Due to the poor economic considerations of the general public in Japan, various metal alloys other than precious metals are in wide use in the field of clinical dentistry. We have no doubt that they will be used in increased number in the future. For this reason, it is a very important task to know as to how these alloys behavein the oral cavity where they are employed Being keenly interested in this matter, I have been conducting investigations on the subject for a long time. Now, at the 51 st Philippine Dental Congress heldin Manila, I like to take this opportunity to make public some of these results so that they may prove useful for the work of the practicing dentists and as pertinent data for the specifications of dental materials at the same time. If they should prove of value to you, I feel my labors will have been amply rewarded.
A part of this study appeared previously as part I in this journal, vol.I, no.3.Theformer report revealed that bovine lamella is a tissue, running in the enamel, which consists of enamel rods and interrod substance. It contains more abundant organic matter than normal enamel. The author attempted to investigate, in this research, the lamella tissue of human deciduous and permanent teeth. The result of this study clarified that human lamellae also are composed of organic enamel rods and interrod substance. Occasionally a section of lamella less than one micron wide is seen composed merely of interrod substance. Some lamellae show only their organic and nearly non-structural tissue.Therefore, distinction between enamel rods and interrod substance is almost impossible. By tracing morphological behaviors of enamel rods that remain along the lamella-enamel border, careful observation seems to reveal that these lamellae are also composed of enamel rods and interrod substance. A part of an enamel rod is sometimes clearly seen along the lamella enamel border that composes a part of the lamella tissue. These findings suggest that lamellae are not cracks ordefects in enamel filled withsoft tissue or organic matter as claimed by some scholars. Even though the lamella seems to be nearly non-structural, enamel rods and interrod substance likely compose the lamella tissue. This morphological finding can probably be assumed to be lamellation (chang ing to lamellae) of enamel rods and interrod substance. However, the author has not intended to gain evidence to determine whether lamellation appears primarily or secondarily from an embryological viewpoint. Needless to say, “lamella” and “lamellation” as compared by the author here have a nebulous histological differentiation. The findings are described below accompanied with explanations of several electronmicrographs.
Branch of dentistry in the field of industrial hygiene, which had been sadly neglected in Japan for a long time, has recently come to be taken up with due attention. Relationship between dentistry and industrial hygiene on the whole may be placed in the following two classes: 1) Relationship of two major dental diseases (dental caries and alveolar pyorrhea) among the industrial workers. 2) Other dental diseases which are caused by the nature of occupations in which they are engaged, i.e., occupational diseases. Problems under 1) are to be met with in any kind of industry. The susceptibility percentage of dental caries and alveolar pyorrhea among the Japa nese is quite high, running anywhere from 80 to 90%. This high percentage can be regarded as directly reflective of that of the industrial workers. Of 119, 031, 000 medical cases among the industrial workers reported in the year of 1957, 16, 853, 095 have been the dental cases (14.2%). When calculated in terms of money, expenses for the whole medical cases were 407, 694, 444 dollars and 26, 486, 944 dollars out of it were spent on the treatment connected with dental cases. On the supposition that half an hour has been spent on the treatment of one dental case, the total figures will be 40, 399, 796 hours (4, 611 years, 309 days and 20 hours). Therefore, problems of dental hygiene among the industrial workers are such as to be handled with utmost attention from the viewpoint of expenses and time involved. Although the percentages of these dental cases in Asian countries are not so high as that of Japan, there is reported a warning that these figures are on the increase year after year. In view of this fact, it is absolutely necessary that some sound measures should be established to tackle the dental problems at this stage.