Marcotte Mechanics INDIAN DENTAL ACADEMY Leader in continuing dental education www.indiandentalacademy.com www.indiandentalacademy.com
Deep Overbite Correction Bite opening mechanics for deep bite cases 1. Extrusion of the posterior teeth. 2. Intrusion of the anterior teeth. 3. Combination of the two
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Extrusion of the posterior teeth. Correction of deep overbite by this method is often indicated in patients having a steep occlusal plane.
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The four types of extrusive mechanisms are; Tip-back mechanism Base-arch mechanism 0.016-inch distal extension Parallel eruption of the buccal segment
a) b) c) d)
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Tip-back mechanism (extrusion mechanism)
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The tip back mechanism can be used when arch length required is around 1-2mm. Center of rotation is at the distalmost aspect of the lower second molar. Once the buccal segment is upright, space appears between the first premolar and the canine. Activation of the hook over the anterior segment produces a negative moment and an eruptive force to the buccal segment.
The indications for the use of tip back mechanism are ; 1. In growing patients with a forward growth rotation. 2. For a deep curve of spee in the lower arch. 3. For a deep overbite. 4. For slight arch length inadequacy (1-2mm per side) 5. For a steepened natural plane of occlusion
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Tip back mechanism consists of: 1. 2. 3.
0.036-inch lingual arch 0.018 x 0.025 inch anterior segment Buccal stabilizing segments of 0.018x0.025
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If the anterior segment has a normal inclination, the hook should be placed between canine & lateral incisor. (Approximate center of resistance of anterior segment)
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If the lower anterior segment is slightly flared with the canines higher than the incisors, the depressive force should be placed distal to the center of resistance of the anterior segment.
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Base Arch Mechanism • • • • • •
Some times also called an intrusive arch . this is also used for extruding teeth in a deep overbite correction. The main difference between tipback mechanism and base arch is in the location of the center of rotation. C-rot for base arch is located close to the mesial root of lower first molar. The buccal and anterior archwires are similar to that of tip - back mechanism. The lingual arch wire is also placed. The base arch mechanism is made from 0.018x0.025inch stainless steelwith helices. The force system is identical to that of tip back spring,except there is no anterior hook free to slide anteroposteriorly.
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• 1. 2. 3. 4.
If the base arch is preactivated and no lingual arch is present,eruption and rotation of the buccal segments will occur along with lingual crown torque. However ,with the lingual arch in place,we can notice Eruption and a negative rotation of the buccal segment (flattening of the plane of occlusion) No increase in arch length. That the roots of the buccal segment move forward. That second molars appear to be buried.
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0.016 – Inch Distal Extension •
In order to level a deep curve of Spee, both anterior and posterior segments need to be erupted and rotated. This eruption can be done with 0.016-inch distal extension.
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In order to use this appliance, there should be:
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Good growth increments remaining, since the appliance is eruptive. A significant second- order discrepancy between the canines and the incisors; Incisors should be higher than the canines. Minimal arch length required (2-3mm per side) A deep curve of Spee. Extraction of teeth, usually the first premolars.
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The appliance consists of: 1. 2.
3.
0.018x0.025 inch base arch 0.016-inch distal extention. Immediately mesial to the canine bracket a vertical loop is placed and immediately distal to canine bracket a helix is placed. 0.036-inch lingual arch.
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Higher alpha moments [ anterior ] result in more eruption and rotation of the anterior segment;
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Higher beta moments result in more eruption and rotation of the buccal segment.
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Parallel eruption of the buccal segment •
It is used in the upper arch only for parallel eruption of buccal segment
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Here cervical head gear with long outer bow bet at about 60° causes negative moment by bringing the outer bow down to the line of action of headgear strap. Once it is engaged the line of action of force, away from center of resistance produce positive moment.
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Both moments tend to cancel each other & pure extrusive forces to the buccal segment is left
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Intrusion using base arch For intrusion of 4 anteriors, the same base arch used for extrusion is used here. The difference is not involving canine. The force is 100 gms in the midline. The base arch is tied back from the helix to the buccal tube, to prevent flaring of the incisors. To prevent the rotation and eruption of 25. jpg buccal segment , an occipital headgear with short outer which counters the +ve moment from the base arch is used.
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Staged Intrusion of Six Anterior Teeth •First four incisors are intruded then canine is separately intruded using canine intrusion springs. •This avoids avoids large moments on the buccal segment .
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