bio mechanical considerations in

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Biomechanical Considerations in

Treatment with Miniscrew

Anchorage

Part 1- Sagittal plane

Part 2-Horizontal & Transeverse

planes

MIN-HO JUNG, DDS, MSD, PHDTAE-WOO KIM, DDS, MSD, PHD

J Clin Orthod 2008


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Introduction

Anchorage control is one of the most important aspect oforthodontic treatment.

Traditionally extraoral anchorage has been used to reinforceintraoral anchorage.

But, the disadvantage is the patient co-operation


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Introduction

The use of miniscrews for reinforcement of orthodontic

anchorage has become increasingly popular in recent years .

Especially in adult patients who do not want to wear extraoralappliances


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4

Structure of an ImplantStructure of an Implant

Implant

Head Body

(Serves as)

Abutment in prostheticrehabilitation

Attachment source forelastics & coil springs inorthodontic treatment


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5

The portion that is embedded in the bone is termed as Body.

The Body is divided into 2 types

a) Screw type

b) Plate type

TheportionthatisembeddedintheboneistheBODY

Itisof2types

1.Screwtype

2.Platetype


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Introduction

Property Prosthodontic implant Orthodontic implant

Composition Titanium Titanium

Duration of use Permanent Temporary

Type of load Axial Non axial

Diameter Large Small


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Miniscrews are

convenient,

save time, and

produce good treatment results with no need for patient cooperation.

In some patients treated with miniscrews, however, mechanicalfactors can produce unusual changes or side effects.

The present article explains these mechanical variations andprovides tips for solving the problems


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The sagittal plane

Anchorage reinforcement is most commonly needed in patientswith severe protrusion.

In conventional retraction with sliding mechanics after first

premolar extractions, the molars typically move forward 3.6-3.8mm.

Anterior retraction with sliding mechanics


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What happens when miniscrews are

used for anchorage reinforcement?

ROTATIO

NOF

ENTIRE

ARCH

AROUND COResistance

ROTATIO

NOF

ANTERI

OR

SEGMENT

AROUND COResistance

EITHER OR


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Miniscrews in cases of severe protrusion

DEEP

OVERBITE

POSTERIOR

OPEN BITE

The use of precurved archwires will result in an even stronger intrusive

force on the posterior segment


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Redirecting the Retraction Force

To pass through center ofresistance of the anteriorsegment

Which is located between thelateral incisor and canine roots,

6.76mm above the cervicalarea


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Redirecting the Retraction Force

Limitations :1. Higher line of force

promotes irritation of softtissue by elastomeric chain or

coil springs because ofarchwire curvature

2. Limited width of gingivaltissue precludes highplacement of miniscrew

3. Insertion in the mobilemucosa increases the risk ofinflammation around theminiscrew and may lead to

failure

Optimum position

of the miniscrew


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Posterior Intermaxillary Elastics

Light 3/16" intermaxillaryelastics, worn only at night,can prevent posterior openbite

Not recommended for

patients with vertical skeletalpatterns


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Vertical Retraction Forces

Apically positioned miniscrews andocclusally oriented hooks producemore vertical retraction force

INDICATIONS:

In patients with gummy smiles orother factors favoring intrusion of anentire arch

To control overbite during retractionin cases of deep overbite.


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Anterior Biteplanes

Occlusal plane rotation due to forces ofocclusion can be prevented by bondinganterior bite planes to the lingual surfacesof the anterior teeth at the beginning ofretraction


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Additional Anterior Miniscrews

Additional anterior miniscrewscreate vertical force to counteractocclusal plane rotation and maintaintorque.

In a patient with a gummy smile or

over -erupted upper incisors

Anterior miniscrews positioned between

roots of lateral incisors and canines


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The Horizontal Plane

Center of resistance of anterior and posterior segment ofthe upper arch in horizontal plane


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If the anterior teeth are retracted en masse, each segment movesaround its center of resistance


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If miniscrews are used for anterior retraction, the right and left quadrants rotate around each center of resistance, and

the molars tend to tip palatally

To counteract these effectsTPA and lingual stabilizing arch arenecessary


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Patient with midlinedeviation and occlusal

plane canting

Upper midline shifted to

left of facial midline

Lower midline are shifted

to right of facial midline


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Use of anterior midline elastics increases canting of

occlusal plane.


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Anchorage from upper left and lower right miniscrews used to

correct midline deviation and occlusal plane canting


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Patient with occlusal plane canting and deviation of

upper and lower midlines to right of facial midline.


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Conventional use of miniscrew

anchorage

Increases canting of

occlusal plan


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Miniscrew added in upper anterior region for vertical

correction of occlusal plane canting


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Age / Sex: 32yr/ F

C/O: PROTRUSIVEprofile

H /o: mandibular first

molar extracted in herteenage

class II div 1malocclusion

Overjet : 13mm

Deep overbite

Lower midline deviatedto right

Occlusal plane cant

Upper left quadrant

Lower arch


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Miniscrew anchorage used to retract anterior teeth and

correct occlusal plane canting.


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Long hooks soldered to archwire for bodily movement of maxillary

anterior teeth

Additional miniscrews in the anterior region


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Lower arch


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Age : 26yr/ F

C/o: right TMJ

discomfort andmandibular anterior

crowding

Severe class III molar

relation

Lower midline shifted to

left


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Slight rotation of mandibular occlusal plane and development of overbite


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Conclusion

If the clinician keeps in mind these probable sideeffects which can be caused in the sagittal , horizontaland transeverse planes by the use of miniscrews and

takes proper measures to counteract them , best resultscan be achieved.


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