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Biomedical subjects

D C Watts

Publications and source records attributed to D C Watts.

At least 109 records · Page 6Linked to original sources
PubMed1987

Temperature-dependence of compressive properties of human dentin.

The effect of temperature on compressive stress/strain behavior of human dentin obtained from recently extracted permanent lower molar teeth has been determined over the range 0-80 degrees C. Dentin specimens were loaded uni-axially in a direction perpendicular to the tubule orientation. A statistically significant, linear regression relationship was found between modulus (E) and temperature (T): E (GPa) = 15.55-0.0734 . (T degrees C). The observed temperature coefficient of the modulus is in close agreement with that observed for cortical bone. Proportional limit, compressive strength, and resilience were also found to undergo a linear decrease with increasing temperature. Mechanical failure of specimens generally occurred along lines determined by maximum shear stresses, approximately 45 degrees to the axial load direction.

Cold Temperature↗
PubMed1987

Thermal diffusivity of composite restorative materials.

The substantial increases in the filler volume fraction of the current generation of composite resins, and the incorporation of radiopacifying heavy elements in many of these fillers, constitute significant changes which may affect thermal transport properties. Thermal diffusivity has been determined for 21 of these composite materials recommended for anterior and posterior applications. For radiopaque hybrid and for microfine composites, there was, however, only a gradual trend to increased thermal diffusivity with increasing volume fraction of inorganic filler. The diffusivity values were not greatly in excess of the level observed for dentin. Nevertheless, a small group of materials, incorporating substantial amounts of quartz or silicon nitride filler particles, exhibited high rates of thermal diffusion, up to three times the level exhibited by dentin.

Composite Resins↗
PubMed1986

Fracture toughness of human dentin.

Plane strain fracture toughness (KIC) was determined for coronal dentin using compact tension test-pieces obtained from recently extracted permanent lower molar teeth. Specimens were prepared and tested such that the moving crack front was aligned parallel to the tubule orientation. The fracture toughness (KIC) was temperature-invariant in the range 0-60 degrees C, and the mean value obtained was 3.08 MN.(m)-1.5 (SD: 0.33). The critical strain energy release rate (GIC) of dentin was also calculated utilizing modulus data and was found to increase slightly with temperature, possibly as a consequence of significant temperature-dependence of the modulus: GIC = 2.31 (T degree C) + 653.2 (J .m-2) The fracture toughness of dentin is midway in the range (0.23 - 6.56) observed for cortical bone and is a factor of two greater than that exhibited by most current restorative materials.

Dental Stress Analysis↗
PubMed1985

Fetal plasma carbonic anhydrase III in prenatal diagnosis of Duchenne muscular dystrophy.

Carbonic anhydrase III (CAIII), a skeletal-muscle-specific enzyme which is elevated in the plasma of Duchenne muscular dystrophy (DMD) patients, was measured by radioimmunoassay in fetal plasma in order to evaluate its application to prenatal diagnosis of DMD. Using fetoscopy, pure fetal blood samples were taken at 17-24 weeks gestation from 25 fetuses at risk for DMD and from 78 control fetuses. Care was taken in the handling and storage of all samples. Normal sons were born in eight cases at risk for DMD. The CAIII levels in the infants were not significantly different from those of the control infants. Pregnancies were terminated in the remaining 17 at-risk cases. The CAIII levels in the fetuses were significantly different (p = 0.0034) from those of the control fetuses, although the distributions overlapped. Based on prior maternal risk, seven affected fetuses were expected in the terminated group; five had CAIII levels at or above the 95th centile of the control range. It is suggested that measurement of CAIII achieves partial discrimination between affected fetuses and their normal at-risk brethren.

Carbonic Anhydrases↗
PubMed1985

Evaluation of carrier detection of Duchenne muscular dystrophy using carbonic anhydrase III and creatine kinase.

Carbonic anhydrase III (CAIII) and creatine kinase (CK) were measured in plasma samples from a series of females at-risk as carriers of Duchenne muscular dystrophy and compared with control groups. Both plasma CAIII and CK levels were raised in a proportion of carriers. Although measurement of CAIII and CK was no more successful in identifying carriers than CK alone, CAIII could fulfill a useful confirmatory role, particularly for cases with a marginally elevated CK or where the sample is poorly preserved. The difference between the CK and CAIII results could indicate biochemical heterogeneity in the expression of Duchenne muscular dystrophy.

Carbonic Anhydrases↗
PubMed1985

Gastrocnemius muscle lipids in relation to diet in two mouse mutants, 129Re-dy and A2G-adr, with abnormal muscle function.

The lipids of gastrocnemius muscle from normal and dystrophic (dy) mice of the Bar Harbor, 129Re strain were studied. Animals were fed diets containing either 3.1% or 1.1% of total calories as linoleic acid. Lipid analyses were also done on muscle from a new mouse mutant, A2G-adr, which has abnormal muscle function, characterised by an arrested development of the righting response. These animals were fed the "high" linoleic acid diet only. Total lipid, triacylglycerol, and cholesterol were elevated in the 129Re-dy irrespective of the diet, whereas A2G-adr possessed significantly higher levels of cholesterol. Total phosphorus (micrograms P/g muscle) and cholesterol/phospholipid ratios were elevated in the dy strains only. Cardiolipin was raised in the dy ("low" linoleic diet) and adr muscle, whereas phosphatidylcholine was lower in the adr strain only. Linoleic acid esterified to phosphatidylcholine, phosphatidylethanolamine, and phosphatidylserine was elevated whereas arachidonic acid in phosphatidylserine was decreased in both mutants. Docosahexanoic acid (22:6) in all three dy phospholipids was decreased, independent of dietary treatment. The adr strain possessed normal levels of this fatty acid. The results specifically point to an abnormality in long-chain polyunsaturated fatty acid metabolism in gastrocnemius muscle in the 129Re-dy mutant; in the adr mutant they could reflect an abnormal increase in the number of muscle mitochondria.

Animals↗
PubMed1985

Time-dependent deformation of composite restorative materials in compression.

The strain of six composite resins, including microfine and conventional types, has been measured in compression as a function of time. Compressive loads have been used in separate experiments to produce a wide range of applied stress in samples of clinically-appropriate size. The magnitude of visco-elastic response generally decreases with increasing % of filler in the composite. Additionally, the very substantial linear strain, up to 20%, observed in some microfine composites suggests the visco-elastic deformation of both organic filler, as well as resin matrix, at high stress levels. Caution is therefore indicated with regard to the clinical use of microfine restorative materials in high-stress-bearing situations.

Acrylic Resins↗
PubMed1984

Acrylic 'allergy'?

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Acrylic Resins↗