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PubMedDate not supplied

The treatment of giant cell tumors by curettage and filling with acrylic cement. Long-term functional results.

Curettage and filling with acrylic cement in the treatment of para-articular giant cell tumor (GCT) has multiple advantages as compared to other methods; nonetheless, the possibility of progression in arthrosis is still a drawback. The literature does not report long-term functional results when this method was used. Four cases are presented with a mean long-term follow-up of 13.5 years (minimum 11, maximum 18). Clinical results, evaluated by the Enneking system (18), were excellent, and there were no radiological modifications, so that we believe that this is the method to choose for Campanacci stage I and II GCT (1), and in some stage III cases, as joint function is not compromised in time.

Acrylates↗
PubMed1998

Fabrication of an amalgam core using a customized acrylic resin shell.

This article describes a build-up technique that uses a customized acrylic resin shell for restoring endodontically treated molars that are involved in three-unit fixed partial denture design. The shell confines the amalgam without impinging on the periodontium to ensure a proper core foundation, an ideal tooth preparation, and a more predictable final restoration.

Acrylic Resins↗
PubMed1998

Adhesion to denture acrylic surfaces and relative cell-surface hydrophobicity of Candida parapsilosis and Candida albicans.

C. parapsilosis is an opportunistic emerging pathogen which together with C. albicans causes diseases in immunocompromised patients. Adhesion of Candida species to various surfaces is an important event in colonization and pathogenesis, and the relative cell-surface hydrophobicity (CSH) of the organism is a contributory physical force involved. Therefore, in vitro adhesion to acrylic surfaces and relative CSH of 24 isolates of C. parapsilosis and 10 isolates of C. albicans were studied. There was no significant difference in relative adhesion of C. parapsilosis isolates and C. albicans, although the former demonstrated a tendency for increased adhesion. There was significant intra-species variation in adhesion among isolates of C. parapsilosis (p=0.0001), but not C. albicans. In general, C. parapsilosis isolates demonstrated a two-fold greater relative CSH than C. albicans (p=0.0003). When the relative CSH of superficial and systemic isolates of C. parapsilosis were compared, the former showed a significantly higher (49.15%) relative CSH than their systemic counterparts (p<0.01). A highly significant positive correlation between adhesion and relative CSH of C. parapsilosis (p=0.74, p<0.0001) was also noted. Taken together, these data suggest that the attributes of adhesion and relative CSH of Candida species may contribute differentially in varying disease states of the human host, such as superficial and systemic Candida infections.

Acrylic Resins↗
PubMed1998

[The tissue reaction to acrylic plastics modified by supercritical extraction with carbon dioxide].

The process of extraction of admixtures from acryl plastic widely used in dentistry by means of supercritical carbon dioxide (sc-CO2) was studied and effects of extraction conditions on biocompatibility and toxicity of resultant materials assessed, sc-CO2 effectively purified the specimens from toxic compounds (monomers and low-molecular oligomers, methylmethacrylate, dichloroethane) and notably improved the biocompatability of polymer implants. Tissue reaction to ethacryl and protacryl depends on the degree of implant polymerization and duration of extraction of toxic substances from polymer.

Acrylic Resins↗
PubMed1999

Bond strengths of silicoated and acrylic resin bonding systems to metal.

STATEMENT OF PROBLEM: The Kevloc bonding system is based on the bond of acrylic resin with the metal surface, in contrast to the Silicoater system, which covers the metal surface with a SiOx-C layer. Bonding prevents the occurrence of the marginal gap between the metal and the resin, which causes weaker bond strengths and discoloration. PURPOSE: This investigation examined the bond strength values achieved by using the Kevloc technique on Ag-Pd and Co-Cr alloys, and compared them with those obtained by the Silicoater technique. After artificial aging, shear testing of the specimens was performed. MATERIAL AND METHODS: A microscope image analyzer measured the thickness of bonding layers to reveal any marginal gap. RESULTS: No marginal gap was noticed for either technique. The Kevloc technique provided better results than Silicoater regardless of alloy used. Immersion in water (7.64 to 8. 05 MPa) and thermocycling (6.12 to 6.95 MPa) reduced the initial bond strength values (12.52 to 12.94 MPa), but the breakdown occurred between the opaque layers or between the opaque and the resin, thus giving a cohesive type of failure. CONCLUSION: The dental alloy used did not affect bond strengths and artificial aging caused reduction in bond strengths. The Kevloc bonding system exhibited higher bond strengths than Silicoater, but the marginal gap was not seen for either bonding system.

Acrylic Resins↗
PubMed1998

Study of polymerization of acrylic bone cement: effect of HEMA and EGDMA.

The polymerization reaction of standard surgical Simplex-P radiopaque bone cement was investigated by differential scanning calorimetry to determine the influence of hydroxyethyl methacrylate (HEMA) and ethylene glycol dimethacrylate (EGDMA) on the polymerization reaction. From the kinetic analysis, the polymerization reaction of the modified acrylic bone cement was found to be approximately a first-order reaction. The reaction rate constants (k) were determined. It was found that the effects of HEMA and EGDMA contents on the rate and the heat of polymerization can be explained by the frequency factor and the activation energy. An increase in HEMA content tends to result in an increase in the values of both frequency factor and activation energy, whereas an increase in EGDMA content tends to induce a decrease in the frequency factor and activation energy.

Bone Cements↗
PubMed1998

Application of long chain amine activator in conventional acrylic bone cement.

A long chain acid derivative bearing an aromatic tertiary amine group, 4-N,N-dimethylaminobenzyl laurate (DML), which acts as an activator for the curing of acrylic cements at low temperature, has been synthesized and characterized to reduce the biological adverse effects usually associated with the classical activator N,N-dimethyl-4-toluidine (DMT). The effectiveness of the activator was tested on commercial formulations (e.g., Palacos R) and on experimental bone cements based on poly (methyl methacrylate) by using different benzoyl peroxide/amine molar ratios. The exotherms of polymerization were followed at three different temperatures: 25, 30, and 37 degrees C. The DML activator was found to be more sensitive to temperature than the corresponding DMT. DML provided exotherms of polymerization with decreasing peak temperatures and increasing setting times without impairing the mechanical properties. Residual monomer content was analyzed in a range of activator concentrations by keeping the benzoyl peroxide concentration constant. In all cases the residual monomer content was lower than 5%, indicating its good efficiency in the benzoyl peroxide initiated polymerization.

Bone Cements↗
PubMed1999

Effect of mixing method and storage temperature of cement constituents on the fatigue and porosity of acrylic bone cement.

The influence of the storage temperature of the cement constituents prior to mixing (21 vs. 4 degrees C) and the mixing method (hand mixing vs. vacuum mixing) on the uniaxial tension-compression fatigue performance and porosity of Palacos R acrylic bone cement was studied. The fatigue results were analyzed using the three-parameter Weibull equation. The fatigue performance was expressed as an index I, which was defined as the product of the Weibull characteristic fatigue life and the square root of the Weibull slope. Statistical analyses of these results show that although the mixing method (for a given storage temperature) exerts a significant influence on the fatigue performance and areal porosity, the effect of storage temperature (for a given mixing method) on either of these parameters is not significant.

Biocompatible Materials↗
PubMed1999

Characterization of new acrylic bone cement based on methyl methacrylate/1-hydroxypropyl methacrylate monomer.

New formulations of acrylic bone cement based on methyl methacrylate/1-hydroxypropyl methacrylate (MMA/HPMA) monomers were developed with the purpose of obtaining more ductile materials with reduced polymerization shrinkage. In this way, the ductility of such materials increased, but the introduction of high percentages of the hydrophilic component produced an important decrease in Young's modulus and strength. To ascertain the reason for the deterioration of the tensile parameters, an analysis by scanning electron microscopy of these formulations was carried out; it revealed poor adhesion between the matrix and poly(MMA) beads. We also observed that the polymerization shrinkage increased as the amount of hydrophilic monomer in the formulation decreased, and the 50% (v/v) HPMA modified bone cement compensated for this volume reduction with its water uptake swelling. Measurements taken on the setting time and polymerization exotherm showed a decrease in the former and an increase in the latter, because of the introduction of a more reactive monomer in the bone cement formulation.

Bone Cements↗
PubMed2000

Heck reactions of iodobenzene and methyl acrylate with conventional supported palladium catalysts in the presence of organic and/or inorganic bases without ligands

The vinylation of iodobenzene with methyl acrylate has been studied with several supported palladium catalysts in N-methylpyrrolidone in the presence of triethylamine and/or sodium carbonate. The reaction can be performed in air without any solubilizing or activating ligands. It was found that significant amounts of palladium leach out into the solvent and these dissolved Pd species essentially catalyze the reaction. It is interesting, however, that almost all the palladium species in the solution can redeposit onto the surface of the supports after the reaction has been completed (at 100% conversion of iodobenzene). Thus, the catalysts were recyclable without loss of activity. The use of both inorganic and organic bases is very effective in the promotion of the palladium redeposition as well as in the enhancement of the reaction rate. For Heck reactions with bromobenzene and chlorobenzene it was found that the use of triethylamine and sodium carbonate increases the selectivity of the Heck coupling product (benzene is also produced for these two substrates), but the mixed bases do not affect the overall rate of reaction as much.

Journal Article↗
PubMed2000

Tensile characteristics of ten commercial acrylic bone cements.

The mechanical properties of acrylic bone cement, used in orthopedic surgery, are very influential in determining successful long-term stability of a prosthesis. A large number of commercial formulations are available, differing in chemical composition and physical properties of both powder and monomer constituents. In this study, the static and dynamic tensile characteristics of a number of the most commonly used bone cements (Palacos R, Simplex P, CMW 1 & 3, Sulfix-60, Zimmer Dough), along with some newer formulations (Endurance, Duracem 3, Osteobondtrade mark and Boneloc), have been investigated under the same testing regimes. Testing was performed in air at room temperature. Significant differences in both static and fatigue properties were found between the various bone cements. Tensile tests revealed that Palacos R, Sulfix-60, and Simplex P had the highest values of ultimate tensile strength, closely followed by CMW 3, while Zimmer Dough cement had the lowest strength. Fatigue testing was performed under stress control, using sinusoidal loading in tension-tension, with an upper stress level of 22MPa. The two outstanding cements when tested in these cyclic conditions were Simplex P and Palacos R, with the highest values of Weibull median cycles to failure. Boneloc bone cement demonstrated the lowest cycles to failure. While the testing regimes were not designed to replicate exact conditions experienced by the bone cement mantle in vivo, there was a correlation between these results and clinical outcome.

Bone Cements↗
PubMed2006

Capillary electrophoresis-mass spectrometry of a new cross-linker with acrylic functionality.

Analytical characterization of dimethacrylate-tyrosine-lysine-tyrosine (DMTLT, a new biodegradable acrylic cross-linker synthesized at our laboratory) is carried out using CE-MS. DMTLT is a pseudopeptide composed by tyrosine-lysine-tyrosine amino acids linked through urea bonds with two methacrylic groups, one at each end of the molecule, making this compound an excellent cross-linker for polymerization reactions and for obtaining new biodegradable materials. A new CE-MS method is developed for the characterization of DMTLT and its products of degradation after basic hydrolysis. In order to carry out an exhaustive examination of such degradation products methods based on CE coupled to IT and TOF-MS are employed. Based on CE-IT-MS results and the elemental composition of the degradation products obtained by CE-TOF-MS, conclusions on the mechanism and kinetic of hydrolysis of DMTLT are obtained confirming both the usefulness of CE-MS to characterize new biomaterials and the applicability of DMTLT for preparing new biodegradable polymers. These results are corroborated through the CE-MS detection of the identified products of degradation in a dimethyl acrylamide polymer cross-linked with DMTLT.

Cross-Linking Reagents↗
PubMed2002

Self-curing acrylic formulations containing PMMA/PCL composites: properties and antibiotic release behavior.

Partially biodegradable acrylic composites containing poly(methyl methacrylate)-poly(epsilon-caprolactone) (PMMA/PCL) systems were prepared by mixing the corresponding PMMA/PCL beads (89:11, 86:14, 83:17, and 77:23 weight ratio) used as solid phase with methyl methacrylate (MMA) (liquid phase) in a solid/liquid ratio of 1.5:1. The physical and chemical microheterogeneity of these beads influenced significantly the curing parameters, because several aspects involved in the polymerization reaction are closely related to both morphology and size distribution of the particles. In vitro behavior was studied by immersion in simulated body fluid at pH = 7.4 and 37 degrees C for more than 8 weeks and the composition was followed by 1H-nuclear magnetic resonance spectroscopy. Approximately 2% wt/wt weight loss was observed after a period of 8 weeks for the composites richest in PCL. Mechanical properties of the dry and wet specimens were evaluated by compressive and tensile tests. In all cases, the presence of PCL in the composites provided a significant decrease in both compressive strength and elastic modulus compared with plain PMMA. Tensile and compressive strength also decreased significantly after 2 weeks of immersion in simulated body fluid compared with dry specimens. The self-curing composites based on PMMA/PCL beads and loaded with 3% wt/wt vancomycin were evaluated as carriers for local release of antibiotics. The composite prepared with beads of PMMA/PCL ratio 86:14 was the most effective. It eluted 64% of the initial drug within the first 5 h, allowing progressive release of nearly the total amount of the initial drug (90%) in approximately 2 months. The results obtained suggest that the described composites can be suitable for antibiotic release in non-load bearing graft applications.

Biocompatible Materials↗
PubMed1975

Degree of polymerization of acrylic bone cement.

Self-curing powder-liquid admixed acrylic systems are used for internal fixation fo total hip and total knee prostheses. Gel permeation chromatography revealed that the polymer chain length distributions of set cements were basically unaffected by their curing pressures. However, a decrease of approximately 11% in porosity coupled with a measured increase in mechanical strengths could be induced through the use of high curing pressures well beyond those attainable by the surgeon in the current arthroplasties. The conclusion of the investigation was that, to improve such cements, attention should be focused on elimination of porosity rather than attempting to produce higher degree of polymerization.

Bone Cements↗
PubMed1976

Mechanical strength of acrylic bone cements impregnated with antibiotics.

Admixing of several antibiotic powders which were insoluble in methyl methacrylate did not decrease the compressive and diametral tensile strengths of two acrylic bone cements when tested after setting for 1 day and after leaching 40 days in water at 37 degrees C. When antibiotics were added as water solutions, the included water resulted in a significant decrease in these bulk mechanical properties. Storage in water for 40 days caused surface irregularities only on specimens of the set antibiotic admixtures. Approximately 0.5% of the admixed dosage of these water-soluble antibiotics could be leached from the set cements. The observed surface channels, presumably left by the loss of antibiotic, suggest further study of surface-sensitive mechanical properties may be needed. The bulk mechanical strengths presented here are conclusive only for the particular combinations of antibiotics and cements investigated, and should not be generalized at this time to any or all antibiotic admixtures or other mechanical properties.

Anti-Bacterial Agents↗
PubMed1978

Antibiotics in acrylic bone cement. In vitro studies.

The effect of combining gentamicin and cephalothin with Surgical Simplex bone cement was tested in vitro. Experiments were designed to determine (1) quantitative elution rates and period of time the antibiotics were eluted and (2) effective bactericidal qualities. Both antibiotics were eluted from polymerized acrylic cement in large quantities within 24--48 hr after coming in contact with fluid and continued to be released in smaller amounts for 21 days to more than 175 days. This varied with the antibiotic, concentration of antibiotic in the cement, surface area of cement, and volume of elution fluid. Quantitative determinations of numbers of bacteria in broth cultures demonstrated that sufficient quantities of antibiotics were released to be bactericidal to microorganisms within 45 min to 20 hr. This was dependent on the type of antibiotic, type of bacteria, concentration of antibiotic in the cement, and time of contact.

Arthroplasty↗
PubMed1981

The effects of drug and water incorporation upon some physical properties of cold cured acrylic.

The addition of drugs to the cold cured acrylics has been demonstrated to variably affect their mechanical properties. This study investigated the effects, to the mechanical properties of a cold cured denture base material, of the addition of drugs and water. Chlorhexidine acetate was incorporated into the denture reline material at 10% w/w in the polymer phase of the material. Specimens also contained 10, 20, or 30% water w/w in the monomer phase of the material with or without the drug. The hardness of the specimens decreased with the addition of water to drug containing or drug-free specimens. Furthermore, there was a significant reduction in the modulus of elasticity of the material with the addition of drugs and water or water alone, which was progressive as the amount of water increased. The load at fracture was similarly reduced as the water incorporation increased. The results demonstrated the considerable effects drug and water incorporation had upon the material. However, this would not negate the use of the material in the oral cavity in the reline or rebase situation employing existing prostheses. Moreover, the reduction in material strength may have the advantage of progressive loss of material with a resulting improved release pattern of the contained drug.

Chemical Phenomena↗
PubMed1984

Long-term compressive creep deformation and damage in acrylic bone cements.

Compressive creep tests were performed on five commercially available acrylic bone cements under conditions simulating in vivo usage. Measured creep strains are quite large, generally exceeding elastic strains. Large variations in creep response were noted among the various cements, with a carbon-reinforced cement by far the most resistant to creep. The empirical model epsilon = a exp(b sigma)tn was found to predict creep strains within about 10% of the measured values. Microscopic examination of some specimens after testing revealed significant cracking, resulting from long-term loading, that could be a contributing cause of time-dependent failure.

Bone Cements↗