Abstract
Plaster models were taken from the mouth of a total 572 infants aged 3 to 5 years and the morphology of their dental arches with no permanent tooth erupted was measured with respect to age, sex and regional difference. Analysis of data obtained gave the following conclusions. 1. Breadth of Dental Arch Sex : Male exceeded female with every age stages of infants. Regional : With both sexes, the breadth of every regions of dental arch was larger in upper jaw than in lower jaw. The extent to which the breadth of dental arches of upper and lower jaws differed was respectively 6.2 to 6.9 mm in male and 6.4 to 6.8 mm in female at the deciduous canine, 4.7 to 5.0 mm in male and 4.8 to 5.2 mm in female at the first deciduous molar, and 4.6 to 4.8 mm in male and 4.3 to 4.8 mm in female at the second deciduous molar. Age : The breadth was largest in 5-year-old infants, followed by 4-year-old and 3-year-old infants with both sexes. The percentage magnitude of dental arch between 3-year-old infants and adults was respectively in the range of 84.7 to 91.1% in male and in the range of 84.4 to 92.0% in female. 2. Length of Dental Arch in Right and Left Quadrants Sex : Male exceeded female in both quadrants with length of dental arch. Upper and lower jaws : Upper jaw exceeded lower jaw in every regions of dental arches of both sides with every age stages of infants. Age : In the male infants, there is hardly any difference between individuals, while in the female infants, 3-year-olds showed largest individual difference, which decreased towards 4-year-old and 5-year-old infants groups. 3. Breadth of Alveolus in Lower Jaw Sex : Male exceeded female in the breadth of alveolus at every regions measured and with every age stages of infants. Age : In male infants, little difference was noticed between 5-year-old and 4-year-old infants in the breadth, its magnitude being smallest in 3-year-old infants. In female infants, the breadth was largest in 5-year-old group, decreasing towards in 4-year-old and 3-year-old groups in order. 4. Antero-posterior Length of Dental Arch Sex : Sex difference was hardly noticed between 3-year-old and 4-year-old groups, whereas in 5-year-old infants male exceeded female in the magnitude of antero-post-erior length of dental arch. Age : Individual difference was largest in 3-year-old male, while negligible difference existed in 4-and 5-year-old male groups. This was also true for 3-year-old female, and the difference diminshed towards 4-year-old and 5-year-old female groups. Upper and Lower Jaws : The antero-posterior length of dental arch in upper jaw was larger than in lower jaw in both sexes and for every age stages. 5. Length-Breadth Index of Dental Arch Sex : Sex difference was hardly present with 3-year-old and 5-year-old infants groups, while with 4-year-old infants female exceeded male in this respect. Age : Individual difference was largest in 3-year-old infants and it decreased towards 4-year-old and 5-year-old groups.
