A cone cut is a clear (unexposed) area on the image, usually with a curved or straight edge, where the x-ray beam missed part of the receptor. The beam has a fixed size at the end of the PID. If the PID isn't centered over the receptor, part of the receptor gets no radiation and comes out blank.
Finding the cause
Nearly every cone cut comes from one of these:
- The PID wasn't centered on the aiming ring of the holder. Line it up, then bring it flush and parallel to the ring before you expose.
- The ring slid on the arm after you placed the holder. It moves when the patient bites or closes. Recheck it right before the exposure.
- The PID got tipped to chase the ring after it was seated. Tipping shifts the beam off one edge.
- Rectangular collimation leaves less margin than a round PID. It's better for the patient's dose, but it punishes sloppy alignment.
Reading the pattern
The side of the image that's cut tells you which way the beam was off. If it's always the same edge, that's your habit, not bad luck. Change that one variable, re-expose, and compare. Retakes are taken under the dentist's direction and within your state's rules.