A comparison of five different bone resorption markers in osteosarcoma-bearing dogs, normal dogs, and dogs with orthopedic diseases.

BACKGROUND: Various bone resorption markers in humans are useful for supporting the diagnosis of malignant skeletal pathology, with certain bone resorption markers appearing to be more discriminatory for detecting cancer-induced osteolysis than others. Canine osteosarcoma (OSA) is characterized by focal bone destruction, but a systematic investigation for determining which bone resorption marker best supports the diagnosis of OSA in dogs has not been reported. HYPOTHESIS: Dogs with OSA will have increased concentrations of bone resorption markers compared with healthy dogs and dogs with orthopedic disorders. Differences will exist among various bone resorption markers for their ability to support the diagnosis of malignant osteolysis in dogs with OSA. ANIMALS: Single time point, cross-sectional, cohort study including dogs with OSA (n = 20) or orthopedic disorders (n = 20) and healthy dogs (n = 22). METHODS: Basal concentrations of urine and serum N-telopeptide (NTx), urine and serum C-telopeptide (CTx), and urine deoxypyridinoline (DPD) were compared among all 3 groups. RESULTS: Compared with healthy dogs and dogs with orthopedic disorders, urine NTx, serum NTx, and serum CTx concentrations were significantly increased in dogs with OSA. For urine NTx and serum NTx, the calculated lower and upper 95% confidence limits in dogs with OSA did not overlap with dogs diagnosed with orthopedic disorders or healthy dogs. CONCLUSIONS AND CLINICAL IMPORTANCE: Of the markers evaluated in this study, urine NTx and serum NTx appear to be the most discriminatory resorption markers supporting the diagnosis of focal malignant osteolysis in dogs with OSA.

An optimization model for mastication and swallowing in mammals.

Mammalian mastication is a process combining simultaneous food comminution and lubrication. The initiation of swallowing, which is voluntary, has been thought to depend on separate thresholds for food particle size and for particle lubrication. Instead of this duality, we suggest that swallowing is initiated when it is sensed that a batch of food particles is binding together under viscous forces so as to form a bolus. Bolus formation ensures that when the food mass is swallowed, it will pass the pharyngeal region safely without risk of inhaling small particles into the lower respiratory tract. Crucial for bolus formation is food particle size reduction by mastication. This allows the tongue to pack particles together tightly by pressure against the hard palate. A major function of salivation is to fill the gradually reducing spaces between particles, so increasing viscous cohesion and promoting bolus formation. If swallowing is delayed, excessive saliva floods the bolus, separating particles and reducing cohesion. Swallowing then becomes more precarious. Our model suggests that there is an optimum moment for a mammal to swallow, defined in terms of a peak cohesive force between food particles. The model is tested on human mastication with two foods, brazil nut and raw carrot, which have very different particle size breakdown rates. The peak cohesive force is much greater with brazil nuts but both foods are predicted to be swallowed after similar numbers of chews despite the very different food particle size reductions achieved at that stage. The predicted number of chews to swallow is in broad agreement with published data.

Relationship between jaw movement and food breakdown in human mastication.

Different quantities and sizes of peanuts were offered to six human subjects for mastication at two or three experimental sessions during which jaw movements and chewing cycle duration were measured. The amplitude of vertical movement and cycle duration depended on the position of a chew in a sequence of chews (masticatory sequence). Cycle duration also depended on the position of a given masticatory sequence during the first experimental session, the earlier sequences tending to be longer. Lateral jaw movements fluctuated about a reasonably constant value during a sequence and were unaffected by different food inputs. The amplitude of vertical movements increased markedly with an increase in food weight but was unaffected by change in the initial food particle size. These results were analyzed in the light of previous reports on the comminution of peanuts. It is hypothesized that observed jaw movements were unrelated to food particle size but that the amplitude of each vertical movement depended on the volume of food that was broken by the teeth during the next closing stroke. This food volume was provided and selected by bulk movements of the tongue during the preceding jaw opening.

Food properties that influence neuromuscular activity during human mastication.

The rate of breakdown of food in mastication depends on the ratio of two mechanical properties of the food--the toughness and modulus of elasticity (Agrawal et al., 1997)--a result which can be predicted by an analysis of the energetics of fracture. The work input to produce food fragmentation is provided by the masticatory muscles, the activity levels of which depend on sensory feedback from the mouth. Here, we test the hypothesis that the activity of a representative of this musculature is modulated by the above combination of food properties. The surface electrical activity (EMG) of the anterior temporalis muscles of ten human subjects was recorded while subjects chewed standardized volumes of 15 food types. The integrated EMG in these muscles was highly significantly related to the square root of the ratio of the above two food properties. Significant correlations were found between this food property index and integrated EMG, both when data for all chews and all subjects were lumped together (r = -0.86; p < 0.0001) and when correlation coefficients between the index and EMG were plotted for each chew made by each subject. Except for two subjects in the first chew, these coefficients reached and maintained highly significant levels throughout the masticatory sequence. Thus, a clear relationship between the electrical activity of a jaw-closing muscle and the mechanical properties of food has been found for the first time.

Alternative seed-handling strategies in primates: seed-spitting by long-tailed macaques (Macaca fascicularis).

The seeds in fruits consumed by primates may be chewed and digested, swallowed and defecated intact, or separated from the flesh and spat out. We show by a combination of close field observations and experiments with caged animals, that long-tailed macaques (Macaca fascicularis) have a remarkably low threshold of 3-4 mm for swallowing seeds and also that wild macaques rarely break them. The seeds of 69% of the ripe fruit species eaten are spat out intact or cleaned outside the mouth and dropped. Seed-spitting significantly reduces the swallowed food bulk and may lessen the risk of releasing seed toxins during mastication. However, it requires that even small fruits are processed in the mouth one or a few at a time. We suggest that fruit storage in the cheek pouches of cercopithecine monkeys allows them to spit seeds individually without excessively slowing fruit intake while feeding on patchily distributed fruit. In contrast, Apes and New World monkeys apparently swallow and defecate most ripe seeds in their diet and colobine monkeys break and digest them, detoxifying seed defenses by bacterial fermentation.

An analysis of the canine tooth size of old world higher primates in relation to mandibular length and body weight.

Canine crown heights, measured from the cement-enamel junction to the cusp tip, were directly proportional to mandible length for 37 species of catarrhines (males and females plotted separately). The ratio canine height/mandible length was much greater for males than females. An allometric analysis revealed close relationships between canine size and body weight in males when the sample was split into hominoid, cercopithecine and colobine groups but not close for females. It is suggested that canine size in males is controlled by differences in mandibular form. Reasons for the variability of canine size in females remain unresolved.

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.

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.

Swallow thresholds in human mastication.

Brazil-nut particles were broken down and classified by sieves into four classes of particle size. Samples of these classes were suspended in plain yoghurt in varying concentrations and presented to nine humans for chewing. Both the number of chews made before swallowing and the time needed to swallow increased significantly with particle size and concentration but the chewing frequency (number of chews/time) decreased. The rate of change of the chewing frequency, averaged over the chewing sequence (chewing frequency/time), was calculated for each food input and termed the swallowing index. This index did not differ significantly for concentrations above 20%, but increased sharply at lower concentrations. These results were interpreted in terms of a model in which food is swallowed only when particles are both small enough and sufficiently lubricated. For our food mixture, the lubrication threshold was satisfied by a 20% concentration and the particle-size threshold was 1.4 mm. Chews made with concentrations lower than this and containing smaller particle sizes were few in number and slow, reflecting the need to detect particle size with the oral mucosa.

The effects of food fragmentation index on mandibular closing angle in human mastication.

Jaw movements were recorded using a three-dimensional magnetic sensing system (Sirognathograph, Siemens) in 10 human volunteers while chewing standardized volumes of 15 food types, ranging from soft cheeses to hard nuts. The maximum horizontal amplitude inside the chewing loop (width of the loop), the height of the loop (vertical amplitude) and the closing angle made by the jaw during the late closing phase of the cycle relative to the vertical were calculated. The most highly significant correlation was between the closing angle and the square root of the ratio of two mechanical properties of the food - the toughness (R) and modulus of elasticity (E)(r = -0.85, p<0.001). The width of the chewing loop was also significantly correlated with the above combination of food properties (r = -0.75, p<0.01) whereas the vertical amplitude was not. Thus, the mechanical properties of foods appear to influence the pattern of mandibular movements in human mastication similarly to their reported effect on food breakdown rates and anterior temporalis activity during mastication.

Mechanical properties of foods responsible for resisting food breakdown in the human mouth.

The fragmentation of foods (breakage function) was measured in five humans on "bagged' single particles of 28 foods from three food groups. The change in the square root of the specific surface of the particles (the specific surface being the area of particle silhouettes, measured by image analysis, divided by original particle volume) produced by one bite, averaged for all participants, was inversely linearly related to the square root of the toughness of the foods divided by the square root of their Young's moduli(r = -0.86; p < 0.00001). This relation is predicted by an analysis based on food fragmentation within a limited jaw displacement. Thus, resistance to jaw movement appears to provide sensory information on the deformation fracture and fragmentation of foods. It is believed that this is the first time that a relation between the breakage of food particles by the teeth and their material properties has been found, and the finding has considerable implications for human masticatory studies, for the analysis of dentition and diet in mammals and for texture studies in food science.

Association between surface electromyography of human jaw-closing muscle and quantified food breakdown.

Simultaneous recordings of the activity of the masseter and anterior temporalis and of jaw movement were made on 10 healthy dentate volunteers while they chewed roasted peanuts in their habitual manner. The quantity of food taken was altered by varying (a) its total weight (mouthful) between 8 and 1 g, but with a fixed initial particle size and (b) by varying its initial particle size between median sizes of 9.2 and 2.4 mm, but keeping the mouthful constant. Significant differences were found in the peak and mean (r.m.s.) estimates of muscle activity (particularly in the masseter), and the dimensions of jaw movements. These differences were associated with the variation in both the size of the mouthful and of the initial particles but were much greater with changes in the mouthful. A dimensional argument treating both the weight of food in the mouth and initial particle size as volumes showed that initial particle volume had been varied by approximately 50 times as much as mouthful volume and therefore that the mouthful was a far more critical factor in masticatory physiology than was the particle size of the food. The reasons for this probably lie in an understanding of mechanisms of food comminution.

The effects of prior exposure to sulphur dioxide and nitrogen dioxide on the water relations of timothy grass (Phleum pratense) under drought conditions.

Studies of the growth and water relations of the grass Phleum pratense L. (Timothy) were made after simultaneous exposure to SO(2) and NO(2) at concentrations ranging from 80 + 57.4 microg m(-3) to 240 + 172.2 microg m(-3) (SO(2) + NO(2)). Decreased partitioning to the roots was evident during exposure to the pollutants, but when the plants were returned to clean air restrictions in root growth did not persist. Shoot to root partitioning was, however, complicated by the additional factor of changes in the nutritional status of the soil after additional columns of fresh soil were attached to the original tubes. The rate of use of soil water was nevertheless substantially increased by the pollution treatment and after a period of 23 days in which water was withheld, a clear pollution x water stress interaction was seen. The ability of polluted leaves to conserve water under severe water stress was tested by excising the leaves and measuring their water loss over time. The results from this second experiment showed that conservation of water by the leaves was appreciably affected after exposure to 80 + 57.4 microg m(-3) or 133.3 + 95.6 microg m(-3) SO(2) + NO(2). It seems likely that damage to the cells in the epidermal layer, leading to malfunctioning of stomata, is mainly responsible for the reduced ability to conserve water under conditions of extreme stress.

A large-scale fumigation system for investigating interactions between air pollution and cold stress on plants.

A new large-scale closed chamber fumigation system with cooling facilities is described for studying effects of low concentrations of SO(2), NO(2) and O(3) and low temperatures on woody species and herbaceous plants. The system is based on modified hemispherical greenhouses with a forced air ventilation system. This provides a chamber environment with low spatial variability of pollutant gas concentrations and rapid air circulation which allows exposure of plants at near ambient temperatures and relative humidity. Large capacity cooling units come into operation when ambient temperatures fall below 0 degrees C, and these allow chamber temperatures to be lowered by an additional 4 to 8 degrees C in experiments designed to test whether exposure to pollutants enhances the frost sensitivity of plants.

Relationship between foliar injury and changes in antioxidant levels in red and Norway spruce exposed to acidic mists.

Elevated levels of total glutathione and enhanced activities of glutathione reductase and ascorbate peroxidase were found in needles of red spruce which had been exposed to acidic mists. Reduced levels of ascorbate were also detected. Such observations suggest that oxidative stress is involved in processes which resist foliar injury caused by acidic misting. Different ionic compositions of the acidic mists applied had pronounced effects on the levels of these antioxidants and the activities of related enzymes. Sulphate was found to be most effective in causing increases in glutathione, while additions of ammonium and/or nitrate mitigated the effects of sulphuric acid. Moreover, it is the composition of ions in the applied mists, rather than the levels of acidity, that determines the extent of the overall response of red spruce. By contrast, although acidic mists caused similar increases in glutathione content of Norway spruce needles, no statistically significant changes of ascorbate or related enzymic activities were found.

Effects of reactive hydrocarbons and hydrogen peroxide on antioxidant activity in cherry leaves.

One-year-old cherry trees were fumigated with propene and gas-phase hydrogen peroxide, singly and in combination, in controlled-environment chambers for an 8-week period during the summer season. A UV light source was included with the combined propene and hydrogen peroxide regime to provide a source of hydroxyl radicals and ozone, and thus all the constituents of a photochemical smog. Measurements were made of soluble protein concentration and of glutathione reductase activity in leaf extracts from two or three leaf classes in plants from each treatment regime at the end of each fumigation period. Significant increases in soluble protein concentration with respect to the controls were found in plants fumigated with propene and hydrogen peroxide. The occurrence and extent of these differences depended on the leaf class and on the timing of the fumigation period over the summer with respect to bud break. The activity of glutathione reductase was found to be significantly increased in mature lower leaves of plants which had been fumigated with hydrogen peroxide. This effect was independent of the timing of fumigation with respect to bud break. Enzyme activity was also increased in propene and in propene plus hydrogen peroxide treatments, but only when plants were fumigated early in the growth season.

Circular polarisation in star-forming regions: possible implications for homochirality.

Our discovery of high degrees of circular polarisation in some star-forming regions provides an attractive mechanism for the origin of homochirality. The largest degrees of circular polarisation, so far observed at near-infrared wavelengths, are thought to arise from the scattering of stellar radiation from aligned dust grains and are calculated to extend down to UV wavelengths. The extent of the region where circularly polarised light (CPL) of a single handedness originates is very large, and it is likely that the whole of a planetary system would see a single handedness of CPL also. We present the observational data, models of the scattering that leads to the production of CPL, and a model for the origin of homochirality. We also discuss briefly future laboratory and space-based experiments.

Are the incremental lines in human cementum laid down annually?

A local Singaporean study of the presence of incremental lines in the cement of extracted teeth of 41 identity card-holding subjects is reported. The undecalcified roots of these teeth were sectioned transversely, some of which were stained with alizarin red. The lines observed were counted by one observer while blind to the actual ages of the subjects. A previous suggestion that these lines are deposited annually could not be supported in this sample, the number of lines tending to produce a lower estimated age than that registered on the identity card. The Pearson correlation coefficient for the line counts between two observers on 26 teeth was 0.73 (r2 = 0.535) which reflected difficulties in visualising the lines.

A review: neural control of mastication in humans as influenced by food texture.

This review summerizes recent approaches to the physiology of the masticatory system in humans that aim to understand how the process is influenced by the material properties of foods. The centerpiece is a group of experiments that show that the rate of breakdown of food in human mastification depends principally on the combination of two mechanical properties of foods: toughness(R) and modulus of elasticity (E). Two mechanical indices are constructed from these properties: the square root of their product, (ER)0.5, is predicted to explain the resistance to an incisal bite, while the square root of their ratio, (R/E)0.5 is predicted to control the rate of fragmentation during a postcanie bite. Evidence for the latter is reviewed, which also appears to modulate the activity of jaw closing muscles and the extent of lateral mandibular movement during mastication. These studies provide a quantified link between the food stimulus and the physiological response of the mastiatory system for which we know of no parallel. Attempts to extend this analysis have been made by psychophysical investigations of food texture. These support some sensitivity to the mechanical index that we have identified, but are not conclusive. Finally, we provide a chart summarizing physiological responses to food texture that could interest dentists, food scientists and also those interested in the analysis of dentition and diet in mammals.