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8/3/2019 Locating the Center of Resistance of Maxillary Anterior
http://slidepdf.com/reader/full/locating-the-center-of-resistance-of-maxillary-anterior 1/17
Instructor: Dr.林錦榮 Reporter:北醫TR2尹姵今
8/3/2019 Locating the Center of Resistance of Maxillary Anterior
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Moment-to-force ratio :type of tooth movement
uncontrolled tipping, controlled tipping, bodily movement, root thrusting
Retraction force in relation to the location of the center of resistance (Cres)
predict ant. teeth esthetic tooth movement
Changing the vertical vector of the force
8/3/2019 Locating the Center of Resistance of Maxillary Anterior
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Retraction force on anterior teeth
Establishment of absolute anchorage
Lingual approach - esthetic braces & critical torquecontrol of anterior teeth
Longer retraction hooks beyond the level of Cres are
possible
Disadvantage: Anterior torque loss and verticalbowing of the occlusal plane
8/3/2019 Locating the Center of Resistance of Maxillary Anterior
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Additional torquing springs with helixes
Slide along the palatal miniscrew (vertical support)
Counterbalancing the torque loss of anterior teeth&intrusionwith distal tipping of canine teeth(when en mass retraction)
Bodily-like parallel retraction of anterior teeth
8/3/2019 Locating the Center of Resistance of Maxillary Anterior
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8/3/2019 Locating the Center of Resistance of Maxillary Anterior
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Standard dentiform (12 teeth, bilateral first premolar ext )
3D finite element model
PDL: 0.25mm
Compact bone thickness: 2mm
Socket of the first premolar tooth: only cancellous bone
All materials were isotropic, homogeneous, and linear elastic
Any interface was assumed to be perfectly bonded
8/3/2019 Locating the Center of Resistance of Maxillary Anterior
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Midpoint on the linebetween the incisal pointsof both central incisors
Transverse x-axis (+: left, -:
right); anteroposterior y-axis (+: anterior, -: posterior);vertical z-axis (+: up, -: down)
The plane formed by theincisal edge and
mesiobuccal cusp of bothmaxillary first molars
8/3/2019 Locating the Center of Resistance of Maxillary Anterior
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DJR: 0.8mm diameter
The retraction lever arms - on the
lateral incisors The torquing springs - on the canines
The retractor force was 200 g per side
8/3/2019 Locating the Center of Resistance of Maxillary Anterior
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Miniscrew: sagittally placedbetween the secondpremolar and the firstmolar
6, 7, 8, 9, and 10 mmapically from the cervical
line of the first molar
8/3/2019 Locating the Center of Resistance of Maxillary Anterior
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A: The midpoint of the incisal edge of the incisalteeth and the cusp point of the canine tooth
B: The root apex
A’
and B’
: The new positions of A and B
Displacement ratio
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8/3/2019 Locating the Center of Resistance of Maxillary Anterior
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8/3/2019 Locating the Center of Resistance of Maxillary Anterior
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8/3/2019 Locating the Center of Resistance of Maxillary Anterior
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Cres: 12.2 mm level from the incisal edge of the central incisor in the XY plane
Correspoding to 8 mm from the cervical lineof the first molar
55.56% apical to the incisal edge
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Diverse modeling conditions producedifferent outcomes among studies
The 3D finite element analysis is onlytheoretical and has limitations
Teeth displacement is affected primarily bythe vertical position of palatal miniscrews
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The Cres of six maxillary anterior teeth waslocated vertically 12.2 mm (55.56%) apical tothe incisal edges of central incisors, in
accordance with the 8 mm level of miniscrewsfrom the cervical line of the first molar