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Biomedical subjects

K D Gordon

Publications and source records attributed to K D Gordon.

11 recordsLinked to original sources
PubMed2003

Kinematics of ulnar head arthroplasty.

This in vitro study evaluated the performance of an ulnar head replacement. A joint simulator was employed that produced active forearm rotation in cadaveric specimens, with motion measured using an electromagnetic tracking system. The kinematics of the intact forearm were compared with a partial ulnar head replacement and a full replacement (with and without soft-tissue reconstruction) and a full excision of the ulnar head. There were no differences between intact kinematics and those following prosthetic reconstruction. However, ulnar head excision produced distal radioulnar joint instability in the form of radioulnar convergence and increased anteroposterior translations.

Arthroplasty↗
PubMed1988

A review of methodology and quantification in dental microwear analysis.

Dental microwear analysis is a method of inferring oral events (primarily food processing and aspects of masticatory biomechanics) from microscopic abrasion patterns retained on the enamel surfaces of teeth. Although some qualitative pattern differences may be easily distinguishable, most of the significant results produced thus far have derived from quantified studies of SEM images of occlusal enamel. It often goes unnoticed by readers of microwear reports who are not themselves specialists that microwear analysis is essentially a statistical method, not a visual one. In this review of current techniques and methods, several problems in current approaches are detailed. It is noted that feature definition can have significant effects on ultimate pattern differentiation. Sampling bias is also a major concern, as most microwear studies are carried out on samples which are very small. Compounding this are the effects of magnification level choices, and the effects of SEM instrumentation on feature visibility. Finally, the interpretation of pattern differences requires careful attention to comparisons of within-group and between-group variability.

Dental Enamel↗
PubMed1985

Taste responses to amino acids in the southern leopard frog, Rana sphenocephala.

Integrated taste recordings of the glossopharyngeal (IX) nerve innervating the tongue of the southern leopard frog were studied in response to various amino acids and quinine hydrochloride. Amino acids and quinine hydrochloride elicited primarily phasic taste responses. Acidic (L-aspartic and L-glutamic) and basic (L-lysine and L-arginine) amino acids, adjusted to pH8, were effective taste stimuli. All glossopharyngeal nerve twigs that responded to amino acid stimuli also responded to quinine; however, not all quinine-sensitive IX nerve bundles were responsive to amino acids. Electrophysiological thresholds for amino acids were estimated to be 2.5-10 mM, whereas threshold for quinine hydrochloride averaged approximately 10 microM.

Amino Acids↗
PubMed1984

The assessment of jaw movement direction from dental microwear.

In order to resolve several controversies about unusual jaw movements such as thegosis and orthal retraction, information about direction of jaw movement is essential. Ryan (1979a,b) proposed that asymmetry of microwear striations might provide such data. In vivo occurrences of asymmetric striations on chimpanzee molars are presented and analyzed. Results suggest that either thegosis contacts commonly occur on chimpanzee molars or that Ryan's model, as developed in vitro, does not accurately apply to naturally occurring molar microwear.

Animals↗
PubMed1984

Orientation of occlusal contacts in the chimpanzee, Pan troglodytes verus, deduced from scanning electron microscopic analysis of dental microwear patterns.

Analysis of dental microwear may be used to detect species differences in diet and to secure information about occlusal relationships and biomechanics of the jaw. Microscratch-orientation data evaluated with reference to several hypotheses about functional, wear-related, sex and age influences on occlusal contacts indicated significant effects of facet type on scratch orientation, with less marked and sometimes paradoxical effects of molar wear and sex. Age per se seemed not to be related to scratch-orientation patterns. Orientations showed a considerable breadth of occlusal contact pathways, possibly indicating that in the chimpanzee, as in modern man, occlusal guidance is not precise.

Age Factors↗
PubMed1984

Pitting and bubbling artefacts in surface replicas made with silicone elastomers.

Pitting or bubbling on the surface of epoxy resin replicas is a frequently encountered artefact associated with the use of silicone rubber impression materials. Several variants of this type of artefact are illustrated. It is suggested that bubbles or pits form at the mould:epoxy interface during curing of the epoxy, and that they are caused by gas escaping from the mould material itself. Duration of silicone rubber polymerization, base-catalyst ratios, and surface porosity of the object may all influence the occurrence of mould degassing.

Dental Amalgam↗
PubMed1984

Hominoid dental microwear: complications in the use of microwear analysis to detect diet.

Analysis of dental microwear on chimpanzee molars reveals much variation that reflects jaw mechanics and occlusal function rather than diet. Observed microwear pattern differences relate to variations in molar position, facet type, and overall age of the tooth. Gradients in the amounts of shear and compression generated at different points in the molar series relative to the condyle probably account for pattern variations associated with molar position, while differences in facet inclination may affect the vectors of compression and shear, resulting in facet differences. Age-related pattern differences may be a result of surface and subsurface variations in enamel hardness. These results demonstrate that intraspecific and intra-individual differences in microwear may be extreme, and care must be taken to distinguish normal variation due to occlusal mechanics from variations due to dietary difference. The finding that microwear variations are reflective of subtle changes in occlusal forces and vectors along the tooth row might in itself be a clinically useful phenomenon.

Age Factors↗
PubMed1983

Playing 'possum: a microwear experiment.

A recent experiment to evaluate the reliability of dental microwear as an indicator of diet seems to show that differences in diets fed to laboratory animals are not reflected by their tooth wear. We feel that these results are misleading, and reflect not so much the limits of microwear analysis per se, but rather result from the problems of design and execution inherent in any experimental simulation of natural feeding behavior. The experiment in question was flawed in several respects, and we think that changes in the methods and assumptions of the study are necessary before the experimental approach can yield meaningful results with which to test hypotheses about microwear analyses.

Animals↗
PubMed1982

A study of microwear on chimpanzee molars: implications for dental microwear analysis.

Recent investigations of dental microwear have shown that such analyses may ultimately provide valuable information about the diets of fossil species. However, no background information about intraspecific variability of microwear patterns has been available until now. This study presents the results of an SEM survey of microwear patterns found on occlusal enamel of chimpanzee molars. Methods of pattern analysis are described. Selected sites on the occlusal surface included shearing, grinding, and puncture-crushing surfaces formed by both phases of the power stroke of mastication. The microwear patterns found in this sample of chimpanzees showed a high degree of regularity. However, certain parameters such as relative pit-to-striation frequencies, feature density, striation length, and pit diameter were significantly affected by facet type and molar position. Sex and age of individuals also influenced some microwear parameters, but due to the small sample size these findings are considered to be preliminary. These results show that microwear within a single species may vary because of factors that are due more to biomechanics than to diet. The study also supplies some metrical estimates of "normal" pattern variability due to functional and morphological influences. These estimates should provide a useful baseline for assessing the significance of microwear pattern differences that may be found between species of differing diets.

Animals↗