In contact sports especially, accidents often lead to serious injuries to the spinal cord and cervical spine injuries.In this paper, attention was paid to the neck and surrounding muscles, because these are the major areas concerned in the prevention of trauma and injuries due to contact sports, and are vital for the resumption of sports. Several types of resin splint of the upper jaw, having different occlusion supportive areas, were used in this study to investigate what happens when the stomatognathic conditions are altered. The effects on cervical back strength and the activity of the neck and mastication muscles were observed.As a result, it was suggested that the use of a mouth protector having a limited occlusion supportive area or in an oral cavity lacking a tooth or teeth will not control muscle activity sufficiently for cervical back strength. Thus it was indicated that appropriate measures for the occlusion supportive area are vital in terms of both safety and athletic performance.