It has been reported that, during a single athletic season, there is a one in ten chance of suffering a facial or dental injury, and the lifetime risk of such an injury is estimated to be 45%. It is also estimated that an athlete is sixty times more likely to sustain a dental injury while not wearing a mouthguard. Thus, there is an expectation that mouthguards can help prevent these types of injuries. The positive effects of wearing a mouthguard are indicated in various epidemiological surveys and experiments. Most of these studies revealed that mouthguards have, to some degree, an injury-preventing effect. This book indicates that there is a necessity for improving the impact absorption ability of mouthguards by considering how to achieve a full-balanced occlusion, improving design and developing new materials.