Much attention has been focussed on the morphology of human upper incisor teeth not only from anatomical viewpoint but also from practical dental prosthetic consideration. The physical traits of these teeth also provides a variety of significant problems of anthropology and their regressive phenomena, especially of lateral incisors have been studied most extensively from the evolutional viewpoint as these usually showed most marked signs of regression second to the wisdom teeth. The present author, therefore, undertook a series of measurement on the upper incisor teeth and examined the morphology of their crown and root and made comparative study on some of their physical traits. The study has yielded several facts of interest summarized as follows. 1. The labial surface of crown in central incisors generally showed ladder-like and inverted wide U-form, and that in lateral incisors generally showed inverted slender U-form. When viewed from the direction of incisal margin, the labial surface of both incisors showed a flattened surface in most cases, except that there were some 17% of central incisors showing concave surface that corresponded the so-called double-shovel form. It was confirmed further that the shape of labial surface view from the incisal margin showed no correlation with the contour of labial side view of the same teeth when tested by means of chi-square test, and this suggested that the labial surface morphology might have been produced in the above stated form as result of the developmental difference of individual ridges. 2. The contour of the lingual side view of the teeth showed generally a slender triangle in most cases, particularly with lateral incisors. This means that the constriction from incisal margin toward cervical direction in these teeth was more marked in the lingual side than in the labial side of the teeth. 3. The occurrence of the shovel-shaped incisors was considerably high with percent frequency of 56.8 in the central incisors and 66.9 percent frequency in the lateral incisors and this may be regarded as one of characteristic traits among mongoloid race that includes the Japanese. A positive correlation was found to exist between the above trait and the marginal ridge of the teeth, and just as in the case of double-shoveled trait, this shovel-shape trait was also considered to have resulted from accentuated growth of the marginal ridge. 4. The percent frequency for the spine of the incisors was respectively 28.1% in the central incisors and 29.2% in the lateral incisors, that for the occurrence of the foramen cecum was 7.8% in the central, 55.1% in the lateral incisors respectively, and that for the linguo-gingival fissure was respectively 21.9% in the central, 35.7% in the lateral incisors. The statistical analysis on the possible relations between these traits including the shovel-shaped incisors and the mesio-distal, labio-lingual width of the crown has revealed that although the occurrence of foramen cecum might be one of the tooth's regressive traits, it could not deserve to be concluded as such in any definite term. On the contrary, the linguo-gingival fissure and the shovel-shaped forms of the incisors my be considered to represent the primitive traits of the teeth, and occurrence of spine was not considered to have any phylogenetic significance. 5. Measurement of size done on the individual teeth showed that the lateral incisors suffered marked reduction in every items studied as compared with the central incisors, and the most reduced was the mesio-distal width of crown, followed by the labio-lingual width and length of crown and root of the teeth in this order. Comparison of the corner angles of incisal margin showed that there was no appreciable difference between both mesial and distal corner angles with the central incisors, while with the lateral incisors the one at the distal corner was significantly greater than the one at the mesial corner.

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A statistical study was conducted on the rate of existing deciduous teeth, the rate of decayed and filled teeth (df-t) and that of decayed (d-t) vs. decayed and filled teeth (df-t) among infant population of Miyazaki city and possible age change was sought in the data obtained. The subjects were consisted of 1029 boys and 976 girls aged 3 to 6 years at the time of investigation extending from April to May 1972. Results obtained were summarized as follows. 1. Rate of Existing Deciduous Teeth (1) Difference between Right and Left Quadrants : No appreciable difference was found between same-named teeth of both sides in subjects of both sexes. (2) Difference between Upper and Lower Quadrants : Hardly any difference existed between upper and lower teeth of same names except that the rates for the lower central and lateral incisors in six-year-aged subjects of both sexes were respectively slightly smaller than the rates for antagonizing teeth in upper jaw. (3) Age Change : Reduction in the rate of existing teeth was larger with the lower deciduous central incisor than with the rest from 3-year-old subjects toward 6-year-old subjects. Other teeth did not show any fluctuation in the rate with age stage of the subjects. 2. The Rate of d-t/df-t (1) Difference between Teeth of Four Quadrants : There was hardly any difference in this rate among comparable pairs of teeth of four quadrants. (2) Age Change : No appreciable age change was noted in this rate with every teeth examined. (3) Difference in the Rates between Individual Teeth : The rate for the deciduous incisors was larger compared to that for the deciduous molars. The rate of treated cases (f-t rate) was slightly greater in the deciduous molars than in the incisors. (4) The Rate of d-t/df-t in 3-year to 6-year old subjects : The rate amounted to 99.1% in the male and 95.0% in the female subjects of 3-year age stage, 91.6% in the male and 88.8% in the female subjects of 6-year age stage, indicating the presence of a greater number of d-t which needed urgent treatment as compared to f-t. 3. The Rate of df-t (1) Difference between Right and Left Quadrants : Hardly any difference was noted between same-named teeth on both quadrants of jaw regardless of sexes of subjects. (2) Difference between Upper and Lower Jaw Teeth : The rate for the deciduous incisors and canines of upper jaw was higher than that of lower jaw through both sexes of subjects while the rate for the deciduous molars of lower jaw was inversely higher than that of upper jaw. (3) Age Change : The number of deciduous incisors slightly diminished from 3-year age stage toward 6-year age stage, while the number of deciduous canines and molars slightly increased during the same period through both sexes of subjects.

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The two-rooted mandibular canines were found in 13 cases among specimens of extracted human canine teeth as collected in the laboratory of Oral Anatomy, Kyushu Dental College. Findings observed were summarized as follows. 1) The two-rooted mandibuar canines of man were found in thirteen cases, seven right, six left among a total of 4364 specimens. 2) The frequency was 0.29 percent, there was not clearely opposed to the hypothesis of independence in exhibition of right and left by chi-square test. 3) These roots were bifurcated in labial and lingual side. 4) The two-rooted canines almost revealed a bifurcation in the middle of root. 5) Comparing with the measured values between the two-rooted canines and the single-rooted canines, the former were smaller than the latter in length of root, mesio-distal diameter of crown and labio-lingual diameter of crown, above all, the most difference in length of root. 6) By T-test, labial roots of the two-rooted mandibular canines were greater than lingual root in comparison between mesio-distal diameter in bifurcated point.

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