One common coping approach for compulsive chewing which is indeed associated with ADHD (and co-morbid anxiety that's pretty common with it) is "here, wear this

One common coping approach for compulsive chewing which is indeed associated with ADHD (and co-morbid anxiety that's pretty common with it) is "here, wear this plastic thingy on a necklace and chew on it instead of other stuff".