I am not usually a clencher. I have an Italian no-name bent that I like to smoke at work that has an acrylic stem. Someone had left a football in the warehouse and a coworker and I started tossing it around. I was foolish enough to keep smoking my pipe while we were passing. I used to run with scissors a lot when I was a kid so I didn't think too much about it. After 20 minutes I think every muscle in my face was aching from clenching so hard, but there wasn't one tooth mark on the stem. I was very surprised.