Biomedical subjects

C L Davidson

Publications and source records attributed to C L Davidson.

At least 19 recordsLinked to original sources

PubMed1995

Dentine permeability and bond quality as affected by new bonding systems.

OBJECTIVES AND METHODS: The relationship between dentine bonding and the condition of dentine for four dentine bonding systems (All Bond 2, Clearfil Liner Bond, Scotchbond MP and XR Bond) has been examined. Different dentine conditions were evaluated and correlated with adhesion values. Dentine permeability was calculated using a hydraulic pressure apparatus working under physiological pulpal pressure (6.9 kPa), while remaining dentine thickness (RDT) was measured using pincer calipers. Scanning electron microscopic (SEM) examinations were effected to analyse dentine morphology. These evaluations were considered as an index of the condition of dentine. Shear bond strength tests were used to evaluate adhesion. Dentine samples after the bonding systems application were stored for 24 h under pulpal pressure before bond strength was tested. RESULTS: Scanning electron microscopy examinations indicated that the application of bonding system conditioners caused the removal of smear layer, the demineralization of dentine and the formation of a layer of collapsed collagen fibrils in the intertubular and peritubular dentine. Primers were able to infiltrate the collagen fibrils. A layer of resin infiltrated/reinforced dentine (the so-called 'hybrid layer') was observed for All Bond 2, Clearfil Linear Bond and Schotchbond MP. CONCLUSIONS: Significant correlations were observed only for XR Bond, which proved very sensitive to RDT and dentine permeability despite the presence of smear layer. The other three materials did not show any correlation with dentine conditions. By contrast they showed the highest bond values.

Acid Etching, Dental↗

PubMed1994

In vitro flexural fatigue limits of dental composites.

The flexural fatigue test equipment developed was used to study the fatigue behavior of dental restorative composites, using a "staircase" approach. Three commercial composites were tested after dry and wet storage conditions. The findings indicate that the method is accurate and reliable, and that changes due to water sorption are clearly reflected: The flexural fatigue limit decreases after water sorption. From the present results it seems that under environmentally controlled conditions, the fatigue behavior is characterized by a well-defined fatigue stress level above which the composites tested fail rapidly, and below which they survive.

Dental Materials↗

PubMed1994

Silane treatment of filler and composite blending in a one-step procedure for dental restoratives.

The aim of this study was to investigate whether a one-step procedure of silane treatment of filler and composite blending could also produce the strong resin-filler integrity, as can be obtained for dental composites in two steps by pretreating the filler with a silane coupling agent before blending. Resin mixtures containing either a silane-functional methacrylate or a non-silane-functional methacrylate were blended with silane pretreated or non-treated filler particles. The resin-filler integrity of the composites was determined from the wear performance in three-body wear tests. For composites with the non-silane-functional methacrylate the wear rates dramatically decreased when the silane pretreated filler was used instead of untreated filler, showing the efficacy of the silane treatment. For composites with the silane-functional methacrylate the decrease was small, indicating comparable resin-filler integrity for the one-step and the two-step procedures.

Analysis of Variance↗

PubMed1994

Dual cure luting composites--Part II: Clinically related properties.

Thirteen dual cure luting composites were compared in function of film thickness, consistency, and working time by using the American National Standard/American Dental Association (ANS/ADA) specifications for zinc phosphate cement and direct filling resins. The effect of temperature and setting reaction on the film thickness was also evaluated for some representative products. All three clinically related properties varied widely among the products investigated. A strong linear correlation was found between film thickness and consistency. This relation is supported by the temperature dependence of film thickness of dual cure luting composites. Cooling of the material increased the consistency, resulting in a larger film thickness, while heating reduced the film thickness because of the lower consistency. However, one product with a rather short working time at room temperature occasionally exhibited a dramatically enlarged film thickness after heating, probably caused by accelerated chemical polymerization. No correlation emerged between film thickness and maximum filler size or between consistency and filler weight content. Maximum filler size and filler weight content had been measured previously in Part I of this study. Scanning electron microscope (SEM) analysis of the cured film thickness samples revealed that the largest filler particles had been crushed under the heavy load pressure during film thickness measurement. The lack of correlation between consistency and filler weight content can be explained by the multifactorial determination of the consistency. It is concluded that the great diversity in the currently available luting composites makes clear specifications with regard to the optimum composition of luting composites urgently needed. Furthermore, more adequate methods for testing the film thickness of luting composites are also required.

American Dental Association↗

PubMed1994

Effect of occlusal load cycling on the marginal integrity of adhesive Class V restorations.

The objective of this study was to evaluate the gingival wall marginal integrity of adhesive Class V restorations subjected to occlusal load cycling. Extracted lower first and second molar teeth were used. For each tooth, a Class V cavity was prepared in the buccal or lingual surface with the gingival margin in the cementum. The cavities were restored with eight different adhesive systems: (1) Ketac-Fil; (2) Fuji II LC; (3) Ketac-Bond/Pertac; (4) Photac-Bond/Pertac; (5) Scotchbond 2/P50; (6) Scotchbond Multi-Purpose/P50; (7) Clearfil Liner Bond/Clearfil Photo Posterior; and (8) OptiBond/Herculite XR. For each material-combination, three test procedures were carried out: no loading (control), loading at 125 N and at 250 N. Six specimens were prepared for each procedure. The samples were loaded for 5000 cycles in a dye solution and kept in the dye for 24 hours after loading. Control samples were stored in the dye for the same period. All teeth were sectioned and dye penetration at the gingival wall was scored from 0 to 4. Under control condition, only groups 2, 6, 7 and 8 showed perfect marginal integrity. After loading at 125 N, groups 1, 3 and 5 showed significant increase in leakage (P < 0.05). Increasing the load to 250 N resulted in significant deterioration in the marginal adaptation of all test groups, except 6 and 7. This study indicates that the marginal integrity of occlusally stressed adhesive Class V restorations can only be preserved by a few products.

Bisphenol A-Glycidyl Methacrylate↗

PubMed1994

Dermatomyositis occurring during psoralen A (PUVA) therapy.

Dermatomyositis (DM) developed in a 35-year-old woman after 2 months of psoralen ultraviolet-A (PUVA) therapy for presumed psoriasis. Her disease was characterized by symmetrical proximal muscle weakness and cutaneous lesions compatible with DM. In addition, laboratory abnormalities included a positive antinuclear antibody, and elevated levels of creatine kinase and aldolase. This is the first report of DM developing during PUVA therapy.

Adult↗

PubMed1993

Expression of a human homeobox-containing gene is regulated by 1,25(OH)2D3 in bone cells.

The murine msh-like homeobox-containing gene Msx-2 (Hox-8) has a multiphasic pattern of embryonic expression which includes the developing skull bones and teeth. In order to determine whether this gene might be expressed in adult mineralizing tissues, an adult human bone cell (osteoblastic) cDNA library was screened with a murine Msx-2 probe. One of the positive clones obtained was sequenced in full and shown to be highly homologous to the murine Msx-2 gene. Expression of this gene, MSX2, was studied in human bone-derived cells, where a low level of expression was detected which was greatly induced by stimulation with 1,25(OH)2D3. Little or no increase in expression was detected with retinoic acid or TPA stimulation. In cultures of skin fibroblasts no stimulation of expression with 1,25(OH)2D3 was detected. MSX2 is the first homeobox-containing gene to be shown to be regulated by 1,25(OH)2D3 and to be expressed in adult human bone cells. These results suggest a possible role for MSX2 in bone cell differentiation and/or calcium homeostasis.

Amino Acid Sequence↗

PubMed1993

Setting stresses in composites for two different curing modes.

As a continuation of a study into the development of the polymerization shrinkage stress of chemically initiated composites (CC), the development of the polymerization shrinkage stress of light-initiated composites (LC) in relation to the configuration-factor was determined. During setting, the LC composites generated a higher polymerization shrinkage stress, developed higher cohesive strength to resist this stress and showed less flow than their CC analogues. Trying to find a comprehensive explanation for the differences in behavior of stress development in LC and CC composites, the effect of mixing-in of porosity was also investigated on LC composites. Mixing-in of porosity slowed down and decreased the shrinkage stress development. This was attributed to either oxygen inhibition due to admixed air or to an increase of free surface from the presence of pores within the bulk of the composite.

Composite Resins↗

PubMed1993

True linear polymerization shrinkage of unfilled resins and composites determined with a linometer.

A device, which was given the name "linometer", has been developed for measuring linear polymerization shrinkage of both unfilled resins and composites. The results were in agreement with those obtained with the mercury dilatometer. The present method is simple, fast, insensitive to temperature fluctuations, is operational at any temperature and, if desired, samples can be maintained in a 100% relative humidity environment. The linometer offers an easy means for routine polymerization shrinkage determinations and therefore may be useful in evaluating new monomer systems for dental composites. The linear polymerization shrinkage for several unfilled resins and composites was measured with this device.

Acrylic Resins↗

PubMed1993

Derangement of composite filler distribution inside syringe-type delivery systems.

Used and almost emptied syringes of two brands of composites contained material close to the pestle-head that appeared to be more granular and dry, as compared to the composite obtained from unused syringes. The present results suggest that a derangement of filler and matrix phases occurred inside the used syringes when compared to unused controls. Stress imposed on the composite material inside the unused syringes resulted in a comparable derangement of filler and matrix phases. Although this derangement was limited, the effect could contribute to intra- and interlaboratory scattering of data.

Analysis of Variance↗

PubMed1993

Polymerization contraction and conversion of light-curing BisGMA-based methacrylate resins.

The aim of this study was to investigate the polymerization contraction and the conversion of light-curing methacrylate resins based on bisphenol-A bis(2-hydroxypropyl)methacrylate (BisGMA) diluted with triethylene glycol dimethyacrylate (TEGDMA), methyl methacrylate (MMA), hydroxypropyl methacrylate (HPMA) or (+/-)-2-ethylhexyl methacrylate (EHMA). The contraction measurements were carried out with a linometer, a simple device to determine true linear polymerization contraction of liquid monomers at ambient temperature. The contraction increased with the amount of diluting monomer. The estimated conversion of the BisGMA-TEGDMA, calculated using the contraction, is consistent with literature values. The BisGMA-HPMA mixtures showed high conversions at moderate contraction.

Composite Resins↗

PubMed1993

Shear bond strength and microleakage of new dentin bonding systems.

The aim of this study was to evaluate the shear bond strength and microleakage of three new bonding agents. Eight specimens were prepared from each material and shear bond strength was measured using a universal testing machine at crosshead speed of 0.5 mm/minute. Fracture pattern was studied by stereomicroscope and scanning electron microscope (SEM). For the microleakage test, Class V cavities were prepared in the buccal or lingual surface of extracted lower molar teeth and restored with resin composites after application of the accompanying adhesives. The restored teeth were loaded at 125 N for 5000 cycles in a dye solution, sectioned and inspected for microleakage. Bond strengths of 17.7 +/- 4.1, 16.3 +/- 3.8, 15.7 +/- 5.8 MPa were measured for Scotchbond Multi-Purpose, Clearfil Liner Bond and Optibond respectively. Restorations of Scotchbond MP and Clearfil LB showed no leakage, while those of OptiBond showed leakage in only one out of eight fillings.

Analysis of Variance↗

PubMed1993

[Sources of mercury].

Mercury and its compounds arising from many sources, among which dental amalgams, are present everywhere, usually in low concentrations. Mercury is absorbed by inhalation, ingestion and skin from the air, diet and water. A large proportion of the population absorbs also mercury vapour and amalgam particles from amalgam restorations. Mercury may lead to allergic and may cause toxic reactions. Presumably due to the mass media and instigated by acupuncturists, an unknown number of patients ascribe a large diversity of complaints to their amalgam restorations. Many of the complaints do, however, not fit the symptoms of mercury poisoning. If the amalgam restorations underlie the complaints indeed, the material has to be banned. Moreover, for the Netherlands estimated 70-120 million restorations of amalgam should be replaced by fillings of another material. The question then is which material(s) must be used to perform such an almost impossible large and expensive task.

Dental Amalgam↗

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↗