Polymethylmethacrylate Powder Research Articles

Fabrication of Porous Structure of BCP Sintered Bodies Using Microwave Assisted Synthesized HAp Nano Powder

Using microwave synthesized HAp nano powder and polymethyl methacrylate (PMMA) as a pore-forming agent, the porous biphasic calcium phosphate (BCP) ceramics were fabricated depending on the sintering temperature. The synthesized HAp powders was about 70-90 nm in diameter. In the porous sintered bodies, the pores having 150-180 μm were homogeneously dispersed in the BCP matrix. Some amounts of pores interconnected due the necking of PMMA powders which will increase the osteoconductivity and ingrowth of bone-tissues while using as a bone substrate. As the sintering temperature increased, the relative density increased and showed the maximum value of 79.6%. From the SBF experiment, the maximum resorption of Ca2+ ion was observed in the sample sintered at 1000°C.

Use of antibiotic-loaded polymethylmethacrylate beads for the treatment of extracavitary prosthetic vascular graft infections

This study was conducted to assess the efficacy of antibiotic-loaded polymethylmethacrylate (PMMA) beads in the management of lower extremity extracavitary prosthetic arterial graft infection. This was a retrospective review of 34 patients treated for vascular surgical site (VSS) infections involving 36 prosthetic lower extremity arterial bypasses using antibiotic-loaded PMMA beads and culture-specific parenteral antibiotics for 4 to 6 weeks. Sites of graft infection were explored, debrided, and cultured. As determined from the results of Gram's stains of VSS purulence, PMMA powder was polymerized with an antibiotic (vancomycin, daptomycin, or tobramycin/gentamicin, or a combination), molded into a chain of beads, and implanted adjacent to the infected graft after debridement and pulsed-spray antibacterial lavage. All wounds were closed primarily with planned exploration to verify sterilization before a graft preservation or in situ replacement procedure. Treatment outcomes, including wound sterilization, were analyzed based on tissue culture isolates, procedures for persistent infection, and freedom from graft infection. Cultures isolated 42 pathogens, (32 gram-positive, 9 gram-negative, 1 Candida albicans) with methicillin-resistant Staphylococcus aureus (MRSA) cultured from 16 (44%) of 36 surgical site infections. As determined from the initial operative Gram's stain or a prior culture result, vancomycin PMMA beads were implanted in 29 of 36 VSS infections at the first procedure; daptomycin (n = 4) or tobramycin (n = 3) beads were implanted in the rest. Repeat VSS exploration and culture results led to an average of 2.5 antibiotic bead replacements before definitive treatment. A sterile (no growth on tissue culture) VSS was achieved in 87% of cases before a graft preservation (n = 16) or in-situ replacement of an infected graft (n = 20) procedure. No patient deaths occurred. Early and late limb salvage was 100%. Infection recurred in 4 (11%) VSSs during a mean 23-month follow-up period, one within 3 months owing to unrecognized bowel injury associated with in situ replacement of an aortofemoral graft limb. Antibiotic-loaded PMMA beads may be a useful adjunct in the contemporary surgical management of VSS infection involving a prosthetic graft. Wound sterilization was achieved in most VSSs before graft preservation or an in-situ replacement procedure, including infections caused by MRSA, a pathogen isolated in half of the extracavitary prosthetic graft infections. This preliminary trial shows the potential benefit of this new technique, but further study is required to prove efficacy.

Antibiotic–polymethylmethacrylate strut: an option for treating cervical pyogenic spondylitis

Antibiotic-polymethylmethacrylate (PMMA) cement and beads constitute an effective system of local drug delivery of antibiotic agents in patients with bone and soft-tissue infections. Debridement followed by implantation of antibiotic-PMMA beads and systemic administration of antibiotic agents has achieved a 100% success rate in treating chronic osteomyelitis; however, there have been no reports of an antibiotic-PMMA strut for treating spinal pyogenic spondylitis. In this case report we describe a 57-year-old woman with C5-6 pyogenic spondylitis, progressive kyphotic deformity, and neurological deficits. The patient underwent anterior C-5 and C-6 corpectomy and spinal reconstruction in which we used an antibiotic-PMMA strut. The strut was 14 mm in diameter and contained PMMA and vancomycin powder. The operation was technically successful, and no complication related to anesthesia or the surgical procedure occurred. At the 12-month follow-up examination, dynamic radiographs revealed cervical spine stabilization. The patient's neck pain subsided and she recovered neurologically with no residual infection. No antibiotic-PMMA strut dislodgment or failure was identified; however, 9.8% subsidence of the strut into the vertebrae was observed. The long-term outcome in this case requires further evaluation.

Preparation and Characterization of SrAl2O4:Eu2+, Dy3+ Doped Polymer Composites

Long after-glow luminescent composites were fabricated by embedding phosphor SrAl2O4:Eu2+, Dy3+ powders into polymethyl-methacrylate (PMMA) using solution casting and hot-press methods. In the first method, PMMA were dissolved in chloroform forming a homogenous solution and the phosphor powders were doped into the solution with different volume fractions. Transparent samples were obtained by air drying the solution in a container. Their optical properties were studied by transmittance measurement and emission spectroscopy. For tensile and impact tests, samples were obtained by pressing mixed phosphor and PMMA powders at 190°C. Based on these studies, the mechanical and optical properties of these composite were investigated.

Microstructure and mechanical properties of porous yttria stabilized zirconia ceramic using poly methyl methacrylate powder

Abstract Porous t -ZrO 2 ceramic was fabricated by pressureless sintering, using commercial t -ZrO 2 and different volume percentages of poly methyl methacrylate (PMMA) powders (20–80%). The spherical pores ranged from about 120 to 170 μm in diameter. By increasing the PMMA content, the number of pores, material properties and pore morphology were changed dramatically. The values of relative density, elastic modulus, bending strength and hardness of the 60 vol.% PMMA content sample, sintered at 1550 °C, were about 43%, 40 GPa, 170 MPa and 248 Hv, respectively.

Homogenous alumina tube with controlled pore morphology

Porous alumina tubes with homogenous microstructures were prepared from commercial alumina and polymethylmethacrylate (PMMA) powders with two kinds of particle sizes using a centrifugal molding technology. PMMA powders were used as the pore-forming agent and the proportion of fine to coarse particles was adjusted to control the pore morphology of the alumina tubes. The open porosity and air permeability was optimized with respect to the proportion of PMMA powders. The fracture strength decreased with increasing porosity and was insensitive to the proportion of fine to coarse PMMA powders despite the changing pore morphology. Analysis of the Weibull statistics showed that specimens with higher porosity exhibit a narrower scatter in fracture strength. A 50:50 mixture (v/v) of fine and coarse PMMA particles showed the lowest fluctuation in fracture strength. The present study paves the way to more reliable material design using porous materials.

Synthesis of bioactive PMMA bone cement via modification with methacryloxypropyltri- methoxysilane and calcium acetate

Bone cement consisting of polymethylmethacrylate (PMMA) powder and methylmethacrylate (MMA) liquid is clinically used for fixation of implants such as artificial hip joints. However, it does not show bone-bonding ability, i.e., bioactivity. The lack of bioactivity would be one of factors which cause loosening between the cement and the implant. The present authors recently showed the potential of bioactive PMMA-based bone cement through modification with gamma-methacryloxypropyltrimethoxysilane (MPS) and calcium acetate. In this study, the effects of the kinds of PMMA powder on setting time, apatite formation and compressive strength were investigated in a simulated body fluid (Kokubo solution). The cement modified with calcium acetate calcined at 220 degrees C could set within 15 min when the PMMA powder had an average molecular weight of 100,000 or less. The addition of calcium acetate calcined at 120 degrees C in the PMMA powder required a much longer period for setting. The modified cements formed an apatite layer after soaking in the Kokubo solution within 1 day for cement starting from PMMA powder with a molecular weight of 100,000 or less. Compressive strengths of the modified cements were more than 70 MPa for cements starting from 100,000 and 56,000 in molecular weight. After soaking in Kokubo solution for 7 days, the modified cement consisting of PMMA powder of 100,000 in molecular weight showed a smaller decrease in compressive strength than that consisting of 56,000 in molecular weight. These results indicate that bioactive PMMA cement can be produced with appropriate setting time and mechanical strength when PMMA powders with a suitable molecular weight are used. Such a type of design of bioactive PMMA bone cement leads to a novel development of bioactive material for bone substitutes.

Bioactive PMMA bone cement prepared by modification with methacryloxypropyltrimethoxysilane and calcium chloride.

Bone cement consisting of polymethylmethacrylate (PMMA) powder and methylmethacrylate (MMA) liquid is used extensively for fixation of implants such as artificial hip joints with living bone. This type of cement, however, does not show direct bonding to the living body, and hence the fixation is liable to loosen over a long implantation period. Bioactive materials have received much attention because of their capability for bone-bonding, i.e., bioactivity, when implanted in bony defects. Osteoconduction of the bioactive materials is caused by formation of a bone-like apatite layer through a surface reaction between the material and surrounding body fluid. The apatite formation can be induced by a silanol (Sibond;OH) group formed on the materials as well as a dissolution of calcium ion (Ca(2+)) from the material. Incorporation of alkoxysilane and calcium chloride (CaCl(2)) may provide PMMA bone cement with bioactivity, because alkoxysilane gives Sibond;OH after hydrolysis, whereas CaCl(2) releases Ca(2+). In this study, we investigated the potential on bioactivity of the modified PMMA bone cement with alkoxysilane and calcium chloride. PMMA powder was mixed with various amounts of CaCl(2), and MMA liquid with various amounts of 3-methacryloxypropyltrimethoxysilane (MPS). The mixed paste was immersed in a simulated body fluid (Kokubo solution) that has a similar concentration in inorganic constituents to human blood plasma. After soaking for various periods, apatite formation on the cement was examined. Apatite formation was observed by the addition of CaCl(2) with contents of 16 mass % and more. Incorporation of MPS accelerates the apatite formation. Setting time of the cement was significantly elongated after the addition of MPS, whereas compressive strength significantly decreased with increasing the contents of CaCl(2) and MPS. The hardened cement containing 20 mass % of CaCl(2) in the powder and 20 mass % of MPS in the liquid showed a tendency to be more osteoconductive to living bone after implantation in rabbit tibiae than the unmodified cement. These results indicate that bioactivity of the modified PMMA bone cement increases with increasing amounts of MPS and CaCl(2). Bioactive bone cement is successfully obtained when it contains appropriate concentrations of alkoxysilane and calcium chloride.

Bioactive PMMA-Based Bone Cement Modified with Methacryloxypropyltrimethoxysilane and Calcium Salts-Effects of Calcium Salts on Apatite-Forming Ability-

Bone cement consisting of polymethylmethacrylate (PMMA) powder and methylmethacrylate (MMA) liquid is clinically used for fixation of implants such as artificial hip joints. However, it does not show bone-bonding ability, i.e. bioactivity. The essential prerequisite for an artificial material to bond to bone is the formation of an apatite layer on its surface when implanted in a bony defect. This apatite layer can be, for example, formed in a simulated body fluid (Kokubo solution) with ion concentrations similar to those of human extracellular fluid. The present authors recently showed the potential of bioactive PMMA-based bone cement through modification with y-methacryloxypropyltrimethoxysilane (MPS) and calcium chlorides. In this study, the effects of the kinds of calcium salts on apatite-forming ability were examined by exposure to Kokubo solution. PMMA powder (molecular weight of 100000 and 14 μm in average particle size) was mixed with 20 mass% of calcium salts consisting of calcium chloride (CaCl 2 ), calcium acetate (Ca(CH 3 COO) 2 ), calcium hydroxide (Ca (OH) 2 ), calcium lactate (Ca(CH 3 CHOHCOO) 2 ), calcium benzonate (Ca(C 6 H 5 COO) 2 ) and calcium methacrylate (Ca(CH 2 = C (CH 3 )COO) 2 ), while 20 mass% of MPS was added in the MMA liquid. The appropriate setting time was obtained by the usage of calcium acetate or calcium lactate, although the modification with MPS and calcium salts leads to an elongation of the setting time of the cement. Apatite formation could be detected after soaking in Kokubo solution for 1 d when the cements were modified with calcium chloride, calcium acetate, or calcium methacrylate. Apatite formation could be observed on the modified cement with calcium hydroxide after 7 d of soaking in Kokubo solution. The higher solubility of calcium salts allows for a higher rate of apatite formation in Kokubo solution. Furthermore, changes in pH after exposure of the cement are related to the apatite-forming ability, because the addition of calcium hydroxide also gives the cement the ability of apatite formation, even if the cement releases a small amount of calcium ions into the surrounding fluid. Smaller dissolution of calcium salts results in less decrease in compressive strength after exposure to a body environment. The release of calcium ions, followed by changes in pH, must be controlled to achieve a successful design of bioactive PMMA bone cement by modification with MPS and calcium salts.

Polymethylmethacrylate–montmorillonite composites: preparation, characterization and properties

The objective of this work was directed to solve a problem of polymerization shrinkage in acrylic resin polymethylmethacrylate (PMMA) material. Organophilic montmorillonite (claytone) was added up to 1% by weight to one commercial type of PMMA powder to form PMMA–MMT composite. Acrylic specimens were processed by the conventional heat curing method following manufacturer's instructions. Thermogravimetric analysis data indicates that polymer–clay composites exhibit significant increase in thermal stability with very small amount of inorganic content. The morphology of the composites was verified using scanning electron microscopy revealing the absence of large mineral aggregates. Interlamellar spacing was measured from wide angle X-ray diffraction. The d(001) spacing of clay was expanded to 18Å in claytone and the intensity of the peaks is progressively reduced with increasing the concentration of polymer in the composites samples. Warpage and linear dimensional change measurements were achieved using ‘traveling microscope’ and one way analysis of variance was employed to compare results. The results indicated that there was a significant decrease of warpage and linear dimensional changes between PMMA specimens and that of PMMA–MMT composite materials.

Bioactive bone cement: effects of phosphoric ester monomer on mechanical properties and osteoconductivity.

A new bioactive bone cement, designated GBC, has been developed. It consists of polymethyl methacrylate (PMMA) as an organic matrix and bioactive glass beads as an inorganic filler. The bioactive beads, consisting of MgO--CaO--SiO(2)--P(2)O(5)--CaF(2) glass, have been newly designed, and a novel PMMA powder was selected. The purpose of the present study was to evaluate the effects on mechanical properties and osteoconductivity of adding a phosphoric ester (PE) monomer to the cement as an adhesion-promoting agent. Four kinds of cements were prepared: GBC, GBC with PE (designated GBC/PE), a cement consisting of the same PMMA used in GBC with apatite- and wollastonite-containing glass-ceramic (AW-GC) powder (designated AWC), and AWC with PE (designated AWC/PE). Each filler was added to the cement at 70 wt %. Adding PE to either GBC or AWC resulted in increases in the bending strength and decreases in the Young's modulus compared with the unmodified cements. Cements were packed into the intramedullar canals of rat tibiae to evaluate osteoconductivity as determined by an affinity index. Rats were sacrificed at 4 and 8 weeks after operation. The affinity index (length of bone in direct contact with the cement expressed as a percentage of the total length of the cement surface) was calculated for each cement. Adding PE to either GBC or AWC resulted in significant increases in the affinity index compared with the unmodified cements. The affinity index for GBC was significantly higher than that of AWC, and that for GBC/PE was also significantly higher than that of AWC/PE. The affinity indices for each cement increased significantly with time up to 8 weeks. Our study revealed that the higher osteoconductivity of GBC/PE was due to the large alkyl group in the PE monomer, to the hydrophilicity of the phosphoric acid in the PE monomer, and to the higher bioactivity of the bioactive glass beads at the cement surface. GBC/PE shows promise as an alternative bone cement with improved properties compared with conventional PMMA bone cement.

Prevention of fibrous layer formation between bone and adhesive bone cement: In vivo evaluation of bone impregnation with 4‐META/MMA‐TBB cement

We have studied a new adhesive bone cement, that consists of 4-methacryloyloxyethyl trimellitate anhydride (4-META) and methylmethacrylate (MMA) as monomers, tri-n-butyl borane (TBB) as the initiator, and polymethylmethacrylate powder (4-META/MMA-TBB cement). This cement has shown remarkable adhesive properties to bone in vitro. In this study, we assessed the interface in vivo periodically. The femora of rabbits were fenestrated and filled with either the 4-META/MMA-TBB cement or a conventional polymethylmethacrylate cement. The animals were killed after 1, 4, 12, and 24 weeks to analyze the interface by optical microscopy and transmission electron microscopy. Optical microscopic examinations showed that the cured 4-META/MMA-TBB adhesive cement bonded to bone directly for 24 weeks, whereas a fibrous tissue layer was observed between the bone and cured conventional cement at 12 weeks after the operation. The transmission electron microscopy views of 4-META/MMA-TBB cement bonded to bone demonstrated a unique “hybridized bone” with the cement in the subsurface of the substrate in every case. The formation of the hybridized bone indicates the bonding mechanism of the adhesive cement to bone, which prevents the fibrosis intervention between bone and cement. These results suggest that the biomechanical and adhesive properties of 4-META/MMA-TBB cement make it a useful bone-bonding agent in orthopedic surgery. © 2000 John Wiley & Sons, Inc. J Biomed Mater Res, 52, 24–29, 2000.

Bioactive polymethyl methacrylate-based bone cement: Comparison of glass beads, apatite- and wollastonite-containing glass–ceramic, and hydroxyapatite fillers on mechanical and biological properties

A new bioactive bone cement (designated GBC) consisting of polymethyl methacrylate (PMMA) as an organic matrix and bioactive glass beads as an inorganic filler has been developed. The bioactive beads, consisting of MgO-CaO-SiO2-P2O5-CaF2 glass, have been newly designed, and a novel PMMA powder was selected. The purpose of the present study was to compare this new bone cement GBC's mechanical properties in vitro and its osteoconductivity in vivo with cements consisting of the same matrix as GBC and either apatite- and wollastonite-containing glass–ceramic (AW-GC) powder (designated AWC) or sintered hydroxyapatite (HA) powder (HAC). Each filler added to the cements amounted to 70 wt %. The bending strength of GBC was significantly higher than that of AWC and HAC (p < 0.0001). Cements were packed into intramedullar canals of rat tibiae in order to evaluate osteoconductivity as determined by an affinity index. Rats were sacrificed at 2, 4, and 8 weeks after operation. An affinity index, which equaled the length of bone in direct contact with the cement expressed as a percentage of the total length of the cement surface, was calculated for each cement. At each time interval studied, GBC showed a significantly higher affinity index than AWC or HAC up to 8 weeks after implantation (p < 0.03). The value for GBC increased significantly with time up to 8 weeks (p < 0.006). The handling property of GBC was comparable with that of PMMA bone cement. Our study revealed that the higher osteoconductivity of GBC was due to the higher bioactivity of the bioactive glass beads at the cement surface and the lower solubility of the new PMMA powder to MMA monomer. In addition, it was found that the smaller spherical shape and glassy phase of the glass beads gave GBC strong enough mechanical properties to be useful under weight-bearing conditions. GBC shows promise as an alternative with improved properties to the conventionally used PMMA bone cement. © 2000 John Wiley & Sons, Inc. J Biomed Mater Res, 51, 258–272, 2000.

Plasma deposition of polymer films on pmma powders using vacuum fluidisation techniques

Thin organic films were deposited on polymethylmethacrylate powder particles by combining the techniques of plasma polymerisation and vacuum fluidisation. The treated powders were characterised by scanning electron microscopy, energy dispersive X-ray analysis, and time of flight secondary ion mass spectrometry. The primary objective of the investigation was to demonstrate the efficacy of the two techniques in combination for modifying the surface properties of particulate materials.

In vitro release studies of methylmethacrylate liberation from acrylic cement powder

Bone cement or polymethylmethacrylate (PMMA) is commonly used for anchoring cemented prosthesis to the bone. Cytotoxic effect of culture media exposed to PMMA powder may be related with long term problems associated with acrylic cement application, being the monomer (methylmethacrylate) one of the cement’s component partly responsible for the cytotoxic effect. The present work reports the studies of monomer release from acrylic bone cement powder under different experimental conditions: setting time of PMMA (in solution and air) and different culture media composition. High-performance liquid chromatography was used for the determination of residual monomer. Mathematical models were applied to experimental dissolution data revealing that monomer release is lightly affected by the studied variables. The monomer release seems to be a surface phenomena, suggesting that the possible actions of monomer will mainly be due to the initial loss of non polymerized monomer rather than to further depolymerization of the already polymerized cement.

Interfacial strength of compression-molded specimens between PMMA powder and PMMA/MMA monomer solution-treated ultra-high molecular weight polyethylene (UHMWPE) powder.

The interface between bone cement and ultra-high molecular weight polyethylene (UHMWPE) has been considered a weak link of cemented UHMWPE acetabular cup in total hip replacement (THR). For the improvement of this weak interface, adhesion between the UHMWPE acetabular cup and bone cement made of polymethylmethacrylate (PMMA) has been investigated in our laboratory. Virgin UHMWPE powders were treated with methyl methacrylate (MMA) monomer and PMMA/MMA solution. The treated UHMWPE powders were then compression-molded with virgin UHMWPE powders or PMMA powders, creating two different interfaces, i. e., treated/virgin UHMWPE powder and treated UHMWPE/PMMA powder. For the present study, the interfacial strengths between PMMA powder and the treated UHMWPE power were investigated following the same protocol previously set. The maximum interfacial strength was 17.0 +/- 0.25MPa with the same molding condition of 166.5 degrees C, 38.7 MPa and l h. In addition to the molding condition, we tested the strengths for the treated UHMWPE powders, which have different ratios between PMMA/MMA solution and MMA-treated UHMWPE powders. Significant differences on the interfacial strengths resulted due to the ratio change; more PMMA in the PMMA/MMA solution-treated UHMWPE powder exhibited higher interfacial strength. Scanning electron microscopic (SEM) pictures showed that the interface is composed of three major portions: PMMA powder, UHMWPE, and coated PMMA, indicating strong mechanical interlocking of UHMWPE and PMMA powder matrix and chemical bonding between PMMA powder and the precoated PMMA onto the UHMWPE. In addition, another interfacial strength between PMMA powder, which is equivalent to the outermost part of the cup, and bone cement was investigated. The average strength reached up to 42.4 +/- 3.6 MPa, close to the tensile strength of bone cement itself.

Prevention of fibrous layer formation between bone and adhesive bone cement: in vivo evaluation of bone impregnation with 4-META/MMA-TBB cement.

We have studied a new adhesive bone cement, that consists of 4-methacryloyloxyethyl trimellitate anhydride (4-META) and methylmethacrylate (MMA) as monomers, tri-n-butyl borane (TBB) as the initiator, and polymethylmethacrylate powder (4-META/MMA-TBB cement). This cement has shown remarkable adhesive properties to bone in vitro. In this study, we assessed the interface in vivo periodically. The femora of rabbits were fenestrated and filled with either the 4-META/MMA-TBB cement or a conventional polymethylmethacrylate cement. The animals were killed after 1, 4, 12, and 24 weeks to analyze the interface by optical microscopy and transmission electron microscopy. Optical microscopic examinations showed that the cured 4-META/MMA-TBB adhesive cement bonded to bone directly for 24 weeks, whereas a fibrous tissue layer was observed between the bone and cured conventional cement at 12 weeks after the operation. The transmission electron microscopy views of 4-META/MMA-TBB cement bonded to bone demonstrated a unique "hybridized bone" with the cement in the subsurface of the substrate in every case. The formation of the hybridized bone indicates the bonding mechanism of the adhesive cement to bone, which prevents the fibrosis intervention between bone and cement. These results suggest that the biomechanical and adhesive properties of 4-META/MMA-TBB cement make it a useful bone-bonding agent in orthopedic surgery.

ESR study of MMA polymerization by a peroxide/amine system: bone cement formation.

Electron spin resonance (ESR) spectroscopy was used to gain insight at the molecular level into the curing of bone cement. Methyl methacrylate was polymerized using a N,N-dimethyl-p-toluidine (TD)/benzoyl peroxide (BPO) redox system in the presence of polymethyl methacrylate (PMMA) powder. The conventional nine-line ESR spectrum for the growing polymer radical was detected at the gel stage of polymerization. While the optimum free radical concentration was observed near the equimolar amine/BPO concentration, excess amine led to a change in the chemical structure of the trapped radical and inhibited the polymerization process. At a high amine/BPO ratio the nine-line signal disappeared and a three-line nitroxide-based radical appeared. The appearance of this nitroxide signal seems to depend on the amine/BPO molar ratio and on the presence of PMMA. An excess amount of amine with respect to BPO was found to inhibit the polymerization process. When BPO was removed, the system still polymerized but with a longer gelation time and a lower radical concentration. These results demonstrate that trapped free radicals in the bulk polymerization of MMA convert to polymeric peroxides that act as initiators in bone cement. When the accelerator 4-dimethylamino phenethyl alcohol (TDOH) was used, a higher radical concentration was observed in the polymerizing system. TDOH shows potential for being a more effective accelerator than TD for bone cement curing.

Reinforcement of denture base resin with glass fillers.

This study evaluated the effect of short glass fibers on the transverse strength of a heat-polymerized acrylic resin denture base material. Four groups of specimens (n = 10) were fabricated according to the ISO standard for the transverse strength test. E-glass fibers were triturated to produce short fibers of different lengths. Specimens for Group 1 (control) were made of unfilled polymethylmethacrylate (PMMA). For group 2, the PMMA powder was modified with 0.1 g of dry glass fibers. For group 3, the PMMA powder was modified with 0.1 g of silanized glass fibers. For group 4, the PMMA powder was modified with 0.2 g of silanized glass fibers. A three-point loading test was used to determine the transverse strength of the tested specimens. The fracture surface of each specimen was evaluated using SEM. The addition of untreated glass fibers increased the transverse strength by 11% but produced some porosity in the polymeric matrix. The addition of silane-treated glass fibers increased the transverse strength of PMMA by 28% for group 3 and by 26% for group 4, and produced a dense structure for the polymer-fiber composite. The transverse strength of PMMA can be slightly increased by the addition of short glass fibers.

Tissue response to particulate polymethylmethacrylate in mice with various immune deficiencies.

We examined the tissue response to subcutaneous injections of particulate polymethylmethacrylate powder in fully immunocompetent C3Hf/Sed mice as well as three strains of mice with different levels of lymphocyte dysfunction. Five weeks after the injection, we found clearly demarcated granulomas. Histological and immunohistochemical studies showed that these granulomas were similar among all strains, with either paucity or absence of lymphoid cells. In situ hybridization with use of complementary RNA probes indicated that macrophages were synthesizing interleukin-1 beta messenger RNA (mRNA), a marker of macrophage activation, and a cytokine implicated in pathological bone resorption. We concluded that, in mice, there is a lymphocyte-independent pathway of macrophage activation in response to particulate polymethylmethacrylate. This suggests that the foreign-body response to particulate orthopaedic biomaterials is macrophage-initiated and maintained and that lymphocytes are not essential to this response, although they may modulate it.