Tooth can not bite hard things have the following possibilities: First, filling material off, if the tooth has been done filling treatment, in the case of loosening of the filling material is easy to appear pain when biting, and checking the mouth found that the filling material has shifted, this situation needs to be re-filling of the tooth, if there has been a leakage of the nerve needs to be done root canal treatment. Second, the teeth can not bite hard things may be due to the teeth have hidden cracks, if the teeth have cracks, in biting hard things or bite tough things especially prone to pain, so when eating must pay attention to avoid eating too hard food or choose to do ceramic braces repair. Third, the tooth can not bite hard things may be due to the root tip of the tooth has inflammation, so in the bite is easy to press the root tip of the alveolar bone lesions, easy to appear pain, so this time you need to do the root canal treatment of the tooth. Fourth, cysts or granulomas in the apical part of the tooth, this situation requires surgical excision treatment.