Biomedical subjects
Publications and source records attributed to G Wing.
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Amalgam beam specimens were subjected to sub-modulus of rupture loads at 37 degrees C. The specimens tested underwent varying degrees of deformation and ultimate fracture determined by the degree of specimen bend and time to fracture. The property most closely related to the sub-fracture loading behaviour was creep, particularly the 72-h determination of this property. Time and temperature of testing are also significant factors. The present study indicates the importance of the use of 37 degrees C testing in low-load stressing of dental amalgam. The study has confirmed the nature of failure of amalgam in relation to its rheological properties at the temperature at which amalgam functions clinically.
The behaviour of amalgam beam specimens subjected to a sub-modulus of rupture load at 37 degrees C was compared in static and cyclic modes. Testing was performed using identical equipment, with cyclic testing conducted by intermittent load application for both tests. The specimens tested exhibited varying degrees of deformation and times to fracture in both tests. The mode of load application, either cyclic or static, did not appear to have a significant effect on the degree of amalgam deformation or time to fracture. The most important factors relating to deformation are time of total load application, creep of the specific amalgam and temperature of testing.
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An in vitro study was conducted in which a range of amalgam alloys was condensed into Class I cavity preparations. The force of condensation and increment size were varied to determine the effect of these operator variables on the adaptation, of the alloys investigated, to the prepared cavity walls. Specimens were sectioned, metallographically polished and examined using light and scanning electron microscopes. For each specimen ten random points on the pulpal and both vertical walls were selected to measure the adaptation of the amalgam to the tooth structure. For the Class I cavity preparation the adaptation of all alloys to the vertical walls was better than the adaptation to the pulpal walls. The overall adaptability of the alloy did not appear to be determined by the particle size, shape or composition. Condensation force was the most important factor in influencing adaptation of amalgam to the cavity walls. Heavy condensation forces produced better adaptation for all alloys particularly when condensing small increments.
The adaptation of a range of amalgam alloys to the cavosurface margin of Class I cavity preparations was examined for two condensation techniques. The marginal contour of amalgam condensed into the cavity preparation and packed approximately 1 mm past the cavosurface margin was compared with amalgam margins of restorations which were packed to final contour with minimal carving. The effect of burnishing and/or polishing the cavosurface margin was compared with carving the amalgam to the cavosurface margin. Specimens were sectioned, metallographically polished and examined using a light microscope. The technique of overpacking amalgam produced a greater number of acceptable amalgam margins at the cavosurface margin than the condensation technique of packing to final contour, the best cavosurface margin was produced when specimens were burnished and polished, the carved margin being the least desirable. The cuspal incline also influenced the quality of the marginal finish with the difficulty of marginal finishing increasing with the steepness in cuspal incline.
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Extensive botryomycosis was diagnosed in a patient with diabetes mellitus with chronic active hepatitis. Peptostreptococcus organisms and Staphylococcus aureus grew from the sulfur granule cultures. The patient's neutrophils showed notable inhibition of chemotaxis toward endotoxin-activated normal serum. The patient's serum also had an inhibitor to neutrophil chemotaxis, This inhibiting substance was probably antistreptolysin O. Results of other tests of neutrophil function and skin tests to evaluate cell-mediated immunity were normal.
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Eight materials were placed as bases on the pulpal surface of cavities prepared in extracted teeth. Seven minutes after mixing of the material commenced, amalgam was condensed on to the lined cavity. The restored teeth were sectioned subsequently for microscopic examination. The results suggested that all uniformly mixed, carefully placed base forming materials that have reached the state of "clinical set" are able to withstand loads applied during amalgam condensation irrespective of their strength.
Eleven base forming materials used under amalgam restorations were examined for the rate of development of their compressive and tensile strengths. Materials from three categories were compared. Under in vitro conditions of testing, it was found that, immediately after a state of clinical set had been reached, the quick-setting zinc oxide-eugenol materials possessed strengths significantly greater than the calcium hydroxide cements but significantly weaker than the zinc phosphate cements. Calcium hydroxide cements possessed the lowest compressive strength to tensile strength ratio and modified zinc oxide-eugenol materials the highest.
The influence of several manipulative variables on the compressive and tensile strengths of eight base forming materials has been investigated. The most important manipulative variable from the point of view of influencing the development of strength was found to be the powder-liquid ratio. In particular, thicker mixes produced greater early strengths. The setting time of each material was found to be influenced more by the temperature during setting than the ambient temperature or presence of moisture.
Modified zinc oxide-eugenol and calcium hydroxide cements are frequently used as bases beneath restorations. Investigation reveals that the bond strength between different types of dement may be less than that between different consistencies of the same type of dental cement. In some clinical situations, the choice of the type of cement as a base forming material beneath inlays and crowns should be made bearing in mind the type of luting material to be used.
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Explore the source record for details and available documents.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Explore the source record for details and available documents.