Distal movement of upper permanent molars using midpalatal mini-implant.

OBJECTIVE To assess whether palatal mini-implants are effective as direct anchorage for distal movement of the upper molars. METHODS It was used an acrylic model of the upper dental arch. After making a groove in the region corresponding to dental alveolus, acrylic teeth were fixed in this groove with #7 wax, with the roots being previously immersed in adhesive wax. The orthodontic appliance was placed according to the Edgewise technique and then a mini-implant (SIN, São Paulo, Brazil) was inserted at the site corresponding to the palatal raphe. A 0.019 x 0.025-in stainless steel archwire was made and attached to the upper arch with elastics. A transpalatal bar (0.019 x 0.025-in) was mounted and two hooks were welded to it in order to retain chain elastics (Unitek, Brazil) to be connected to the mini-implant under a force of 1.5 N on each side. The maxillary model was immersed in water 40 times and photographed after each immersion, for observing dental movements. Analysis of variance (ANOVA) and Tukey's test were used for analyzing the obtained data. RESULTS Molars displaced distally 3.1 mm, in average, with distal inclination ranging from 3 to 5 mm. CONCLUSIONS Molar movements occurred due to distal inclination, with a slight rotation and no extrusive effect.