Sharc's correct, I spit out a few teeth in Pro Source's indoor track one winter. Losing my teeth in MX during the winter when I'm a hockey player seemed backwards.......... so I decided to leave MX for the summers and Hockey for the winters to keep things in perspective from then on. Everyone assumes I lost my front teeth from playing hockey, but MX did them in! Plus my large bore 4 strokes aren't really made for the tight confines of indoor riding.... I'm better off recharging my MX passion in the winter by taking the season off.
Ray's is where I'll do my winter riding on a bicycle now, but the possibility of losing teeth in there is still high with a face plant into the cement.