CATEGORY AUSTRALASIAN DENTIST 53 LINICAL For each activation, a quarter turn is given. One quarter turn will produce 0.25 mm activation. Toothmovement is about 1mm/ month created by exerting pressure on the teeth in contact with the plate, thus mostly dentoalveolar expansion is created. The appliance is intended to be worn day and night, except for meals and tooth brushing. Disadvantages u Expansion plates are patientdependent for both wearing and activation. u Excessive activation causes dislodgement of the appliance. u Requires readjustment, even if the appliance is not worn for one day. u Appliances are bulky. Modifications of expansion plate Apart from the horizontal placement for transverse expansion, screws can be placed in the following ways: 1. Screws are placed in the anterior aspect of the palate parallel to mid-palatal suture for anterior expansion. E.g., cases of anterior crossbite. 2. A ‘Y’-shaped plate will produce simultaneous lateral expansion of posterior teeth and anterior expansion. or when there is significant lingual tipping of the posterior dentition. u The appliance is activated once per week. It produces on an average 3–4 mm arch length interiorly. b. Coffin Spring The coffin spring was introduced by Sir Walter Coffin in the year 1875. This appliance is capable of producing slow expansion, even though it has been shown to split the palate especially when used in patients in the earlymixed dentition Appliance Framework Wire used: 1.25-mm heavy stainless steel wire. The appliance consists of an omega shaped wire, with the base of the omega placed posteriorly in the midline. The distal ends of the U loop are limited to the distal of the first permanent molar. Anteriorly, the loop gets constricted and recurved into the baseplate. Two separate acrylic wings are made around the wire framework on the slopes of the palate, these also contain the retentive clasps. Indications u Expansion of constricted maxillary arch. u Correction of crossbite (unilateral cross bites) u Conditions requiring differential expansion. Advantages u Cheaper when compared to expansion screws. u Differential expansion of arch in the premolar or molar region is possible. u Less bulky. Disadvantage u Coffin spring tends to be unstable, if it is not made precisely. c. Removable quad helix appliances Removable quad helix is inserted into the lingual attachment (lingual sheath) which is welded or soldered to the molar band. This permits adjustment of the appliance outside the mouth. Schwarz appliance Coffin spring 3. Distalization of buccal segments can be achieved using expansion screws. 4. Expansion plates can be modified for asymmetric expansion. Schwarz appliance is the first removable appliance with jackscrew. It is a horseshoe-shaped removable appliance that fits along the lingual border of the mandibular dentition, with a midline expansion screw. u It is indicated in patients with mild crowding in the lower anterior region Activation Simply pulling the wings apart activates the appliance. This should be done first in the premolar region and then in the molar region. It can also be activated using a three-prong pliers at the base of the omega, but are rarely used as they tend to distort the spring. Care must be taken to maintain the sides of the appliance in the same plane during adjustment. Ideally, marking holes should be drilled on the two wings and a divider should be used to measure the amount of activation given. An expansion of 2–3 mm is made during activation. Removable Quad Helix FIXED APPLIANCE FOR SLOW EXPANSION a. W-arch appliance The W-arch appliance was introduced by Ricketts 1975. Appliance framework Constructed with 0.036-inch stainless steel wire. Wire is adapted to the form of ‘W’ which extends from the first permanent molar to the canine in the anterior palate. Free ends of the ‘W’ are adapted closely to the palatal surfaces of premolars/ deciduous molars. Appliances should be away from the palatal mucosa to prevent tissue irritation. Lingual arch is soldered to bands on molars. The finished appliance is cemented to the first permanent molars.
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