CATEGORY 50 AUSTRALASIAN DENTIST LINICAL phase of treatment which usually lasts from 2-4 weeks. It is capable of providing sutural expansion of 11mm within a very short period of wear and a maximum of 13mm can also be achieved. RPE utilizes large forces to produce maximal orthopaedic repositioning with a minimum of orthodontic movement. Bonded RME appliance The bonded RME was first described by Cohen and Silverman in 1973. In bonded RME, instead of bands, metallic cap splints or acrylic covering is used. 1. Cast metal cap splints: Cast cap splint to all the teeth is prepared to which the screw is soldered. The entire assembly is cemented/bonded. 2. Acrylic splints: Thick gauge stainless steel wire is closely adapted around the posterior teeth from premolars to molars both buccally and palatally. The screw is soldered to the wire. Acrylic is covered over the occlusal, buccal and palatal occlusal third of all the posterior teeth. The assembly is cemented/ bonded. depending upon the age of the patient and form of the appliance. According to Proffit, most screws open 1mm per complete revolution, so that a single quarter turn produces 0.25mm of tooth movement. The suture expansion is around 20 to 50%of the total screwexpansion (Bazargani et al., 2013). RME also leads to an increased dimension of the nasal cavity (Ballanti et al., 2010) and moderate evidence exists that RME in growing children improves the conditions for nasal breathing from a shortterm perspective (Baratieri et al., 2011). For adults, the recommended two turns each for the first two days followed by one turn per day for the next 5 to 7 days and then only one turn every alternate day until the desired expansion is achieved. Surgery can be used as an adjunct to RME therapy in adult patients, especially in the third decade of life or later. 6. Clinical implications of RME u Mid-palatal suture does not open evenly but opens in a ‘V’ fashion. u The broad end of V is in anterior region and apex of V is at the posterior region. u Appearance of median diastema. u Occlusal and PA cephalometric radiograph will reveal the suture opening. u Usual treatment period is 2 weeks. u Relapse is higher after RME; hence overcorrection is advised. Advantages of bonded RME: u Bonded appliances are useful in highangle cases. u The occlusal acrylic covering prevents the increase in mandibular angle by acting as a splint. u Reduced posterior teeth tipping and extrusion. u Provides bBite block effect to facilitate the correction of anterior crossbite. 5. RME Appliance management The basic principle of the appliance involves the generation of forces that are capable of splitting the mid-palatine suture for expansion but some dentoalveolar expansion effects are also produced. Hence, the forces should be definitely more than the usually used orthodontic forces. The forces generated are close to 10 to 20 pounds. An expansion of 0.2 to 0.5mm should be achieved per day. The screw when turned 90 degrees, the midpalatalmid-palatal suture will open by 0.2 mm and narrows the periodontal membrane by 0.1 mm on each side. The screw is activated at between 0.5 to 1mm per day and about 1 cm of expansion can be expected in 2 to 3 weeks. The activation schedules tend to vary In Haas and Hyrax, the screw is activated once or twice a day, normally 0.2 mm per activation, and both appliances have been shown to be effective in correcting transverse maxillary deficiency (Weissheimer et al., 2011). Every turn of the screw opens the appliance by 0.25 mm. Each turn involves 90° activation. Timms has suggested an activation of 90°, morning and evening for patients up to the age of 15 years.: In patients above this age, he suggests an activation of 45° four times per day. Zimring and lsaacson recommended, two turns per day for initial 4 to 5 days followed by one turn per day in growing individuals. “V” pattern of mid-palatal suture opening Midline Diastema RME can also be successfully achieved for unilateral or bilateral posterior crossbite without engaging the permanent teeth (Cozzani et al., 2007). Amodified Haas-type RME appliance is used, and the appliance is anchored to the maxillary primary molars and canines. Modified Haas type Temporary anchorage devices (TADs) can be used as skeletal anchorage in combination with the expansion appliance. Thus, miniscrews can be inserted on each side of the median palatal suture to replace teeth as anchorage units (Ludwig et al., 2013).
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