Measurement of fine structures in roentgenograms II. Studies on canals in dentine models

Abstract

Abstract

This study deals with the objective experimental recording of the roentgenographic reproduction of narrow canals in dentine objects of various sizes, intended to simulate the root canals of teeth. A common dental film was used and the roentgen tube voltages were in the range usual in dental practice. A bone phantom was constructed to simulate clinical conditions. Densitometric measurements of canal breadth in the plane of the film with the apparatus and method used were higher than the true values. The error became greater as the thickness of the dentine object increased. Varying the voltage between 50, 60 and 90 kV had little effect on the results. Over- or underexposure of the films did not improve the accuracy of breadth measurement of the canals with the recording method used. The differences in densitometer reading between the canal and the dentine walls were expressed in metal equivalents with the aid of an aluminium penetrometer exposed and reproduced simultaneously with the object. This gave a measure of the difference in substance of the object. The same densitometer reading could also be used to measure the image contrast of the canal on the film. This was expressed in «optical density units» (ODU), making it possible to compare different tube voltages and degrees of blackening. The broadest canals in narrow objects were less well reproduced. The tube voltage had little effect on the results but in most cases, as expected, the highest tube voltage (90 kV) gave the poorest contrast. The average film density was important in determining the contrast between the image of the drilled canal and the dentine walls.