- Professor of Biomaterials (retired) in the Dental School at the University of Texas Health Science Center at San Antonioedit
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Fluoride, one of the most celebrated ingredients for the prevention of dental caries in the 20th century, has also been controversial for its use in dentifrices and other applications. In the current review, we have concentrated primarily... more
Fluoride, one of the most celebrated ingredients for the prevention of dental caries in the 20th century, has also been controversial for its use in dentifrices and other applications. In the current review, we have concentrated primarily on early-life exposure to fluoride and how it may affect the various organs. The most recent controversial aspects of fluoride are related to toxicity of the developing brain and how it may possibly result in the decrease of intelligence quotient (IQ), autism, and calcification of the pineal gland. In addition, it has been reported to have possible effects on bone and thyroid glands. If nutritional stress is applied during a critical period of growth and development, the organ(s) and/or body will never recover once they pass through the critical period. For example, if animals are force-fed during experiments, they will simply get fat but never reach the normal size. Although early-life fluoride exposure causing fluorosis is well reported in the li...
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Polymethyl methacrylate (PMMA) is widely used to treat traumatic head injuries (cranioplasty) and orthopedic injuries (bone cement), but there is a problem with implant-centered infections. With organisms such as Acinetobacter baumannii... more
Polymethyl methacrylate (PMMA) is widely used to treat traumatic head injuries (cranioplasty) and orthopedic injuries (bone cement), but there is a problem with implant-centered infections. With organisms such as Acinetobacter baumannii and methicillin-resistant staphylococcus aureus developing resistance to antibiotics, there is a need for novel antimicrobial delivery mechanisms without risk of developing resistant organisms. To develop a novel antimicrobial implant material by generating silver nanoparticles (AgNP) in situ in PMMA. All PMMA samples with AgNP's (AgNP-PMMA) released Ag(+) ions in vitro for over 28 days. In vitro antimicrobial assays revealed that these samples (even samples with the slowest release rate) inhibited 99.9% of bacteria against four different strains of bacteria. Long-term antimicrobial assay showed a continued antibacterial effect past 28 days. Some AgNP-loaded PMMA groups had comparable Durometer-D hardness (a measure of degree of cure) and modulus to control PMMA, but all experimental groups had slightly lower ultimate transverse strengths. AgNP-PMMA demonstrated a tremendously broad-spectrum and long-intermediate-term antimicrobial effect with comparable mechanical properties to control PMMA. Current efforts are focused on further improving mechanical properties by reducing AgNP loading and assessing fatigue properties. © 2011 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 100B: 409-415, 2012.
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Research Interests: Engineering, Nanoparticles, Dental Materials, Humans, Controlled release, and 15 moreSilver, Diffusion, Orthopedic, Hardness, Antimicrobial, Dental Material, Pilot study, Composite resins, Silver Nanoparticle, Materials Testing, Pilot Projects, Biocompatible Materials, Polyethylene Glycols, Medical and Health Sciences, and Methacrylates
Dual-cure (DC) resins are mainly used as cements due to high initial color (generally yellow) and large color shift (ΔE*) after polymerization as compared to light-cured resins. However, even as cements, this color shift is clinically... more
Dual-cure (DC) resins are mainly used as cements due to high initial color (generally yellow) and large color shift (ΔE*) after polymerization as compared to light-cured resins. However, even as cements, this color shift is clinically unacceptable, especially when used to cement thin veneers. To develop a novel DC initiator system with both lower initial color (less yellow, i.e., whiter) and smaller ΔE*. The effect of using an allyl thiourea (T)/cumene hydroperoxide (CH) self-cure (SC) initiator system in combination with a photo-co-initiator, p-octyloxy-phenyl-phenyl iodonium hexafluoroantimonate (OPPI), in a commercial DC resin cement (PermaFlo DC, Ultradent Products, Inc.) was investigated. Initial color and ΔE* were assessed for 6 weeks in vitro under accelerated aging conditions (75°C water bath). Rockwell15T hardness was used to assess degree of cure (DoC) and the three-point bending test was used to assess mechanical properties. PermaFlo DC (control) was significantly harder than all experimental groups without OPPI but had up to three times higher initial color and four times greater color shift (ΔE*=27 vs. 8). With OPPI, hardness in the experimental groups increased significantly and several were comparable to the controls. Initial color and ΔE* increased slightly (ΔE*=9), but was still 3 times less than that of PermaFlo DC. DC samples containing OPPI had comparable modulus and ultimate transverse strengths to those of the controls. DC resins that use the T/CH initiator system are weaker but have extremely low color and ΔE*. The addition of OPPI increases DoC and mechanical properties to clinically acceptable levels and maintains extremely low color and ΔE*. With this novel initiator system, DC resins potentially can now have comparable color and color stability to light-cure resins and be used in broader esthetic dental applications to improve color stability and reduce shrinkage stress in restorative composites.
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Research Interests: Engineering, Materials Science, Photochemistry, Polymers, Dental Materials, and 15 moreMedicine, Color, Terpenes, Composite Material, Chalcones, Composite resins, Time Factors, Polyurethanes, Structure activity Relationship, Absorption Spectra, Composite Resin, Polyethylene Glycols, Synergistic effect, Medical and Health Sciences, and Methacrylates
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The polyol route, with zirconium oxychloride as the metal ion source, was used to synthesize nanocrystalline ZrO2 powder. The complete process for the synthesis of nanocrystalline ZrO2 was monitored by TG/DTA, FTIR, XRD and TEM. Thermal... more
The polyol route, with zirconium oxychloride as the metal ion source, was used to synthesize nanocrystalline ZrO2 powder. The complete process for the synthesis of nanocrystalline ZrO2 was monitored by TG/DTA, FTIR, XRD and TEM. Thermal behavior of the intermediate powder was investigated using TG/DTA analysis. The structural coordination and phase of the intermediate, as well as the synthesized ZrO2 powder, were investigated by FTIR and XRD respectively. The microstructure of the synthesized nanocrystalline ZrO2 powder was identified using transmission electron microscopy.
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ABSTRACT Silver nanoparticle functionalized nanocrystalline ZrO2 was fabricated by using Anacardium occidentale leaf extract assisted bioreduction process at ambient conditions. Introducing A. occidentale leaf extract into an aqueous... more
ABSTRACT Silver nanoparticle functionalized nanocrystalline ZrO2 was fabricated by using Anacardium occidentale leaf extract assisted bioreduction process at ambient conditions. Introducing A. occidentale leaf extract into an aqueous mixture of silver nitrate and ZrO2 particles caused the speedy reduction of the silver ions and efficiently lead to their nucleation as highly stable, silver nanoparticles on the ZrO2 surface. A reaction mechanism for the fabrication of functional interfaces was developed to illustrate this process. SEM–EDS and TEM investigations, together with UV–vis spectroscopy, confirmed the formation of 5–20 nm silver nanoparticles on the surfaces of ZrO2 particles. Further, the X-ray diffraction analysis confirms the phase pure face-centered cubic (fcc) crystal structure of silver nanoparticles formed on the surface of ZrO2 particles. Increasing concentration of leaf extract in the reaction mixture caused the rapid reduction of silver ions and inhibits the formation of silver nanoparticles over the surface of ZrO2 particles significantly.
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The acrylamide assisted polymeric citrate route was investigated for the synthesis of nanocrystalline ZrO2 powders, using zirconium oxychloride as the source for metal ion along with citric acid and acrylamide as chelating as well as... more
The acrylamide assisted polymeric citrate route was investigated for the synthesis of nanocrystalline ZrO2 powders, using zirconium oxychloride as the source for metal ion along with citric acid and acrylamide as chelating as well as polymerizing agents. The complete process for the synthesis of nanocrystalline ZrO2 powders was monitored by TG/DTA, FTIR, XRD and TEM techniques. Thermal decomposition of the polymeric intermediate was investigated using TG/DTA analysis. Structural coordination and phase of the synthesized ZrO2 powders were investigated by FTIR and XRD analysis respectively. The microstructure of the synthesized nanocrystalline ZrO2 powder was identified using transmission electron microscopy, which showed ~10nm agglomerates of still finer ZrO2 particles.
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ABSTRACT The development of improved bonding, tensile, and toxicologic properties of a polyphosphazine fluoroelastomer is documented. This elastomer is used as a soft liner in removable dentures over anatomic areas that pinch the soft... more
ABSTRACT The development of improved bonding, tensile, and toxicologic properties of a polyphosphazine fluoroelastomer is documented. This elastomer is used as a soft liner in removable dentures over anatomic areas that pinch the soft tissues against bone, or on atrophic oral mucosa.
ABSTRACT Export Date: 19 October 2012, Source: Scopus
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The fracture toughness of dental composites containing zirconia nanoparticles dispersed in a bisphenol A glycol dimethacrylate-based monomer blend (GTE) was studied for several yttria contents. Three-point bend test bars with and without... more
The fracture toughness of dental composites containing zirconia nanoparticles dispersed in a bisphenol A glycol dimethacrylate-based monomer blend (GTE) was studied for several yttria contents. Three-point bend test bars with and without a notch were tested at ambient temperature to determine elastic modulus, flexure strength, and fracture toughness. The ZrO2 nanoparticles increased the fracture toughness of the nanocomposites compared to
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ABSTRACT ResumenEl par de electrones aislados del heteroátomo tiene dos orbitales; uno de no unión, orbital -n, el cual es del tipo s̀y es ortogonal con respecto a los orbitales de los electrones; y otro de union orbital l, que está... more
ABSTRACT ResumenEl par de electrones aislados del heteroátomo tiene dos orbitales; uno de no unión, orbital -n, el cual es del tipo s̀y es ortogonal con respecto a los orbitales de los electrones; y otro de union orbital l, que está relacionado con los electrones π, a un grado en que depende del ángulo de torsión entre el eje del orbital l y el orbital 2pπ del anillo aromático vecino. La excitación de electrones a partir de los orbitales n ó l a orbitales de anti-unión del tipo π es tratada como una transición de transferencia de carga int amolecular. Se desarrolla un detallado análisis teórico del elemento matricial órbita-spin para una mezcla singlete-triplete de las promociones 1 a π en anilinas, usando dos centros integrados. El momento de la transición singlete triplete depende del ángulo de torsión entre el eje del orbital 1 y el piano del anillo aromático. Se provee evidencia experimental para predicir la dependencia angular usando una serie de anilinas restringidas estericamente con distintos ángulos de torsion. El recíproco de la vida media de la fosforecencia de estas anilinas tiene una correlación muy satisfactoria con la función teórica, lo cual apoya el uso del elemento matricial spin-órbita.
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Caffeine (CAF), a methyl-substituted xanthine, interacts with polyaromatic DNA intercalators and has been hypothesized to interfere with their intercalation into DNA. Optical absorption spectroscopy was used to determine the binding... more
Caffeine (CAF), a methyl-substituted xanthine, interacts with polyaromatic DNA intercalators and has been hypothesized to interfere with their intercalation into DNA. Optical absorption spectroscopy was used to determine the binding affinities (K(assoc)) and structural effects of a series of methyl-substituted xanthines and a series of methyl-substituted uric acids (8-oxoxanthine) with the known DNA intercalator acridine orange (AO). There is evidence that complexation occurred (K(assoc) > or = 150 M(-1); binding curve saturation approximately > or =50%) between AO and 1,7-dimethylxanthine (155 M(-1)), 1,3-dimethylxanthine (theophylline, 157 M(-1)), 1,3,7-trimethylxanthine (CAF, 256 M(-1)), 1,3-dimethyl-8-chloroxanthine (413 M(-1)), 1,3,7,9-tetramethyl-8-oxyxanthine (tetramethyl uric acid or TMU, 552 M(-1)), and theophylline ethylenediamine (aminophylline, 596 M(-1)). No definitive evidence of complexation occurred between AO and 16 other substituted xanthines or purines, although there was some evidence of weak complexation (K(assoc) < 150 M(-1)) between AO and eight of the sixteen. Three common structural similarities were identified among those compounds found to form significant bonding with AO: (i) the N(1) or N(3) on the xanthine structure must be substituted with a methyl group; (ii) oxygen or chlorine substitution at C(8) increases binding affinity to AO when resonate states remain unchanged; and (iii) K(assoc) increases with an increase in number of methyl group substitutions on the 1- or 3-methylxanthine core structure. These results are explained on the basis of complex stabilization due predominately to hydrophobic attraction, with a contribution from charge transfer between donor and acceptor components. This information can be used in the manipulation of the physical or chemical characteristics of biologically active polyaromatic molecules.
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As a part of the continuous pursuit to develop an ideal resinous dental restorative material for use in large posterior cavity restorations, this article reports the easy, high-yield synthesis and the incredibly low polymerization... more
As a part of the continuous pursuit to develop an ideal resinous dental restorative material for use in large posterior cavity restorations, this article reports the easy, high-yield synthesis and the incredibly low polymerization shrinkage property of a new bifunctional liquid crystal (LC) monomer. This new polymerizable nematic liquid crystal is the next higher homolog of the acrylate monomer reported in a previous work.1 It remains liquid crystalline between room and mouth temperatures and can be polymerized to isotropic polymer with the use of the same visible light inhibitor system as used with conventional monomers. The structure of this new monomer has been confirmed to be 2-(t-butyl), 1,4-bis-[4-(6-methacryloxy-hexan-1-oxy)-benzoyloxy]-benzene. Unlike the synthesis of its acrylate homolog, when the same procedure is adopted for the synthesis of this compound, the recovery of the product is not split by a sizable amount of the by-product. Therefore, the reaction is cleaner, with high yield and a less labor-intensive purification procedure. Thus, the synthetic methodology has the potential for easy commercial scale-up. The monomer (V) polymerizes at room temperature with a shrinkage of about 2 vol %, as compared to > 8 vol % for conventional control (GTE), at similar degrees of conversion.
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The purpose of this study was to examine the use of a dynamic mechanical analyzer (DMA) system to study the viscoelastic nature of bone. Cortical bone specimens from human femora were tested isothermally for 150 min at 37 degrees C and... more
The purpose of this study was to examine the use of a dynamic mechanical analyzer (DMA) system to study the viscoelastic nature of bone. Cortical bone specimens from human femora were tested isothermally for 150 min at 37 degrees C and the loss factor (tan delta) and storage modulus (E') were measured. To explore the effects of test conditions on tan delta and E', different levels of applied stress, two specimen sizes, and two hydration conditions (wet and vacuum-dried) were evaluated. Finally, nonisothermal tests were performed, wherein specimens were heated up to 70 degrees C at different heating rates: 1 degrees C/min, 3 degrees C/min, and 5 degrees C/min. The results indicated that a threshold level of minimum applied stress was required to obtain repeatable and relatively constant values of tan delta. Specimen size did not significantly affect tan delta although it influenced E'. Moisture content had a significant effect on tan delta; vacuum-dried specimens exhibited a lower tan delta compared to wet specimens. Lastly, heating rates influenced tan delta values with lower rates producing more consistent results. The study demonstrated that DMA can be used as an effective tool to test bone.