The Application Of Tweed-Merrifield Technique For Treatment Of Missing First Molars

Objective: By analyzing the changes of jaws and teeth of patient with missing first molars after being treated with Tweed-Merrifield technique by moving second molars mesially to close edentulous space, and evaluating the effect of teeth movement, provide clinical references for a better control of the molar movement.Materials and Methods: A 20 years old female patient with missing first molars, diagnosed with class 1 occlusion relationship, was selected. Despite normal overbite and overjet, her left upper first molar was residual root, bilateral mandibular first molars were missing, besides convex face, high FMA angle, crowding upper arch and lower arch. Treatment plan was made after oral examination, occlusion model analysis, and cephalometric analysis. At the beginning of the orthodontic treatment, 4 first premolars, right upper third molar and left upper first molar were extracted. Tweed-Merrifield technique was used to move the second and third molars mesially to close the edentulous space. Tweed cephalometric analysis and cephalograms overlap were measured to assess the effect of this treatment.Results: After 32 months treatment, all the teeth were well aligned. Bilateral molars were moved forward to position(27 to 26, 28 to 27, 37 to 36, 38 to 37, 47 to 46, 48 to 47). A stable occlusion relationship was established. FMA angle maintains 38, which shows a great anchorage control in the vertical direction. The convex profile shows magnificent improvement(Z angle turns from 67 to 69). The cephalogram overlap of pre and post treatment shows no obvious rotation of the upper and lower jaws, intruded and retracted anterior upper teeth, retracted lower anterior teeth, and moved forward second molars. The panoramic radiograph of post-treatment shows paralleled roots,up-righted molars with no obvious root resorption, and unserious contamination of periodontal tissues.Conclusion: A better treatment effect can be obtained by using Tweed-Merrifield technique to move second molars forward to replace first molars.