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PubMed2000

PMMA-based composite materials with reactive ceramic fillers: part III: radiopacifying particle-reinforced bone cements.

New acrylic bone cements were prepared from alumina particles previously treated by 3-(trimethoxysilyl)propylmethacrylate (gamma-MPS), able to act both as radiopacifying and reinforcing agents. The present study deals with the handling characteristics and the compressive behavior of such cements. The influence of the particles morphology, their surface-modification by gamma-MPS bonding agent, their concentration in the cement, the powder-to-liquid ratio and the benzoyl peroxide concentration are reported. The role of grafted gamma-MPS molecules as coupling agent was confirmed. For several formulations, compressive strength and modulus reached 150 MPa and 3400 MPa respectively. Limitations in the use of such formulations are also comprehensively discussed.

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PubMed2001

Comparison of the material properties of PMMA and glass-ionomer based cements for use in orthopaedic surgery.

The intrinsic benefits of low exotherm and bioactivity have generated interest in utilizing glass-ionomer cements (GIC) as a bone cement replacement in orthopaedic surgery. This paper is concerned with evaluating the mechanical properties of compressive strength, flexural strength, and fracture toughness for two traditional GICs, one resin-modified GIC (an experimental bone cement) and two polymethylmethacrylate (PMMA) cement systems. To determine the suitability of a GIC system for use in the clinical orthopaedic setting, the additional characteristics of setting exotherm and setting time have also been evaluated. The characterization of these two vastly different cement systems has raised some concern as to the applicability of using the current orthopaedic standards for the testing of GIC systems. In particular, issues relating to the strain rate dependence of PMMA cement and the exothermic basis for determining setting time are not applicable as these factors are not characteristic of GIC systems. Whilst the intrinsic benefits of current GIC systems are well understood and generally accepted, this study has shown their intrinsic mechanical properties to be inferior to current PMMA cements. Improvement in the mechanical properties of traditional GICs have been achieved with the addition of a resin component (HEMA).

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PubMedDate not supplied

The influence of hydroxyapatite: zinc oxide ratio on the setting behavior and mechanical properties of polyalkenoate cements.

The influence of hydroxyapatite (HA) content on the setting behavior and mechanical properties of hydroxyapatite-zinc oxide-poly(acrylic acid) (HA-ZnO-PAA) composite cements were investigated as a function of HA content. The working time increased with HA content up to 45 wt % HA and then decreased whilst the setting time increased with increasing HA content. Mechanical properties were determined after storage in water at 37 degrees C for 1, 7 and 28 days. Young's moduli and compressive strength go through a maximum at approximately 30 and 45 wt % HA. Young's modulus increases with time, which is consistent with an ongoing crosslinking reaction.

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PubMed2000

A study of alternative metal particle structures and mixtures for dental amalgams based on mercury additions.

The perception that mercury in dental amalgam is toxic to the human organism has prompted worldwide efforts by the scientific community to develop alternative amalgam-like materials that utilize little or no mercury. In this investigation, an attempt is made to develop a new dental alloy system by adding liquid mercury to silver-coated Ag4Sn intermetallic particles in lesser amounts than are used in conventional amalgam alloys. An effort to precipitate the important eta-prime (Cu6Sn5) phase was made by adding pure Cu and Sn powders to the alloy formulation during trituration. Tytin a popular Ag-Sn-Cu single-composition, spray-atomized conventional dental alloy was used as the control to obtain baseline data for comparisons of microstructures and mechanical properties. Amalgamation of the coated particles with mercury, with or without the addition of Cu and Sn powders, mostly produced specimens with chemically non-coherent microstructures that were relatively weak in compression. These results were due, in part, to mercury's inability to chemically wet the Ag-coated particles and Cu and Sn powders because of naturally occurring surface oxide films. The strongest specimens tested had silver dendritic coatings, resulting in compression strength values up to 40% of the control's. Their higher strength is attributed to mechanical interlocking at the particle/matrix interfaces.

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PubMed2002

Study of a hydraulic calcium phosphate cement for dental applications.

Calcium phosphate-based cements (CPCs) have attracted much interest because of their good osteoconductivity for bone reconstruction. We obtained CPCs by mixing calcium bis-dihydrogenophosphate monohydrate (MCPM) and calcium oxide with water or sodium phosphate buffers (NaP) as liquid phase. Cement samples with different calcium-to-phosphate ratios (Ca/P), liquid-to-powder ratios (L/P) and liquid phases were analyzed by X-rays diffraction (XRD), pH-metry, extensometry and calorimetry. Antibacterial activity on two bacterial strains (Streptococcus mutans, Lactobacillus acidophilus) and a polycontaminated bacterial inoculum was also studied using the agar diffusion method. The best mechanical properties (approximately 25 MPa) corresponded to Ca/P ratios between 1.67 and 2.5, a 1 M sodium phosphate buffer pH 7, as liquid phase and a L/P ratio of 0.6ml g(-1). The final setting time increased with the Ca/P ratio. The setting expansion, around 1-2%, depended on the Ca/P and L/P ratios. The inner temperature of the cements rose to 45 degrees during setting then decreased rapidly. The injectability was 100% up to 3.5 min and then decreased. It increased with increasing the L/P ratio but to the detriment of the compressive strength and setting time. XRD analysis indicated that the setting reaction led to a mixture of calcium hydroxide and calcium-deficient hydroxyapatite even for a Ca/P ratio of 1.67. Consequently, the pH of the surrounding fluids rose to 11.5-12 during their dissolution. Bacterial growth inhibition was only clearly observed for Ca/P>or=2. This bioactive calcium phosphate cement can potentially be employed for pulp capping and cavity lining as classical calcium hydroxide-based cements, but it is not usable, in the present formulation, for root canal filling because of its short setting time.

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PubMed2002

PLGA bone plates reinforced with crosslinked PPF.

In this study a matrix of poly(propylene fumarate) (PPF) was crosslinked with N-vinylpyrrolidone (NVP), 2-hydroxyethylmethacrylate (HEMA), or a mixture of NVP and ethyleneglycol dimethacrylate (EGDMA) in the presence of poly(lactide-co-glycolide) (PLGA) to reinforce and preserve the form of PLGA bone plates. The degree of crosslinkage varied depending on the crosslinker as shown by the rapid and almost complete leaching of NVP upon incubation in phosphate buffered saline at 37 degrees C in 900 h and retention of 92% of HEMA. With the reinforced bone plates extracted for 72 h at room temperature methylene chloride, the extracted PLGA from NVP/PPF, NVP-EGDMA/PPF, and HEMA/PPF were 75.42% (w/w), 59.52% (w/w), and 30.86% (w/w), respectively. The flexural modulus and compressive strength of the crosslinked PPF reinforced bone plates were higher than that of the unreinforced bone plate. Atomic force microscopy showed that NVP/PPF reinforced PLGA bone plates eroded substantially (a mean surface roughness of 19.319 nm) whereas NVP-EGDMA-PPF reinforced bone plate showed a distinct crystalline organization (and a higher roughness, 43.525 nm). In conclusion, we propose the consideration of NVP-EGDMA/PPF reinforced PLGA as a biodegradable orthopedic implant material that has a lower likelihood of warping or failing catastrophically than the currently available materials.

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PubMed2002

Assessment of treatment alternatives for laboratory cod wastewater: a practical comparison with emphasis on cost and performance.

This study focused on investigation of treatment alternatives for COD wastewater from academic laboratories, using a number of technologies including chemical reduction/precipitation, ion exchange and adsorption by chitosan. Results showed that high concentrations of 375 mg l(-1) chromium, 1,740 mg l(-1) mercury and 993 mg l(-1) silver in COD wastewater can be reduced to 2.34 mg l(-1), 3.65 mg l(-1) and 1.89 mg l(-1) respectively, by the chemical reduction/precipitation process. Results from ion exchange at a flowrate of 20 ml min(-1) showed breakthrough effluent concentrations obtained at 0.59 mg l(-1) chromium, 3.92 microg l(-1) mercury and 0.65 mg l(-1) silver corresponding to 75.6 l at 63 hr, 40.8 l at 34 hr and 33.6 l at 28 hr respectively. Kinetic and isotherm studies revealed that chitosan can adsorb Cr6+, Hg2+ and Ag+ ions most effectively at a flowrate of 20 ml min(-1) and the optimum pH for feed solution is 4. Chitosan column experiments indicated that average effluent concentrations at breakthrough point for chromium, mercury and silver are 0.76 mg l(-1), 6.04 mg l(-1) and 0.51 mg l(-1) respectively with throughput volumes and retention times of 120 l at 100 hr, 60 l at 50 hr and 48 l at 40 hr. Results of solidification experiments for chemical sludge and residual chitosan based on compressive strength and metal leachability tests showed, that the acceptable ranges of the solidification parameters were: sludge/cement = 0.1-1.0 (weight/weight), water/cement = 0.5-0.6 (weight/weight) and sand/cement = 0.5-3.0 (weight/weight). Operating cost per litre of COD wastewater treated, based on the current prices in Thailand was found to be Baht 19.95 for the chemical reduction/precipitation process, Baht 96.35 for ion exchange treatment and Baht 18.29 for chitosan adsorption.

Adsorption↗

PubMed2002

A study of cements formed by aqueous lactic acid and aluminosilicate glass.

A study is reported of the formation of cements from aqueous lactic acid and aluminosilicate glass of the type used in dental glass-ionomer cements. These cements were found to set quickly, and were shown by infrared spectroscopy to have undergone a neutralization reaction to yield mainly calcium lactate. They were very soluble in water at 1 h, but became progressively less so over time; when matured for 6 h before being placed in water, they had become almost insoluble. No spectroscopic differences could be detected between the cements at 1 h or 6 h, indicating that insolubilization arises from a reaction that does not alter the part of the infrared spectrum examined. This suggested that a wholly inorganic reaction between the ion-depleted glass fragments is responsible for the formation of the insoluble structure. After 24 h, the cements were found to have compressive strengths in the range 9-35 MPa, the actual value varying with concentration of lactic acid used to form the cement, and there was no statistically significant increase in strength for the strongest of these after one month.

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PubMed2002

Physical and mechanical properties evaluation of Acropora palmata coralline species for bone substitution applications.

The search for ideal materials for bone substitution has been a challenge for many decades. Numerous natural and synthetic materials have been studied. For this application, exoskeletons of coral have been considered a good alternative given its tendency to resorption, biocompatibility and similarity to the mineral bone phase. Very few studies of these materials consider a detailed analysis of the structure-property relationship. The purpose of this work was to carry out the microstructural characterization of a coralline species named Acropora palmata and the determination of the mechanical and physico-chemical properties. Measurements of hardness, compressive strength, bulk density and apparent porosity were performed. From these results it was determined that this marine coral species could be an alternative xenograft due to its mechanical properties and osteoconductive nature.

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PubMed1997

Effect of diluent upon the properties of a visible-light-cured dental composite.

Four long-chain aliphatic organic diluents, triethylene glycol dimethacrylate (TEGDMA), ethylene glycol dimethacrylate (EDMA), triethyleneglycol diacrylate (TEGDA) and tetraethylene glycol diacrylate (TTEGDA) were used as diluents for preparing a visible-light-cured dental composite. Cured samples of pastes prepared using the above diluents were stored separately for a period of 60 days in distilled water at 37 degrees C and tested for changes in compressive strength, diametral tensile strength and microhardness at specific intervals of 1, 7, 14, 21, 28 and 60 days. Samples prepared using TEGDMA showed better strength values initially compared with the composite specimens prepared using the rest of the diluents although they are found to deteriorate slowly upon storage in distilled water up to 60 days. Samples prepared using EDMA showed retention in properties whereas samples prepared using TEGDA and TTEGDA showed large deviations in strength values during the first 28 days, did not deteriorate further and were found either to show improvement upon ageing or to remain constant. Sorption values seem to reach a maximum for all composites and then to decrease further after 14 days whereas solubility is found to increase with time.

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PubMed2002

pH-metric study of the setting reaction of monocalcium phosphate monohydrate/calcium oxide-based cements.

Hydraulic calcium phosphate cements (CPCs) that are used as osseous substitutes, set by an acid-base reaction between an acid calcium phosphate and a basic calcium salt (often a phosphate). In order to gain a better understanding of the setting of the monocalcium phosphate monohydrate-calcium oxide cement that we developed and in the aim to improve its mechanical properties, the setting reaction was studied by pH-metry. The two methods described in the literature were used. In the first, cement samples were prepared then crushed after different storage periods at 37 degrees C, 100% RH. The powder was then immersed in pure water with stirring and the pH was measured after equilibration. In the second technique, the starting materials were poured into water while stirring and the pH were followed over time. The two methods gave different results. The first procedure provided information concerning the pH of the surrounding liquid following the partial dissolution of the cement components, rather than any information about pH changes during setting. The second method is more appropriate to follow the pH variations during setting. In this second procedure, the effects of different parameters such as crushing time, stirring rate, liquid-to-powder (L/P) ratio and temperature were investigated. These parameters may impact substantially on the shape and position of the pH=f(t) curves. One or three pH jumps were observed during the setting depending on the composition of the liquid phase. The time at which these pH jumps occurred depended on the pH of the liquid phase, the concentration of the buffer, the crushing of starting materials, the L/P ratio and the temperature. Good linear correlations were obtained (i) between the time of the pH jumps and the L/P ratio and the temperature and (ii) between the time of the first pH jump and the compressive strength and the final setting time of the cements prepared with different liquid phases. It may be assumed in view of these correlations that the results obtained in dilute solution may be extrapolated to the conditions of cement sample preparation and that the mechanical properties of the cement are directly related to the phenomena that occur at the first pH jump which corresponds to precipitation of dicalcium phosphate dihydrate.

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PubMed2002

Acrylic-phosphate glasses composites as self-curing controlled delivery systems of antibiotics.

New antibiotic delivery systems based on self-hardening methyl methacrylate (MMA)/polymethyl methacrylate (PMMA) systems and phosphate glasses (PG) in the system P(2)O(5)-CaO-Na(2)O have been developed. Self-curing formulations were prepared by mixing the solid component containing PMMA beads, different proportions of PG (30-70 wt %) and vancomycin (5 wt %) as antibiotic, with the liquid component made of MMA monomer. Dough and setting times increased with the content of PG but peak temperature decreased to values well below to guarantee the chemical stability of the antibiotic drug, gentamicin or vancomycin. Mechanical properties of the PMMA/PG composites were evaluated in compression test giving rise to values of compressive strength in the range of 100 MPa. The release of vancomycin was analyzed in vitro by immersion of samples in phosphate buffer of pH=7.4. Release profiles were influenced by the content of PG present in the cement. An initial burst of drug release was observed in all cases. The composites with 70 wt % PG released nearly the total amount of drug loaded in a period of 45 days, and those containing 60 wt % PG released the 70% of the vancomycin in the same period of time. However, either the control of the composite with 30 wt % PG released only the 30% of the drug in 10-15 days. The surface of the drug-loaded composites before and after release experiments was analyzed by ESEM. The deposition of some aggregates at certain points of the surface was detected for the specimens immersed in buffer phosphate after 45 days. This material was characterized by FTIR and Raman spectroscopy as an amorphous phosphate formed by calcium ortho and pyrophosphates, and indicates an interaction between the hydrated layer at the place of the glass and the surrounding medium.

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PubMed2003

Gelatin manipulation of latent macropores formation in brushite cement.

Macroporous brushite cement was prepared from a mixture of beta-tricalcium phosphate (beta-TCP) and monocalcium phosphate monohydrate (MCPM) using gelatin powder as a latent templates. In a setting reaction coexisting with gelatin, closed packed, open-pore structure with 100-200 microm macropores are obtained after immersion of the set cement into PBS buffer (pH 7.4) at 37 degrees C for 1-4 weeks. The macroporous brushite cement has compressive strength of 15 MPa originally, which reducing to 5.5 MPa with macropore formation gradually in comparison to that of cancellous bone (5-10 MPa).

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PubMed2003

Biphasic calcium phosphate bioceramics: preparation, properties and applications.

Biphasic calcium phosphate (BCP) bioceramics belong to a group of bone substitute biomaterials that consist of an intimate mixture of hydroxyapatite (HA), Ca(10)(PO(4))(6)(OH)(2), and beta-tricalcium phosphate (beta-TCP), Ca(3)(PO(4))(2), of varying HA/beta-TCP ratios. BCP is obtained when a synthetic or biologic calcium-deficient apatite is sintered at temperatures at and above 700 degrees C. Calcium deficiency depends on the method of preparation (precipitation, hydrolysis or mechanical mixture) including reaction pH and temperature. The HA/beta-TCP ratio is determined by the calcium deficiency of the unsintered apatite (the higher the deficiency, the lower the ratio) and the sintering temperature. Properties of BCP bioceramics relating to their medical applications include: macroporosity, microporosity, compressive strength, bioreactivity (associated with formation of carbonate hydroxyapatite on ceramic surfaces in vitro and in vivo), dissolution, and osteoconductivity. Due to the preferential dissolution of the beta-TCP component, the bioreactivity is inversely proportional to the HA/beta-TCP ratio. Hence, the bioreactivity of BCP bioceramics can be controlled by manipulating the composition (HA/beta-TCP ratio) and/or the crystallinity of the BCP. Currently, BCP bioceramics is recommended for use as an alternative or additive to autogeneous bone for orthopedic and dental applications. It is available in the form of particulates, blocks, customized designs for specific applications and as an injectible biomaterial in a polymer carrier. BCP ceramic can be used also as grit-blasting abrasive for grit-blasting to modify implant substrate surfaces. Exploratory studies demonstrate the potential uses of BCP ceramic as scaffold for tissue engineering, drug delivery system and carrier of growth factors.

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PubMed2003

Surface modification of a porous hydroxyapatite to promote bonded polymer coatings.

Porous hydroxyapatite (Hap) blocks were sintered at several temperatures and methyl methacrylate (MMA) grafted onto the surface in a 2-step heterogeneous system as a model example for surface modification. First, sintered porous Hap was modified with 2-methacryloyloxyethylene isocyanate (MOI) monomer in anhydrous dimethyl sulfoxide using di-n-butyltin (IV) dilaurate as a catalyst and hydroquinone as an inhibitor. Amount of the introduction of MOI monomer on porous Hap was 1.62 wt % at sintered temperature 800 degrees C, 0.68 wt % at it of 1000 degrees C, and 0.59 wt % at it of 1200 degrees C. Scanning electron microscopy (SEM) showed that porous Hap pore size and shape before and after MOI treatment were unchanged. Second, graft polymerization with MMA through the vinyl bond on porous Hap was conducted using alpha,alpha'-azobis isobutyronitrile (AIBN) as an initiator. Amount of Grafted PMMA on the MOI modified porous Hap was 2.84 wt % at sintered temperature of 800 degrees C, 6.97 wt % at it of 1000 degrees C, and 6.27 wt % at it of 1200 degrees C. MOI-modified and PMMA-grafted porous Hap were characterized using Fourier transform infrared (FT-IR) spectroscopy. The compressive strength of sintered porous Hap with grafted PMMA increased about 2.7-6.7 times compared to intact porous Hap. This 2-step surface modification on porous Hap is widely applicable to graft polymerization with vinyl polymer and conjugation with a protein or an oligopeptide, such as growth factor or an adhesion molecule, to improve Hap mechanical properties and functionality.

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PubMed1999

Effect of filler content and size to properties of composite resins on microwave curing.

The effect of filler content and size to property of composite resin using high purity spherical silica particles on microwave curing was examined by mechanical means and electron microscope observation to develop microwave-curing composite resin inlay. Increasing filler content in three kinds of filler particles (0.45, 0.96 and 1.46 microm) resulted in increasing compressive strength, diametral tensile strength and knoop hardness and indicated the highest values at the operative mixing limit. The effect of particle size was that the mechanical property of the 0.96 microm filled resin was highest, followed by 1.46 microm and 0.45 microm on the same filler content. The 0.96 microm filled resin had about the same knoop hardness on both surfaces of the cured sample, which means that uniform polymerization occurred in the cured sample. With electron microscope observation, the bubbles of about 1.0 microm and the cracks between the fillers and the matrix were observed in each cured resin. This is caused by the excessive absorption of microwave energy in fillers and surface treatment materials of fillers. Therefore, improvement of the composition of filler and surface treatment material of filler are needed, which makes it harder to absorb the microwave energy.

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PubMed2004

Effects of clodronate and alendronate on local and systemic changes in bone metabolism in rats with adjuvant arthritis.

We compared the effects of nonaminobisphosphonate (nonamino-BP; clodronate) and amino-BP (alendronate) on the changes in local and systemic bone metabolism associated with chronic inflammation in adjuvant-arthritis rats. A given rat received one of the BPs orally each day for 28 days from the day of adjuvant inoculation. Hindpaw swelling was observed from day 10 after adjuvant inoculation up to day 28 (peak, day 21). Clodronate slightly decreased the hindpaw swelling at doses of 12.5 and 25 mg/kg, p.o./day; however, alendronate (0.125-0.5 mg/kg) did not. Radiological examination of the distal limb joints revealed that only clodronate decreased bone deformation. Urinary deoxypyridinoline increased as arthritis developed, and it was decreased by clodronate. On day 29, pQCT analysis of the 5th lumbar vertebra revealed trabecular bone loss and cortical bone thinning in the arthritis control group, leading to compressive strength being reduced. Both BPs prevented this bone loss and strength reduction. These data suggest that only clodronate decreases inflammation and local bone deformation, while both BPs inhibit the arthritis-related decreases in systemic bone mass and bone strength. Clodronate would be useful in the treatment of inflammation-induced bone deformation and osteopenia.

Alendronate↗

PubMed2003

Effect of micro- and macroporosity of bone substitutes on their mechanical properties and cellular response.

The control of porosity morphology and physico-chemical characteristics of calcium phosphate bone substitutes is a key-point to guaranty healing success. In this work, micro- and macroporosity of materials processed with 70% Hydroxyapatite (HAP) and 30% beta-tricalcium phosphate (beta-TCP) were controlled by sintering temperature and porogen addition, respectively. Porosity was quantified by scanning electron microscopy (pore size) and mercury intrusion porosimetry (interconnection between pores). The content of macrointerconnections and their size were dependent on porogen content, shape, and size. Mechanical properties (compressive strength) were strongly dependent on macroporosity size and content, on the basis of exponential laws, whereas microporosity ratio was less influent. Relying on those results, three types of materials with contrasting porous morphologies were processed and assessed in vitro, in primary culture of human osteoblasts and fibroblasts. With both types of cells, an exponential cellular growth was effective. Cells colonized the surface of the materials, bridging macroporosity, before colonizing the depth of the materials. Cell migration across and into macroporosity occurred via the emission by the cells of long cytoplasmic extensions that hanged on microporosity. Both macroporosity and macrointerconnectivity size influenced the penetration of cells. An interconnection size of 15 microm appeared to be effective to support this invasion without bringing down mechanical strength.

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