What factor primarily contributes to air shadow on an OPG?

The presence of an air shadow on an Orthopantomogram (OPG) is primarily due to the lack of proper tongue positioning during the imaging process. When the patient does not place their tongue against the roof of their mouth, a space is created that allows air to be present in the oral cavity. This air does not absorb the X-rays in the same way that bone and soft tissues do; as a result, the area where the air is located appears as a dark shadow on the radiograph. Proper tongue positioning is crucial for obtaining clear images and reducing artifacts caused by air shadows. By ensuring that the patient keeps their tongue in the correct position, the radiographer can improve image quality and accurately represent the anatomical structures of interest.