東京都における9ヶ月児の歯牙の萠出について

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Out of the nursing babies of the Kyobashi area in Tokyo medically examined as provided in the Child Welfare Law, a total of 1, 045 nine-month-old babies have been examined chosen and observed minutely in respect of the teeth of eruption each month, each season during the period from June 1957 to June 1959. Again, out of these babies, especially of those who were examined in September. October and November, 1958, the relations between the average number of their teeth and their hereditary, congential, and acquired factors were researched, and the findings there may be summarized as follows: I. Number of Teeth of Eruption by Calender Months and Seasons (1) The average number of teeth of eruption is : April, 2.21, or the smallest; October, 3.87, or the greatest. Namely, it shows a tendency to be less remarkable in spring and remarkable in fall. (2) The numbers of teeth of eruption in upper and lower jaws by teeth show a tendency similar to that of the aforesaid average number of their teeth of eruption. It seems, however, that in the numbers of milk central incisors in the lower jaw, the varia tion by calendary months is rather small, and in the numbers of milk central teeth in the upper jaw, milk lateral teeth in the upper jaw and milk lateral teeth in the lower jaw, the variation by calenclary months and seasons becomes, increasingly noticeable each in the written order. II. Relations between Average Number of Teeth of Eruption and Hereditary, Congenital and Acquired Factors (1) A study was made of the relations between the number of teeth of eruption and mother's ages and their physical conditions, and the findings are as shown in the following tables: (2) In respect to the relations between the use of nutriment or no nutriment by mothers during the period of pregnancy and the numbers of teeth of eruption by their babies. 75 babies whose mothers had taken nutriment were found to have 3.23 ± 0.29 teeth each an average, and 32 babies whose mothers had taken no nutriment, 3.01 ± 0.32 teeth. The difference can not be considered to be significant between them. (3) In respect of the relation between the teeth of eruption and life environment, 71 babies living in well-lighted houses were found to have 2.94 ± 0.26 teeth each an average, and 20 babies in poorly-lighted houses 2.85 teeth, and the difference cannot be considered significant between them ; also 73 babies in well-ventilated houses were found to have 2.88± 0.25 teeth each an average, and 17 babies in badly-ventilated houses 2.94 ± 0.58 teeth, and the difference cannot be considered significant, either. (4) A study was made concerning the relation between the teeth of eruption and the development of their babies and the finings there of are shown in the following table: III. As stated above, the relation between calender months and the teeth of eruption could be made clear, and at the same time, the conclusion could be drawn out that the variations in the number of teeth of eruption were related to the mothers' ages and their physical condition, the use of nutriment by mothers, babies' life environment, and the tooth-development on the part babies themselves.
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東京都における9ヶ月児の歯牙の萠出について

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