Rapid Maxillary Expansion in the Mixed Dentition Using Deciduous Teeth as Anchorage: Behavior of First Molars in Patients With and Without Lateral Crossbites

This preliminary report describes our evaluation of the behavior of permanent maxillary first molars subsequent to rapid maxillary expansion (RME) in the mixed dentition in crossbite and non-crossbite cases; maxillary deciduous canines and second molars were used as anchorage. The RME appliance was cemented on the maxillary deciduous second molars and canines in 19 (13 females, 6males) patients with unilateral or bilateral permanent molar crossbites (Group A) and in 13 (10 females, 3 males) patients who had no lateral crossbites (Group B). After a mean appliance activation period of 15 days for 6-8mm expansion, the appliance was stabilized and kept in place as retention for 5-10 months. Neither active nor passive retention was applied on first permanent molars. Dental casts were produced and evaluated at different points of time: Before treatment (T1), after active expansion (T2), after removal of the RME appliance (T3). In Group A, the mean maxillary permanent intermolar width was 40.6mm at T1, 46.0mm at T2, and 46.3mm at T3. In Group B, 42.4mm at T1, 46.3mm at T2, and 45.4mm at T3. In Group A the crossbite was corrected; the maxillary permanent intermolar distance increased spontaneously and remained stable. The mean spontaneous expansion of permanent maxillary molars was approximately half of the mean expansion of the screw/the anchor deciduous teeth.