Something in the tobacco - sounds like cheap quality tobacco - probably lit up and shocked him, causing him to crash and knock out his teeth. The "explosion" itself most assuredly did not have the force to knock out his teeth.

As far as "Greg's" statement goes - that is a very ignorant thing to say about people who choose to smoke. I personally do not smoke and do not like it, but I am not and nor do I think anyone is righteous enough to judge someone's quality of being based solely on whether or not they smoke. Also, wouldn't you feel so badass smoking a cigarette on a motorcycle?