Teeth have no strength to chew things may be hidden cracks, tooth decay or periodontal disease, specific need to go to the hospital to confirm the diagnosis. 1. Cracked teeth. When hit by external forces or bite too hard food, teeth may appear cracks, cracks up to the dentin may appear symptoms of tooth sensitivity, appear up and down the bite or eat acidic food to produce pain and discomfort. 2. Dental caries. When tooth decay occurs, caries is about to penetrate the pulp cavity or has penetrated the pulp cavity, there may be symptoms of pulpitis, up and down bite, due to food mechanical or chemical stimulation caused by tooth pain or discomfort. 3. Periodontal disease. Periodontal disease can occur attachment loss, alveolar bone resorption, will lead to loose teeth, chewing food due to loose teeth, will appear chewing weakness phenomenon. Teeth have no strength to chew things specifically need to go to the hospital to check the oral cavity, if necessary, combined with CT examination to diagnose the cause of the disease.