Vertical Angulation: How do I know if I can follow the aiming ring?
Maxillary teeth require some amount of positive vertical angulation, while mandibular teeth require some amount of negative vertical angulation. Remember, the path of radiation must include the entire tooth and active sensor…or something will be ‘cut off’ the image. With the patient sitting straight in the chair and the midsagittal plane vertical, level the occlusal plane and identify the position of the roots in the jaw (the long axis of the teeth) as you look directly at the patient (Figure 4). Your goal should always be to position the sensor parallel to the long axis of the teeth. Let’s look at maxillary and mandibular teeth in detail.
Mandibular Posterior Periapical: Correct positioning is verified when the sensor is parallel with the long axis of the teeth, and when this is achieved, the aiming ring can be followed (Figure 11 shows purple parallel lines of the teeth and the PID). In Figure 12, the sensor is not paralleling the mandibular teeth, the sensor holder is out of position, and the PID’s vertical angulation is excessive, as evidenced by the foreshortened molar in the image.
Figure 11 - Madibular Molar Periapical: Ideal
(A) Sensor position, long axis of teeth, aiming ring, and PID are parallel. Aiming ring should be followed. (B) Ideal length of molar roots
Figure 12 - Madibular Molar Periapical: Foreshortened
(A) Sensor aiming ring, and PID are not paralleling the teeth. The vertical angulation is excessive, as evidenced by the foreshortened roots in (B)
It is better to follow the teeth when positioning the PID, even if the aiming ring and sensor are not paralleling the teeth (Figure 13).
Figure 13 - Madibular periapical:
For a non-foreshortened image, the PID should parallel the long axis of the roots (purple lines), even though the sensor and aiming ring are not.