Horizontal Angulation: What is it? How do I find it?
First, find the teeth you are imaging. Place your finger along the marginal ridges of the contacts of interest, this is the horizontal angulation needed to ‘open’ those contacts (Figure 5). Stand in that path as you bring the sensor into the mouth. The operator identifies the correct horizontal angulation / radiation path before positioning the active area of the sensor correctly to ‘catch’ the teeth desired on the image. Remember, tooth position dictates sensor placement and PID placement!
FIRST: Find the horizontal angulation. SECOND: Place the sensor.
Your mind’s eye has to see the path of radiation you are creating (sensor and teeth within the path) to ‘catch’ the image (just like the baseball). It’s only by knowing the horizontal angulation that the operator can place the sensor in the mouth with confidence, knowing that the active sensor will be behind the required teeth and in the radiation path.
Figure 5 - Horizontal Angulation
(A) Finger is parallel with the marginal ridge between 20-21 and 21-22. (B) Aiming rod is parallel with the same marginal ridges. The aiming ring can be followed.
For bitewings, follow the marginal ridges of the maxillary teeth. The mandibular contacts usually open too. If the maxillary contacts open but the mandibular do not, the operator may need to expose another image while focusing on the lower contacts only. Depending on the position of the teeth in the jaw, all contacts may open in one image, or as seen in Figure 6C, the mesial and distal contacts of both first premolars are open, but the molar contacts are not. This indicates that the marginal ridges are not all parallel. In this case, premolar and molar contacts must be opened on separate images.
Figure 6 - Premolar Bitewing Horizontal
(A) Looking through the aiming ring at #12, which reflects the parallel finger in (B). (C) Active sensor in the correct horizontal path captured the distal canine crowns, and opened the contacts aroundthe first premolars.