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Presented by Dr. K. M. Rukhshad Asif Zaman KhanDepartment of Orthodontics andDentofacial Orthopaedics

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1. Pressure Tension Theory by Schwarz: or Tissue Reaction to Orthodontic Forces:When force is applied on a tooth to bring about orthodontico!e ent" it results in for ation of areas of Pressure and Tension

around the tooth. #reas of Pressure are for ed in the $irectionof the tooth o!e ent" while areas of Tension for in the opposite$irection.

%one is a li!ing tissue which reacts to pressure and tension in acertain defined anner. %one surface sub&ected to Pressurereacts by bone resorption while bone sub&ected to Tension e'hibit$eposition.

Biology of tooth

movement

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When a tooth is o!ed due to application of an orthodontic force"there is bone resorption on the pressure side and new bonefor ation on the tension side.

Biology of toothmovement

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Phases of Tooth MovementStudies ha!e shown that tooth o!e ent progresses through threeStages. %urstone categories the stages as:a. (nitial Stage b. )ag Phase c. Post )ag Phasea. (nitial Stage: $uring this phase" !ery rapid tooth o!e ent isobser!ed o!er a short distance which then stops. This o!e entrepresents displace ent of tooth in the P$) space and probablybending of al!eolar bone to a certain e'tent. %oth light and hea!yforces displace the tooth to the sa e e'tent during this phase.Tooth o!e ent in the initial phase is between *.+ to *., and

usually occurs in a wee- s ti e

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b. )ag Phase: $uring this phase little or no tooth o!e ent occurs.this phase is characterized by for ation of hyalinized tissue in the

P$) which has to be resorbed before further tooth o!e ent canoccur. The duration of the lag phase depends on the a ount offorce used to o!e the tooth. (f light force are used" the area ofhyalinization is s all and frontal resorption occurs.(f hea!y force are

used" the area of /yalinization is large" resorption in this case isrearward and longer lag period occurs to eli inate the hyalinizedtissue. The lag phase usually e'tends for 0 2 wee-s. $uration ofthis phase depends upon the density of al!eolar bone" age of the Pt."and e'tent of the hyalinized tissue

Phases of Tooth Movement

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c. Post )ag Phase: #fter the lag phase" tooth o!e ent progressesrapidly as hyalinized zone is re o!ed and bone undergoesresorption. $uring the post lag period" osteoclasts are found o!er alarge surface area resulting in direct resorption of bony surfacefacing the periodontal liga ent.

FORCE

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Tissue Reaction to Orthodontic Forces

Pressure Side: 3 P 4

5P$): 6o pressed to about 172 rd of its thic-ness5%one: %one Resorption Occur

Tension Side: 3 T 45P$): Stretched

5%one: %one For ation

FOR68T

P

T

P

T9 OST8O%)#ST 68)) 3 %one For ation 4

P9 OST8O6)#ST 68)) 3 %one Resorption 4

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Opti al Forces for $ifferent Tootho!e entsMovements Optimal

Forces1. Tipping ;*

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Optimum Orthodontic ForceOpti u orthodontic force is one which o!es the teeth ostrapidly in the desired direction" with the least possible da age to

tissue and with ini u patient disco fort. Fro a clinical pointof !iew" opti u orthodontic force has the following characteristics:1. Produces rapid tooth o!e ent0. ini u patient disco fort

2. The )ag phase of tooth o!e ent is ini al+. ?o ar-ed obility of teeth being o!ed

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Types of Forces based on duration of

application%ased on the duration of #pplication" force can be di!ided into:1. 6ontinuous Force: it is an acti!e orthodontic force that

decreases little in agnitude between appoint ent periods.

8g. )ight wire appliance0. (nter ittent Force: it is an acti!e orthodontic force the decays to zero agnitude or nearly prior to ne't appoint ent.2. (nterrupted Force: it is an orthodontic or orthopeadic force that

is inacti!e for inter!als of ti e between appoint ents.8g. /ead gear.

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(nterrupted Force

6ontinuous Force

(nter ittent Force

$uration of #pplication

F

o r c e

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Types of Tooth MovementThe pri e oti!e of orthodontic treat ent is to o!e the teeth intoore fa!orable and corrected positions. To achie!e this goal" theteeth undergo a !ariety of o!e ents in three di ensions such as

sagittal" coronal and trans!erse. Tooth o!e ents within the oralca!ity can be listed as follows:1. Tipping0. Rotation

2. 8'trusion+. %odily o!e ent;. =p righting>. (ntrusion

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1. Tipping: $uring tipping" crown of the tooth o!es in the directionof the force and the root in the opposite direction. (t can be of tw

types: a. 6ontrolled tipping b. =ncontrolled tipping

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0. Rotation

Rotations are labial or lingual o!e ents of a tooth around its longa'is. (f line of force does not pass through the long a'is of the tooth(t results in rotation. 6orrection of rotation re@uires 6ouple force.

F

F

ROTATION

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2. 8'trusion

8'trusion is the bodily displace ent of a toothalong its long a'is in an occlusal direction

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+. %odily o!e ent AtranslationB

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;. =p righting$uring RC. The crown of certain teethWill be tipped in a esio lingual

$irection with the roots tipped(n the opposite way. Tipping theseRoots bac- to get parallel orientation(s ter ed up righting.

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FORCE

Occlusal plane

>. (ntrusion

(ntrusion is the bodily displace ent of a toothalong its long a'is in an apical direction

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References:

1.Orthodontics The !rt and "cienceFifth Edition ". #. $hala%hi&.Te'tboo( of Orthodontics M. ". Rani

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