The meta-analysis technique of literature review was applied to a tota
l of 26 previous studies to assess the longitudinal stability of postr
etention mandibular intercanine width. Weighted averages and standard
deviations for the means of 1,233 subjects were compared for linear ch
anges in intercanine transverse dimensions during treatment (T1), imme
diately after treatment (T2), and after removal of all retention (T3).
Net change was defined as the difference between means at T3 and T1.
Dimensional changes were also evaluated on the basis of patient pretre
atment Angle classification, extraction, and nonextraction treatment m
odalities of each group. Paired two-tail t-tests were performed betwee
n T3 and T1 means on all groups at the a priori level of significance
set at a less than or equal to 0.05. Statistically significant differe
nces were observed for the following groups: all patients; nonextracti
on; extraction; Class I; Class I extraction; Class II extraction; and,
Class I Division 1 nonextraction. The findings of this study indicate
that regardless of patient diagnostic and treatment modalities, mandi
bular intercanine width tends to expand during treatment on the order
of one to two millimeters, and to contract postretention to approximat
ely the original dimension. While statistically significant difference
s could be demonstrated within various groups, the magnitudes of the d
ifferences were not considered clinically important.