CATEGORY AUSTRALASIAN DENTIST 55 LINICAL bands. An indent on the lingual attachment locks the expander to the molar band ensuring patient protection. For increased protection, an elastomer may also be placed. The appliance has got a central component and a lateral component. The central component is made of thermally- activated NiTi alloy the lateral arm, which is bracing the palatal aspect of the maxillary posterior teeth, is made of stainless steel. the molar with a screw attached to the centre. The spring provides a continuous force, sufficient to promote a dentoalveolar remodelling that is biologically ideal and biomechanically controlled. The screw has a self-stop mechanism at the end of expansion to prevent it from disassembling in case of excessive activation. Activation Depending on the need of expansion SLE can produce either a 500g or 800g of force. The device is activated on average, 4-8 activations (0, 4, 8 mm) every 6 weeks. A different number of activations will not alter the intensity of the force delivered to the dental structures, as this stays constant (500 or 800 g). There is no risk of over-expansion as the screw, upon reaching the pre-determined expansion, will become passive. However, by changing the activation pattern, rapid maxillary expansion can also be achieved using SLE. Comparison of effects of slow and rapid palatal expansion u When the effects of both slow and rapid maxillary expansions are compared, there is no net difference in the skeletal and dental changes produced by rapid and slow maxillary expansions. u According to various studies, after RME 10 mm of expansion is achieved of which skeletal expansion is 8 mm and dental expansion is 2 mm. u After 4 months, 10 mm of the dental expansion is still present and only 5mm of skeletal expansion is present. Hence, there is 5 mm of skeletal expansion and the remaining 5 mm account for dental movement. u With slow maxillary expansion, after a 10-week period of expansion, the same amount of 5 mm of skeletal and dental expansions is produced. u In rapid expansion, there is more skeletal relapse due to delay in the bone fill in the mid-palatal region after rapid expansion during which the relapse of the skeletal expansion occurs, whereas in slow maxillary expansion, the rate of expansion is close to the maximum rate of bone fill (physiological expansion). CONCLUSION The severity of the transverse discrepancy, age, and the appliance are the most important factors in determining appropriate treatment and prognosis. To achieve optimal skeletal correction, the Haas, bonded occlusal, or bone pin expanders that use palatal contour for anchorage and produce orthopaedic response, minimizing adverse dental tipping, are recommended. As the patient matures, the skeletal expansion obtained can be less than onethird of the expansion produced at the level of the jackscrew. A post-expansion PA cephalogram or CBCT view is useful to evaluate the amount of skeletal correction achieved. Palatal Expansion in the Primary and Early Mixed Dentition Three methods can be used for palatal expansion in children: (1) a split, removable plate with a jackscrew or heavy midline spring, (2) a lingual arch, often of the W-arch or quad-helix design, or (3) a fixed palatal expander with a jackscrew, which can be either attached to bands or incorporated into a bonded appliance. Palatal Expansion in Preadolescents (Late Mixed Dentition) By the late mixed dentition period, sutural expansion often necessitates placement of a relatively heavy force directed across the suture, which micro-fractures the interdigitated bone spicules so that the halves of the maxilla can be moved apart. A fixed jackscrew appliance (either banded or bonded) is necessary. Palatal Expansion in Adolescents (Early Permanent Dentition) / Adults In mid-adolescence, there is a near-100% probability of opening the midpalatalmidpalatal suture with a banded or bonded expansion device, but as the adolescent growth spurt ends, interdigitation of the Spring Loaded Expander Activation At room temperature, the expander is too stiff to be compressed and inserted into the maxillary arch. The transition temperature of theNiTi alloy used in the expander is 94°F, which is close to intraoral temperature. For the appliance to be inserted into themouth, it is chilled so that the central part softens and can be easily inserted. Once the appliance is fitted, the expander warms to the body temperature, becomes stiff and returns back to its original position. The expander delivers constant force as it deactivates. The expander is available in various sizes from 26 to 44 mm in eight different intermolar widths generating 180–300 g of force. The 26–32 mm sizes have softer wires to produce low level force in children. Clinically, the correct size is estimated by measuring the amount of expansion needed and then by adding 3 mm as overcorrection. d. Arch Expansion Using Fixed Orthodontic Appliances Mild degree of arch expansion can be brought about byusing expandedarchwires with fixed mechanotherapy. Appliances such as quad helix or transpalatal arch can be used with fixed mechanotherapy. e. Spring-Loaded Expander The spring- loaded expander (SLE) was introduced by Leone in 2003. The SLE is a new expansion device that produces slow palatal expansion with light, continuous forces. The appliance is indicated in patients whose growth is completed. They produce accurate force levels due to the control on the spring. Appliance framework Theapplianceconsistsofbandssurrounding
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