Secondary caries refers to the cavity that occurred after the filling of a tooth that once suffered from worm tooth. There are more methods to judge the secondary caries clinically, as follows: 1.Whether there is experience of filling or not, and the teeth start to appear hot and cold stimulation, sensitivity and blockage for a period of time after filling, or the teeth around the original filled teeth become black again, all may be the symptoms of secondary caries; 2.Select the professional dentistry consultation, and the dentist will apply the examination instrument, such as probe to detect whether there is obvious gap around the repair material or If there is obvious texture change of the tooth, if the probe can be stuck or there is obvious gap, secondary caries may also occur; 3, imaging examination can be applied to assist diagnosis, by taking local dental film, observe whether there is obvious low density image around the original restoration material, if it is confirmed that there is low density image, secondary caries may also occur.