[Torque control evaluated by lateral cephalometric radiography and cone-beam CT after retraction of the upper...

To investigate the relationship between torque control and movement type of the teeth and to investigate the correlation between reconstruction of the alveolar bone and retraction of the upper anterior teeth.

Cephalograms of pre-treatment and post-treatment of 111 cases and cone-beam computed tomography of pre-retraction and post-retraction of 7 cases were collected. The inclination degree of the upper anterior teeth, the horizontal and vertical displacement of edge and apex,and the thickness of the alveolar bone at the apex level were measured. Student's t test and Pearson χ2 test were performed for statistical analysis with SAS 8.02 software package.

Cases who received torque control during the period of retraction displayed less change of inclination degree of the upper anterior teeth, less lingual displacement of the edge, more lingual displacement of the apex. The total thickness of the alveolar bone at the apex level and the length of the teeth significantly decreased after retraction(P<0.05). The amount of the alveolar bone rebuilt after retraction was less than that of the tooth movement, and there was no significant difference between teenagers and adults.

During retraction of the upper anterior teeth, cases who received torque control showed less inclination degree change of the upper anterior teeth, less lingual displacement of the edge, more lingual displacement of the apex. More bodily movement and partially controlled tipping movement as well as higher incident rate of severe root resorption would also arise. There was correlation between reconstruction of the alveolar bone and the tooth movement. Since the amount of adaptive reconstruction of the lingual alveolar bone was limited, and there was no difference between teenagers and adults, excessive lingual displacement would surpass its adaption ability, and gave rise to alveolar bone and tooth damage.