Dyanne,
I had exactly the same problem you describe and was VERY worried about it. It finally resolved itself---and I didn't need braces. Here's most of what I wrote, on this forum, December 19, 2005:
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I bit my lip while eating a sandwich a week ago. Since then, i've been biting it, accidently, almost always while chewing, almost everyday, if not every day. I've had successive involuntary lip biting episodes in the past, but none that seemed to last quite this long.
I've been trying to chew much more slowly and carefully, but I can almost never manage to go without chomping down on it during a meal once or twice. It's usually sort of a sudden, spasmodic bite, while i'm trying to move food around in my mouth, usually after taking too big a bite, which I have a habit of doing. This worries me. I've heard cheek biting might cause cancer. Can lip biting too?
I have moderate to advanced periodontitis, and I suspect a bite problem (malocclusion?) so I fear this may be the cause. I've been slightly, now and then, snagging the inside lip with my front teeth, but could this be due to swelling from the intermittent biting?
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James/Idiopathic12