A descriptive study of mandibular incisor alignment in untreated subjects.

Introduction: The development of mandibular incisor crowding appears to be a continuous process throughout life, but more evidence is needed to understand why changes occur.

Methods: In this study, we describe the longitudinal dental changes in untreated children (n = 15) who had records at 3 times and in an untreated adult group (n = 18) (parents) who had records for 2 times. The mean numbers of years between initial and final observations were 29.8 years for the children and 33.7 years for the parents. All subjects were participants in the original Burlington Growth Research Project at the University of Toronto. The following variables were measured to an accuracy of 0.01 mm: overjet, overbite, mandibular intercanine width, mandibular interfirst premolar width, mandibular intermolar width, mandibular arch length, Little's incisor irregularity index, mandibular anterior space analysis, and Carey's space analysis.

Results: There were no statistically significant (P >.01) differences between the sexes for the variables measured. Little's irregularity index continued to increase in all groups (P <.01), although this rate appeared to be lower in the parent group. Intercanine and interfirst premolar widths and arch lengths continued to decrease with age.

Conclusions: These results underline the importance of studies showing that untreated dentitions change over time. Orthodontic patient education is imperative about retention protocols and late developmental crowding.