###### Abstract  
The aim of this study was to clarify the effect on the postural control function of equalizing the occlusal contact state by wearing a mouthguard. Method: Participants included 23 untrained adults, 11 gymnasts, and 10 weightlifters. Custom mouthguards were fabricated and adjusted so that all teeth were in even contact with light clenching. The standing postural control function was evaluated by the displacement of the center of foot pressure (COP) measured using a gravity center fluctuation meter. Measurement conditions were with and without a mouthguard. Statistical analyses were performed on the differences in COP displacement among participant groups and between mouthguard conditions and the difference in the reduction rate of COP displacement when wearing a mouthguard among participant groups. Results: COP significantly decreased in the order of untrained adults to weightlifters to gymnasts, irrespective of the mouthguard condition. The reduction rate in COP displacement after wearing a mouthguard was greatest in gymnasts. Conclusions: The effect of the mouthguard on postural control function was more pronounced in gymnasts than in untrained adults and weightlifters, and this study suggests that equalization of the occlusal state by wearing a mouthguard contributes to improving postural control function.  
occlusal contact state; postural control function; gravity center fluctuation; center of foot pressure; mouthguard +
Footnote †: journal:  
Occlusion is the state of contact between the teeth of the maxilla (upper jaw) and mandible (lower jaw) [15]. The maxilla is part of the lower skull, whereas the mandible is attached to the skull via the temporomandibular joint and suspended by several muscles in the head and neck. The contraction and relaxation of these muscles cause the mandible to move, with the temporomandibular joint acting as a fulcrum. Therefore, the teeth, muscles, temporomandibular joints, and the central nervous system are all involved in occlusion, and a problem with any one of these can affect occlusion.  
Because occlusion is involved in somatosensory input from the stomatognathic region and in vestibular input, many studies have been conducted on its relationship with postural control [4; 5; 6]. It has been shown experimentally that imparting occlusal interference increases COG sway [5] and that equalization of occlusal contact by use of an intraoral appliance suppresses COP displacement [6]. In addition, in the postural control of athletes, the weighting of sensory inputs has been reported to differ according to the characteristics and level of the sport, with the differences evident only under conditions that match the training environment [11]. It is expected that such information about postural control will be applicable to training and rehabilitation [11; 16; 17; 18; 19].  
The aim of this study was to clarify the effect on the postural control function of equalizing the occlusal contact state by wearing a mouthguard. Therefore, the difference in COP displacement among athletes and non-athletes was examined with and without a mouthguard. The null hypothesis was that COP displacement would not be affected by wearing a mouthguard, regardless of whether the wearer is an athlete or non-athlete.