DescriptionAdvances in mouthguard design applied the dental technique of jaw-repositioning to not only prevent negative effects but to enhance athletic performance. Improved posture and proprioception have been observed with use of jaw-repositioning appliances (1-4). In a previous study, a jaw-repositioning mouthguard improved muscular power in athletes (5). We compared a neuromuscular dentistry-designed jaw-repositioning mouthguard to a standard mouthguard in a randomized, crossover study evaluating muscular endurance and anaerobic capacity in male athletes. The advanced jaw-repositioning mouthguard led to improved muscular power performance (6). Although effective, the neuromuscular dentistry-designed mouthguard was highly expensive causing it to be impractical for the typical athlete. The next two studies utilized affordable versions of the above mouthguard to expand the practical application of the findings. We evaluated the effects of two jaw-repositioning mouthguards on other aspects of physical performance including balance, flexibility, agility, power and strength in male athletes. A battery of exercise tests was completed in a randomized, controlled, crossover study. No significant differences between the jaw-repositioning mouthguards, the placebo mouthguard, and the no-mouthguard control were observed in these aspects of physical performance. Our final study evaluated the effects of two jaw-repositioning mouthguards on aerobic performance. Jaw-repositioning devices treat sleep apnea by increasing the size of upper respiratory airways (7-11). Jaw-repositioning mouthguards may have similar effects on the airways in athletes lending to improved aerobic performance. The effects of two jaw-repositioning mouthguards on aerobic dynamics at rest and during a graded treadmill test in male athletes were evaluated. No significant differences between the jaw-repositioning mouthguards and the controls were observed in respiratory functional tests, ventilation, gas exchange, or maximal aerobic performance. These results indicate that the affordable jaw-repositioning mouthguards did not have any effect, positive or negative, on various performance aspects. This information can be used to encourage mouthguard compliance and dissuade the concerns of performance impediments. Incorporation of advanced dental techniques and individualized design may be necessary to obtain an “optimal jaw position” that promotes positive physical responses. Future research on jaw-repositioning mouthguards should use advanced dental techniques and explore effects on other aspects of physical performance.