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Biomedical subjects

C L Davidson

Publications and source records attributed to C L Davidson.

At least 19 recordsLinked to original sources
PubMed1992

Clinical evaluation of fifty-six patients referred with symptoms tentatively related to allergic contact stomatitis.

During a 7-year period, 56 patients were referred to the Department of General Pathology and Internal Medicine and the Department of Dental Materials, University of Amsterdam, to determine whether contact allergic reactions to dental materials were the cause of their complaints. On the first consultation with the patient a detailed history focusing on the complaints themselves, general medical history, and special clinical history of allergic skin reaction was obtained. Oral examinations were performed, and all patients were referred to the allergy clinic at the department of dermatology for skin tests. There was a strong female predominance in the referred group. Most of the patients with allergic contact stomatitis mentioned a burning sensation in the mouth. In only 16 of the 56 patients could the diagnosis of allergic contact stomatitis be established. From this study it can also be concluded that the combination of a positive allergic history and positive allergic skin reactions with or without visible oral signs are important for the diagnosis of allergic contact stomatitis.

Acrylic Resins↗
PubMed1992

The influence of polymerization shrinkage of resin cements on bonding to metal.

During the setting of a resin composite cement (RCC) used as an adhesive between a resin-bonded bridge and tooth structure, the adhesion may be disrupted by the development of shrinkage stress. The aim of this study was to investigate the influence of the shrinkage stress of three different RCCs on their adhesive and cohesive qualities when bonded to metal surfaces in a rigid set-up. Two opposing parallel NiCr discs (Wiron 77) were mounted in a tensilometer at a mutual distance of 200 microns and cemented with Panavia Ex, Clearfil F2, or Microfill Pontic C. The alloy surfaces were treated by either electrolytic etching, sand-blasting, silane-coating, or tin-plating. During setting, the discs were kept at their original mutual distance to simulate the extreme clinical situation of "complete" rigidity, where the casting and the tooth cannot move toward each other. The developing shrinkage stress was recorded continuously. During setting, the adhesive strength of the RCCs to silane-coated surfaces was always higher than their early cohesive strength. Electrolytically-etched surfaces as well as sand-blasted surfaces showed, in almost all cases, adhesive failure. The tin-plated samples showed mainly adhesive failure at the metal/resin interface. The highest bond strength values were found for silane-coated surfaces in combination with Clearfil F2.

Acid Etching, Dental↗
PubMed1992

The dependence of shrinkage stress reduction on porosity concentration in thin resin layers.

The development of polymerization contraction stress was determined as a function of the surface area of porosity, so that the contribution of voids in resin composite to stress relief could be investigated. Experiments were carried out on 200-microns-thick layers of resin bonded from wall to wall in a restrained condition. The resin samples were divided into three groups: Group A was without porosity, group B contained a small number of pores, and group C contained a large number of pores in comparison with group B. For each group, porosity area, maximal stress, and stress development rate were determined. The mean maximal stress and stress development rate were inversely proportional to the mean porosity surface. These characteristics differed significantly (p less than 0.01) between group A and C. For determination of whether shrinkage stress reduction has to be ascribed to flow from the outer surfaces of the voids or to inhibition of the setting reaction by oxygen in the voids, resin containing only nitrogen bubbles was also tested. The results indicated that both aspects contributed substantially to shrinkage stress relief. Incorporation of pores by the stirring of a luting cement contributes to stress reduction and can therefore be considered as a contribution to the maintenance of marginal integrity.

Analysis of Variance↗
PubMed1991

Destructive stresses in adhesive luting cements.

In this study, curing shrinkage stress development was monitored in a glass-ionomer and a BisGMA composite luting cement adhesively placed at film thicknesses ranging from 30 to 200 microns. The nature and magnitude of the stress development depended greatly on the formulation and film thicknesses of the lute. The thicker the layer, the faster the stress development in the glass ionomer and the slower in the composite. The contraction stress had a detrimental effect on the cohesive strength of the glass ionomer and on the adhesive strength of the composite cement.

Adhesiveness↗
PubMed1991

[Dental ethics, esthetics and cosmetics].

By means of adhesive dentistry sound teeth can be made more beautiful without damaging tooth structure. This is called cosmetic dentistry. Within the dental profession there is a discussion about the following questions: is cosmetic dentistry real dentistry? Is it ethical to render cosmetic services to patients? In this article arguments are displayed to answer this question in a positive manner.

Adult↗
PubMed1991

[Longevity of restorations in composite and etched porcelain].

Due to continuing alterations in composition of dental products and materials, prognoses about longevity of restorations in composite or etched porcelain are extremely difficult to make. Strength, wear resistance and resistance against disintegration determine durability of stress bearing restorations. Elasticity in combination with bond strength are determinant for prevention against premature leakage. Indication, cavity form and careful handling of the materials are prerequisites for longevity of the restoration. The prognosis of the favourably located but stress bearing class IV is far better than that of the unfavourable located, non stress bearing class V-composite restoration. For the etched porcelains, the veneers offer the best perspectives with respect to durability thanks to the favourable shrinkage pattern.

Acid Etching, Dental↗
PubMed1991

[Waterbed dentures: clinical studies (2)].

In this study the clinical performance and applicability of the liquid supported denture were investigated. Functional properties such as retention and stability were studied, as well as the reaction of the supporting tissues to the denture. It was concluded that the liquid supported denture is well accepted as alternative denture and provides a solution in a variety of prosthodontic problems, especially in cases where the mandible is in an advanced resorbed state.

Adult↗
PubMed1990

Liquid-supported dentures. Part I: Theoretical and technical considerations.

A complete denture is designed so that the base is covered with a preshaped, close fitting, flexible foil containing a thin film of high-viscosity liquid. This technique allows continued adaptation and eliminates the disadvantages of denture designs based on the application of temporary tissue conditioners or soft liners. In contrast to the traditional tissue conditioners and soft liners, the foil remains elastic and preserves the plasticity of the liquid.

Denture Bases↗
PubMed1990

Liquid-supported dentures. Part II: Clinical study, a preliminary report.

A clinical study was made of 11 selected patients wearing liquid-supported dentures. The experiences and opinions of the patients were assembled and the results are discussed. The most important conclusions of this study are that it is possible to make a liquid-supported denture that in general fits and feels comfortable, has proper retention, a slightly diminished masticatory function, and that can provide a solution to some problematic prosthodontic situations.

Adult↗
PubMed1990

Marginal integrity related to bond strength and strain capacity of composite resin restorative systems.

The shear strength of composite resin restorative systems bonded to dentin was measured and marginal integrity of class V restorations was assessed. A correlation between bond strength and marginal adaptation could not be demonstrated. The application of an intermediate layer of unfilled resin or the use of low-stiffness composite resins to improve the strain capacity of the restoration significantly influenced the quality of the marginal integrity.

Animals↗
PubMed1990

Quantitative determination of stress reduction by flow in composite restorations.

In this study, the reduction of the polymerization shrinkage stress by flow of four chemically-initiated composites was investigated in relation to the cavity configuration. In an experimental set-up simulating restorations bonded to cavity walls, the developing shrinkage stress accompanied by flow was recorded as a function of time for several configurations. For each configuration, theoretical shrinkage stress curves were also drawn, excluding stress reduction by flow. These data were obtained from Young's modulus determinations at the early setting stage and the corresponding polymerization shrinkage. By comparison of the theoretical stress with the experimentally determined stress, a measure for the ability to flow in the bonded situation could be obtained. It was found that the flow strongly depended on the type of composite and on the configuration of the cavity.

Composite Resins↗
PubMed1990

Early marginal leakage and shear bond strength of adhesive restorative systems.

The aims of this study were to assess in vitro the early marginal seal effectiveness in Class V restorations at the cemento-enamel junction, and the early shear bond strength of several composite and dentin bonding system combinations. The seal effectiveness was studied by evaluating the dye penetrations: (a) along the superficial margin of restorations (width of surface microleakage); (b) along the dentin cavity walls (length of microleakage); and (c) toward the pulp (depth of microleakage). Good correlations were demonstrated among the seal evaluations, but no relationships were apparent between these and shear bond strength. Our study suggests that the marginal seal is influenced by composite properties more than by bonding agents. The shear bond analysis indicates only the adhesive potential of the materials without considering the composite shrinkage effects on marginal gap after the photocuring setting reactions.

Composite Resins↗
PubMed1990

Determination of the corrosion rates of six dental NiCrMo alloys in an artificial saliva by chemical analysis of the medium using ICP-AES.

So that the influence of salivary components upon the corrosion rate of six dental NiCrMo alloys could be established, their mass loss was determined in a medium consisting of a modified Fusayama's artificial saliva to which 300 mg KSCN/L had been added (pH 5.0). Nickel was the main element released; its loss vs. immersion time curves on a log-log plot resembled straight lines. The total nickel losses after one week ranged from 0.4 to 12.5 micrograms/cm2. From the nickel loss, corrosion currents were calculated. The corrosion currents at 24 hours of immersion were up to 67% larger than the currents in a previous study of these alloys, where the medium consisted of a 20 mM KCI-5 mM phosphate buffer solution (pH 7). The alloys with the least molybdenum content showed the largest corrosion current increase.

Chromium Alloys↗
PubMed1990

Annealing as a mechanism of increasing wear resistance of composites.

The objective of this study was to examine the influence of a short-term exposure to heat (125 degrees C) on the wear resistance of composites. Both light- and chemically initiated materials improved by 20-60%. However, the improvement was also attained in the course of time if the materials had not been exposed to heat. The heat-induced improvement could not be explained by a continuation of polymerization but rather by stress relief, which is common for annealing processes. Polymerization shrinkage stresses, initially concentrated mainly around the filler particles, became more homogeneously distributed by the heat treatment. The long-term improvement of the non-heat-treated materials was based on the same mechanism, but proceeded more gradually.

Composite Resins↗
PubMed1990

Electrical potentials of restorations in subjects without oral complaints.

The electrical potentials of 183 amalgam and 11 precious metal restorations, and one set of brackets, were measured. None of the 28 subjects had galvanism, leukoplakia, oral lichen planus, or toxic or allergic reactions to restorations. The potentials of the amalgam restorations increased with age, from about -350 mV NHE at 30 days, to about +100 mV NHE after more than 1000 days. In most subjects potential differences of more than 50 mV were present between restorations; this phenomenon is therefore assumed to be common in healthy populations.

Corrosion↗
PubMed1990

Relaxation of polymerization contraction shear stress by hygroscopic expansion.

We studied relaxation by hygroscopic expansion of the interfacial polymerization shear stress of bonded resin composites. In the experimental set-up, resin composite-cured-to-glass strips bent due to the polymerization shrinkage. The strips were stored wet or dry. The curvatures of the bent strips were recorded, by the scanning of the glass surfaces with a contact profilometer, periodically over a period of two months. From the measured deflections, we calculated the maximum tangential bending stress in the resins near the adhesive interface, which provided an estimation for the maximum shear stress values occurring at both ends of the strips. In the particular experimental set-up, the shear stresses in Bis-GMA/TEGDMA and urethane dimethacrylate-based resins were either fully relieved or converted into an "expansion stress" by hygroscopic expansion. The hydrophobic tricyclodecane dimethacrylate-based resins showed very little stress relaxation.

Absorption↗
PubMed1990

Complete marginal seal of Class V resin composite restorations effected by increased flexibility.

The use of adhesive resin composites for restoration of Class V lesions often results in cervical marginal gap formation due to polymerization contraction. In this laboratory study, flexible linings applied between the bonding agent and the bulk restorative appeared to preserve the marginal integrity of Class V restorations during curing. Measurements of the polymerization contraction stress showed 20 to 50% relief due to various flexible intermediate materials. Apparently, reduction of the total stiffness by application of an intermediate layer can render the total restoration sufficiently flexible to compensate for that part of the stress that would otherwise exceed the bond strength.

Animals↗