The followings are dealing with 10 dental alloys with less then 30% gold, manufactured by S company 7, and by H company 3. We could find several noticable things by examining them about tarnish and corrosion with human saliva and several other chemicals, and through metal microscopy. 1) After the samples were submerged in human saliva for 3 months, the colour of the samples were no remarkable change. 2) taking a consideration of the error of santorius balance, also there had been little corrosive changes in human saliva. 3) The colour of A-4 was changed into red in 0.05% HCI solution, while that of P-B was changed into black in 0.1% Na₂S solution and severely corroded samples, P-B, X, and Z lost their original colour and turned black. 4) In case of submerging in H₂NO₃reagent, 50%, it caused serious diminishing changes in weight, that is, X 2.7%, Pb 31.0%, Z 40.5%, and there happened tremble corrosive reaction. 5) Seeing them through metal microscopy, we can obserre the corroded samples changed into the shape of.

Sometimes in clinic, we have found that cast crown construction is necessary to fit the existing partial denture clasp, when the abutment is involved with caries, a failing restoration, periodontal disease, or fracture. This is important not only to protect the abutment tooth from missing, but to restore retention, bracing and support for partial denture. For constructing the cast crown, several methods have been reported by many of previous authors. The number of techniques reported during the past are ideal but have uncertain results However, with more improved and practical technic developed by me, the problem becomes more successful. One method in which does not need the laboratory technecian is the wax pattern has been made in chairside waxing by doctor himself. The other in which requires the laboratory technician is to use special impression method and articulator for laboratory waxing. In one case of the reported here, we have successful results in restoring the abutment with cast crown for original denture clasp.

Simplified debris, Calculus and oral hygiene indices of 145 mental Disorders examined in order to appraise oral hygiene status were Calculated and compared wicth the findings of other investigators. The obtained results were as follows; 1) Oral hygiene status of mental Disorders was very poor and became worse by ageing 2) Sexual characterics influenced slightly to oral hygiene status 3) No salient differences were found in the oral hygiene status among the intellegence quotient groups

The bacterial behaviour against antibiotics and pattern were examined with 88 strains of 10 species, isolated from pus collected in the infirmary of college of dentistry, and Seoul national university hospital during recent 7 years. 1. Isolated bacterial species and their relative incidences were, as follows, coagulase positive staphylococcus 50%, alpha hemolytic streptococcus 17%, Pseudomonas aeruginosa 10% and coagulase negative staphylococcus 8%. 2. Gentamycin reveals the highest sensitibity and cephalosporine follows it.

The author conducted an experiment on the relativity between the mandibular buccal and lingual cusp inclines by means of measuring full arch plaster cast teeth of the fifty student subjects of the College of Dentistry, Seoul National University. The results were as follows: 1. The statistical relativity between the mandibular buccal and lingual cusp inclines in individual tooth was hardly recognized. 2. In the cusp incline data of the whole posterior teeth, the rough basis for the harmonizing with the other occlusion factors was recognizable. 3. The cusp inclination itself was incomplete in mechanical balance, therefore, it might be said that there were a lot of possibilities that the cusp incline may act as a potential etiological factor to give rise to occlusal diseases.

The author fabricated duplicate dentures by means of alginate-duplicated plaster dentures. The effect in duplicate dentures were the same as the original dentures in function as well as in shape, therefore, such technique was considered to be fully applicable in the clinic.