For dentistry, apical shadow refers to the low-density shadow at the root tip of the tooth in dental films or curved tomograms, which is commonly seen in apical diseases of teeth, and there are three types as follows: 1. periapical granuloma; 2. periapical abscess; 3. periapical cyst. Periapical granulomas are substantial and are more clearly delineated on dental films, whereas periapical abscesses are not well delineated. Because periapical cysts have a layer of cyst wall, a white line can be seen around the apical area, and all 3 are manifestations of apical hypodense shadows. By doing systematic root canal treatment, most of them can get better, and if the periapical cyst is large, sometimes further surgery is needed.