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Biomedical subjects

C A Lefebvre

Publications and source records attributed to C A Lefebvre.

33 records · Page 2Linked to original sources
PubMed1994

Cytotoxicity of eluates from light-polymerized denture base resins.

This study examined the metabolic effects of eluates from four light-polymerized denture base resins and one heat-polymerized denture base resin on oral epithelial cells in vitro. The eluate was cell culture medium that contained either or both of apparently nonpolymerized components and reaction products that diffused out of the resin samples. Eluates were prepared by daily transfer of sample disks in a cell culture medium over 10 days. Toxicity of eluates was tested immediately after transfer (fresh) and after storage for 30 days (aged) by use of radioisotope incorporation and cell viability studies. The fresh eluates inhibited cell metabolism, whereas the aged eluates stimulated then inhibited the responses. Results suggest that the components that leach out of the tested materials do so at different rates and have prolonged toxic effects on cells. Thus soaking prosthesis in water before insertion may be beneficial.

Acrylic Resins↗
PubMed1994

Characterisation of the beta adrenergic response cascade in fetal guinea pig lung.

BACKGROUND: Suitable models for the study of lung development are needed. The suitability of the guinea pig for studying the role of the beta adrenergic response cascade in fetal lung development has been evaluated. METHODS: Radioligand binding assays with iodine-125 labelled iodopindolol were performed to identify and characterise the beta adrenergic receptors. To demonstrate that these receptors were functional, isoprenaline and forskolin stimulated generation of cyclic AMP (cAMP) in the lung tissue was quantitated by radioimmunoassay. RESULTS: The concentration of beta receptors increased with gestational age from 23 fmol/mg at 35 days to 140 fmol/mg at 64 days. Competition binding studies were consistent with a predominance of beta 2 receptors. The ability of isoprenaline to stimulate cAMP generation was greater during the saccular phase than during the canalicular phase of lung development. Incorporation of tritium labelled choline into phosphatidylcholine increased significantly between the canalicular and saccular phases. CONCLUSIONS: The beta adrenergic response cascade in fetal guinea pig lung exhibits similar characteristics to those previously described in fetal human lung and is therefore a good model in which to study the effects of beta agonists on fetal lung development.

Adrenergic beta-Antagonists↗
PubMed1993

Enhancing retention in complete dentures for patients with atypical muscle attachments: case reports.

Preprosthetic surgery is often indicated to obtain a firm, resilient covering that is uninterrupted by frena, scars, or redundant tissue. However, surgical intervention is contraindicated for some patients, especially the medically compromised. This paper presents a viable alternative to surgical intervention of atypical tissue attachments--the use of beading on the master cast. This procedure requires minimal time and is easily accomplished.

Contraindications↗
PubMed1993

A zinc phosphate cement-luted and resin-luted fixed partial denture: a case report.

An innovative fixed partial denture design for restoring a posterior edentulous space is described. The distal retainer is conventionally luted with a zinc phosphate cement, and the mesial retainer is luted with a resin cement. Contingency planning, which involves placement of a nonrigid connector between the pontic and the distal retainer, allows recementation of the resin-luted segment if the resin bond fails.

Adult↗
PubMed1992

Insulin inhibits beta-adrenergic responses in fetal rabbit lung in explant culture.

Infants of diabetic mothers are at increased risk of a number of problems at birth. Among these problems are increased risks of respiratory distress syndrome and transient tachypnea of the newborn. Because surfactant synthesis, surfactant secretion, and lung fluid resorption are all mediated in part by beta-adrenergic responses, we asked if excess insulin interferes with the beta-adrenergic response cascade in fetal lung. Lungs from fetal rabbits (26 day) were grown in explant culture in hormone-supplemented culture medium. The explants were harvested after 48 h exposure to hormones and processed for determination of beta-adrenergic receptor concentration, guanine nucleotide regulatory proteins (Gs, Gi), beta-agonist stimulated adenosine 3',5'-cyclic monophosphate (cAMP) generation, cAMP-dependent phosphodiesterase activity, and choline incorporation into phosphatidylcholine. Although insulin did not change the concentration of beta-adrenergic receptors, it decreased the ability of isoproterenol to stimulate cAMP generation. Increase in stimulation over basal was similar in explants treated with dexamethasone and dexamethasone plus insulin, but absolute levels of isoproterenol-stimulated cAMP were less in the explants treated with dexamethasone plus insulin. We speculate that insulin inhibition of cAMP generation may be important in the pathogenesis of the respiratory problems of infants of diabetic mothers.

Animals↗
PubMed1992

Overdentures and the periodontium.

Several periodontal factors are critical to the prognosis of overdenture abutment teeth. This literature review outlines these factors and discusses the documented effects of long-term overdenture use on periodontal health. The efficacy of a professional periodontal maintenance program, which is coordinated with a home oral hygiene program, is related to the success of overdenture therapy.

Dental Abutments↗
PubMedDate not supplied

The cytotoxic effects of denture base resin sealants.

Previous studies have shown that light-polymerized denture base resins have a cytotoxic effect on oral epithelial cells. The purpose of this in vitro study was to examine the effects of two denture base resin sealants when used on three light-polymerized denture base resins. Sample disks were examined for their effect on protein synthesis. Results indicate that one sealant protected the cells against toxic effects of the materials (P < .05), while one sealant enhanced toxicity up to 88% above that attributed to the resin alone.

Acrylic Resins↗
PubMedDate not supplied

Effects of denture base resins on oral epithelial cells.

The current proliferation of light-polymerized denture base resins and the continual modification of their formulations make standardized biocompatibility testing a necessity. The biocompatibilities of three light-polymerized denture base resins were compared using an in vitro epithelial cell culture system. The effect of varied lengths of polymerization of denture base resin on cell toxicity was examined. This study indicated that light-polymerized denture base resins have an effect on oral epithelial cells that appears to be related to the specific formulation of the material and not to the type of polymerization required. Varying the polymerization time or light-polymerization unit appeared to have little effect.

Acrylic Resins↗
PubMedDate not supplied

Biocompatibility of visible light-polymerized denture base resins.

The biocompatibility of three commercial formulations of visible light-polymerized denture base resins was studied to determine its effects on the RNA and DNA synthesis of oral epithelial cells in vitro. Isotope incorporation into RNA or DNA was measured after 24 hours of incubation with isotope and 48 hours of exposure to resin. The resins were shown to significantly inhibit the synthesis of both nucleotides as compared to a heat-processed resin control. Increasing the polymerization time can mitigate the toxicity of some of the resins. The air barrier coatings used to prevent oxygen inhibition of polymerization increased the toxic effects of two resins and decreased that of one of the materials. These investigations suggest that visible light-polymerized denture resins may impair the replication of oral epithelial cells. DNA synthesis is more sensitive to the toxic effects of the materials, which may relate to the ability to cause mucosal pathology. The cytotoxic effects may relate to the presence of unpolymerized resin constituents or polymerization by-products.

Acrylic Resins↗
PubMedDate not supplied

The effect of pH on the cytotoxicity of eluates from denture base resins.

This in vitro study examined the effects of environmental pH on elution of potentially toxic substances from heat-, light-, and dual- (chemical plus light) polymerized denture base resins. Eluates were prepared by daily transfer of disks to fresh buffers at pH 4.0, 5.0, and 6.8 over a 5-day period. Oral epithelial cells were plated in culture dishes in medium containing the eluate. After 24 hours, cellular RNA synthesis was assessed by measuring tritiated uridine uptake. Effects of materials were compared to identical cultures that contained the appropriate buffer without the eluate. The results indicate that the cytotoxic components leach out of the denture base resins in different amounts and at different rates, and the amount of leaching can be affected by pH.

Acrylic Resins↗
PubMedDate not supplied

Endotoxin adherence to and elution from two casting alloys.

The purpose of this study was to compare the relative affinity of bacterial lipopolysaccharide for two casting alloys with varied surface finishes by measuring lipopolysaccharide adherence and elution. Air borne particle abraded and polished Rexillium III and Harmony Hard alloy discs were exposed to 600,000 endotoxin units/mL E. coli lipopolysaccharide in water for 24 hours, whereas control discs were placed in 37 degrees C, lipopolysaccharide-free water. Lipopolysaccharide-exposed and control discs were then transferred every 24 hours to fresh, lipopolysaccharide-free water for up to 96 hours, and previously incubated eluates were tested for the presence of lipopolysaccharide. Initial lipopolysaccharide adherence to abraded Rexillium III discs was significantly greater than lipopolysaccharide adherence to the other groups (P < .05). Polished and abraded Rexillium III also exhibited significantly greater lipopolysaccharide elution (P = .0001). However, after 96 hours, more than 99% of the initially adhering lipopolysaccharide remained on both Rexillium III and Harmony Hard discs, regardless of surface treatment.

Chromium Alloys↗
PubMedDate not supplied

Relationships between denture base resin cytotoxicity and cell lipid metabolism.

Substances that elute from denture base resins may inhibit cell growth and disrupt various metabolic processes. This study investigated the effects on cell lipid metabolism of eluates from several denture base resins. Cultured oral epithelial cells were exposed in vitro to eluates of discs made from several denture base resins. Lipid metabolism of the cells was measured using isotopic labeling with 14C-acetate. Results demonstrated that the metabolism of several lipid classes found mainly in the cell membrane was altered by the resin eluates. Eluate from one resin caused the appearance of two previously unrecognized classes of lipids. The alterations of the cell lipids and the presence of the previously unrecognized lipids may be the basis for some clinically evident cytotoxic and allergic reactions.

Acrylic Resins↗
PubMedDate not supplied

Effect of pH on Porphyromonas gingivalis endotoxin affinity for resins.

This study evaluated the effect of pH on Porphyromonas gingivalis lipopolysaccharide (LPS) affinity for polymethyl methacrylate, polyethyl methacrylate, and polyethyl and polyisobutyl methacrylate resins. Specimens were exposed to 1,010 endotoxin units LPS in potassium phosphate buffer at pH 6, pH 7, or pH 8. Control specimens were incubated in LPS-free water. Sequence I evaluated LPS uptake and release from resin when exposure and elution pH were identical, whereas Sequence II evaluated LPS release from resin when elution pH differed from exposure pH. A slightly acidic pH decreased LPS affinity for all resins compared to pH 7. A slightly alkaline pH increased LPS affinity for the polyethyl methacrylate resin but decreased LPS affinity for the others compared to pH 7. The pH may affect resin-LPS affinity by altering LPS molecular charge.

Analysis of Variance↗
PubMedDate not supplied

Cytotoxicity of denture base resins.

This in vitro study examined the effect of eluate from heat-activated, chemically activated, and microwave-activated denture base resins on cell viability of primary cultures of human gingival fibroblasts. Eluates corresponding to 24, 48, 72, and 96 hours of resin disk immersion were prepared. Fibroblasts were plated at a density of 3 x 10(4) cells in 96-well plates and exposed to a medium containing eluate. After 24 hours, the cytotoxic effect was determined by cellular mitochondrial function. The effect of eluates was compared to control cultures containing culture medium without eluate. Results indicated that at all time periods tested, all three resins leached materials that were cytotoxic to the fibroblasts. Eluate from chemically activated resin disks was more cytotoxic than eluate from heat-activated and microwave-activated disks. In general, cytotoxicity appeared to diminish as disk immersion time was increased. The greatest cytotoxic effect on cell viability was observed with eluates recovered after 24 hours of disk immersion, and the least cytotoxic effect was observed with eluates recovered after 96 hours of immersion.

Acrylic Resins↗