locating the center of resistance of maxillary anterior

8/3/2019 Locating the Center of Resistance of Maxillary Anterior

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Instructor: Dr.林錦榮 Reporter:北醫TR2尹姵今



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



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



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



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



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



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



Miniscrew: sagittally placedbetween the secondpremolar and the firstmolar

6, 7, 8, 9, and 10 mmapically from the cervical

line of the first molar



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



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



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



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

locating the center of resistance of maxillary anterior

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