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Biomedical subjects

C L Davidson

Publications and source records attributed to C L Davidson.

At least 145 records · Page 8Linked to original sources
PubMed1984

Contact stomatitis and dermatitis to nickel and palladium.

17 subjects were tested epicutaneously with 22 materials, including Ni, Pd, Cr and Co. 5 subjects with a positive allergic skin reaction to Ni were tested with a pure metallic nickel plate 3 X 5 mm, which was attached to the buccal side of one lower premolar. These 5 subjects all developed local allergic contact stomatitis on the mucosa of the cheek adjacent to the metal plate. This was confirmed histologically. The same oral test with pure metallic palladium gave no reaction in subjects with a positive patch test. A control group gave no reactions to the metal plates. Allergic contact stomatitis was diagnosed with the help of both clinical and histological examinations.

Dental Materials↗
PubMed1984

Relaxation of polymerization contraction stresses by flow in dental composites.

The hardening stresses in wall-to-wall bonded composites were measured and related to calculated values obtained from freely shrinking materials. Since the ultimate tensile strength of the materials contracting under restricted conditions was not lower than that of composites which were not hindered during the polymerization shrinkage, the conclusion was drawn that the contraction was compensated for by flow instead of internal disruptions.

Acrylic Resins↗
PubMed1984

The competition between the composite-dentin bond strength and the polymerization contraction stress.

The influence of contraction stresses, developed during the polymerization of composites, on adhesion to dentin treated with a dentin adhesive was studied for a chemically- and a light-activated microfilled composite. In both linear and 3-D models. The linear model consisted of an arrangement set up in a tensilometer in which the composites could be applied to a flat dentin surface fixed to the stationary cross-head at one end, and mechanically clamped to the cross-head connected to the load cell at the other end. The increase of the bond strength was measured at different time intervals from the start of mixing and was compared with the developing contraction stress. Throughout the complete polymerization process, the adhesion survived the contraction stress, which is explained by flow relaxation, which can occur sufficiently in this configuration. In the three-dimensional model, the composites are attached to more than two dentin walls. In this situation, flow is severely limited, and contraction stress values can exceed the bond strength, leading to separation. This was demonstrated in Class V cavities. The shape of the cavity is considered to be of great importance in conservation of the composite-dentin bond.

Acid Etching, Dental↗
PubMed1983

The influence of shelf life and storage conditions on some properties of composite resins.

This study demonstrated that the rate of strengthening and the ultimate strength of composite resins depend on the storage record of the material before polymerization. It is likely that both properties are related to the concentration of an effective initiator at the moment of use. For dental practice a somewhat delayed setting is inconvenient but acceptable. A decrease of ultimate strength, however, is an indication of less effective polymerization. Thus, premature disintegration may be expected from such material. Because no specification offers a measure for the shelf life of a composite resin, a reduction of the diametral tensile strength (for example, 20%) may be a useful test to indicate decomposition.

Chemical Phenomena↗
PubMed1982

Clinical significance of polymerization shrinkage of composite resins.

The volumetric polymerization shrinkage of some composite resin restorative materials was measured with a modified dilatometer. It is emphasized that only the shrinkage from the start of the gelation, the rigid contraction of the material, is of clinical relevance. The amount of gelation was determined with an instrument that indicates the first moment at which the setting material is rigid enough to exert tensile forces. In addition, the influences of storage, testing conditions, and mixing ratio on the rigid contraction were studied for one light-cured as well as some chemically cured composite resins.

Chemical Phenomena↗
PubMed1982

Unreacted methacrylate groups on the surfaces of composite resins.

The unreacted methacrylate groups on the surface of conventional composites and microfilled composites were studied by means of multiple internal reflection infrared spectroscopy. The influences of polymerization time, temperature, and the effect of polishing were studied. We also attempted to relate the results of some mechanical tests to the degree of chemical unsaturation measured in the different resins. All surface treatment and manipulative variables caused a decrease in double bond content and interfacial bond strength.

Acrylates↗
PubMed1981

In vitro studies on susceptibility of enamel to caries attack after orthodontic bonding procedures.

Oral hygiene plays an important role in the prevention of caries. Therefore, when one is investigating the possible effects of acid etching on caries susceptibility, oral hygiene aspects and the supplementation of fluoride have to be considered. The objective of this investigation was to study the caries susceptibility of etched enamel surfaces in vitro. To simulate the in vivo situation, much attention was given to the influence of remineralization of saliva and fluorides. It was shown that etching and subsequently fluoridating and remineralization increases resistance of enamel against a caries attack.

Acid Etching, Dental↗
PubMed1981

Loss of surface enamel after acid etching procedures and its relation to fluoride content.

The etching of an enamel surface with a strong acid causes loss of surface contour together with a roughening of the enamel, which is necessary for proper adhesion of the bonding agent. It is known that the fluoride concentration plays an important role in the reduction of enamel solubility. The objective of this investigation was to measure the bulk enamel loss because of acid etching with phosphoric acid, with special emphasis on the fluoride content of tooth enamel. It was shown that fluoridated enamel has a high acid-resistant layer 2 to 4 microns in thickness. In some teeth the enamel is locally so resistant that, even after a 3-minute etching period, practically no material is removed. Since considerable amounts of topically applied fluoride ions are known to leak out, it is advisable to omit fluoride application shortly prior to the bonding procedure.

Acid Etching, Dental↗
PubMed1981

The influence of temperature on some physical properties of dental composites.

In this study diametral tensile strength and microhardness of composites were investigated in relation to various temperatures during curing. It has been demonstrated that temperatures elevated up to 60 degrees C can improve the mechanical properties considerably. Also the stability of the resin system in aggressive environments was improved due to more efficient cross-linking. Thermal analysis of the material showed an endothermic reaction between 60 and 70 degrees C that is believed to be responsible for the initiation of the extra cross-linking. Heating of composite fillings during clinical use is suggested.

Acrylic Resins↗
PubMed1981

Structural changes in composite surface material after dry polishing.

The purpose of this study was to investigate the properties of composite materials that had been heated to temperatures which may occur during dry polishing. Bulk composite material was submitted to thermal analysis from R.T. to 200 degrees C. Two distinct stages of thermal reaction in this range could be identified. One at approximately 70 degrees C, which could be related to a further initiating of unreacted groups, and one above 100 degrees C, which could be related to the glass transition. The glass transition was also observed microscopically. Hardness measurements were carried out on the warm material at different temperatures as well as on the material being cooled down to R.T. With temperature rise, a continuous increase in hardness and abrasion resistance could be demonstrated. The observed phenomena for bulk material are related to the properties measured on dry polished surfaces.

Acrylic Resins↗
PubMed1980

The resistance of superficially sealed enamel to wear and carious attack in vitro.

The resistance to wear and carious attack has been investigated in vitro for enamel that has been subjected to several stages of the sealing procedure: etching, etching and remineralization in whole saliva and etching followed by sealing. After partial mechanical removal of the sealant, the remaining surface enamel proved to be resistant to carious attack as long as the resin tags were present. An estimation is made of the thickness of the affected layer. Pretreatment with monofluorophosphate has proved to influence the extent of the histological changes due to etching. A discussion on these phenomena is given.

Acid Etching, Dental↗
PubMed1980

The curing pattern of photo-initiated dental composites.

In this study the curing of photo-initiated composites was investigated. After irradiation, the material in an experimental cavity could be divided into three zones: zone A which showed physical properties comparable to those of chemical initiated composites, zone B which was markedly softer than the first one, and zone C which showed no signs of curing at all. The location of the zones was dependent on the energy of the u.v. radiation, the exposure time, the storage time, and the storage conditions. The uncured material of zone C showed no tendency to set. The clinical implications of the observations are discussed.

Chemical Phenomena↗