The modal analysis on vibration in the human dry skull with and without mouthguards was performed in order to clarify which elasticity modulus of the material and what form of the mouthguard are the best. Nine different mouthguards were prepared for this study from three materials with different elasticity moduli and three different forms: Soft MOLTENO® mouthguards of long, middle, and short forms, Regular MOLTENO® mouthguards of long, middle, and short forms, and Hard MOLTENO® mouthguards of long, middle, and short forms. Thirty-five measurement points were established on the skull. The main measurement system was composed of a 512-D Vibration Generator, LV 1300 Laser Doppler Vibrometer, CF 6400 FFT Analyzer, PC 9821Xn personal computer, and Vibrant PC modal analysis software. The decay rate was calculated to evaluate effectiveness of the absorption of vibration of the skull with and without mouthguards when stress was put on the skull.
The results showed that the skull fitted with the long and middle form mouthgua1ds made of Regular MOLTENO® had a higher decay rate than the skull without the mouthguard, and that the material properties of the mouthguards influenced the absorption of the skull vib1ation more intensively than did the forms of the mouthguards.