One of my front teeth is an implant (titanium screwed into the jawbone with a crown on top), and I'm always a bit nervous of being hit there as a solid impact would be quite nasty (titanium is harder than jawbones!). I have a gumshield made by my dentist, which is quite good, but would welcome opinions on anything better.
You could get a plexiglass faceshield, I believe they run about 40-50 bucks. You could also try and get a fencing mask or kendo mask (they might cost more). I've never worn a kendo mask, but I do have experience with faceshields and fencing masks.... I don't like them personally, as they screw with your vision and your breathing. But hey, it beats a nasty injury.
The mouthguard made by your dentist is probably the best one to go with. I recently had mine made by my dentist, and it is the best one I've had so far. As for a Face mask, I have a wire one that I used for eskrima practice when we'd spar. But like the claw mentioned, it does tend to mess with your vision, especially your peripherals.
