Changes in the maxillary and mandibular tooth size-arch length relationship from early adolescence to early adulthood. A longitudinal study.

The purpose of this study was to determine the association between the changes in maxillary and mandibular tooth size-arch length discrepancies (TSALD) and various dentofacial variables for 18 male and 14 female subjects with normal occlusion. All subjects were participants in the Iowa Longitudinal Growth Study and records were evaluated at two stages of dental development: stage I, when the permanent second molars initially erupted into occlusion (X age = 13.3 years); and stage II, at early adulthood (X age = 26.0 years). The following sets of variables were evaluated: mesiodistal crown diameters of single and groups of permanent teeth, dental arch widths and lengths, curve of Spee, maxillary and mandibular anterior and total crowding or spacing, anterior tooth rotations, and various cephalometric dentofacial parameters. Student's t test were used to compare subjects with the most and least changes. Regression analyses also were used to assess the relationships between these parameters and the changes in the maxillary and mandibular tooth size-arch length relationship. The most consistent finding from the t test comparisons is the significantly greater reduction in the available arch length in the group with the most TSALD at early adulthood. No other variables were found to be consistently different in the comparisons between the two groups. The results of the regression analysis indicated that a number of dentofacial variables are associated with the changes in the maxillary and mandibular TSALD--for example, the mesiodistal diameter of different teeth and the changes in anterior and posterior facial heights. The clinical implications of the present findings are discussed.