b. Horizontal angulation is the side-to-side movement of the tube head or x-ray
beam. Correct horizontal angulation for successful radiographs exists when the central
ray is perpendicular to the facial surfaces of the teeth and parallel to the mesial and
distal surfaces (see figure 4-7). If the horizontal angulation is incorrect, overlapping will
occur on the radiograph. Overlapping results when the proximal surfaces of adjacent
teeth are superimposed over one another (see figure 4-8). When this occurs, there will
be a light area where the two teeth are overlapped or superimposed. The resultant light
area is the inability of the x-ray beam to penetrate the two dense surfaces. Correct
horizontal and vertical angulation of the x-ray beam is necessary to obtain radiographs
of diagnostic quality.
Figure 4-7. Correct image resulting from proper horizontal projection of the central ray.
Figure 4-8. Overlapping images caused by incorrect horizontal projection of the central