YEARS OF AGE

vestigations, only those by Cohen6 and Woods'6 "follow throughout a long span of time the process of growth in each child of a representative group of children. "7 Cohen worked from dental casts, Woods from roentgenograms; each used a sample of less than thirty children; neither dealt with width be-tween the buccal surfaces of the deciduous second molars. OBJECTIVES Major aims of the present investigation are: 1. To present findings on the reliability of records for maximum rectilinear distance between the buccal surfaces of the deciduous sec-ond molars. Reliability coefficients are reported for each dental arch at 3 different ages. 2. To statistically describe interbuccal width at the deciduous second molars on 12 age-arch-sex subgroups of North American white children. Central tendency and variability values are tabled, specific for dental arch and sex, at ages 4, 6, and 8 years. 3. To analyze longitudinal data pertaining to growth in dental arch width between 4 and 8 years of age. For a series of 77 children, changes with age in transverse diameter between the lateral-most points of the deciduous second molars are subgrouped according to arch and sex, and the resulting distributions portrayed and discussed. 4. To investigate a number of dental arch relationships. Correla-tion statistics are used to depict the association between (a) arch width at 4 years and arch width at 8 years, (b) arch width at 4 years and change in arch width from 4 to 8 years, (c) maxillary width and mandibular width at 4 years, (d) change in maxillary and mandibular widths from 4 to 8 years, (e) maxillary width and upper face width at 6 years, and (f) mandibular width and lower face width at 6 years