Localized orthodontic space closure for unilateral aplasia of lower second premolars

The present study aimed to determine whether routine orthodontic space closure can be successfully achieved in patients with unilateral aplasia of the lower second premolars without extracting contralateral or opposing teeth. The dental records and lateral cephalograms of 17 consecutively treated subjects (11 females, 6 males) aged between 14.8 and 19.3 years at the end of active treatment (mean 16.1 years) were analysed. The spaces were closed by 'push-and-pull' mechanics (PPM). Pre- and post-treatment data were compared using a Student's t-test. At the end of active treatment, all parameters (ANB, SNA, SNB, ML/NL, U1-NA, L1-NB, overbite and overjet, upper and lower midline, upper and lower space balance) presented mean values close to accepted norms with satisfactory standard deviations (SDs). Five indicators of success changed significantly: (1) Space closure in the aplastic region was achieved. (2) On the aplastic side, a mean mesial molar relationship of 1.12 (SD 0.18) cusp width (cw) was achieved. The mean alteration from pre- to post-treatment was 1.53 cw (SD 0.29, P <or= 0.001). (3) The corresponding values on the contralateral side were 0.02 cw (SD 0.11), with an alteration during treatment of 0.49 cw (SD 0.22, P <or= 0.001). (4) The overjet was reduced, on average, by 1.06 mm (SD 1.91 mm) to a mean value of 2.47 mm (SD 0.86 mm, P <or= 0.05), and (5) the maxillary incisors were proclined by a mean of 4 degrees (SD 6.21 degrees, P <or= 0.05) to 22.41 degrees (SD 5.37 degrees). Analysis of patient characteristics demonstrated that successful outcomes were routinely achieved in subjects with balanced, vertical or horizontal growth patterns, in those with basal and dental distal and neutral sagittal relationships, and in those with a moderate lack, or excess, of space and balanced space ratios.