[Cone-beam CT evaluation of volume and surface area changes of impacted upper central incisors before and after orthodontic treatment]

The purpose of this study was to quantitatively evaluate root resorption by cone-beam computer tomography (CBCT) after orthodontic treatment of impacted upper central incisors.

Ten patients (12 impacted incisors and 8 contralateral corresponding teeth) were included in this study. With self-designed modified nance arch and straight wire arch, the impacted incisors were treated by combined orthodontics and surgery approach. CBCT images of all patients were taken before and immediately after the treatment. Mimics software was used to build three-dimensional images. The upper central incisors were isolated. Volumes of teeth and superficial area were calculated. The difference between pre- and post- treatment was statistically evaluated with paired samples t test using SPSS13.0 software package.

Significant difference in volume and superficial area was found between pre- and post- treatment (P<0.05). The average whole dental volume increase was (9.67±10.86) mm³, and the superficial area increase was (28.97±14.36)mm². Statistical significance was achieved among 12 impacted incisors. The average whole dental volume increase of the control group was（12.38±10.22）mm³, and the superficial area increase was（30.64±16.74）mm². There was no significant difference between the impacted and the control group in dental volume and superficial area before and after treatment (P>0.05).

The treatment by combined orthodontics and surgery approach could promote tooth development for impacted incisors without causing root absorption, which can be safely performed.