Geometric morphometric analyses of dental arch changes: A 40-year follow-up in patients with initial mild and severe crowding treated with 4 premolar extractions
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Published on: February 23, 2024
Caroline Martins Gambardela-Tkacz1, Gabriela de Domênico Alcaraz Ros1, Paula Cotrin1
1Department of Orthodontics. Bauru Dental School, University of São Paulo, Bauru, São Paulo, Brazil.
Introduction:
This research aimed to evaluate changes in dental arch shape during orthodontic treatment and long-term follow-up (T3) in patients treated with 4 premolar extractions because of mild to severe initial dental crowding using the geometric morphometric analysis.
Methods:
The sample consisted of 32 patients treated with 4 premolar extractions divided into 2 groups according to the Little's irregularity index (LII) at pretreatment (T1; mild or severe crowding). Group mild crowding: 15 subjects with an initial LII of ≤6 mm, and mean T1, posttreatment (T2), and T3 ages of 13.52, 16.05, and 55.15 years, respectively. The mean treatment and T3 times were 2.53 and 39.09 years, respectively. Group severe crowding: 17 subjects with an initial LII of >6 mm with mean T1, T2, and T3 ages of 13.43, 15.48, and 54.41 years, respectively. The mean treatment and T3 times were 2.05 and 38.92 years, respectively. The images from the digital dental models at T1, T2, and T3 were analyzed with principal components analysis and canonical variates analysis on shape variables after a generalized procrustes analysis, to examine intragroup and intergroup arch shape changes at T1, T2, and T3.
Results:
The principal components analysis revealed that the arch shape variations at T1 were related to the displacement of incisors and canines. At T2, the variations were due to the 4-premolar extractions and anterior retraction. The variation after nearly 40 years was related to both the relapse of anteroinferior teeth and the aging of the occlusion. The arch shape changed with treatment and remained acceptable at T3. The canonical variates analysis illustrated that the maxillary and mandibular shape of dental arches were similar for both groups.
Conclusions:
Dental arch shape was modified during orthodontic treatment and remained relatively stable at T3 in both groups, despite some degree of relapse and maturational changes in the occlusion.
