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Relapse of mandibular anterior crowding in angle class II division 1 malocclusion treated by tandem mechanics without extraction of permanent teeth : a retrospective analysisYavari, Javid; School of Graduate Studies (1998-12)The mandibular incisor segment has been described by several authors as the segment that is most likely to exhibit relapse following active treatment and retention. Therefore, relapse of the mandibular anterior teeth after treatment and retention phases is a challenge that clinicians need to address. The amounts of mandibular anterior crowding .were measured before treatment, after treatment, and after post-ret~ntion in a longitudinal study . . of 31 subjects with Angle Class II Division 1 malocclusion. These measurements were made, retrospectively, using dental models and lateral cephal9metric radiographs. All patients were treated by the same orthodontist who used tandem mechanics without the _prior extraction of permanent teeth. The post-retention period ayeraged 5.2 years with a range of 2 to 19 years. AdditioD;ally, this gr<:;>up of 31 subjects was divided into two subgroups according to their change in irregularity-index. Group D (N=17) showed a decrease. or no change ·in irregularity index while Group I (N=14) showed an increase in irregularity index. The variables studied were: intercanine distance, intermolar distance, overjet, overbite, irregularity index, lower incisor to mandibular. plane angle (IMPA). Irregul~rity decreased significantly du.ring treatment. The mean value ·for the complete sample (N=31) for irregularity index was reduced from 4.5mm before treatment to 1.0mm after treatment. The irregularity index was stable at 1.0mm through the end of the post-retention follow-up·.period. The mean post-retention fqllow-up time for Group D was 3.8 years, and for Group I the mean was 7 . 0 years. The mean difference of 3.2 years between· Group D and I was statistically significant (p=0.0159). Group D showed better stability of ·treatment induced expansion of intercanine distance than Group I (0.9mm. expansion vs. 0.6mm of expansion loss) . This difference was significant (p=0.0288). Group I had_a statistically significant overjet correction compared to Group D (8.3mm vs. 5.9mm, p=0.0031). In contrast to previous studies, irregularity correctio~ in this study was stable over a mean of 5. 2 years of pos·tretention follow-up. The groups of subjects ·experiencing relapse of mandibular anterior crowding had more overjet and had less stable.treatment induced intercanine expansion.