In recent years the cobalt-chromium alloys are widely used as cast denture bases and the author is concerned here with the composition analysis of present alloy and casting body, such mechanical properties as hardness, tensile strength, elongation together with its structure both microscopically and roentgenologically on two representative casting alloys; Mitsubishi dentallium (the former) of Japan and ticonium (the latter) of U. S. A. The flow of melting alloy was also observed with the use of a radioisotope ⁶³Ni. As a result, much difference was found in the compositions of these two different alloys. The latter contained Mo, Al, Ti and Be which are related to such factors as uniformity, minuteness of crystal grains and melting temperature of alloys, while the former contained W instead of Mo. The former contained a greater quantity of C which plays an important part in mechanical properties as compared with the latter. On the other hand, less than half the quantity of Ni was found in the former as against the latter and Co content was slightly more in the former. As regards Cr, nearly the same quantity was observed in both alloys. Si content as a deoxidizer was more in the former than the latter, but this was reverse in the case of Mn. The composition of casting body contained a higher ratio of Ni, Cr, Co and W as compared with present alloy. As for hardness, the former showed a greater value than the latter but a smaller hardness value was measured in the area of sprue attachment in common with both alloys. In the tensile strength and elongation tests, a slightly smaller value was measured in the former as against the latter. The structure images of present alloys and casting bodies were either solid solution structure or eutectic consisting of one kind of solid solution and another kind of solid solution, where the crystal grains were larger in the former and they were arranged in an irregular fashion. Casting body equipped with the reservoir was found to have somewhat larger crystal grains than non-reservoir casting body. In non-reservoir casting body, casting porosity and coarse image were concentratedly formed in the area of sprue attachment and within a casting body among the sprue attachment, scarcely being found elsewhere. In casting body with the reservoir, on the other hand, casting porosity and coarse image were not recognized, . they were formed in the reservoir concentratedly. The flow of melting alloy was uniform in casting body with the reservoir, while the flow was ununiform in non-reservoir casting body. Also in the case of one-piece cast denture base, casting porosity took place in the area of sprue attachment and its neighborhood without reservoir, hardness value in these areas being correspondingly smaller. Generally speaking, the tip of clasp showed a greater hardness value than in the base itself. It was impossible to determine any appreciable difference in respect of difficulty and ease in operation between the two alloys, when high frequency centrifugal casting was effected.

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Either systemic or characteristic complaints resulting from the use of dentures are manifested by the following four symptoms: (A) mental nerve compressions, (B) anterior palatine nerve compressions, (C) compressions of those branches of the mental nerve interwoven in the lower lip, and (D) disorders caused by habitual close bites while individual bite is demolished by unfitting dentures, endentulous jaw, or remaining teeth.
Causative factors of these manifestations have been investigated by the author anatomically in 53 halves of mandibles and 210 dry crania kept as specimens at the Department of Anatomy, Faculty of Medicine, Kyushu University, and clinically in 1, 406 individualsf of whom 216 are edentulous patients, living at 21 principal homes for the aged in the Kyushu are and 45 outpatients under the dental care of this author. The data obtained in the series of investigations are as follows:
1. Pressure sense on the occipital area, pressure pain, fatigue, anxiety, headache, dizziness, nauses, vomiting, insomania, and amnesia are systemic manifestations common to all of the said four cases.
2. As a rule, characteristic symptoms are manifested under unsymmetrical conditions in the case of both mental nerve compressions and compressions of those branches of mental nerve interwoven in the lower lip, and under symmetrical conditions in the case of anterior palatine nerve compressions and disorders caused by habitual close bites. Even in the latter case, however, the symptoms are sometimes manifested under unsymmetrical conditions.
3. Patients having edentulous jaws, those lacking molars, or those whose foramen mentale translocation suffer mental nerve compressions or compressions of those branches of the mental nerve interwoven in the lower lip, owing to the fact that inferior borders and inner surfaces of their dentures exert continued pressure on nerves located immediately underneath them.
4. Apparent drift of the mandibular foramen generally results from either missing molars or habitual unilateral mastication due to the use of ill-fitting dentures.
5. Apparent drift of the mandibular foramen Occurs not merely on mandibles having flat ridges, but also on those having normal alveolar ridges.
6. Independent of mandibular foramen, compressions on those branches of the mental nerve interwoven in the lower lip occur when continuous pressure exerted by the edge of the denture causes the buccal frenum, as seen in the mandibular premolar region, to become painful.
7. Anterior palatine nerve compressions are caused when anterior palatine nerve foramens are pressed by the tissue surfaces of the palatine portions of the upper denture.
8. An anterior palatine nerve foramen is located, in the case of a normal palate, near the median line on an imaginary straight line which passes across the second premolars. In the case of an edentulous jaw, it is located in reference to the farthest wrinkle from the teeth in the palatal rugae.
9. In the anatomical investigations, anterior palatine nerve foramens were found located symmetrically in five of the 210 crania. They were remarkably greater in size than the foramens of nearby nutrient canals.
10. The ends of nerve bundles were observed to emerge from the greater palatine nerve foramen, to pass near the median line, and to enter the anterior palatine nerve foramen.
11. An injection of 0.3 to 0.4 cc of Xylocaine in the anterior palatine nerve foramen served satisfactorily to anesthetize either lingual side between the central incisor and the second premolar. An injection of 0.15 to 0.2 cc of Xylocaine at the interdental gingivae on the buccal surface made possible the extraction of five teeth at one sitting. From the foregoing, it was inferred that the anterior palatine nerve foramen could be an ideal area for performing conductive anesthesia.

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