way back in the day deer species used to have tusks, large fang looking teeth, that they used for fighting and defense. this was way back when before they had antlers. whether today's deer evolved from those deer, or those deer were a separate species all together could be debated. in any case, it is likely still in a deer's genetic profile to sprout some fang-like teeth. it would be extremely rare to actually happen, but possible. it also could have been just from some freak mutation. anyway, I havent specifically heard of it happening or seen it before, but from my knowledge of the history of deer, that's my two cents on it. for sure, post a pic if you can, that's pretty cool.