In many instances, we have obtained the diagnostic information through the help of radiogrphs.
In evaluating radiographic emulsion, we tend to choose the films by only two factors which are sensitivity of emulsion and phtographic contrast.
Furthermore, many studies have been performed on the kilovoltage in dental radiography. The conclusions were essentially following two: 1. so-called “eye-pleasing” radiographs were obtained from lower kilovoltage radiography but radiation dose was higher. 2. higher kilovoltage radiography produced lower contrast radiographs but radiation dose was lower and had a greater range of interpretive detail.
Thus, the photographic emulsions and the kilovoltages of the tube are the factors which can not be overlooked.
This study was designed and performed as follows.
1) The radiation contrast (subject contrast) of the tube potentials from 45 to 110 kVp was estimated by photographic method on the several parts of anatomical landmarks in intraoral radiographs.
Five different kilovoltages were chosen, i.e. 45, 60, 75, 90 and 110 kVp.
2) The radiation contrast of each kilovoltage expressed by numerical value were applied to three H-D curves. The“L-value” introducing by the author which was drawned from the conception meaning a kind of allowance of the film properties was given. The “L-value” did not always mean latitude or gradient.
3) The “L-value” may be calculated from the following equation; L=log
10 D
3/D
0.3-log
10 B/Dc
D
3 is radiation dose producing a density 3 on a given film, and D0.3 is a dose making a density 0.3 on the same film.
B/Dc is radiation contrast value between the crown of the tooth (approximately enamel) and background area.
4) The “L-value” was calculated at each of the kilovoltages, and the optimal radiographical factors were selected theoretically.
5) To reduce the radiation dose in dental radiographic procedure, the relationship between the “L-value” and the other factors (photographic contrast and exposure dose to the emulsions) was discussed.
The author suggests to establish the criteria on the choice of the radiographic emulsions and the improvement of the dental x-ray apparatus in Japan.
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