Pain when eating hard things in the back teeth may be caused by periodontal disease, apical periodontitis, etc. Periodontal disease does not need root canal treatment, and apical periodontitis needs root canal treatment. 1. Periodontal disease: teeth in the advanced stage of periodontal disease appear loose or even periodontal abscess, and there will be pain when eating hard things. In this case, the teeth are firstly treated with supragingival scaling and subgingival scraping, and then root planing, and periodontal surgery is chosen according to the looseness of the teeth, and regular oral maintenance is done, and the symptoms of periodontal disease will be significantly improved. 2. Periapical periodontitis: when the tooth has periapical periodontitis, there will be biting pain when eating hard things, the best treatment is to carry out root canal treatment on the tooth, after root canal treatment, the inflammation of the root tip of the tooth will be significantly relieved, and the tooth will gradually disappear from the pain of eating hard things. The best way to treat the pain when eating hard things is to go to the hospital in time and get a clear picture of the cause of the pain, so as not to delay the condition.