Biomedical subjects
Publications and source records attributed to S Molnar.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
The dental casts made from Aboriginal children during the course of a longitudinal growth study in Central Australia provided material for analyzing tooth wear under known environmental conditions. The wear facets produced on the occlusal surfaces were clearly preserved on the dental stone casts and recorded the progress of enamel attrition from ages 6 to 18. These casts were photographed and traced by electronic planimetric methods that automatically recorded the location and size of wear facets on the first and second permanent molars. These areas of worn tooth surface were compared to the total tooth surface. The worn surface was regressed on age to calculate wear rates of each tooth. Discriminant analyses were also performed to determine the significance of dental attrition differences between the sexes at each age group. The total wear on each tooth was highly correlated with age as expected but females wore their teeth at a significantly higher rate than males. The mandibular molars wore more rapidly than maxillary teeth in both sexes. The discriminant analysis successfully grouped 91% of the cases according to age and sex. Pattern of wear, the location, and size of wear facets also differed between age groups and sex. The questions of why there is a difference between male and female wear or why there is greater wear on one arch or arch region have no ready answers. The differing rates and pattern of dental wear do suggest that arch shape and growth rates may be the answer though it has yet to be tested. However, the occlusal surface wear is useful for age estimation in a population and provides a record of shifting masticatory forces during growth.
Most reports of Aboriginal tooth wear have been descriptive, and few have dealt with the question of wear rate. This study records cusp heights of dental casts taken from individuals during a growth study of Aboriginal children from ages six to 18. Their rates of wear were greater than those of Europeans, and the most rapid rate was recorded among Aboriginal males. These differences are due to the quantity of dietary abrasives.
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.
Five healthy males volunteered to exercise for 20 min on a motor-driven treadmill at five submaximal intensities (30, 45, 60, 75, and 90% of VO2 max). Peripheral venous blood samples were drawn from an indwelling catheter prior to and at 9, 14, and 19 min of each exercise bout. Blood samples were assayed for whole-blood hemoglobin, total plasma protein concentrations, and hematocrit, with plasma water concentration calculated from these values. The plasma concentration of the electrolytes sodium (Na+), potassium (K+), total calcium (Catot), ionized calcium (Ca2+), chloride (Cl-), and inorganic phosphorus (Pi) were also determined. With plasma and blood volumes the total plasma contents of each of the measured constituents and the concentration of each electrolyte per liter of water were calculated. Statistically significant linear increases in plasma concentrations of Na+, K+, and Cl- relative to exercise intensity were observed, with linear decreases in plasma contents of Na+ and Cl- and linear increases in K+ content. Plasma Pi concentration decreased with a Pi increased content, with plasma Catot concentration elevated at the highest two work loads. Plasma Catot content increased linearly with exercise intensity and duration. Plasma water concentration and content decreased with exercise intensity, resulting in no change in electrolyte concentration per liter of water except at the highest two exercise intensities. These data suggest that extrapolation from plasma electrolyte concentration to muscle concentration and/or content is not supported. Changes in plasma volume and plasma water must be considered when postulating a role for electrolytes in the physiological responses of the human to exercise.
Explore the source record for details and available documents.
The incremental lines of von Ebner frequently have been described as ultradian markers of dentin calcification. To determine the relationship between these lines and the quantity of dentin formed, reference was made to an in vivo marker of calcification, tetracycline. These markers were produced by injecting four juvenile monkeys periodically over a period of 175 days. These animals had been subjects in the heat stress study and were exposed to a series of heat stresses and cortisone injections. At the end of the study, undecalcified thin sections of premolars and second molars were prepared by standard histological techniques. We found that linear apposition rates increased in a gradient toward the pulp chamber. These rates varied within each tooth but not in corresponding parts of different teeth. Also, we determined that dentin apposition can be temporarily depressed by certain metabolic stresses. Heat load and cortisone significantly slowed dentin formation. Each depression, however, was followed by a "catch-up" period. Incremental line distances also increased as a function of the distance from the dentoenamel junction. There was, however, no systematic relationship between apposition rates and incremental line distance; these distances did not deviate from the observed trends during periods of slowed apposition. Incremental lines may by interpreted, not as natural growth markers, but as structural phenomena which are a function of dentin geometry and tubule bending.
In a balance trial with growing rats the influence of dietary ribonucleic acid (RNA) on N-metabolism was tested. Yeast-RNA was supplied at four levels ranging from 7.8% to 31.2% of diets nitrogen (1.64% in DM from casein + DL-methionine). The mean apparent digestibility of the RNA-N ingested was determined as 95%. Of the RNA-N consumed 16.6% were retained as measured by N-balance technique, whereas no retention of the RNA-N was observed by body-N analysis. This discrepancy in RNA-N retention was attributed to the relatively increased N-losses with higher N-intake when using the N-balance method. By regression analysis it was found that 80.2% of the RNA-N consumed were excreted via kidneys. Of the RNA-N intake 45.5% appeared in urea, 30.9% in allantion, only 1.1% and 0.3% in uric acid and creatinine respectively.
In a feeding trial with growing rats the influence of dietary ribonucleic acid on the composition of body gain was investigated. To a control ration with casein + 50% DL-methionine as the sole protein source (1,64 N% in DM) ribonucleic acid (RNA) from yeast was supplemented at four levels ranging from 7,8% to 31,2% of diets nitrogen. The portion of daily feed and nitrogen intake derived from the basal diet was designed to be equal for all the animals. RNA was ingested in addition. Gain of body fresh and dry matter slightly increased with the dietary RNA-level, due to an increased deposition of body fat. Protein efficiency ratio as well as productive protein value decreased linearly with increasing N-intake. It may be concluded that RNA-N has slightly contributed to body mass gain but was not utilised for protein deposition.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Reconstructing the biomechanics of early hominid mastication is a key element in most models of hominid differentiation. Traditionally, osteological features marking muscle attachment surfaces have served as a reference system from which the vector geometry of the masticatory force system and resultant force distributions could be predicted. To augment traditional morphological and computational approaches, we developed a simulation system capable of replicating human and non-human primate chewing motions. The forces of occlusion are recorded as photoelastic fringes in a urethane alveolar process. Simulation experiments evaluating the functional correlates of topographic diversity in zygomatic root position and mandibular ramus height in early hominids indicated that the mandibles and dentitions of robust australopithecines are well adapted to sustain high magnitude, low gradient load distributions.
Explore the source record for details and available documents.
Since we have found that conventional methods of dentin apposition measurements are inaccurate, we have devised a three dimensional model. This model allows the investigator to measure dentin apposition volumetrically, and simultaneously consider odontoblast activity and the geometric relationships which influence the configuration of the dentin.