If a piece of tooth root erosion is found to have fallen off, there are two reasons to consider: 1. Localized wedge-shaped defect. The formation of wedge-shaped defect is due to the violent lateral brushing method when brushing teeth, and the bristles of toothbrush are hard, and the tooth will have the loss of enamel at the place where the enamel is weak in the neck. 2, it is possible that local decay occurs. When the root surface of the tooth is exposed, it is easy to have food embedment, which will stimulate the tooth bone at the root for a long time and form caries easily. After the caries is formed, it can be treated by restoration and filling.