ABSTRACT
Generally, sport players of boxing or football who contact roughly with other players use mouth guard during match or game to prevent the breaking of jow boneor bursting of soft oral cavity. Moreover, mouth-guard are used for the purpose to lighter the load to root of teeth and to improve the skill and power of sport's player.<BR>The purpose of this study was to examine the charactaristic of unfitted by H shape-mouth guard compared to U shape mouth guard.<BR>The following results were obtained.<BR>1. The H shape-mouth guard of this study could reduce the impact to 1/7 level.<BR>2. A relative decrease in ventilation level was shown when H shape mouth guard fitted.<BR>3. With reference to respiratory function, reduction of the amount of oxygen up-take was not observed at heart rate lower than 170 beats/min, and in this case a player feells subjective symptom of stiffing.