Bruxism is a chronic clenching of the jaws and grinding of the teeth that affects many children. Children under 5 have the highest rates of bruxism, which is particularly likely to involve the back teeth. In addition, many children who clench their teeth also grind them in a sideways, back-and-forth movement. Both clenching and grinding put pressure on the muscles, tissues and other structures surrounding the jaw. This may lead to jaw and ear pain, wearing down of the tooth enamel and other symptoms.

Bruxism tends to occur most often during deep sleep, particularly in the early part of the night. Many children are not aware that they clench or grind their teeth overnight. Bruxing may also occur during waking moments when a child feels particularly stressed or anxious. Girls and boys experience bruxism equally, although girls may be more likely to clench their teeth.

For reasons that are not completely understood, children tend to grind their teeth with less frequency as they get older. Most children stop grinding and clenching their teeth by age 10, after their permanent teeth erupt. Permanent teeth are more sensitive to pain than baby teeth, and this may discourage bruxing. However, other children continue to grind their teeth into adolescence and/or adulthood.

The exact cause of bruxism remains unknown, but it appears to occur more often in children whose top and bottom teeth are not aligned properly (malocclusion). Stress and suppressed frustration are suspected as major contributors to bruxism. Children may tend to grind their teeth more often before a big test or before a stressful event, such as an impending move to a new city. Friction with family or friends and general feelings of anxiety also can trigger bruxing. 

Some children may grind or clench their teeth in response to pain, such as the discomfort that accompanies earaches. Experts believe such clenching may be soothing to children in discomfort.

Children who have been diagnosed as hyperactive may be at increased risk for bruxism. It also is more common in children with medical conditions such as cerebral palsy and severe mental retardation. Use of antidepressants has been associated with some rare cases of bruxism.