Abstract
The aim of this study was to investigate changes in tooth positions in the maxilla before and after treatment for anterior crossbite in patients with primary dentition using three-dimensional (3D) analysis in order to evaluate the effectiveness of use of a functional orthodontic appliance (FOA-M). Twenty pairs of cast models obtained before and after treatments were analyzed. Dentition models were superimposed digitally using a reference plane and 14 reference points were dimensionally measured. Differences of each of the 3 coordinates x, y, and z in dentition in measurements taken before and after treatment were determined. The following results were obtained.
1)In the anterior-posterior direction (y-coordinate), we found a significant movement of anterior teeth, in which the primary central incisor showed the greatest amount of forward motion (p ＜0.000). In the vertical direction (z-coordinate), primary anterior teeth changed to an upper direction, while the primary canine did not show change and the primary molar showed a significant change to extrusion (p＜0.000).
2)The amount of 3D tooth movement was the greatest at the Am-point of the frontal teeth (average 1.4 mm), while movement of the molar Do- and Eo- points was smaller (average 0.7 mm).
3)There was a significant change of direction in the θz angle, as θz of the Am-point showed －0.6 rad, indicating a change to the upper direction, that of the Co-point showed a value that was nearly 0 rad, indicating nearly no change for the primary canines, and that of the Eo-point showed a change of ＋0.6 rad, indicating that the second primary molar showed a change to extrusion (p ＜0.000).
4)There was a negative correlation between the amount of 3D movement of the Eo-point, and θxand the occlusal plain angle (p＜0.05).
In conclusion, when patients with an anterior crossbite in primary dentition were treated by FOAM, their crossbite improved by movement of the maxillary primary anterior teeth in an upper and anterior direction, while also spreading laterally and enlarging the primary canine to the outside. As a result, the molars changed to extrusion while spreading in a lateral manner.
