Tooth acidity is due to the sour and swollen feeling of teeth after eating sweet and sour food, which belongs to dentin hypersensitivity, mostly caused by periodontitis, dental caries, wedge-shaped defects, etc., as follows: First, periodontitis: patients with periodontitis will have different degrees of gum recession and root exposure, which will lead to dentin hypersensitivity. When eating sweet and acidic food, hot and cold alternating food, teeth have sour and even sore feeling. Second, dental caries: dental caries will lead to the exposure of dentin tubules and cause the symptoms of tooth acidity. Thirdly, wedge-shaped defect: wedge-shaped defect in the neck of teeth is also a main cause of tooth soreness. The wedge-shaped defect in the neck of teeth is caused by incorrect brushing method and excessive brushing force, which leads to the appearance of deep and shallow grooves in the neck of teeth, causing the exposure of dentin tubules, resulting in tooth soreness.