This is second of a two-part series on the history and effectiveness of mouthguards (MGs) for protection from orofacial injuries. MGs are hypothesized to reduce orofacial injuries by separating the upper and lower dentation, preventing tooth fractures, redistributing and absorbing the force of direct blows to the mouth, and separating teeth from soft tissue which helps prevent lacerations and bruises. The single study on MG use in military training found that when boil-and-bite MGs were required for four training activities, orofacial injury rates were reduced 56% compared with when MGs were required for just one training activity. A recent systematic review on the effectiveness of MGs for prevention of orofacial injuries included 23 studies involving MG users and nonusers and a wide variety of sports. For cohort studies that directly collected injury data, the risk of an orofacial injury was 2.33 times higher among MG nonusers (95% confidence interval, 1.59-3.44). More well-designed studies are needed on the effectiveness of MGs during military training. Despite some methodological limitations, the current data suggest that MGs can substantially reduce the risk of orofacial injuries in sport activities. MGs should be used in activities where there is a significant risk of orofacial injuries.