Technical factors in fractal analysis of periapical radiographs.

OBJECTIVES: Fractal analysis quantifies complex geometric structures by generating a fractal dimension, which can measure trabecular bone density. The use of non-standardized radiographic techniques potentially limits the reliability of fractal analysis. The objective of this study was to determine how variations in radiographic technique affect fractal dimension. METHODS: Periapical radiographs of maxillary incisors taken on eight dry human skulls at varying angulation, tube potential and impulse settings were subjected to Fourier transform fractal analysis. RESULTS: A significant (p < 0.05) difference in fractal dimension, ranging from 2.5 to 2.9, was found between the skulls, potentially reflecting variations in bone trabeculation. However, variations in angulation, tube potential or impulse did not have a statistically significant effect (p > 0.05) on fractal dimension, with the standard deviation of the fractal dimension ranging from +/- 0.005 to +/- 0.062 at various radiographic machine settings. CONCLUSIONS: This study indicates that non-standardized periapical radiographs may provide a reliable method for determining fractal dimensions, which could be useful in analysing changes in alveolar bone density in various bone disorders.

Management factors and grass tetany in dairy cattle.

The relationship between intensity of production and the occurrence of hypomagnesaemia and grass tetany in dairy cattle was investigated from 1966-1970 at the Ellinbank Dairy Research Station, Warragul, Victoria. Hypomagnesaemia and/or grass tetany occurred in cows grazing at both high (3.2 cows/hectare) and low (2.2 cows/hectare) stocking rates over the four-year period. Pasture Mg concentrations remained relatively high (0.2% dry matter) throughout this period, except in the low stocking rate pastures in one year, 1967. It is concluded that hypomagnesaemia and grass tetany was precipitated by a combination of low dry matter intake in winter and the effects of a gradual increase of K concentration in autumn and winter pastures, following the heavy application of K fertilizer. Under these conditions, MgO supplementation was inadequate to prevent grass tetany occurring in some animals.

Handling information in general practice--using feature cards with computers.

A two-tier system of handling information has been developed for use in general practice. Punched feature cards, with the conventional patients' record cards are used for the handling of primary data in the doctor's surgery. At the same time the feature cards provide an input to the computer using a feature card reader, converter, and paper-tape punch. This is especially useful where information has to be collected together centrally, for more advanced statistical analysis and where multiple searches of individual feature cards are required.