April 19, 2011
Micro implants are widely used for the correction of individual molars in a crossbite malocclusion. To correct the crossbite one has to simultaneously intrude and retract the tooth1. Various authors have achieved such correction by placing a micro implant and stretching an elastic or e- chain over the occlusal surface of the tooth. Though this technique was effective in correcting the crossbite, some limitations and clinical problems were addressed. Problems such as the precision of the point of force application for stabilizing the elastics on the precise points of the occlusal surface was not achieved and slippage of elastics was also seen their by consuming more time to provide effective results. Here is an illustration of an upper second molar in buccal crossbite, (Figure 1,2)
where the force is applied and stabilized with a Y design elastic stretching from the buccal surface of the tooth and forming a tripod exactly on three cusps ( tripod force) of the occlusal surface of the tooth and loaded to a micro implant.
A micro implant was placed in the palatal alveolar process between the first and second molar roots. (Figure 3)
Two lingual buttons were bonded on the buccal surface of the upper second molar and four composite blocks were bonded on the occlusal surface. Two on either slopes of the palatal cusp and another two blocks, each on the mesial slope of the mesiobuccal cusp and distal slope of distobuccal cusp. These blocks prevented the slippage of the elastics and held the elastic in the shape of a Y. A red elastic was stretched from the lingual buttons crossing over the occlusal surface between the composite blocks in the shape of a Y and engaged to the micro implant (Figure 4).
The purpose of a placing an elastic in the shape of a Y
The V part of the Y design elastic on three cusps of the occlusal surface of the tooth provides a tripod force and an effective intrusion is achieved due to the precise transmission of a tripod force on the root apex. The I part of the Y design provides the palatal tipping of the crown or retraction (Figure 5).
The Y design elastic, stretching from the buccal surface of the second molar, forms a tripod on the occlusal surface and is effective in simultaneously intruding and retracting the tooth out of crossbite. (Figures 6,7)
A light force and with precise force application for intrusion
Composite blocks prevent slippage of the elastic from the occlusal surface
Effective intrusion and retraction in a shorter period of time
Routine mechanics can be carried out from the first molars for correction of the malocclusion
1) Hyo-sang park, Bong-kyu jang and Hee moon kyung: Maxillary molar intrusion with microimplant anchorage. Aust.orthod. 21: 129-135,2005
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