[Three dimensional measurement and analysis of maxillary protraction treatment in skeletal Class III malocclusion]

To study the three-dimensional mechanism of maxillary protraction in skeletal Class III malocclusion by cone-beam CT (CBCT).

Fourteen patients (6 males and 8 females with a mean age of 10.9 years) of early permanent dentition with skeletal Class III malocclusion were treated with maxillary protraction. CBCT was used to obtain the Dicom data both before and after treatment, and then digitized with the software Dolphin 11.0 was used to reconstruct and establish the tridimensional coordinate system. 23 landmarks were chosen for measurement and analysis. The data was analyzed using SPSS 17.0 software package.

After maxillary protraction, A- coronal plane distance, SNA and ANB increased significantly (P<0.01); A- horizontal plane distance, ANS-PNS increased significantly (P<0.05), suggest maxillary growth was forward and downward. Po-S-N increased significantly (P<0.01), while SNB decreased significantly (P<0.05), suggesting that the chin was rotated downward and backward, and mandibular growth was inhibited. U1j - the coronal plane distance increased significantly (P<0.01), suggesting that the upper incisor moved forward; U1-SN angle increased significantly (P<0.05), suggesting anterior teeth inclined labially. The distance between U6j- horizontal plane and U6j- the coronal plane increased significantly (P<0.05), suggesting that maxillary molar elongated and moved mesially. Frontomaxillary suture changed on the three-dimensional direction, but without significant difference (P<0.05).

Three-dimensional measurements confirm that growth and remodeling of bone suture (such as pterygopalatine suture) play an important role in maxilla development. The maxilla and maxillary teeth move forward and downward, while the mandibular growth is inhibited after maxillary protraction.