The root of the tooth is not protected by enamel and is very close to the dental nerve, so it is easy to appear sensitive to cold, hot, sour and sweet, causing sour teeth when eating. 4, cervical wedge defect, wedge defect is caused by improper brushing, such as lateral brushing, excessive brushing force, wedge defect occurs in the neck of the tooth causing cervical defect, thus causing the symptoms of tooth sensitivity.