Case Report: Combination Of Rapid Maxillary Expansion And Self-ligation Technique In Treatment Of Skeletal Class Ⅲ Complicated With Bilateral Posterior Crossbite

Objective: To explore the treatment of bilateral posterior crossbite in clinicalOrthodontics and to evaluate the curative effect of bilateral posterior crossbite byrapid maxillary expansion devices combine with self-ligation brackets.Methods: A male Class III malocclusion patient (16year old) was selected asthe model of bilateral posterior crossbite. Patient’s description: skeletal malocclusionClass III, maxilla and mandible’s development basically normal; bilateral molarsrelationship were mesial relationship; canine relationship were both neutral; incisorswas in edge-to-edge occlusion position; dentition midline already aligned;22waspalatal dislocation, bilateral first permanent molars were crossbite; upper arch’scrowding was9.5mm, lower arch’s crowding was4.5mm. The therapeutic regimencater to the patient’s chief complaint was confirmed after the inquiry，specializedexamination, analysis of X-ray film and the measurement of record model. Firstlyrapid maxillary expansion device was used to widen the upper arch for relieving thecrossbite of molars, SmartClipTMself-ligation brackets was utilized for aligning the upper and lower arch, leveling the curve of occlution and maintain the width ofmaxillary arch. Then intermaxillary traction was used to regulate the sagittalincongruity. Panoramic and lateral radiographs, facial and occlusal images was takenbefore and after the treatment for observing and measuring by24items to assess thechanges of face, teeth and skeleton.Result: Process of treatment lasts31months. After the correction, both upperand lower dentition were arranged in neat rows, bilateral canines and molars becameneutral relationship, dentition midline still aligned, overjet and overbite of front teethestablished regular criteria, temporomandibular joint no abnormalities. TheMeasurement and analysis of study models shows:(1) Length of anterior part in upperarch and length of middle part in upper arch both increased by1.5mm, length ofposterior part in upper arch unchanged; length of anterior part in lower arch increasedby2mm, length of middle part in lower arch increased by1.5mm, length of posteriorpart in lower arch unchanged. It’s clearly that the length of upper and lower archincreased after the treatment, and may provide the space for solving crowding and theunmatching between maxilla and mandible.(2) Width of anterior part in upper archincreased by4.5mm, width of middle part in upper arch increased by4.5mm, width ofposterior part in upper arch increased by6.0mm; width of anterior part in lower archdecreased by0.5mm, width of middle part in lower arch increased by1.5mm, widthof posterior part in lower arch decreased by2.0mm. It’s very obviously that thecombining of rapid maxillary expansion devices with self-ligation brackets brought alarge amount of the width increase in upper arch and it may play a key role to relievethe crowding and posterior crossbite. The decrease of width in lower arch was tomatch the upper arch then to attain the regular overjet and overbite. The contrast ofthe lateral radiographs before and after reveals:(1) ANB had an increase of2.5°which shows the ameliorating of uncoordination between maxilla and mandible.(2)U1-SN increased by0.5°, U1-NA increased by1°, L1-MP increased by5°, L1-NBincreased by4.5°, U1-L1decreased by7.5°, which means the angles of front teethwere still under control.(3) MP-SN increase by1.5°, MP-FH increased by2.5°,shows vertical relationship was heighten a little bit after the treatment.(4) Ls-E, Li-Eincreased by0.5mm，ULP unchanged, LLP increased by1mm, NLA increased by5°,the patient get a better profile via correction. Conclusion: Through the combination of rapid maxillary expansion devices andself-ligation brackets, the patient got a benign curative effect: bilateral posteriorcrossbite was released while edge-to-edge occlusion position of front teeth wasrelieved; bilateral canines and molars were corrected to neutral relationship; overjetand overbite of front teeth got epistrophy while cusp fossas got tight occlusion. Thecombination of rapid maxillary expansion devices and self-ligation brackets solvedthe problem of insufficient width in upper arch and the crowding of both arches—andit regulated the inclination of front teeth, improved the profile meanwhile. So it’sthus obvious that the combination of rapid maxillary expansion devices andself-ligation brackets is an efficacious method to correct bilateral posterior crossbite.