The possible reasons for a 5-year-old baby to grind his teeth in bed are mainly the following: 1, children lack of calcium or vitamin D, children with severe calcium deficiency, such as children with rickets will have the phenomenon of night grinding. 2, the baby’s teeth are not clean before going to bed, there are food residues on the surface of the teeth and tongue, food residues stimulate the taste buds will cause the occurrence of baby night grinding. 3, children eat too much before going to bed, or eat indigestible 4, 5-year-old baby’s permanent teeth will gradually erupt in the mouth, with the continuous eruption of permanent teeth, so that the milk teeth will have individual teeth cusp early contact, the baby’s temporomandibular joint and chewing muscles are very sensitive to the contact of the cusp angle, will subconsciously carry out the enhancement of the parafunctional movement, resulting in the phenomenon of night grinding. 5. Babies suffer from dental diseases such as dental caries, pulpitis or periapical inflammation in the mouth, which leads to the phenomenon of night grinding due to the pain and discomfort of the teeth.