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Biomedical subjects

L Ehrnford

Publications and source records attributed to L Ehrnford.

15 recordsLinked to original sources
PubMed1984

Surface characteristics of composite resins comprising a porous reinforcing filler. An in vivo study.

The surface of composite restorations with filler particles comprising an ultrafine sintered glassfiber network were examined in vivo. The effect of different finishing methods and clinical wear was studied with SEM on replicas. Smooth and lustrous buccal surfaces were obtained with finishing discs. On occlusal surfaces a microfine finishing diamond gave a good surface finish. After wear (greater than 7 months) surface smoothness was favored by a close packing of the filler particles. The smoothest surfaces appeared when, in addition, the density of the sintered network was high.

Adult↗
PubMed1984

Cervical gap formation in class II composite resin restorations.

In vitro, class II restorations were made in three materials, one regular, one microfilled composite and one experimental condensable composite with a porous filler. The aim was to study cervical marginal gap widths appearing in composite restorations when acid etch technique was used. The gaps were about 35 micron for the two contemporary materials and about 10 micron for the experimental one.

Acid Etching, Dental↗
PubMed1983

Surface microstructure of composite resins after toothbrush-dentifrice abrasion.

In vitro, conventional, microfilled and experimental composite resin specimens were subjected to toothbrush-dentifrice abrasion. Subsequently, height loss was recorded, and the appearance of the abraded surfaces was studied by light and scanning electron microscopy. In the experimental composite, which had a polymer-impregnated porous glass filler, the glass phase showed flat surfaces. These surfaces were more smooth and lustrous than the surrounding resin. They also showed a rounding-off in the periphery. In the experimental composite smoothness and luster were therefore favored by the presence of large continuous areas of glass in the surface. It was possible to demonstrate the extension of the flat glass areas by the use of optical microscopy. In the conventional composite partly exposed irregular or rounded glass particles were frequent. A microfilled composite showed, except for frequent pores, a relatively smooth and lustrous surface. The wear rate of this material was, however, comparatively high.

Composite Resins↗
PubMed1983

Composite laminate veneers with a continuous inorganic phase comprising microporous sintered glass fiber networks.

Veneers were made from sheets consisting of a three-dimensional network of sintered ultrafine glass fibers. The sheets were molded by a vacuum-pressure technique and then impregnated with a liquid resin. Impregnation was performed with a method that enabled the depth of penetration to be monitored. The resin was cured with UV radiation under N2 protection. By the use of TiO2-containing resins the veneer achieved an enamel-like appearance. An in vitro toothbrush dentifrice abrasion test showed a high wear resistance and persisting surface luster. Scanning electron and light microscopy showed fairly smooth and flat light-reflecting glass structures in the surface.

Composite Resins↗
PubMed1981

Composite resins with a condensable inorganic phase.

Reinforcing filler particles with open porosity can be prepared in three-dimensional networks made from extremely fine sintered glass fibers. Such fillers can be impregnated with a monomer, used for a putty type of composite, or packed into close particle contact by the use of a condensation technique similar to that used with dental amalgam. The condensation technique allows the use of high viscosity liquid resins and need not be accompanied by an increased amount of internal air voids. Condensed composite resins can be made which have a high finishability after curing.

Chemical Phenomena↗
PubMed1981

Stress distribution in diametral compression tests.

In an attempt to find an explanation for an experimentally found strong connection between the extension of the loaded area and the load required for fracture, an analysis of the diametral compression test was carried out by means of the finite element method. The distribution of the stresses in a quadrant of a circular specimen section was studied for varying contact surface but at a given load distribution within this surface. Below a limit value for the width of the contact surface tensile stresses appeared peripherically outside the contact area, which had a magnitude exceeding those stresses which are centrally located and should normally initiate fracture. For that reason, peripheral fracture initiation must be regarded as a possibility. Only marginal importance could be attached to changes in the extension and magnitude of the central tensile stresses, as compared with the potential impact of the peripheral tensile stresses.

Dental Materials↗
PubMed1981

A fracture study of the diametral compression test by means of high-speed photography.

High-speed photography (2000-6000 pictures/sec) was used to register the fracture propagation process in gypsum specimens (diameter 40 mm, length 14 mm) loaded via 2 mm wide, strip-shaped paddings and under direct contact with plane press platens. With paddings in 3 out of 4 experiments the fracture, as it appeared on the first film frame, was asymmetrically located on the loaded diameter. In two direct-contact experiments the initial fracture had its widest part centrally and lateral fractures, of the "triple-cleft" type, appeared subsequent to the cental fracture. Smaller specimens (diameter 7, length 14 mm), manufactured in an investment compound (Ceramigold) were tested by the use of plane and vaulted platens, giving the same width of the loaded area. With vaulted platens the fracture first appeared in a peripherical zone in 3 out of 5 experiments and with plane platens in 6 out of 11 experiments. In two thirds of all cases, where the primary fracture sign appeared peripherically, it appeared in an area immediately centrally of the compression zones. These fractures were probably peripherically initiated and thus non-valid. Specimen appearance after testing gave, however, no clear indication of a non-valid fracture.

Calcium Sulfate↗
PubMed1980

Bone tissue formation within a sintered microporous glass-fiber network implanted in extraction sockets in the rat.

Implants were prepared by sintering glass-fibers into a three-dimensional network with meshes smaller than 20 micron. Oblong 5 x 2 x 0.15 mm sheets of the test material were implanted in maxillary incisor alveoli in eight white rats. The alveoli were closed with a suture in the overlying mucosa. After 3 months the animals were sacrificed and sections from the site of implantation prepared. In three animals only root remnants were found but in the remaining five the implants were wholly or partially embedded in bone tissue. Sections studied with transmitted light, microradiography, and scanning electron microscopy showed that mineralized tissue had also formed within the pores of the network. The intimate contact between the individual fibers and the bone within the network was corroborated through microchemical analysis (EDX).

Alveolar Process↗
PubMed1980

An abrasion test for composite resins.

An abrasive wear test for composite resins was proposed. A slurry of glass pearls and abrasive particles were used. The abrasive effect was examined for different particle sizes. Particle sizes were found which gave the same order of wear as found clinically for an amalgam, a composite resin, and unfilled resin.

Aluminum Oxide↗
PubMed1980

A long-term evaluation of abrasion of dental composite resins.

A long-term study was performed on the abrasion of dental composites stored in different solutions for six months. No difference in wear resistancewas noticeable between the water and lactic acid group. But the composite with regular filler showed reduced wear resistance when compared with a microfiller composite.

Aluminum Oxide↗
PubMed1980

The connection between load distribution and fracture load in the diametral compression test. An experimental study.

Dental stone specimens (diameter 41,5 mm, length 14,0 mm) manufactured with water/powder ratios 0.22 (unimpregnated and polymethylmethacrylate-impregnated specimens) and 0.30 were loaded by direct contact with the platens of the testing device and with interposed soft paddings of varying thickness and width. To ensure an even load distribution, in some experiments, inserts of aluminium with one side vaulted were inserted next to the platens. The experiments showed that: - if strip shaped paddings were inserted which were as wide as the contact surface formed on direct contact, the load required for fracture did not change; - if the contact surfaces were reduced by means of strip-shaped paddings, fracture load was considerably reduced even for small changes in the load bearing area; - if the contact surface was increased, by means of wide paddings or vaulted inserts, the fracture load also increased. The results could not be explained on the basis of statistical fracture theories. This conclusion was supported by some experiments with miniature specimens. A probabel explantation would, however, be that below a critical load distribution parasitic stresses are generated which entail fractures with fracture patterns which do not distinctively deviate from what previously has been considered as typical for valid tensile fractures.

Calcium Sulfate↗
PubMed1976

A method for reinforcing dental composite restorative materials.

A method is presented for reinforcing dental composite restorative materials by incorporation of a polymer impregnated porous inorganic component. A method for producing such an inorganic component in the form of a three-dimensional glass fiber network is described. The structure of the network is demonstrated with the aid of scanning electron microscopy.

Composite Resins↗