This thesis compared tooth widths, arch widths, and arch lengths; their differences between males and females, and changes from early mixed dentitions to adult dentitions. Comparing subjects who were known to have Angle Class I normal occlusion in their permanent dentitions to subjects who were known to be Class I or Class II crowded malocclusions in their permanent dentitions. These comparisons can only be achieved utilizing data from a longitudinal study, such as the Iowa Growth Study. Dental casts in the early mixed dentition (average age of 8.85 years) and in the adult dentition (average age 15.45 years) taken from subjects who did not receive orthodontic treatment during or in the dates prior to data collection were measured for this study. The casts utilized were from the Iowa Growth Study; all of the subjects were of European descent. The longitudinal sample of casts in the Iowa Growth study were made from white dental stone poured into alginate impressions from 1946 until 1960. The objectives of this study were to compare individual tooth widths, mean sum tooth widths, arch widths, arch length segments, and arch perimeters of Class I Normal (CIN) and Class I and II crowded dentitions (CD) in the early mixed (MD) and permanent (PD) dentitions to explore new methods of predicting crowding. The goal was to evaluate the significance of differences between MD and PD for tooth widths, arch lengths, and arch widths in both arches of CIN and CD subjects to determine values that may be useful for MD space analysis. Thirty males and thirty females from the Iowa Growth Study with CIN and CD occlusions were selected from the longitudinal study. Casts of MD and PD subjects were double measured with digital calipers by both the primary and secondary investigators. The average of each investigator's two measurements were used to determine measurement error. All other statistical analysis was based on the mean measurements taken by CPW. Descriptive statistics were computed. The normal non-crowded and crowded samples were compared with two-sample t-test, and changes from MD to PD with paired-sample t-test. Examiner measurement errors were tested with intra-class correlation coefficients. When the mean sums of MD and PD tooth widths were compared, using data from all 60 subjects, the CD group had a significantly greater mean sum of tooth widths than the CIN group. In both genders, crowded dentitions had significantly greater mean sum of tooth widths than CIN's for both the maxilla and mandible in MD and PD. When the mean sums of the arch lengths [Perimeters] were compared using data from all 60 subjects, the arch perimeters of the CD and CIN samples did not differ. It was concluded that total arch lengths Perimeters] were not significant indicators for crowding. Gender comparisons: Within the CIN group, males had numerically larger tooth width sums and arch length sums than females. The sum of maxillary and mandibular tooth widths for CIN's and CD (both males and females) mandibular tooth widths for CIN's and CD (both males and females pooled together and sexes separately. In the MD stage the mean sum of maxillary and mandibular arch lengths in the MD were significantly greater than those in the PD, because arch perimeters decrease during the transition from mixed to permanent dentitions. In summary, the results of this research thesis study showed that the sum of tooth widths in both arches had a significant association with dental crowding. In contrast, the sum of arch lengths [perimeter in both arches] did not differ between the normal and crowded samples. Additional analysis of the measurements taken in this thesis research project, the individual arch length segments, especially the canine and posterior arch length segments in the right and left sides of the lower arch in the mixed dentition casts, and their relation to the sum of the widths of the lower permanent canines and premolars in the normal and crowded malocclusions may give us important information about the development of crowded malocclusions.