It is generally acknowledged that the deciduous dentition in men carries many more primitive characters than does the permanent dentition. For further substantiation of the theory, the present author undertook measurement on the anatomy of lower deciduous molars and made the investigation on the possible primitive traits in their coronal region. Results obtained were summarized as follows. 1. Both the mesio-distal and bucco-lingual diameters in the crown of second deciduous molar (m_2) were significantly greater than those in the first deciduous molar (m_1). In this regard, there was also noticed sex difference which was again more conspicuous in m_2 than in m_1. With regard to the size of both kinds of the teeth, there existed a highly positive correlation between m_1 and m_2. 2. As to the number of occlusal cusps occurring in both teeth, 5-cusp occupied 60.4% in m_1 and exceeded 4-cusp teeth, where as in m_2 5-cusp teeth occupied as much as 100%, suggesting that the former teeth were slower than the latter in the process of cuspal differentiation. 3. As to the patterns in which the fissure occur in the occlusal surface, Y-type was most frequent with 66.4%, followed decreasingly by Cross-type and X-type. this means that the crown pattern is consisted largely of Y5 which occupies 48.7%, followed in decreasing order by +4, Y4 and +5. 4. With respect to the occulusal pattern of m_2, those teeth that showed Dryopithecus pattern (Y5) occupied as much as 96.8% in the male and 92.3% in the female, and no other pattern was noticed to occur except a few instance of occurence of +5. 5. Those traits such as Cingulum, Mesiobuccal ridge, Trigonid incision and Distal trigonid crest could be noticed to occur fairly distinctly in m_1, but rarely noticed in m_2. These traits are considered to belong to the primitive traits of such teeth. 6. Although it has been generally believed that the occurrence of 6th cusp, 7th cusp and Protostylid in m_1 is very rare, the present study revealed the presence, although in trace amount, of each of these traits in frequency percentages of 8.6, 22.8 and 18.9 respectively. 7. On the occlusal surface patterns of m_1, the Type 2 pattern (triangle shape) occurred more frequently than Type 1 pattern (oblong shape) with as much as 69% 8. The development of the central ridge in the Metaconid of m_2 was very complete and the Deflecting wrinkle as produced by the central ridge was noticed to occur in about 2/3 of teeth examined. Although the present author presumed that these findings in m_2 had something to do with the occurrence of Distal trigonid crest in m_1, he failed to confirm any such correlationship at the statistical level. 9. The frequency of occurrence of 6th cusp in m_2 amounted to 44.8% in the male, 35.6% in the female, and that of 7th cusp amounted to 83.3% in the male and 86.3% in the female, showing rather higher occurrence of such traits in m_2 than in the molar teeth. On the other hand, there was no statistical correlation to be found between m_1 and m_2 with regard to the occurrence of 6th and 7th cusp. 10. Occurrence of Protostylid in m_2 amounted to 77.6% in the male, 70.8% in the female showing a greater frequency than that in molar teeth. No statistical correlation was noticed between m_1 and m_2 as far as the frequency of Protostylid is concerned. 11. The occurrence of Trigonid furrow in m_2 was seen in 38.0% in the male, 30.5% in the female, and of this trait more than half of whole cases were of alfa type which represents the most characteristics of primitiveness. 12. Of those physical traits described above, the Deflecting wrinkle, 6th cusp, 7th cusp and Protostylid are more frequently encountered among Mongoloid peoples including Japanese. These traits appeared most frequently in m_2, less frequently in m_1, but were rarely seen in M_2 and M_3 suggesting that these are certainly among the primitive traits of human dentition.

View full abstract

Following conclusions have been reached by the studies on the curve symbol of maxillary right 1st molars and maxillary right 2nd molars and also on the areas participating in its formation : 1. Obvious curve symbol was observed in both 1st molar and 2nd molar. 2. In the 1st molar the curve symbol is most conspicuous in the areas of cementoenamel junction and gets weaker toward the occulusal surface. 3. In the 2nd molar the curve symbol is weakest in the area of cemento-enamel junction and gets stronger toward the occlusal surface. 4. In the outline by occulusal aspect the mesiobuccal angle averages 115.15°and the average distobuccal angle is 134.85°in the 1st molar, while the former in the 2nd molar is 111.75°and the latter is 134.60°. 5. No definite difference between the curve symbols of the 1st and 2nd molars is observed. 6. The area sparticipating the formation of curve symbol are the central 2/3 area of crown length for the mesiobuccal curvature, and most of the distobuccal curvature is formed by the 1/2 area from the central of the crown length toward the cemento-enamel junction.

View full abstract

A statistical investigation was performed on 3, 204 patients who received treatment at the Orthodontic Department of Kyushu Dental College during a 20 year period from 1957 to 1976, concerning distributions of sex, age and time of first treatment, kinds of malocclusion, orthodontic appliances used for active treatment, etc., on the basis of the gnathostatic models, x-ray cephalograms and clinical records which were obtained with these patients. The results were as follows : 1) Out of the 3, 204 total number of the patients, male numbered 1, 069 (33.4%), and female 2, 135 (66.6%). In other words, female accounted for two thirds of the total. 2) Analyzed by ages, patients who received first treatment at the age of 8 formed the largest group, and for older age groups, number of the patients was decreasing yearly. This decreasing tendency was particulaly remarkable with male patients. 3) Analyzed by the kinds of malocclusion, the number of mandibular protrusion cases was the largest among the total number of the patients, that of maxillary protrution cases came next and that of crowding cases came third. Total sum of these three cases accounted for about 80% of total number of the patients. 4) The extraction cases accounted for 40.6% of all cases, and the number of these cases showed increasing tendency year by year. 5) In the frequency of using different kinds of orthodontic appliances for treatment, the use of activators ranked top, that of lingual arch appliances ranked second, that of multiband appliances ranked third, that of chin caps ranked fourth and that of plate appliances ranked fifth. There was observed remarkable increase in the use of multiband appliances during the recent ten year period.

View full abstract

In the course of treatment, functional or aesthetic restoration of various diseases in the oral region, there are numerous occasions on which specialized knowledge and skill of the dental oral surgeons are required. Observations and examinations of the inpatients in the oral surgery category in a general dental clinic were made for a 10-year period from January 1964 to December 1973. The summary of the study is as follows : The total number of the inpatients was 617, of which 361 were males and 256 females. In age, the patients in the thirties showed the highest percentage, the younger groups next and the rate decreased with the older groups. In frequency by disease, inflammation was the highest with 224 cases (36.30%), traumas 110 cases (17.83%), cyst 89 cases (14.42%), others 76 cases (12.32%), malformation 68 cases (11.03%), and tumors 50 cases (8.10%) in order. Referrers to the clinic was mostly by dentists accounting for 50% and by other doctors 13%.

View full abstract