Applying Tweed-Merrifield Directional Force Technique In Adult With Angle Class Ⅲ~S Malocclusion By Extracting Four Premolars

Objectives: Assess the effect on adult patient with Angle class IIISmalocclusion byextracting four premolars and applying Tweed-Merrifield Directional Force Techniqueto retract anterior teeth. To evaluate the changes between the lips and teeth, as well asthe effect on the lip aesthetic.Materials and Methods: An Angle class IIISfemale case was selected from DalianOrtho Clinc in March2012, who was22years old, convex profile, upper and lowermoderate crowding and anterior teeth on edge, maxillary midline shift to the left.Through the patient’s oral examination, model analysis and cephalometric analysis,the patient was treated by extracting15、24、34、44、18、28、38、48and applyingTweed Technique. X-ray was taken pre-treatment and a week before completion oftreatment, measurements from Tweed analysis, measurements of soft tissue associatedwith the lips and superimposition of pre-and post-treatment were used to observe thechanges.Results: After21months，the treatment was finished. Pre and post-treatmentchanges showed: crowding was relieved, class IIISmolar relationship was changed toclass I，normal overbite and overjet were achieved, profile was improved, upper andlower dentition midline was centered and symmetric. After treatment, panoramicradiograph show that roots are substantially parallel and show no significantabsorption, alveolar bone and periodontal tissue are in good health, condyles aresymmetric. Mandible was rotated counterclockwise, mandibular plane angle wasdecreased (FMA decreased from30°to28°). Lower anterior teeth was retracted anduprighted (IMPA95°decreased82°). Obvious improvement of the profile (Z ANGLE 66°increased75°；Li-H line changes from3mm to0mm). Lip morphology of patientis in harmony, patient and parents are satisfied with the results.Conclusion: For the treatment of adult patient with Angle class IIISby extracting fourpremolars, applying Tweed-Merrifield Directional Force Technique to retract anteriorteeth. This technique controls the teeth movement precisely in3D, lips and teethrelationship can be changed, so that patient obtain the aesthetic lip.