Biomedical subjects
D A Luke
Publications and source records attributed to D A Luke.
Optimum mouthful for food comminution in human mastication.
The effect of varying the portion of food offered for chewing (termed the mouthful) on aspects of the oral comminution of salted peanuts was investigated on six human subjects. Particle-size distributions, assessed from a sieving analysis, were similar for different mouthfuls, and could be characterized by a sieve size that would pass 80 per cent of the particles by volume in a distribution. As the food weight was increased, (a) the rate of particle-size reduction of the food declined exponentially, (b) the rate of food surface area production increased, (c) the number of chews to swallow the food increased, (d) the number of chews per unit gram to swallow the food decreased, (e) the food-particle sizes that were swallowed increased. It is hypothesized that the volume of food between the teeth at any chewing stroke depends more on food-particle size than on the weight of food in the mouth. The swallowing of small mouthfuls of peanuts may have depended more on the time to wet particles with saliva than particle size.
Dental anatomy: the salivary glands.
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Epithelial proliferation and development of rugae in relation to palatal shelf elevation in the mouse.
Regional variations in epithelial thickness and proliferation have been examined in the palatal processes immediately prior to shelf elevation in mouse embryos. In general, epithelial thickness and mitotic activity is greater on the lateral than on the medial surface of the process. In addition, epithelial thickenings, corresponding in number and arrangement to the rugae characteristic of the adult mouse palate, are present on the lateral surface before elevation. Where they develop, mitotic activity per unit surface length is locally increased. These regional variations in growth and form may augment the intrinsic shelf force.
Methods for analysing the breakdown of food in human mastication.
A method is described for measuring the rate at which carrot particles are broken down in chewing. In 10 subjects, this rate declined progressively throughout mastication. This was analysed in terms of two variables: (a) the intra-oral selection of particles for fracture, (b) the size distribution of fractured pieces of those particles. When intra-oral selection was measured by different methods, it depended mainly upon particle size. The selection of small particles might depend on the number of chews taken after the food was placed in the mouth. The size distribution of fractured pieces was obtained from one chew on three different particle sizes. These distributions were partially described by two different equations whose characteristics suggest that carrot particles are subjected to only one breakage per chew and that the number of fragments formed per breakage is small. It is suggested that the cusps present on the post-canines were important in determining this breakage pattern, and that the dependence of selection on particle size was primarily responsible for the decline in the rate of breakdown with increasing numbers of chews.
Computer simulation of the breakdown of carrot particles during human mastication.
There are two separable aspects of the mastication of food particles. One aspect describes the probability of the selection of particles for fracture (selection); the other describes the manner of fragmentation of the particles (breakage). Definitions of these concepts were used to produce an approximate equation for food breakdown, which can be solved by iteration in a computer. Values for the selection and breakage functions, obtained from 10 human subjects using carrot as a test food, were used in a computer program which modelled mastication. The model assumed (1) that selection depended only on particle size (2) that fragmentation (range of fractions or sub-particles produced) was similar for all particles, whatever their size. Good agreement was found between the actual particle-size distributions produced by mastication and those distributions generated by the computer. Simulations predicted that the initial particle size of the carrot before mastication could be varied substantially, so producing similar particle-size distributions after 15 chews.
The significance of cusps.
It has been argued that the prolonged retention of cusps in the human dentition is a relatively recent aberration due to the negligible abrasiveness of modern diets and that to achieve maximum efficiency and freedom from disease human teeth should be worn down as they are in many herbivorous mammals. Here we critically review the evidence that has been put forward to support this idea and, after discussing the design of occlusal surfaces in relation to the wide variety of mammalian diets, we conclude that cusps are adaptations for breaking food with specific physical properties.
Sternal and costochondral infections with gentamicin and methicillin resistant Staphylococcus aureus following thoracic surgery.
Six patients in a thoracic unit developed sternal osteomyelitis and costochondritis following median sternotomy. Five of the patients were operated on in another hospital. Gentamicin and methicillin resistant Staphylococcus aureus was isolated in pure culture in each case. The S. aureus isolate from 2 patients was of the same phage type suggesting cross-infection. Antibiotic prophylaxis administered in the perioperative period was ineffective. One patient, treated with amikacin (to which all of the strains were sensitive in vitro) and cefuroxime, died from overwhelming infection in spite of débridement and resuturing of the wound. The remaining 5 patients were cured with vancomycin therapy usually coupled with surgical intervention.
Dental anatomy: the paranasal sinuses.
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Dental anatomy: some anatomical aspects of denture design.
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Effects of rehabilitation on the jaws and teeth of protein-deficient and calorie-deficient pigs.
The growth of the jaws and teeth was examined in pigs which had been fed protein-deficient and calorie-deficient diets for the first year of life and thereafter allowed unlimited food. After 2 years of rehabilitation, jaw size had almost reached that of well-fed controls, although in the mandible the labial alveolar process remained abnormally proclined and in both jaws the crowns of third permanent molars were smaller than in control animals. Calorie-deficient pigs did not recover as well as did protein-deficient animals. Pigs fed a calorie-deficient diet for the first 2 years of life before rehabilitation also made a good recovery and were only slightly smaller in most dimensions than those undernourished for 1 year and then rehabilitated. Despite the excellent recovery in jaw dimensions, some malposition of teeth persisted after rehabilitation, especially in animals which had been undernourished for 2 years.
Dental anatomy: the tongue.
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Preparation of saphenous veins for bypass grafting.
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Epithelial proliferation in explants of mouse palatal mucosa cultured in contact and apart.
Explants of mouse palatal mucosa were cultured on grids either in isolation or with their lateral margins in contact. After 25 h the labelling index (LI) was determined using 3HTdR. At the edge of explants in contact LI was 59% that of explants cultured apart but the mean grain count was similar in the two groups. Metaphase arrest using vinblastine between 24--28 h of culture showed that in the basal cells, the rate of entry into mitosis was 1.1% per hour in explants cultured in contact and 1.9% per hour in explants cultured apart. In both groups the duration of mitosis was 1.0 h. Since in vivo the rate of entry into mitosis in this tissue is 1.2% per hour, the result suggest that an increase in epithelial proliferation does occur near to the edge of cultured mucosal explants and that this is diminished by the proximity of the edge of a second explant.
Distribution of mitoses in mouse palatal epithelium.
Using colchicine as a stathmokinetic agent, regional variations in the distribution of dividing cells were investigated in the palatal epithelium of mice. The mitotic rate, estimated per unit length of epithelial surface or of epithelia/connective tissue (ECT) junction, was greater in the small rugae of the molar region than in the larger rugae behind the incisors. Immediately beneath the crest of each ruga, where tactile corpuscles are present and the epithelium is thin, mitoses were relatively sparse. A more regular distribution of mitoses was obtained if the mitotic index was based on unit length of ECT junction rather than on length of epithelial surface.
Current trends in open heart surgery.
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Histology of mandibular bone from normal, protein deficient and calorie deficient pigs.
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Cell proliferation in epithelium of murine oral mucosa in vivo and in vitro. An autoradiographic study using tritiated thymidine.
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