grind his teeth

Teeth grinding is known as bruxism. The exact cause is not known, but tension, pain, anxiety, misalignment of teeth and pinworms are some purported causes. 38% of children have bruxism. There isn't any huge cause for concern, but it will be good to mention it at his next visit to the dentist. http://www.babycenter.com/0_teeth-grinding-bruxism_1524446.bc