When I taught first grade I had a chewer every year. In 2nd I still saw it, often it was their hair they chewed. I hadn't thought about it until reading your post, but I don't have any chewers in 3rd this year. Maybe moving up in grade levels is the answer?
I know some of the teachers in my building use other things for the child to chew on such as gum or those straw necklaces. The necklaces grossed me out just as much as the shirt chewing. Actually more. At least the clothes get washed regularly. No on washes those necklaces.
I simply handled it by reminding the child that clothes are not food and we only put food in our mouths at school. So each time I saw a child chewing I would say, "Is that food?" and the child would stop chewing, at least for a while.