I think my 4 year old DD chews for comfort and I'm not sure whether to get her a teether again. I bought her a new sports beaker today and the top is already misshapen from chewing, she also bites her nails and puts stuff in her mouth like toy animals etc. She generally does it when she's relaxing and does it more if she's feeling anxious. She used a particular teether for this until she lost it last year and at the time I didn't replace it as I thought she was getting to old for it but since she's just been using other items instead.
She gets anxious around change and a few other things but is getting better at expressing her feelings which I hope will help as she gets older.