A comparative study was made of the process of the growth and development of the cortical bone at the mandibular base in children between Japan and China where methods of raising children, food and climate differ.
One hundred children with normal occlusion and aged from 4 to 8 who came to the out-patient ward, Department of Pediatric Dentsitry, School of Stomatology, Beijing Medical University, were used as subjects. Measurements of the cortical bone at the mandibular base were taken by means of panoramic radiographs and conversions were made in accordance with the magnifications factors used.
The results were as follows.
1. The averages of the thickness of the cortical bone at the mandibular base were, in Japanese children,2.28±0.34 mm for age 4,2.31±0.37 mm for age 5,2.32±0.41 mm for age 6,2.61±0.28 mm for age 7,2.70±0.47 mm for age 8; and in Chinese children,2.57±0.41 mm for age 4,2.59±0.37 mm for age 2.64±0.27 mm for age 6,2.87±0.42 mm for age 7,2.95±0.38 mm for age 8.
The averages, based on sex of the thickness of the cortical bone at the mandibular base in Japanese children were, for males,2.24±0.39 mm for age 6, The averages, based on sex of the thickness of the cortical bone at the mandibular base in Japanese children were, for males,2.24±0.31 mm for age 4,2.20±0.41 mm for age 5,2.30±0.39 mm for age 6,2.58±0.24 mm for age 7,2.68±0.50 mm for age 8; and for females,2.32±0.37 mm for age 4,2.42±0.29 mm for age 5,2.34±0.42 mm for age 6,2.64±0.30 mm for age 7,2.72±0.44 mm for age 8.
The averages in Chinese children were, for males,2.54±0.37 mm for age 4,2.49±0.31 mm for age 5,2.59±0.28 mm for age 6,2.90±0.40 mm for age 7,2.90±0.46 mm for age 8; and for females,2.60±0.42 mm for age 4,2.69±0.40 mm for age 5,2.68±0.30 mm for age 6,2.84±0.44 mm for age 7,3.00±0.25 mm for age 8.
The averages of the side thickness of the cortical bone at the mandibular base in Japanese children were, for the left side,2.23±0.16 mm for age 4,2.30±0.21 mm for age 5,2.42±0.26 mm for age 6,2.57±0.29 mm for age 7,2.73±0.46 mm for age 8; for the right side,2.33±0.39 mm for age 4,2.32±11160.22 mm for age 5,2.22±0.30 mm for age 6,2.65±0.30 mm for age 7,2.67±0.46 mm for age 8.
The averages in Chinese children were, for the left side,2.56±0.36 mm for age 4,2.50±0.24 mm for age 5,2.48±0.25 mm for age 6,2.83±0.40 mm for age 7,2.98±0.28 mm for age 8; for the right side,2.59±0.38 mm for age 4,2.68±0.26mm for age 5,2.76±0.26 mm for age 6,2.91±0.38 mm for age 7,2.92±0.35 mm for age 8.
2. In the t-test, no significant difference was found between the sexes in the thickness of the cortical bone at the mandibular base from ages 4 to 8 in Chinese children. For age 5 in Japanese children, girls however showed significantly higher values the boys.
Between the two ages 4 and 7,4 and 8,5 and 7,5 and 8 in Japanese children, the latter, the higher age, showed significantly higher values than the former. Between the two ages 4 and 7,4 and 8,5 and 8 in Chinese children, the latter, the higher age, showed significantly higher values than the former.
No significant difference was found for the left or right sides at any age.
3. In the t-test of the thickness of the cortical bone at the mandibular base of the children of both nationalities, Chinese children showed significantly higher values for ages 4,5.7 and 8 (p<0.01) and for age 6 (p<0.05) than the Japanese children.