Abstract
It is generally agreed that the radiogram plays a very important role in the diagnosis, treatment and postoperative observations of the periodontal diseases. It is often clinically experienced, however, that the radiographic image does not exactly portray the alveolar bone as it should. That is to say, part of the alveolar bone exists when the radiogram fails to reveal it. Wakamatsu of our Deprtment experimentally proved this phenomenon to be due to the fact that, when Ca content in the alveolar region becomes reduced by about 50%, that portion will appear on the radiogram as if non-existent. On the other hand, acording to Ando it is established that, even if there should take place pathohistologic degenerations in initial change, these will not be radiographically revealed until they have reached the dental root by 1/5.
In the present study, the author conducted a series of experiments for the purpose of determining at what period of time passage changes can be radiographically interpreted in Iinea alba, the outermost portion of the alveolar bone.
For study purposes, the alveolar bone portions of human mandibles were artificially decalcified by the use of hydrochloric acid and changes in Ca were periodically measured and, at the same time, their radiograms were taken. Further, a group of dentists, 30 in number, was asked to interpret the period of disappearance of Iinea alba by using these radiograms. Although half the dentists agreed in their interpretations, opinions were divided in the remaining half, thus attesting to the difficulty of correct radiographic interpretations. In addition, the densities of these radiographic images were analyzed by a microphtometer. As a result of these expriments, the author arrived at the following conclusions.
1. As regards the relationehip between the rate of decalcification and linea alba, when the decalcification by 63.8% took place in the anterior teeth, the radiogram became black beyond the usual visuality necessary for a radiographic interpretation. When the rate of decalcification reached 69.3%, it was impossible to interpret the content of a radiogram.
2. In the molar region, on the other hand, the decalcification by 74.6%, the radiogram became black enough unsuitable for an interpretation, when the decalcification exceeded 86.6%, it was quite impossible to interpret the content of a radiogram.
3. As regards the densities, there were not observed appreciable changes in the anterior teeth till the decalcification was beyond 23% and, in the case of molars, till it was beyond 40%.
4. The above findings are assumed to mean that, even if there should take place the decalcification to a certain degree, it will not be radiographically revealed until it has attained to a given extent or percentage.
