[Eccentric projection for the observation of the root canals of the upper premolars].

Information on the length and the shape of the root canals is necessary in dental care. They are obtained from X-ray examination of teeth. However, it is useful to apply eccentric projection for optimization in dental radiography. We observed 135 teeth and 355 films of extracted upper premolars, and tried to establish the standard of eccentric projection for the observation of root canals of the upper premolars, on the basis of the calculations and the experiments. 1. Shapes of root canals in the upper premolars are classified into 3 types with 3 subtypes. The rate of teeth with one root was 69.6%, but the rate of teeth with two root canals was 43%. These indicate the necessity of the eccentric projection in dental radiography, although there is a limit to the ability of X-ray film for confirmation of real condition of the root canals. 2. Optimal eccentric projection angle was 20 degrees-25 degrees. There is no significant difference between the paralleling technique and bisecting technique. There is no significant difference between the mesial and distal eccentric projection. But, the mesial eccentric projection is more effective for the observation of whole root and the ease of radiographic technique than the distal eccentric projection.