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Changes in the mandibular arch after rapid maxillary expansion in children: A three-dimensional analysis using digital models

Objective: This retrospective study quantitatively evaluated and compared the change in distance between mandibular first molars before and after rapid maxillary expansion (RME) using digital models. Materials and Methods: Twenty-seven (n = 27) plaster models (16 females and 11 males, between 6 and 9 years old) from patients treated at the Interceptive Orthodontic Clinic of the Pontifical Catholic University of Paraná (PUCPR, Curitiba, Brazil) were used. The initial (T1) and final (1 year after, T2) dental casts were scanned. The distances between the mandibular first molars were measured and compared using Geomagic Foundation software (Rock Hill, SC, USA). The central fossa of each mandibular molar was used as the reference point. The mandibular arch perimeter was measured using Orthoviewer (3Shape, Copenhagen, Denmark). Results: The intermolar width increased by 0.23 mm and by 0.75 mm in the arch perimeter. In two patients the intermolar width increased more than 2 mm, and in five patients the values from the initial measurements decreased. Conclusions: RME does not increase mandibular intermolar width distance or the mandibular arch perimeter in growing patients treated with Haas-type palatal expanders when evaluated using digital models.