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At least 1,207 records · Page 67Linked to original sources
PubMed1992

Effect of repair surface design, repair material, and processing method on the transverse strength of repaired acrylic denture resin.

The transverse strengths of blocks of denture base acrylic resin repaired with autopolymerizing monomer and polymer and autopolymerizing monomer and heat-cured polymer were measured with a three-point bending test. Three repair joints were studied: butt, round, and 45-degree bevel. Three processing methods were used: bench cure, hydroflask with hot water for 10 minutes, and hydroflask with hot water for 30 minutes. The strengths of repairs made with round and 45-degree bevel joint designs were similar and significantly greater than those with a butt joint design. The strengths of repairs processed in a hydroflask for 10 minutes and 30 minutes were similar and significantly greater than those cured on the bench top. There was no difference in the strength of repairs made with autopolymerizing monomer and polymer and autopolymerizing monomer and heat-cured polymer.

Acrylic Resins↗
PubMed1992

The dimensional accuracy of rectangular acrylic resin specimens cured by three denture base processing methods.

The dimensional accuracy of rectangular acrylic resin specimens was examined when they were processed by three methods: a conventional method, the SR-Ivocap system, and a microwave curing method. The dimensional accuracy was evaluated by the change of the distance vector V, which is calculated by means of measurements of the distances between fixed points on specimens. The specimen cured by the SR-Ivocap system exhibited less dimensional change (p less than 0.05) than those cured by the conventional and the microwave curing methods. The SR-Ivocap system might produce a more accurate denture base than the conventional and the microwave curing methods.

Acrylic Resins↗
PubMed1993

Technique for controlling the thickness of a facial prosthesis when an acrylic resin core is used.

A technique for evaluating the acrylic resin core before processing a silicone facial prosthesis is described. The technique involves the use of either irreversible hydrocolloid impression material or silicone to identify thin areas in the pattern. This simple yet effective procedure ensures adequate thickness and strength of the silicone prosthesis, which in turn decreases the amount of chair and laboratory time needed at the delivery appointment.

Acrylic Resins↗
PubMed1993

Effects of thermocycling and occlusal force on the margins of provisional acrylic resin crowns.

Transitional acrylic crowns were examined for changes in axial contour and increases in marginal gap width after simultaneous thermocycling and occlusal loading. Two groups of 10 crowns--one with a shoulder finish line and another with a chamfer finish line--were treated with 3400 thermocycles and 50,000 load cycles simultaneously within an artificial oral environment chamber in an MTS Dental Materials Testing System. The marginal gaps were increased for both groups after treatment. However, the group of crowns with the shoulder finish lines demonstrated a smaller gap width (x = 90 microns) after treatment than the crowns with chamfer finish lines (x = 210 microns). A statistical comparison identified a significant difference in gap width between groups (p < 0.01). Changes in the axial profile of the groups were similar, but one crown with a chamfer finish line exhibited a cracked margin.

Acrylic Resins↗
PubMed1994

Factors that affect the rheologic properties of acrylic resin denture base materials.

The rheologic characteristics of different formulations of acrylic resin denture base materials are presented in this study. This is of practical significance in selecting resins with optimum rheologic properties for denture base construction. The materials are characterized in respect to their constituents, mean powder particle size and distribution, molecular weight averages and distributions, and glass transition temperature. A comparison of the polymers indicates that smaller particles saturate with monomer more readily, and this results in a higher viscosity. A higher viscosity for higher molecular weight and lower viscosity for lower molecular weight have been observed. Increasing the percentage of copolymerization increases the viscosity. No correlation has been found between the rheologic properties of denture base polymers and the powder glass transition temperature.

Acrylic Resins↗
PubMed1994

An interocclusal record made of a combination of wax and acrylic resin.

The correct mounting of casts on articulators is a fundamental step in obtaining good clinical results and reducing the time spent in the adjustment of oral prostheses. This procedure for retruded contact mounting of casts, based on a tripod of contacts with a combination of wax and acrylic resin, permits great accuracy in a short period of time.

Acrylic Resins↗
PubMed1979

Occlusal acrylic index used to observe palatal bone cuts.

The use of an acrylic occlusal index prior to wiring a full palatal coverage splint into place offers an easy way to check for "hang-up" areas and help in placement of bone grafts while the segments are held in the predetermined position.

Acrylic Resins↗
PubMed1985

Ethyl acrylate-induced gastric toxicity. I. Effect of single and repetitive dosing.

Ethyl acrylate (EtAc) is widely used in the production of polymers and copolymers for use in the preparation of latex paints, textiles, paper coatings, and specialty plastics. EtAc caused squamous cell carcinomas and papillomas in the forestomach (nonglandular portion of the stomach) of both sexes of F344 rats and B6C3F1 mice when administered chronically by gavage. The current studies were undertaken to investigate and characterize the nature of the acute gastric toxicity caused by EtAc. Gavage administration of a single dose of 100, 200, or 400 mg/kg EtAc (in corn oil) to F344 male rats caused dose-and time-dependent mucosal and submucosal edema and vacuolization of the tunica muscularis in the forestomach and mild submucosal edema in the glandular stomach. Equivalent sc or ip doses did not produce similar gastric lesions. Treatment of rats with two or four consecutive oral daily doses (200 mg/kg each) of EtAc caused mucosal edema associated with vesicle formation, mucosal hyperplasia, submucosal edema and inflammation, and vacuolization of the tunica muscularis of the forestomach. Submucosal edema and inflammation were also observed in the glandular stomach and mucosal erosions or ulcers were observed in both portions of the stomach after repeated oral exposure to EtAc. The absence of systemic toxicity plus the dependency of gastric lesions on the gavage route of administration suggest that the EtAc-induced gastric lesions may be a consequence of localized hemodynamic changes, specifically those characteristic of a classical immediate inflammatory response to an injurious agent at the site of administration.

Acrylates↗
PubMed1986

Ethyl acrylate-induced gastric toxicity. III. Development and recovery of lesions.

Rats receiving 14 daily gavage doses of 100 or 200 mg/kg ethyl acrylate (EtAc) and killed at varying times following the end of dosing exhibited dose-dependent lesions and recovery from lesions in the forestomach. The glandular stomach which was previously shown to be affected by acute exposure to EtAc appeared to have adapted to resist EtAc toxicity with repeat exposure and appeared normal in all animals. Adaptation of the forestomach was characterized by increased papillomatous thickening with dose. Lesions observed in acute exposure to EtAc were still present with repeat dosing and were more pronounced at the high dose. Forestomachs of rats which received 100 mg/kg EtAc for 14 days were recovered to normal within 2 weeks following the last dose. Forestomachs of rats receiving 200 mg/kg EtAc still exhibited numerous lesions 2 weeks following the last dose, and mucosal hyperplasia was present in the forestomachs at 4 weeks postexposure. Two lesions, submucosal fibrosis and foreign body reaction, became more prevalent in high-dose animals with time. Foreign body reaction, which was present in all animals 4 weeks postexposure, appeared to have resulted from entrapment of hair and/or feed particles in forestomach lesions in the course of healing. It is speculated that the increased cell proliferation and the induced foreign body reactions may contribute to the previously demonstrated carcinogenic effect of EtAc on the rat forestomach.

Acrylates↗
PubMed1988

Studies on coagulation, fibrinolysis, kallikrein-kinin and complement activation in systemic and pulmonary circulation during hip arthroplasty with acrylic cement.

This study was designed to evaluate the contribution of the plasma cascade systems to the cardiopulmonary complications, occasionally leading to sudden death during hip arthroplasty using acrylic cement. The intraoperative pattern following uneventful surgery was therefore investigated in 8 patients with osteoarthrosis with frequent sampling from the radial and pulmonary arteries. The following general findings emerged: A gradual consumption of coagulation factors (platelets, fibrinogen, factor VII, antithrombin III), fibrinolytic components (plasminogen, alpha-2-antiplasmin), kallikrein-kinin factors (prekallikrein, kallikrein inhibitor) and complement factors (C3c, C4) was observed. Some intrapulmonary proteolytic inhibition was noticed as evidenced by lower arterial than mixed venous blood levels of alpha-2-antiplasmin and kallikrein inhibitor. Insignificant changes occurred for factor VII-phospholipid complex. A rapid, massive and transient increase in fibrinopeptide A (FPA) values in the radial artery, as opposed to the moderate increase in the pulmonary artery, was found immediately after reaming and broaching of bone. This probably reflected intrapulmonary fibrinogen to fibrin conversion, reaching a maximum 15-20 minutes before the femoral implantation. As estimated from the FPA arterial peak values and the fall in fibrinogen concentrations, approximately 5-10% of the circulating fibrinogen molecules were devoided of FPA during this intraoperative phase. The marked a-v difference in FPA level supports earlier findings of intrapulmonary fibrin formation and deposition. This process, however preceded the critical period of cardiorespiratory collapse (CRC) by at least 15 minutes, and may thus predispose to this complication.

Acrylates↗
PubMed1994

Blood coagulation is inhibited by sulphated copolymers of vinyl alcohol and acrylic acid under in vitro as well as in vivo conditions.

Biological effects of the modification of the sulphate ester and carboxyl group content of poly(vinyl alcohol-acrylic acid) copolymers (PAVAS) and sulphated polyvinyl alcohol copolymers (PVAS) with mol. weight of 5,000 to 20,000 D were studied. The in vitro anticoagulant potency of PAVAS assessed by activated partial thromboplastin time (APTT) increased with increasing the overall anionic charge, while differences in mol. weight yielded few obvious effect. The degree of sulphation played an essential part, but the carboxyl group content also contributed to the in vitro anticoagulant activity of PAVAS. On i.v. administration to rats (40 mg/kg), the anticoagulant potency of PAVAS was found to be comparable to that observed in vitro. The ability of PAVAS to induce a state of leukocytosis and decrease serum triglyceride level in rats was also dependent on charge density, and both these effects were increased with elevation of charged groups content irrespectively of mol. weight. Sulphated polyvinyl alcohol copolymers (PVAS) showed similarity to PAVAS charge-dependent biological activities.

Acrylates↗
PubMed1989

Water sorption of plasticized denture acrylic lining materials.

The objective was to characterize water sorption of plasticized denture acrylic lining materials, with determination both of uptake and diffusion coefficient (D). Feasibility was investigated first for simple binary mixtures of poly(methyl methacrylate), PMMA, and various phthalate plasticizers prepared by radiation polymerization of methyl methacrylate/plasticizer solutions. These were shown to be tractable when samples were saturated with water and then characterized in desorption measurements. Plasticizers were found to decrease the uptake of water. This decrease was attributed to the hydrophobic nature of the plasticizers and also to their ability to fill microvoids in PMMA which, in their absence, would be available to water. Values of D increased monotonically with increasing volume fractions of plasticizer. It appeared that values of D increased more rapidly in cases where large proportions of plasticizer resulted in samples which were above their glass transition temperature, Tg, at the temperature of testing water sorption. Desorption measurements were extended satisfactorily to a model system made from poly(ethyl methacrylate) powder, methyl methacrylate, and dibutyl phthalate, which was polymerized with a conventional redox initiator. Water desorption results were compared with various proprietary materials which were also characterized with respect to Tg and, cursorily, to composition.

Acrylic Resins↗
PubMed1990

Leachability of denture-base acrylic resins in artificial saliva.

We studied the influence of salivary acidity on leachability of denture-base acrylic resins with etiological interest in denture stomatitis because denture surfaces are frequently exposed to acidic conditions in the oral cavities. Auto-, heat-, and microwave-polymerized resins were immersed in artificial saliva with pH ranging from 4.0 to 6.8 at 37 degrees C, and leachables were pursued quantitatively with time. Methyl methacrylate, methacrylic acid, and benzoic acid leached from all resins. Their concentrations in the saliva were markedly high for auto-polymerized resins, while leachability of heat- and microwave-polymerized resins was so low that quantitative analysis of leachables was impossible. Lower pH showed higher concentrations of methyl methacrylate, although no apparent association was confirmed between salivary acidity and its own leachability. The concentrations of methacrylic acid increased remarkably with an increase in pH, which was probably due to hydrolysis of methyl methacrylate. These results suggest that chemotoxic actions of auto-polymerized resins are potentially ascribable to methyl methacrylate under more acidic conditions and to methacrylic acid under less acidic conditions.

Acrylic Resins↗
PubMed1993

Acrylic resin reinforced with chopped high performance polyethylene fiber--properties and denture construction.

A newly developed incremental mixing technique has been used to incorporate over 30 vol % chopped high performance polyethylene fiber into acrylic denture base resin. The reinforcement produced a substantial improvement in several clinically important properties, namely: 1) stiffness and impact strength were higher; 2) the mechanical properties were insensitive to notches that mimic anatomical features; and 3) samples damaged during bending and impact did not break up into separate fragments. Reinforced complete maxillary and mandibular dentures of good esthetic appearance were successfully manufactured and polished with conventional laboratory techniques.

Acrylic Resins↗
PubMed1986

Controlling drug release from acrylic polymers: in vitro studies with potential oral inserts.

The use of a drug modified polymer system which can release drugs such as hydrocortisone sodium succinate and chlorhexidine acetate has been explored. By partially coating the drug loaded acrylic, such that it acts as a core with an impermeable membrane covering most of the surface, the rapid releases of the drug can be prevented and near zero-order rates of release achieved. For chlorhexidine acetate the release time was extended from around 20 d to 80 d with at least 60% of the drug being released. A similar potential for the controlled release of hydrocortisone sodium succinate is described and represents an important stage in the development of an intra-oral insert for drug delivery.

Acrylates↗
PubMed1989

Cross-linking and ring opening during polymerization of heterocyclic methacrylates and acrylates.

Heterocyclic methacrylates have been shown to have low polymerization shrinkage. In this paper, the extent of ring opening has been assessed by the degree of consequent cross-linking. In polymers of tetrahydrofurfuryl methacrylate and acrylate, tetrahydropyranyl and tetrahydropyran-2-ylmethyl methacrylate, fewer than 1% monomer units were involved in cross-linking and hence ring-opening reactions. 2-epoxypropyl methacrylate, when polymerized, was very extensively cross-linked indicating prolific ring opening. However, the polymerization shrinkage of this material was the highest of the heterocyclic methacrylates studied and was that predicted from the known molar volume change of methacrylate esters. Ring opening does not, therefore, appear to be a significant factor in the polymerization shrinkage of heterocyclic methacrylates.

Acrylates↗