Application of polar coordinate method in analyzing the extraction therapy effect of skeletal cross-bite malocclusion

Objective: To investigate the clinical value of polar coordinate measuring method through analyzing effect of adults skele- tal cross-bite malocclusion. Methods: 18 adult skeletal cross-bite patients( aged 18-23,average 20. 8,9 men,9 women) were chosen. In these cases,four premolars were extracted. Lateral cephalograms were taken at central occlusion position for all of them before and af- ter treatment. The system of polar coordinates was established with the Bolton Point( Bo) as the pole,and the Bo-N Line as the polar axis. The polar angles and the polar radiuses of soft and hard tissue marking points of maxilla-mandibular facial region were measured respectively. The measured data were processed by SPSS 17. 0 with pair t test. Results: All cases were treated successfully. Bo-L1 was decreased significantly by 6. 54 mm on average( P 0. 01),Bo-LL was decreased by 3. 51 mm and Bo-U1 was increased by 2. 17 mm on average respectively( P 0. 05). Conclusions: Polar coordinates can be used to accurately describe as a whole the craniofacial fea- tures for the skeletal cross-bite patients. Soft and hard tissue profiles were improved significantly after treatment.