assess the effect of using milled vs. unmilled ACP on these properties. Ion release of all composites was significantly above the theoretical minimum necessary for remineralization. Calcium ion release was not impeded by binding with the carboxylic acid groups of MEP. Increased supersaturation was attained with increasing EBPADMA/TEGDMA ratio in the resin. Variations in resin composition had no effect on BFS or DC of composites. The BFS of the milled ACP composites was higher than the BFS of unmilled ACP composites (56% and 79%, respectively for dry and wet specimens). DC of composites was only moderately reduced (13.6% and 7.3%, for unmilled and milled ACP, respectively) compared to unfilled resins. WS decreased in the following order: unmilled ACP composites>milled ACP composites>copolymers. Fine-tuning of the resin and utilizing milled ACP filler improved the remineralizing potential of ACP composites without impeding their DC, BFS or WS.

Adsorption↗

PubMed2005

Systematic variation of interfacial phase reactivity in dental nanocomposites.

This study was designed to determine the effect of varying the chemistry of the interfacial phase on critical composite properties in dental nanocomposite materials. Silica nanoparticles were silanized with varying ratios of 3-methacryloxypropyltrimethoxysilane (MPTMS) and octyltrimethoxysilane (OTMS) while keeping the total amount of silane constant at 10% by mass fraction relative to the mass of filler. The silanized nanoparticles were mixed into a dimethacrylate resin (60% filler by mass fraction). The mechanical properties of the uncured pastes were assessed by compression testing between parallel plates. The composites were photo-cured and tested by biaxial flexure and three-point bend flexure testing. Fracture surfaces were analyzed by field-emission scanning electron microscopy (FE-SEM). At maximized filler mass fractions, the workabilities of the uncured pastes were better maintained as the fraction of OTMS in the interphase increased relative to MPTMS. The flexure strengths and moduli of the MPTMS silanized and dual silanized composites were similar but decreased as OTMS mass fractions in the silane mixture increased to 7.5% and 10%. FE-SEM images revealed evidence for phase separation in the composites containing silica silanized with high fractions of OTMS. Among the potential practical benefits of dual silanized nanoparticles are the improved workability of composite pastes with higher filler loadings that should lead to higher modulus composites with lower polymerization shrinkage.

Bisphenol A-Glycidyl Methacrylate↗

PubMed2003

Synthesis, characterization and evaluation of urethane derivatives of Bis-GMA.

OBJECTIVES: The aims of the study were to synthesize derivatives of Bis-GMA having pendant n-alkyl urethane substituents and to characterize and evaluate their physicochemical properties. METHODS: Stoichiometric amounts of Bis-GMA and n-alkyl isocyanates were reacted in dichloromethane with dibutyltin dilaurate as a catalyst. Volumetric shrinkage, water uptake, degree of vinyl conversion, refractive index and viscosity of resulting urethane monomers and those of Bis-GMA were measured. The flexural strengths of their corresponding homopolymers and that of Bis-GMA were also measured. RESULTS: These types of urethane derivatives of Bis-GMA exhibited lower viscosities and were more hydrophobic than Bis-GMA. Generally, the viscosity of these experimental monomers decreased with increasing chain length of the alkyl urethane substituent. Photopolymerization of the new monomers gave high degrees of vinyl conversion compared to Bis-GMA. The experimental monomers also yielded polymers with lower polymerization shrinkages at equivalent degrees of vinyl conversion, than Bis-GMA. The refractive indices of these urethane derivatives were similar to Bis-GMA, but the flexural strengths of their polymers were lower than that of the Bis-GMA homopolymer, decreasing with increasing chain length of the alkyl urethane substituent. SIGNIFICANCE: Because of their excellent overall properties, these new derivatives of Bis-GMA have potential as dental monomers that can improve many properties of resin based dental materials that utilize methacrylate monomer systems.

Bisphenol A-Glycidyl Methacrylate↗

PubMed2003

Effect of bifunctional comonomers on mechanical strength and water sorption of amorphous calcium phosphate- and silanized glass-filled Bis-GMA-based composites.

This study seeks to elucidate structure-property relationships in a series of unfilled dental copolymers and their composites. The copolymers/composites were derived from photo-activated binary monomer systems based on 2,2-bis[p-2'-hydroxy-3'-methacryloxypropoxy)phenyl] propane (Bis-GMA) and equimolar amounts of a bifunctional, surface-active comonomer, i.e., 2-hydroxyethyl methacrylate (HEMA), glycerol dimethacrylate (GDMA) or ethylene glycol methacrylate phosphate (PHEMA). Triethyleneglycol dimethacrylate, a widely used comonomer for Bis-GMA, was used as a control. Two types of fillers were investigated: (1) a hydrophilic, silica-modified amorphous calcium phosphate (Si-ACP) and (2) a more hydrophobic, silanized nanosized silica (n-SiO(2)). Both the unfilled copolymers and their composites were evaluated for biaxial flexure strength (BFS), both dry and wet after 30 days immersion in buffered saline, and for water sorption (WS) and their WS kinetic profiles. The Bis-GMA copolymers and composites derived from HEMA and GDMA had BFS and WS values, as well as WS kinetic profiles, similar to the controls. Copolymers and composites based on Bis-GMA/PHEMA had lower BFS and higher WS values. Si-ACP composites had significantly lower BFS values (that were further diminished on soaking) than their copolymers. WS increased as the level of this filler was increased except for Bis-GMA/PHEMA composites. With n-SiO(2) as the filler, a more moderate reduction in BFS occurred compared to the unfilled copolymers. By contrast to Si-ACP composites, the WS of all the n-SiO(2) composites decreased with increasing filler level. From this study it is evident that both the chemical structure of the polymer matrix and the type of filler system can have significant effects on the strength and water-related properties of dental composites.

Absorption↗

PubMed2002

Dental resin composites containing silica-fused whiskers--effects of whisker-to-silica ratio on fracture toughness and indentation properties.

Dental resin composites need to be strengthened in order to improve their performance in large stress-bearing applications such as crowns and multiple-unit restorations. Recently, silica-fused ceramic whiskers were used to reinforce dental composites, and the whisker-to-silica ratio was found to be a key microstructural parameter that determined the composite strength. The aim of this study was to further investigate the effects of whisker-to-silica ratio on the fracture toughness, elastic modulus, hardness and brittleness of the composite. Silica particles and silicon carbide whiskers were mixed at whisker:silica mass ratios of 0:1, 1:5. 1:2, 1:1, 2:1, 5:1, and 1:0. Each mixture was thermally fused, silanized and combined with a dental resin at a filler mass percentage of 60%. Fracture toughness was measured with a single-edge notched beam method. Elastic modulus and hardness were measured with a nano-indentation system. Whisker:silica ratio had significant effects on composite properties. The composite toughness (mean+/-SD; n = 9) at whisker:silica = 2:1 was (2.47+/-0.28) MPa m(1/2), significantly higher than (1.02+/-0.23) at whisker:silica = 0:1, (1.13+/-0.19) of a prosthetic composite control, and (0.95+/-0.11) of an inlay/onlay composite control (Tukey's at family confidence coefficient = 0.95). Elastic modulus increased monotonically and hardness plateaued with increasing the whisker:silica ratio. Increasing the whisker:silica ratio also decreased the composite brittleness, which became about 1/3 of that of the inlay:onlay control. Electron microscopy revealed relatively flat fracture surfaces for the controls, but much rougher ones for the whisker composites, with fracture steps and whisker pullout contributing to toughness. The whiskers appeared to be well-bonded with the matrix, probably due to the fused silica producing rough whisker surfaces. Reinforcement with silica-fused whiskers resulted in novel dental composites that possessed fracture toughness two times higher than, and brittleness less than half of current dental composites.

Carbon Compounds, Inorganic↗

PubMed2002

A microshear test to measure bond strengths of dentin-polymer interfaces.

The microbond test. a single fiber shear test, has been adapted to be a microshear test for the measurement of the adhesion of resin-based dental materials to dentin and enamel. The objective of this study is to improve the design of this microshear test so that it can provide accurate and reliable shear bond strength data. In the current design of the microshear test apparatus, the bonding diameters of the specimens have been as small as 0.70 mm. The smaller diameters give researchers the ability to test several bonded specimens on one flat dentin or enamel surface, thus allowing both for the regional mapping of the mineralized surface and the conservation of extracted teeth needed to provide the necessary substrates. The test corfiguration used in earlier studies has been modified through finite element analysis to address concerns in the test methodology. The results of this study show that the microshear bond test can be a useful tool in helping to understand the complex interactions that occur at the interface between dental composites and dentin and/or enamel surfaces, especially at interfacial sites not amenable to macroshear testing.

Adhesiveness↗

PubMed2002

Effect of thermal cycling on whisker-reinforced dental resin composites.

The mechanical properties of dental resin composites need to be improved in order to extend their use to high stress-bearing applications such as crown and bridge restorations. Recent studies used single crystal ceramic whiskers to reinforce dental composites. The aim of this study was to investigate the effects of thermal cycling on whisker-reinforced composites. It was hypothesized that the whisker composites would not show a reduction in mechanical properties or the breakdown of whisker-resin interface after thermal cycling. Silicon carbide whiskers were mixed with silica particles, thermally fused, then silanized and incorporated into resin to make flexural specimens. The filler mass fraction ranged from 0% to 70%. The specimens were thermal cycled in 5 degrees C and 60 degrees C water baths, and then fractured in three-point bending to measure strength. Nano-indentation was used to measure modulus and hardness. No significant loss in composite strength, modulus and hardness was found after 10(5) thermal cycles (family confidence coefficient=0.95; Tukey's multiple comparison test). The strength of whisker composite increased with filler level up to 60%, then plateaued when filler level was further increased to 70%; the modulus and hardness increased monotonically with filler level. The strength and modulus of whisker composite at 70% filler level were significantly higher than the non-whisker controls both before and after thermal cycling. SEM revealed no separation at the whisker-matrix interfaces, and observed resin remnants on the pulled-out whiskers, indicating strong whisker-resin bonding even after 10(5) thermal cycles. In conclusion, novel dental resin composites containing silica-fused whiskers possessed superior strength and modulus compared to non-whisker composites both before and after thermal cycling. The whisker-resin bonding appeared to be resistant to thermal cycling in water, so that no loss in composite strength or stiffness occurred after prolonged thermal cycling.

Journal Article↗

PubMedDate not supplied

Synthesis and characterization of PEG dimethacrylates and their hydrogels.

Facile synthesis and detailed characterization of photopolymerizable and biocompatible poly(ethylene glycol) dimethacrylates (PEGDM) and poly(ethylene glycol) urethane-dimethacrylates (PEGUDM) are described. Poly(ethylene glycol)s of various molecular masses (M(n) = 1000 to 8000 g/mol) were reacted with methacrylic anhydride or with 2-isocyanatoethyl methacrylate to form PEGDMs and PEGUDMs, respectively. PEGDMs were also prepared by a microwave-assisted route to achieve fast reaction conversions under solvent free conditions. Combined analyses of (1)H NMR and MALDI-TOF MS confirmed the formation of prepolymers of high purity and narrow mass distribution (PD < 1.02). Aqueous solutions of the PEGDMs and PEGUDMs (10% and 20% by mass fraction) were photopolymerized to yield hydrogels. Bovine chondrocytes, seeded in the hydrogels, were used to assess the biocompatibility. Preliminary rheology and uniaxial compression measurements showed varied mechanical response, and biocompatibility studies showed that cells are completely viable in both types of hydrogels after two weeks.

Animals↗

PubMedDate not supplied

In situ formation of blends by photopolymerization of poly(ethylene glycol) dimethacrylate and polylactide.

Blends of cross-linked poly(ethylene glycol) dimethacrylate (PEGDMA) and poly(d,l-lactide) (PLA) were prepared by mixing photoactive PEGDMA (molecular mass: 875 g/mol) and PLA, and subsequently photopolymerizing the mixture with visible light. The effects of PLA molecular mass and mass fraction on the rheological properties of the PEGDMA/PLA mixtures, and on the degree of methacrylate vinyl conversion (DC), as well as blend miscibility, microstructure, mechanical properties, in vitro swelling behavior, and cell responses were studied. PLA-2K (molecular mass: 2096 g/mol) and PLA-63K (molecular mass: 63 000 g/mol) formed miscible and partially miscible blends with cross-linked PEGDMA, respectively. The addition of the PLA-2K did not affect the immediate or post-cure (>24 h) DC of the PEGDMA upon photopolymerization. However, the addition of PLA-63K decreased the immediate DC of the PEGDMA, which can be increased through extending the curing time or post-curing period. Compared to the cross-linked neat PEGDMA and PLA-2K/PEGDMA blends, PLA-63K/PEGDMA blends were significantly stronger, stiffer, and tougher. Both types of blends and the cross-linked PEGDMA swelled when soaked in a phosphate buffered saline (PBS) solution. The attachment and spreading of MCT3-E1 cells increased with increasing PLA-63K content in the blends. The facile and rapid formation of PEGDMA/PLA blends by photopolymerization represents a simple and efficient approach to a class of biomaterials with a broad spectrum of properties.

Acrylates↗