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Results for “ACRYLIC RESINS”

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At least 361 records · Page 20Linked to original sources
PubMed2002

Pressure and temperature changes in heat-cured acrylic resin during processing.

OBJECTIVES: The aims of this study were to measure the pressure and temperature changes of acrylic resin during processing, to record the highest temperature reached when fast cured in boiling water and to determine the elevated boiling point of monomer under high pressure. METHODS: A subminiature pressure transducer (temperature compensated to 94 degrees C) and a thermocouple were placed on the palate of a standardized maxillary complete denture base. A heat-cured resin (Trevalon C) was polymerized by a long heating cycle (72 degrees C for 6.5 h and 92 degrees C for 1.5 h). Recordings of pressure and temperature (n=6) were made at initial clamping of denture flasks and throughout the processing cycles of resin. The temperature of the resin was also monitored during a fast cycle, which was accomplished by placing the flask directly into boiling water for 40 min. RESULTS: The pressure of acrylic dough inside the clamped flask was initially 11.5 atm (SD=3.2) and reached a peak of 22.0 atm (SD=3.5) during the long heating cycle. The elevated boiling point of monomer at increased pressure was calculated to be about 193 degrees C (at 11.5 atm) and 228 degrees C (at 22.0 atm). These elevated boiling points are higher than the maximum temperature 131 degrees C (SD=6.6) reached during the fast curing cycle. No porosity was observed even in the denture bases heat-cured by the fast cycle. SIGNIFICANCE: The highest temperature reached by heating of resin during processing is well below the elevated boiling point of monomer. Monomer therefore does not boil in clamped denture flasks under sufficient pressure. Thus adequate clamp pressure prevents gaseous porosity irrespective of curing cycle used.

Acrylic Resins↗
PubMed2004

In vitro new dialysis protocol to assay the antiseptic properties of a quaternary ammonium compound polymerized with denture acrylic resin.

AIMS: To develop an in vitro protocol in order to assess the antiseptic properties of a quaternary ammonium compound polymerized with acrylic denture resin base, using experimental resin discs and dialysis membranes. METHODS AND RESULTS: Experimental acrylic resin discs were polymerized with Poly 202063A, an ammonium compound (2-50%). Antiseptic properties were assayed against two reference strains (Escherichia coli, Staphylococcus aureus) and a laboratory strain (Candida albicans), using three different conditions (test A, B and C). In test A, according to classical protocols the resin discs were first soaked in large volumes of microbial inoculum (45 ml). An original dialysis protocol was then designed to recreate the small biofilm volume on the prosthetic surface. In test B, discs and bacterial inoculum (600 microl) were introduced in a dialysis bag and dialysed against a sterile buffer. A bactericidal effect was observed against E. coli and Staph. aureus (<0.1% viable cells in initial bacterial suspension). A dose-dependent fungistatic effect was observed against C. albicans. Finally, in test C discs and sterile buffer (600 microl) were introduced in a dialysis bag and dialysed against microbial inoculum. Reduced activity was found outside the dialysis bag, demonstrating that free ammonium was able to diffuse through the dialysis membrane, displaying antiseptic properties. CONCLUSIONS: The present protocol demonstrated that a quaternary ammonium compound remains efficient after heat polymerization with an acrylic denture base resin, both in immediate and distant microbial environments. SIGNIFICANCE AND IMPACT OF THE STUDY: Such removable prosthetic devices with intrinsic antiseptic properties would contribute to improve the long-term management of denture stomatitis.

Acrylic Resins↗
PubMed1995

A customized acrylic resin shell for fabricating an amalgam core on the coronally debilitated, endodontically treated posterior tooth.

This article describes a technique for fabricating a custom acrylic resin shell that will ensure a properly designed amalgam core for the coronally debilitated, endodontically treated posterior tooth. A few simple procedures result in a core foundation for root protection, an ideal crown preparation, and a more predictable final restoration.

Acrylic Resins↗
PubMed1994

The effect of esthetic fibers on the flow properties of an acrylic resin denture base material.

OBJECTIVES: This study was conducted to measure the effect of viscose rayon esthetic fibers on the flow properties of an acrylic resin denture base material. METHODS: Two testing methods using a needle penetrometer and an oscillating rheometer were employed on weighed proportions (0.1%, 0.2%, 0.8%, and 0.3%) of fiber. RESULTS: The results show that the fibers affect the flow properties of the polymer/monomer mix. Increasing the percentage of fibers decreases the flow of the material and reduces the doughing time. With increasing amounts of fiber, a rapid increase in the viscosity occurs with a corresponding adverse effect on flow properties. SIGNIFICANCE: It is concluded that these properties are important for the successful handling of acrylic materials since they can influence the accuracy and quality of the molded denture.

Acrylic Resins↗
PubMed1996

Influence of tablet hardness and hydrophobicity on the adhesive properties of an acrylic resin copolymer.

The adhesive properties--including the force of adhesion, elongation at adhesive failure, the modulus of adhesion, and the adhesive toughness--of an acrylic resin copolymer were determined using the butt adhesion technique. Flat-faced tablets containing up to 30% hydrogenated castor oil were coated with an aqueous dispersion of Eudragit L30D-55. Using data obtained from a Chatillon digital force gauge attached to a motorized test stand, force-deflection profiles, similar to stress-strain curves generated in the tensile testing of free films, were constructed. The surface characteristics of the tablets significantly influenced polymer-substrate interaction. The force of adhesion, the elongation at adhesive failure, and the adhesive toughness decreased as the surface of the tablet became more hydrophobic through the addition of wax to the tablet formulation. Lower adhesive properties were found with increasing tablet hardness, due to a decrease in the effective area of contact between the film coating and the tablet surface. Increased polymer loading resulted in stronger adhesion, indicating a relationship between the mechanical and adhesive properties of the polymer. The present study demonstrated that the area under the force-deflection profile in conjunction with the force of adhesion was more representative of the adhesive properties of the polymer.

Acrylic Resins↗
PubMed1992

Genotoxicity of N-acryloyl-N'-phenylpiperazine, a redox activator for acrylic resin polymerization.

N-Acryloyl-N'-phenylpiperazine is a promoter of redox reactions synthesized recently, and proposed as an activator for the polymerization of acrylic resins for biomedical use. The chemical was analyzed for different genotoxicity endpoints, to obtain both information on its possible mutagenic/carcinogenic potential and a model analysis of a tertiary arylamine, which belongs to a class of chemicals commonly used as polymerization accelerators in the biomaterial field. The genotoxicity endpoints considered were: gene mutation in the Salmonella test; structural and numerical chromosome alterations in Chinese hamster V79 cells, evaluated by the micronucleus test together with an immunofluorescent staining specific for kinetochore proteins; in vitro and in vivo DNA damage, evaluated in V79 cells and in mouse liver by the alkaline DNA elution technique. On the whole, the results indicate that N-acryloyl-N'-phenylpiperazine is to be regarded not so much as a DNA-damaging agent, but as a genomic mutagen. Indeed, it was not mutagenic in Salmonella (though its toxicity did not allow testing concentrations over 70 micrograms/plate), and it was weakly positive in inducing chromosomal fragmentation in vitro (one positive, not dose-related, result out of five different doses tested) and in vivo DNA damage (increases in DNA elution rate never doubling control values). The chemical was, however, clearly positive (with dose-dependent effects up to about 25 times the control value) in causing numerical chromosome alterations, at the maximal non-toxic doses.

Acrylic Resins↗
PubMed1999

Influence of pigment concentration and particle size on adhesion of an acrylic resin copolymer to tablet compacts.

The effects of the particle size and the concentration of pigments in aqueous polymeric dispersions on the adhesive properties of an acrylic resin copolymer were investigated. Aqueous polymeric dispersions containing up to 20% (v/v) pigment were coated onto hydrophilic and hydrophobic tablet compacts, and polymer adhesion was assessed using a novel butt adhesion technique. An inverse relationship was found between the particle size of the pigment present in the aqueous polymeric dispersion and film-tablet adhesion. As the particle size of the pigment increased, the adhesive strength of the polymer to the tablet compact decreased. Increased concentrations of the opacifying agent titanium dioxide in the acrylic dispersion resulted in stronger film-tablet adhesion. No clear relationship could be established between the wettability of the tablet compact by the pigmented polymeric dispersion and the strength of film-tablet adhesion. The hydrophobicity of the tablet compact was found to affect the glass transition temperature of the polymeric film to a greater extent than the particle size, morphology, or concentration of the pigment incorporated into the acrylic dispersion.

Acrylic Resins↗