INTRUSION MECHANICS

Dr Tony Pious

The intrusive tooth movement is used in the correction of overbite.

anterior segment intrusion in deep bite cases

posterior segment intrusion in open bite cases

INTRODUCTION

“Intrusion refers to the apical movement of the geometric center of the root (centroid) in respect to the occlusal plane or plane based on the long axis of the tooth.”

TYPES TRUE INTRUSION OR ABSOLUTE INTRUSION

RELATIVE INTRUSION- achieved by preventing eruption of the

incisors, while growth provides vertical space into which the posteriors erupt.

PSEUDO-INTRUSION - labial tipping of an incisor around its centroid.

PRINCIPLES OF INTRUSION(BURSTONE AJO 1977)

• Controlling force magnitude

• Anterior single point contacts

• Point of force application

• Selective intrusion

• Control of reactive units

• Avoid extrusive mechanics

SELECTIVE INTRUSION

Leveling with a continuous arch or with a sectional wire can produce undesirable side effects.

Many times the overbite is corrected not because of intrusion but by extrusion.

AVOID EXTRUSIVE MECHANICS

Extrusive mechanics such as employing class II or class III elastics should be avoided in patient who need genuine intrusion.

THREE PIECE INTRUSION ARCH

Introduced by Shroff, Lindauer and Burstone ( AJO 1995).

Simultaneous Intrusion and retraction of anterior teeth.

Consists of:Posterior segmentAnterior segmentIntrusive cantilever spring

Posterior anchorage unit

Intrusion cantilever

Anterior segment

with posterior extension

RICKETTS UTILITY ARCH

This auxiliary archwire was developed and refined by Ricketts for bioprogressive therapy.

The utility arch engages only two molars and the four incisors. It is commonly known as a 2 X 4 appliance.

MATERIALS FOR UTILITY ARCH

Blue Elgiloy of 0.016" x 0.016" 0.016" x 0.022”

Dimension in an 0.022" slot.

A utility arch can even be made with 0.014"

or 0.018" round wires.

PARTS OF UTILITY ARCH

Incisal segment

Posteriorvertical

segment

Vestibular segment

Molar segment

Anterior vertical

segment

It produces 60-100 gms on the lower incisors for intrusion.

The overall effect is intrusion and possible torqueing of the lower incisors as well as tipping back of the molars.

5 mm space between the anterior border of the auxiliary tube and the posterior vertical segment of the utility arch allows tying back the utility arch.

Gable bend

Cinching distally

Tip-back bend

• The tip back bend in the molar segment leads to posterior tipping of the first molars.

• Which can be avoided by placing a gable bend in the posterior aspect of the vestibular segment or a transpalatal arch can be used.

K SIR APPLIANCEVARUN KALRA( JCO Sept 1998 )

• The K-SIR ( Kalra Simultaneous

Intrusion and Retraction ) archwire is

a modification of the segmented loop

mechanics of Burstone and Nanda

K-SIR archwire: .019“x.025" TMA archwire with closed U-loops 7mm long and 2mm wide.

• 90o V bend is placed at the level of each ‘U’ loop

• This ‘V’ bend when placed between first molar & canine during

space closure, creates two equal and opposite moments to counter

the moments caused by the activation forces of closing loops.

• Archwire with off-center 60° V-bend placed about 2mm distal to U-

loop.

• Off-center V-bend creates greater moment on molar, increasing

molar anchorage and intrusion of anterior teeth.

• To prevent the buccal

segments from rolling mesio

lingually due to the force

produced by the loop

activation, a 20° anti-

rotation bend is placed in the

archwire just distal to each

U-loop .

A. Trial activation performed on each loop.

B. Archwire after trial activation

Neutral position of loop determined with mesial and distal legs extended horizontally. In neutral position, loop is 3.5mm rather than 2mm wide.

A. K-SIR archwire in place prior to cinching backB. Archwire cinched back to activate loop about 3mm, so that mesial and distal legs are barely separated.

o Simplicity of design

o Less likely to cause tissue impingement.

o 0.019 x 0.025 TMA provides sufficient strength to resist distortion and

enough stiffness to generate the required moments.

o The superior material properties of TMA compared to stainless steel

o Reduced treatment time due to en-masse retraction.

o Frictionless mechanics

o Presence of offset V-bends act as anchor bends

o Molar anchor control is excellent even without headgear.

ADVANTAGES

CONNECTICUT INTRUSION ARCH(By Nanda R, JCO 1998 )

The CTA is fabricated from a nickel titanium alloy

oabsolute intrusion of anterior teeth

omolar tip-back for Class II correction

opreparation of posterior anchorage

oincisor flaring

ocorrection of minor open bites

olevelling of anterior occlusal cants

USES

It incorporates the characteristics of the utility arch as well as those of the conventional intrusion arch.

Preformed with the appropriate bends

Two wire sizes are available: .016 x .022 .017 x .025

Anterior dimensions of maxillary 34mm & mandibular 28mm, respectively.

The bypass, located distal to the lateral incisors, is available in two different lengths to accommodate for extraction, non-extraction, and mixed dentition cases.

The CIA’s basic mechanism for force delivery is a V-bend calibrated to deliver approximately 40-60g of force.

Upon insertion, the V-bend lies

just anterior to the molar brackets.

When the arch is activated, a simple force system results, consisting of a vertical force in the anterior region and a moment in the posterior region.

THANK YOU