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.
Hydroxyapatite (HA)-coating by the plasm a spraying technique, which has been the common method used for HA coating, is not useful for coating the surfaces of porous metal implants because of difficulty in producing a homogeneous HA coating layer less than 30 µm. A new coating method, therml decomposition, has been developed to obtain a dense coating layer with a thickness of 5 µm. In this study, the phase composition, surface morphology and adhesive strength between the coating layer and titanium substrate were evaluated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and tear off testing, respectively.
The biocompatibility of the implant prepared using this coating technique was compared with that of implants obtained using the plasma spraying technique or uncoated titanium following implantation into canine femurs. Bonding strength between the bone and implant was evaluated by pull-out testing. New bone formation was observed by light microscopy and SEM.
The dense coating layer obtained by thermal decomposition method was found to be composed of well-crystallized HA on XRD and SEM, and exhibited high adhesive strength. The biocompatibility of the samples obtained using this coating method was superior to that of the uncoated titanium implants and comparable to that obtained using the plasma spraying technique. The thin coating layer obtained using the thermal decomposition method should be useful for coating porous implants.