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Biomedical subjects

Z Hirschfeld

Publications and source records attributed to Z Hirschfeld.

At least 37 records · Page 2Linked to original sources
PubMed1984

Dycal: physical properties and resistance to amalgam condensation.

Simulated clinical experiments showed that the hand condensation of amalgam on single or multiple layers of Dycal in Class II cavities does not cause significant fracture or displacement of the liner. Cyclic loading experiments demonstrated that the plastic deformation of Dycal decreases and its stiffness increases with each additional load cycle. This indicates that minor displacement of Dycal during amalgam condensation occurs mainly during the first thrusts with the condenser, and that its mechanical properties are improved by repeated condensation with heavy pressure. Cyclic loading tests may be of considerable value in the evaluation of the performance of liners during amalgam condensation.

Calcium Hydroxide↗
PubMed1984

Fluoride enhancement of chlorhexidine uptake by hydroxyapatite and enamel powders.

The purpose of the present study was to examine the in vitro adsorption of chlorhexidine and fluoride to hydroxyapatite and tooth enamel powders. Samples of hydroxyapatite or enamel powder were suspended in aqueous solutions of chlorhexidine gluconate 2.0; chlorhexidine acetate 1.5%; sodium fluoride of various concentrations (0.2%, 1%, 2%) and mixtures of sodium fluoride and chlorhexidine. The data obtained in the study show that chlorhexidine and fluoride adsorb to hydroxyapatite and tooth enamel in vitro. Furthermore, the amount of fluoride adsorbed to hydroxyapatite is reduced in the presence of chlorhexidine in the solution. A probable explanation for this effect may be that there is a competitive adsorption of fluoride and chlorhexidine on to the same binding sites on the hydroxyapatite. Additionally, the presence of fluoride dramatically increases the affinity of chlorhexidine for hydroxyapatite. The fact that fluoride strongly enhanced the adsorption of chlorhexidine to hydroxyapatite and enamel, indicates that fluoride may be of clinical interest beyond the prevention of caries.

Adsorption↗
PubMed1984

New sustained release dosage form of chlorhexidine for dental use: use for plaque control in partial denture wearers.

The aim of this work was to test the effectiveness of a local sustained release application of chlorhexidine in prevention of plaque formation in a group of five partial denture wearers when oral hygiene procedures were withdrawn. The clinical study demonstrates that coating of the partial dentures with ethyl cellulose polymer containing the drug, prevents accumulation of plaque during a period of 12 days. No typical side effects of chlorhexidine such as tooth staining and unpleasant taste were observed during the study.

Aged↗
PubMed1983

Marginal adaptation of glass-ionomer cements.

The effect of thermocycling on the marginal adaptation of two glass-ionomer cements was determined by means of scanning electron microscopy. Small gaps in the cement as well as at the enamel-cement interface were observed after curing, but these phenomena were not enhanced by thermocycling. Localized areas of surface deterioration were observed for both cements after thermocycling.

Dental Bonding↗
PubMed1982

EDTA enhancement of strontium uptake by intact human enamel.

The aim of this research was to study the effect of EDTA on the strontium uptake by intact tooth enamel. EDTA did not significantly affect the strontium uptake in an acid medium of pH 4.5. However, it caused a sharp rise in strontium uptake at pH 6.0. At such a pH, the stability constants of the Ca-EDTA complex are approaching a maximal value, and as a result of it a significant dissolution of the surface enamel, accompanied by a highly effective increase of the contact area for strontium uptake, is taking place. In all the experiments, treatment with strontium solution resulted in a decrease of the solubility and dissolution rate of enamel in an acidic environment. The resistance of enamel to acid attack was proportional to the quantity of absorbed strontium, reaching maximal values after treatment with strontium solutions in 10(-2) M EDTA at pH 6.0.

Dental Enamel↗
PubMed1982

Primary mineralization of dentin in rats after pulp capping with calcium-hydroxide.

It has been previously reported that short term application of calcium-hydroxide to the dental pulp resulted in the formation of a dentin bridge with matrix vesicle calcification. The present study deals with the induction of reparative dentin in rat molar pulps by direct capping with calcium-hydroxide. The teeth were examined after 21 and 35 days. Transmission electron microscopy (TEM) revealed that the calcification process in the newly formed dentin was characterized by apatite deposition in matrix vesicles and the occurrence of calcifying nodules in the matrix. The persistence of these features of primary mineralization, during the experimental period, was associated with the continuous calcium hydroxide contact with pulp tissue, producing changes in its metabolic state.

Animals↗
PubMed1981

Transmission electron microscopy of reparative dentin in rat molar pulps. Primary mineralization via extracellular matrix vesicles.

A reparative dentin bridge was induced in rat molar teeth by pulp exposure and capping with calcium hydroxide. Transmission electron-microscopic examination after 10 days revealed the presence of odontoblastic cells and collagenous matrix with focal calcifications. The calcifying fronts were composed of hydroxyapatite crystals. Numerous extracellular matrix vesicles were scattered between the forming cells and the calcifying fronts. Some of the vesicles contained electron-dense material and in others, apatite crystals were detected. Matrix vesicles could not be identified in normal, mature calcifying dentin matrix. In view of the present observations and studies on surgical manipulations in articular cartilage, it is concluded that matrix vesicle calcification may result from alterations in the metabolic state of mesenchymal tissues. These changes can be induced surgically or chemically.

Animals↗
PubMed1980

The cheek teeth of the rabbit: morphology, histology and development.

A detailed anatomic and histologic description of the cheek teeth of the rabbit, both deciduous and permanent, is presented, together with the chronology of their pre- and postnatal development. The deciduous teeth are of limited growth, while the permanent ones grow continuously. Certain aspects of cementogenesis in these teeth are discussed.

Animals↗
PubMed1979

Reflectance spectra of composite resins on liners.

The reflectance spectra of two types of composite resins were determined on various backgrounds. It was found that the shade differences caused by different "whitish" liners were perceptible only for thin resin specimens and were smaller than those caused by varying the resin type and thickness. Employing a light brown liner gave rise to a difference in shade which was also perceptible on resin specimens of 2.5 mm thickness. Shade differences due to varying the thickness of the specimens were more pronounced on white than on black backgrounds. The clinical significance and the qualitative physical interpretation of the results were discussed.

Calcium Hydroxide↗
PubMed1977

Symphysis menti of the rabbit: anatomy, histology, and postnatal development.

A histologic and anatomic investigation of the symphyseal region in rabbits did not reveal a bony fusion between the two halves of the mandible; these two bones are united in the anterior part by a synchrondrosis, and a definite histologic suture with interdigitating bony rugosities and interposed connective tissue, in the posterior part. Functionally, the two parts are immobile and thus constitute one bone.

Animals↗
PubMed1976

The residual ridge in partially edentulous patients.

The residual ridge which forms after the extraction of teeth is characterized by a loss of substance when compared with the dentulous ridge. The residual ridge shrinks in an apical direction and shifts lingually. This remodeling pattern takes place mainly at the expense of the bony crest, the buccal plate of the alveolar process, and the gingival tissues covering it. The lingual positioning of the residual ridge crest was observed in maxillary and mandibular specimens in all the regions of the jaws and regardless of the number of teeth missing. Cross sections of the residual ridge were square, parabolic, or tapered. The base of the pontic for a fixed partial denture should be made buccolingually as the mirror image of the crest of the residual ridge it is to contact, and it should follow mesiodistally the contour and length of the clinical crowns of the adjacent abutment teeth.

Alveolar Process↗
PubMed1976

Observations on cavity liners for composite resin restorations.

Adhesion or surface roughness and discoloration at the interface between pulpinsulating materials and composite resins were taken as indications for interaction between the resins and the insulating materials. Some interaction occurred between all insulating materials and resins investigated. After separation of the restorative resins, the interaction of Dycal with the different composite resins varied considerably and decreased in the following sequence: Opotow, Natural, and Adaptic. The interactions of ZOE with Natural and with Adaptic were similar and more pronounced than the interaction at the Adaptic-Dycal interface but less pronounced than at the Dycal-Natural interface. A very thin film of Tubulitec was found to adhere to the composite resins in some areas. The adherence of liners containing calcium hydroxide to dentin was found to be generally stronger than the bond between these liners and composite resins. Separation of the composite resins caused tears in the varnishes and frequently in Hydroxyline. Almost completely intact layers of the varnish Copalite were observed on dentin, but Zahnlack apparently dissolved to a great extent in the resins. Among the liners containing calcium hydroxide, Dycal and Tubulitec were found to give rise to a high pH in samples of saliva, but Hydroxyline did not. Porosity and a folded surface were observed for Hydroxyline, indicating the entrapment of the solvent beneath a dry superficial layer.

Adhesiveness↗