Children clench their teeth, usually due to dental discomfort, such as having diseases such as caries of milk teeth, pulpitis and periapical inflammation, and the tooth swelling and itching discomfort cause children to clench their teeth subconsciously. If children clench their teeth at night, it means the symptom of night molar appears, which often needs timely intervention and treatment. 1.Caries of milk teeth: children’s milk teeth caries develop faster and the cavity is bigger in the short term, which can stimulate the tooth pulp and cause pain, and the pain can cause children to clench their teeth. Once parents find that children have milk tooth caries, they need to bring children to treatment as soon as possible, grind out the decayed part, and give filling treatment. Parents can also assist in cleaning the teeth to prevent the occurrence of dental caries if the child is young; 2.Pulpitis and periapical inflammation of milk teeth: children’s dental caries can easily develop into pulpitis and periapical inflammation, but the pain of pulpitis and periapical inflammation of children is usually not as obvious as that of adults, which can only be manifested as itching, swelling and discomfort of teeth, leading children to bite their teeth subconsciously to relieve the symptoms. This causes children to subconsciously clench their teeth to relieve the symptoms. In this case, parents should take children for root canal treatment to remove the infected pulp and give the root canal repeatedly and adequately flushed; 3, night grinding: children clench their teeth during sleep, also known as night grinding, usually because children are too tense and excited before bedtime, the brain nerve will also be localized discharge during sleep caused by night grinding, so children need a quiet and soothing environment before bedtime. In addition, if the child’s milk teeth or mixed teeth exist in the occlusal high point, the individual tooth tip is relatively high, in the sleep process can also subconsciously grinding teeth, the occlusal high point grinding off, belongs to the temporary phenomenon, until the child permanent teeth all grow out, the tooth tip to achieve a uniform and stable occlusal contact, this phenomenon of night grinding can disappear.