In the dynamic tests, the results of only the impact bending, strength tests and the ultrasonic pulse-echo method have been reported, while no reports on the impact compression tests of tooth have been made available.
There for, the author has undertaken a studay with a standpoint what behaviors the tooth will show against the compression force accompanying occlusion and mastication and also to clarifying the anisotropy and the mechanical properties of the tooth. The author used the split hopkinson pressure bar method to take measurements of the elastic modulus, stiffness, the maximum stress, solid viscosity and the maximum energy of the tooth with respect to its crown, neck and root. The measurement were taken on three planes, on the tooth's long axis, medio-distal and bucco-lingual direction. The directions to tailed eight in the direction of 45° against each axis, of 30° and 60° incline from the axis towards the tooth's ax is directions.
As a result of the studay, the author arrived at the following conclusions.
1. The split hopkinson pressure bar method was used to measure some dynamic material propertise porous hard tissues, such as cortical bone and tooth.
2. Elastic modulus have a tendency to increase at tooth's long axis and bucco-lingual direction of root. Stiffness have a tendency to increase at bucco-lingual direction of crown. The maximum stress have a tendency to increase at tocth's long axis direction of root. Solid viscosity have a tendency to increase at tooth's long axis and bucco-lingual direction of root. The maximum energy have a tendency to increase bucco-lingual direction of root.
3. In the medio-distal direction of the tooth, the properties showed a trend similar to those of the bucco-lingual direction, but the elastic modulus, stiffness, the maximum stress and the maximum energy showed values lower than those of the long axial and bucco-lingual directions.
4. In the direction of 45° inclined from the long axial to the bucco-lingual direction, the measured values tended to be lower than those of the other direction.
5. Differences seen in the elastic modulus, stiffness, the maximum stress, solid viscosity and the maximum energy according to the direction and the region of measurement indicated a dependency on the direction.
6. An impact-response model was attempted, and theoretical an alysis were under taken of the anisotrophy.

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The role of cast clasps in the construction of partial denture is very important.
Cast clasps have, in many cases, been prepared by using refractory working models duplicated from working models, but lately the die-investing technique is being applied to a considerable extent largely on account of better operability. In this technique, a special mixing liquid has been made available, and it is attended with the advantage of obtaining good adaptability through control of the expansion rate of the material at the time of settling by changing the liquid density.
The author, in the circumstances, used the gold-silver palladium alloy and the gold alloy for casting use (ADAS Type III), which are frequently used clinically for making cast clasps, and prepared models and cast clasps from the basic model (metal model) assuming the anchor tooth by changing the special liquid density in order to obtain expansion of the investment that will compensate for the casting contraction of such metals. The author further measured the dimensional changes against the basic model on the stage of models and castings and examined the effect thereof on the adaptability. As a result, the following conclusions were arrived at
1. Dimentional changes of molar and premolar models proved the greater the higher the density of the special liquid. No effect of morphological differences was observed.
2. Dimensional changes of the models in the mesiodistal and bucco-lingual directions proved similar with respect to both the molar and premolar models regardless of the density of the special liquid.
3. The casting became larger than the original dimensions at the special liquid density of 50% or higher and smaller than the original size at 25% or less.
4. The respective dimensional changes of the castings prepared with the gold-silver-palladium alloy and the gold alloy showed proximate values.
5. High correlation of the divestment to the special liquid density and the dimensional change of the model and to the dimensional change of the model and the dimensions of the casting was observed.
6. Under the conditions of the present experiment, the optimal density of the special liquid in preparing highly adaptable cast clasps under the die-investing technique using the gold-silver-palladium alloy and the gold alloy was 50%.
7. The dimensional changes of the cast clasps prepared with the model investment showed the special divestment liquid density between 50% and 75%.

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