A CBCT Study Of Changes In Facial Soft Tissue After Orthodontic Treatment With Four Premolars Extracted In Bimaxillary Protrusion In Adults

ObjectiveThe aim of this study was to evaluate soft tissue changes after the orthodontic treatment of class I bimaxillary dentoalveolar protrusion with four premolars extracted in adults cases by CBCT.Materials and MethodsTwenty adult patients were selected from Department of Orthodontic, College of Stomatology, Shandong University,during the year from2009to2012. The study incuded8males and12females(age range:19-28,average age:23). Pre-and post-treatment CBCT scans of20class I bimaxillary dentoalveolar protrusion adults were taken. All of the patients were treated by extraction of four first premolars, and banded by straight wire appliance(SWA) technique. Implant anchorage was used during the treatment progress.11soft tissue parameters, including3angular and8linear parameters, were selected.To avaluate the measuremnet error of the CBCT cephalometric analysis, the method error was calculated according to Dahlberg’s formula. T-test was used to analyze pre-and post-treatment CBCT cephalograms by using SPSS software (version14.0), at the level of P<0.05.Results1.In this study, the random error of identification in x, y, z, was0.34mm,0.30mm and0.25mm, respectively. The random error of linear measurement and angular measurement was0.30mm (standard deviation:0.14mm),0.36° (standard deviation:0.12°), respectively.2.For each soft tissue cephalometric parameter in males and females, changes between the pretreatment and posttreatment measurements, determined by the paired t-test, were satistically different. Changes between males and females showed no satistically difference. P values of the parameters such as, NLA, ULP, LLP, HA, LL-H line distance, sl-H line distance, UL-EP distance, LL-EP distance, were all less than0.01, showed satistically significant. The mean changes of11soft tissue parameters in all patients were showed as followed:Ns-Sn-Pos, NLA, ULL and LLL was increased by1.2°,10.0°,0.8mm and0.6mm, respectively; HA, ULP, LLP, LL-H line distance,sl-H line distance,UL-EP distance and LL-EP distance was decreased by4.5°,1.8mm,2.3mm,2.5mm,2.7mm,6.0mm and4.4mm, respectivly.Conclusion1.For patients who suffered from Class I bimaxillary protrusion with a normally divergent in adults, satisfactory effect was got by applying SWA with four first premolars extracted when implant anchorage was used. It demonstrated a significant improvement in the lower1/3of the facial soft tissue.2.As an advanced imaging means， CBCT can be used to evaluate the changes between pre-and post-treatment in bimaxillary protrusion patients.