Why does he grind his teeth, his sister does not seem to suffer from a similar problem?
Children react differently to certain situations. One theory as to the cause involves a psychological component. Stress due to a new environment, divorce, changes at school; etc. can influence a child to grind their teeth. Another theory relates to pressure in the inner ear at night. If there are pressure changes (like in an airplane during take-off and landing when people are chewing gum, etc. to equalize pressure) the child will grind by moving his jaw to relieve this pressure.
