Abstract
Objective To investigate the differences of alterations of lower arch between two different extraction patterns treated with Alexander Discipline. Methods 52 extraction cases treated with Alexander Discipline were divided into group A (extraction of first premolars) and group B (extraction of upper first and lower second premolars). Arch widths, lengths, curve of Spee and irregularity index (IRR) were measured in digital mandibular casts before and after treatment. IMPA was also measured in cephalograms. Paired t-test and group t-test were used for statistical analysis. Results The lower inter-canine width increased slightly, while lower inter-molar width, depth of curve of Spee and IRR decreased after treatment (P 0.05). The decrease of inter-molar width and depth of curve of Spee were larger in group B, but IMPA was smaller than group A (P 0.05). Conclusions Alexander Discipline is prevailing in maintaining the lower arch width. Extraction of the lower first premolars has advantages in maintaining lower inter-molar width as well as retracting lower incisors. Extraction of lower second premolars might be more appropriate in correcting the distal molar relationship and maintaining the angulation of lower incisors. Key words: Alexander discipline; Extraction treatment; Three-dimension digital cast; Cephalometric analysis
Published Version
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