The purpose of this study was to investigate the various methods used to determine the existence of periodontal disease and (subsequently gingivitis) in Japanese subjects in their middle teens.
This survey was conducted on 634 male high school students (15 to 18 years old) at Kawasaki City, Kanagawa-ken, Japan. Four (4) basic examination procedures were used ; 1. Plaque Index by Sillness and Löe 2. Salivary Blood Test 3. PMA Index by Massller and Schour 4. Community Periodontal Index of Treatment Needs C.P.I.T.N.
The results were as follows
(1) Almost 20% of the group gave a positive indication to the Salivary occult blood test. (2) Using the PMA Index almost all students were judged to have “gingivitis”. (3) Using the C.P.I.T.N. these high school students indicated an incidence rate of periodontal disease equal to 97.5%. (4) Just under 70% of the subjects required professional care. This rate increased with the subject's age. (5) This study showed the C.P.I.T.N. to be a useful tool for determining the prevalence of, and a need for determining the prevalence of, and a need for professional treatment of, Periodontal disease.

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ln the bacterial molds of human dental calculus formed by the extracellular calcification, whitlockite and octacalcium phosphate crystals as well as apatite crystals were occasionally precipitated in the later stages of calculus formation. Thus, the deposits would be similar to the calculus formed by both the intra-and extracellular calcifications.

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The impression technique using a silicone rubber impression material and an abutment tray proved to be the most accurate. However, there was a problem of adhesion between the impression material and the abutment tray with this technique. In this study, five different silicone rubber impression materials (two condensation and three addition types) were used. The impression materials were evaluated to determine their bond strengths with the selfcuring resins (material of the abutment tray)
The results were as follows : 1) Adhesive (tosicon adhesive) in the condensation type and GC adhesive (Hydrophilic EXAFLEX adhesive) in the addition type were superior in bond strength.
2) Tosicon's adhesive or GC adhesive was used with other manufacturer's impression materials. In the condensation type, the bond strength of tosicon's adhesive was less than the manufacturer's recommended adhesive. The bond strength of GC adhesive was the best of the addition type.
There are various levels of bond strength of silicone rubber impression materials. Some adhesives recommended by manufacturers are not always effective. Therefore, it is necessary to use these materials with caution in dental clinic.

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In treatment of skeletal cl. 2 malocclusion with vertical changes, it is said to be critical if an orthodontist could control not only antero-posterior but vertical dimension in the maxillo-mandibular relationship.
The purpose of this study is to investigate what is concerned most with vertical changes in the maxillo-mandibular relationship in orthodontic treatment, and the possibility to find any signs before treatment.
Taking note of changes in vertical dimension, the subjects were divided into two groups according to the increase (PP-MP (+)) and the decrease (PP-MP (-)) in the angle formed by palatal plane and mandibular plane through orthodontic treatment. The two groups were compared with before-and after-treatment, and these differences.
The results were as follows.1.Before treatment, PP-MP (+) was identified with clockwise rotation of the mandible with a wide ramus inclination, and also excessive heights in the maxillary incisor and molar, as well as the mandibular incisor. It seemed to share these features with an open bit ecase, except for the rest of a wide gonial angle, short ramus, and steep mandibular plane.2. In the difference between before and after treatment, PP-MP (-) indicated clockwise rotation of the palatal plane, narrowness of the mandibular plane and gonial angle, while PP-MP (+) presented itself counter-clockwise rotation of the palatal plane, acute mandibular plane and gonial angle, all of which had a corresponding effect on an increase in the vertical dimension on the maxillo-mandibular relationship.
In changes in the denture pattern, PP-MP (-) showed counter-clockwise rotation of the occlusal plane. However, PP-MP (+) indicated lingual inclination of the upper incisors and clockwise rotation of the occlusal plane, whose changes seemed to act in compensation for antero-posterior and vertical relationship of the jaw.

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To determine whether a structural alteration of articular surface in the rat mandibular condyle correlates with developing occlusion and advancing age, the condyles were investigated with light microscope, transmission and scanning electron microscope. In tissue preparation for SEM, to display ditailed organization of fibrillar matrix, Triton X-100-enzymatic treatment was employed. The fibrous zone of the mandibular condyles from rat fetuses, most of which is occupied by fibroblasts, was poor in intercellular matrix. This fibrillar matrix existed in the form of a network. In 1-week-old rats, the fibrils were orderly rearranged and closely packed except fibrillar network in the superficial layer of the condyle. With advancing age, the fibrils were arranged regularly also in the superficial layer. At 8 weeks, three-dimensionally interwoven bundles of fibrils were present and the fibrillar network was less prominent. In mature and senile rats, the fibrillar bundles of the articular surface increased in number and width indicative of a well-development. In rats over the age of 20 weeks, the fibrous zone varied in thickness from less than 30 pm up to a maximum of 280 pm. In the aging rats, the collagen fibrils had a diameter varying from 40 nm to 100 nm. The alteration of fibril arrangement from network to bundle and the development of fibrillar bundle are fundamental to a structural alteration of the condylar articular surface with advancing age. There is no exception to this manner. Structural peculiarities occurred in the mature and senile rat articular surfaces. They were disclosed fibroblasts, lumps of densely interwoven fibrils, rotatory fibrillar bundles and fibrils showing wearing-down-like appearance. The structural alteration that occurs in the condylar articular surface correlates with increasing stress of occlusal compression and aging of the mandibular condyle.

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Recently, the specialist system has been adopted by some dental academic societies. In orthodontic field the accredited orthodontist and instructor system has been also enforced by the committee of Japan Orthodontic Society (JOS) since 1990. As of the end of November in 1993, 1,321 and 385 members in JOS have been registerd as accredited orthodontists and instructors, respectively. At present the eligibility to an accredited orthodontist is granted on condition that a student attends a basic educational program for at least 2 years which is offered exclusively by the department of orthodontics of a dental school followed by a practice limited to orthodontics as a fellow orthodontist for more than 3 years under the direction of an accredited instructor. Therefore, this postgraduate curriculum provided by a dental school should be designed to exceed the minimum requirements established in JOS.
The purpose of this article is to introduce the outline of the postgraduate curriculum running in the Department of Orthodontics, Showa University, in comparison with that of JOS.

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A case of bilateral horizontal impaction of the mandibular second molars is presented. A 28-year-old woman with pain of the right mandibular first molar visited our dental office.
X-ray examination revealed bilateral impaction of the mandibular second molars, and the mandibular third molars intussuscepted on the mandibular second molars.
In the absence of systemic abnormality, facial trauma, and maldevelopment of the jaw, impaction seemed to have been closely associated with some unknown local factor.

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