Aim: The aim of this study was to measure the tooth size and dental arch widths in the deciduous dentition of normal Caucasian children born in the United States and compare these measurements with available Japanese standards for the same age. Methods: The United States sample consisted of 94 sets of dental casts obtained from 44 boys and 50
girls with mean ages of 4.6 and 4.7 years, respectively. The Japanese sample consisted of 158 sets of dental casts obtained from 83 boys and 75 girls with a mean age of 4.2 and 4.1 years, respectively. The mesiodistal tooth size of the deciduous teeth and intercanine and intermolar arch width measurements were compared between the two samples. Results: Boys and girls from the United States had significantly smaller (P < .01) mesiodistal tooth widths than Japanese children in both the maxillary and mandibular arches. Both maxillary and mandibular intermolar widths in boys and girls were also significantly smaller (P < .01)
in the United States sample. Mean maxillary intercanine widths were also significantly smaller in the United States boys but not in girls (P > .05) when compared to their Japanese counterparts. Conclusion: The results indicated significant racial differences in tooth size and arch width dimensions in the primary dentition between children in the United States and those in Japan. Therefore, population-specific standards should be used during orthodontic diagnosis and treatment planning. World J Orthod 2001;2:356–360.