Widths of the dental arches at the permanent first molars in children 9 years of age

Abstract

This article reports a study of dental arch width in the region of the permanent first molars on children 9 years of age. Its opening sections (1) survey the different methods of determining arch width that have been employed, and (2) review previous findings on 9-year-old white children contained in the North American research literature. Succeeding sections of the paper present the results from analyses of original data accumulated on ninety-four Iowa children of northwest European ancestry and above average socioeconomic status. The topics investigated are (1) reliability of arch width measurements, (2) central tendency and variability of arch width distributions for boys and girls 9 years of age, and (3) arch width interrelationships at the age of 9 years. Selected findings are: 1. 1. Both the minimum transverse distance between the lingual surfaces of the permanent first molars and the maximum rectilinear breadth between the buccal surfaces of the permanent first molars can be obtained through the medium of dental casts with high morphologic validity and reliability. 2. 2. Generalizing for the two arches and both sexes, minimum interlingual width at the permanent first molars on the 9-year-old children studied averages 32.5 mm., or 1.28 inches. The corresponding over-all mean for maximum interbuccal width at the permanent first molars is 53.5 mm., or 2.11 inches. 3. 3. On the average, the maxillary arch is wider than the mandibular arch by approximately 1.3 mm. in interlingual diameter at the permanent first molars and 2.9 mm. in interbuccal diameter at the permanent first molars. The average boy has a wider dental arch than the average girl by about 2.4 mm. in interlingual diameter and 3.2 mm. in interbuccal diameter. 4. 4. There is neither a high relationship between the interlingual and interbuccal measurements of a given dental arch nor between the maxillary and mandibular measurements for a comparable diameter. The correlations found on homogeneous age-sex groups are of the order e ̇ r ́ = 0.85 for interlingual widths in relation to complementary interbuccal widths, and e ̇ r ́ = 0.75 for upper arch widths in relation to corresponding lower arch widths.