One of our students lost a front tooth to an elbow strike, through a mouthguard. Luckily his brother is a cosmetic dentist and sorted it out post-haste.
It's my understanding that a mouthguard is to prevent damage to the teeth, tongue and brain caused by the jaw snapping closed when hit from below, e.g. with an uppercut.
Versus a frontal or side impact the positive effects of a mouthguard besides stopping the inside of the lips and cheeks getting cut are minimal. When struck with a sufficiently small surface area, those pearlies are still coming out.
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