MARA
The MARA or Mandibular Anterior Repositioning Appliance is attached to stainless steel crowns on the first
molars. Crowns are preferred over bands to help withstand the tremendous leverage forces generated by the appliance. The MARA was developed to overcome the complaints that patients expressed when wearing a Herbst appliance, particularly the bulk in the lower bicuspid area. In addition to the normal rectangular arch wire tube, the upper first molar has a large .062 square
tube, which accepts an adjustable .060 square “elbow” that hangs vertically.
The lower first molar has the normal rectangular tube as well as a .059 round wire “arm” projecting buccally from the mesial.
The lower arm will hit the upper elbow and prevent the teeth from occluding unless the lower arm and lower jaw are held forward in front of the elbow. Typically, the lower crowns or bands are stabilized by either a lingual arch or lower braces to prevent the resting pressure of the elbows from rotating the lower molars mesio-lingually. The elbows are held in place with both elastics and ligature wire.
Most skeletal Class II cases have normally positioned maxillas, retrognathic mandibles, and constricted maxillary arches. To help develop the narrow maxillary arch, a Hyrax screw is soldered to the lingual of the crowns. If the maxillary arch is normal in width, a transpalatal arch is used to anchor the molars and help distribute the forces generated by the appliance. Occlusal rests
are placed on the first bicuspids. The rests can be bonded with composite for additional retention
類似的產品RMI(rapid molar intruder)(使用上,上下顎舌側必需加上舌弓以增加穩定性),可分為 size M ~~給混合齒列期(MIXED
DENTITION)使用,可以產生800gm的壓入力(intrusive force),與size A~~給成人齒列期(ADULT DENTITION)使用,可以產生1000gm的壓入力,,,病人每隔4周回診一次,完成壓入後,舌弓留置原地當維持之用
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