Weakness of biting on one side of eating may be caused by periodontitis, apical periodontitis and other diseases, as follows. 1. Periodontitis: Periodontitis can cause resorption of alveolar bone and loss of attachment of periodontal tissues, which leads to loosening of teeth and weakness in the exercise of chewing function. It can be accompanied by red, swollen, bleeding and pus-filled gums. 2. Apical periodontitis: the inflammation is located in the periapical tissues, the affected teeth may have occlusal pain symptoms, the patient dares not bite in order to avoid the pain, resulting in the phenomenon of weak bite. The affected tooth may have a history of pulpitis or endodontic treatment. There may be other reasons for a weak bite on one side of the mouth, so it is recommended to go to the hospital in a timely manner to clarify the cause of the problem and then carry out targeted treatment.