Vertical Angulation: Why are the mandibular anterior teeth always foreshortened on periapical images?
Mandibular Anterior Periapical: For an ideal image, place the sensor parallel with the long axis of the teeth, best identified by looking at the patient from the side (Figure 14A). The sensor holder’s bitepiece can position against the teeth with varying amounts of vertical angulation. This often happens when the positioning is painful and the patient’s tongue pushes the sensor out of the mouth over the teeth. The aiming ring is then pointing towards the floor, and if followed by the PID, will create a severely foreshortened image, with the incisal edges often projected off the edge of the image, because there was no active sensor behind them (Figure 14C).
First, level the occlusal plane. Re-examine the anatomy, looking for mandibular tori or a shelf of bone. Move the sensor posteriorly to find more room in the mouth and avoid those sensitive tissues. If the sensor can parallel the long axis of the teeth, the aiming ring can be followed to create an ideal image (Figure 14A). Check this position by looking at the teeth and aiming ring from the side, as in Figure 14. If ideal positioning is not possible, place the PID over the teeth with the suggested vertical angulation for the area. The PID should not follow the ring (as in Figure 13).
Figure 14 - Mandibular anterior periapical setups and resultant images.
The effects of different positions of the sensor holder can be drastic. (A) is ideal, (B) is slightly less than ideal, but still diagnostic, (C) is Non-Diagnostic as the crowns are off the image and the teeth are foreshortened.