There are any number of things in life from which to protect oneself. I suppose one must do what one must if there are strong feelings about a particular danger; however in many cases there is a wide gap between possibility and probability of an incident. I'd expect traumatic tooth injuries to occur more often from participation in sports like basketball and soccer. They are non-contact in name only.
Keep in mind that use of personal protective equipment will present some risk. Full-face helmets are heavier and will stress neck muscles, face cages may catch on something when you slide during a fall resulting in serious trauma.
I'd definitely recommend enhanced protection during cycle jousting.