CATEGORY 54 AUSTRALASIAN DENTIST LINICAL Activation u For anterior expansion – opening of apices of ‘W’ (position 2) u For posterior expansion – opening near anterior region (position 1) The appliance delivers proper force levels, if opened 4–5 mm wider than the passive width and should be adjusted to this dimension before being inserted. The appliance is activated at the rate of 2mm per month until the cross bite is mildly overcorrected. b. Quad/ Tri/Bi Helix appliance Quad helix was introduced by Robert M Ricketts. The appliance is a precursor to the tri- and the bi-helix appliances. They are all named after the number of helices incorporated in the appliance. Appliance framework The quad helix consists of four helicesmade of 0.038” diameter wire (elgiloy or stainless steel wire), soldered to the molar bands. The length of wire increases the range of action and flexibility, and decreases the force levels. The tri- and the bi-helix appliances incorporate only three and two helices respectively. It is a fixed appliance comprising stainless steel bands cemented onto the maxillary first molars and a standard stainless steel arch attached to the palatal surfaces of the teeth. Activation The appliance is capable of producing differential expansion i.e. it can be activated to produce expansion levels in the premolar and molar regions. It can be activated prior to cementation of the bands by stretching the molar bands apart or in the mouth with the use of a three-prong pliers. u In the anterior bridge: Results in expansion in the molar region. u In the palatal bridge: Derotation and expansion of molar on the same side and distalization of molar on the opposite side. u Outer arms are activated to expand canines and premolars. u Opening of posterior helix expands the buccal arm. An initial expansion of 8 mm will produce 14 oz of force. Average force is 200–400 g depending upon the amount of expansion or activation. The expansion of the steel arch (normally 10 mm before insertion) exerts a lateral force on the teeth, resulting in a predominant transverse dentoalveolar expansion of the maxillary arch. If necessary, the appliance can be reactivated after 6 weeks. Once inserted, the appliance is not dependent on patient compliance. Parts of quad helix: (A) posterior helix, (B) palatal bridge, (C) anterior helix, (D) anterior bridge and (E) outer arm. The quad-helix consists of two anterior Indications of quad helix appliance u Narrow upper arch that needs expansion, e.g. in crossbites u Crowded, mixed or permanent dentition in which long range growth can be predicted and requires mild expansion as there is lack of space for the upper laterals. u Class II malocclusions where the upper arch needs effective widening and upper molars need distal rotation. u Class III malocclusions where the upper arch needs effective widening and advances with class III elastics. u Thumb sucking and tongue thrusting cases with theirits modifications. u Unilateral or bilateral cleft palate. Advantages u It provides excellent expansion in cleft palate patients. u Expansion is smooth and controlled. u In young children, skeletal expansion can be achieved. u Anterior bridge with helices acts as reminder for habit breaking. For correction of unilateral posterior crossbite in mixed dentition, it has been proved that the Quad Helix appliance is superior to the expansion plate in terms of effectiveness and cost minimisation and is therefore the preferred method of treatment (Petrén et al., 2013). Disadvantages u One major disadvantage of this appliance is buccal tipping of molars during excessive activation. This can be prevented by torquing the roots buccally. c. Ni-Ti Expanders Wendell V Arndt, in 1993, developed a tandem-loop NiTi, a temperatureactivated palatal expander. This has the capability to produce continuous, light force on mid-palatal suture and uprights, rotates and distalizes maxillary first molars simultaneously. W arch Ni-Ti Expanders and two posterior helices. The portion of wire in between the two anterior helices is called the anterior bridge and that connecting the anterior helices and the posterior helices is called the palatal bridge. The free ends that are usually adapted close to the premolar teeth are called the outer arms. The outer arms are soldered to the molar bands. The posterior helix should not extend more than 2 mm distal to the first permanent molar. Appliance Framework This fixed appliance has stainless steel extensions that could be adjusted and inserted into standard horizontal lingual sheaths which are welded to the molar
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