[Deviations of the central ray in standardized bite-wing radiographs]

Interpretation of serial radiographs without sufficient information of projection geometry is hardly possible. We obtained 51 pairs of bite-wing radiographs in 12 patients by use of a modified filmholder (Duckworth et al. 1983). Two orthodontic wires of different profile, placed coaxially on the perpendicular, cast shadows on the film, which were differentiated by their respective shape. By placing each wire a known distance from the film plane, the angular difference between the perpendicular to the film and the actual direction of the central ray could be calculated. In 63% of pairs the angular deviation of the central rays between the serial exposures was below 0.9 degrees. The results of the present study show that utilization of this type of device can provide radiographs of sufficient quality to allow their use in image subtraction.