Agree that a little info will help, but most likely you're not going to damage it. Vulcanite (hard rubber) stems are more prone to show bite marks than lucite ones. They're also usually smaller, thinner, & more subject to bite-through than lucite. Lucite ones are thicker & more comfortable if you're a "clencher." I've always preferred lucite because it's more comfortable generally, but if I like a pipe, I'll buy it, regardless of stem material.
If you're clenching too hard, your teeth & jaw will usually let you know. Some people just naturally hold their pipes tighter in their teeth than others.