The Effects of Primary Canine Loss on Permanent Lower Dental Midline Stability.

Purpose: The purpose of this study was to compare changes in the lower dental midline position after premature unilateral loss of a primary mandibular canine with dental midline position after normal primary mandibular canine exfoliation. Methods: Dental casts were identified from growth studies at the University of Iowa and the University of Toronto. Two groups of dental casts were identified: (1) premature unilateral loss; and (2) normal asymmetric exfoliation of a single primary mandibular canine. The first set of casts displaying unilateral primary canine loss (time one) and the second set of casts displaying full permanent dentition (time two) were collected. The palatal rugae and palatal raphe were used to construct a median palatal plane (MPP). Dental midline position at each time point was measured from the MPP. Results: A total of 56 cases (15 premature, 41 normal) were identified. The mean lower dental midline changes from time one to time two for the premature and normal loss groups were 1.32±0.83 mm and 0.97±0.91 mm, respectively. This difference was not statistically significant regarding group (P=0.62), gender (P=0.91), or the interaction effect of group and gender (P=0.85). Conclusions: There was no significant difference in midline shift between the 15 individuals with premature unilateral primary canine loss and the 41 individuals with normal, asymmetric unilateral loss of a primary canine.