Maxillary expansion effects on mandibular transverse dimension: Comparison of different activation protocols

The purpose of this prospective study was to investigate medium-term indirect effects of Maxillary Expansion (RME) therapy on mandibular arch dimensions using two different clinical protocol activation. Sixty patients in mixed dentition (mean age 7.8 y) showing maxillary deficiency and/or unilateral or bilateral cross-bite were treated with RPE (Haas type) on second deciduous molars. For patient in RME group (rapid maxillary expansion), treatment protocol consisted of 2 turns per day: For patient in SME (slow maxillary expansion) group treatment protocol consisted of 2 turns per week. Study models were taken before (T1) and after expansion (T2) with 12 ± 4 months interval. Dental cast were digitized with a 3D scanner (3Shape, DK) and a set of landmarks was digitized on each digital model. Mandibular intermolar distance (MID), mandibular molar torque (MMT), mandibular intercanine distance (MIcD) and mandibular canine torque (MCT) were assessed. At T1, no differences at baseline were found between groups. At T2, in RME group, mandibular intermolar distance (MID) increased 1.2 mm and MMT increased 6.5°. In SME group MID increased 1.3 mm and mandibular molar torque (MMT) increased 6.2°. There was a significant effect on mandibular intercanine distance (MIcD) (RME +0.8 mm, SME +0.9 mm) and on and mandibular canine torque (MCT) (RME +3.4°, SME +3.8°). The improvement in transversal and torque measurement did not differ between groups. In conclusion, both rapid and slow maxillary expansion protocols have a significant medium-term widening effect on the mandibular first molars and canines.