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Biologic basis of Orthodontic Treatment

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Biologic basis of Orthodontic Treatment

State of equilibrium Classification of Orthodontic Forces Theories of Tooth Movement Types of Orthodontic tooth movement Orthopedic effects of Forces Iatrogenic effects of Orthodontic forces


Why do teeth not move under normal circumstances?

--- Equilibrium theory, which states that the forces from the extraoral and the intraoral areas balance each other, aided additionally by the periodontium.


THE BASIS OF ORTHODONTIC TOOTH MOVEMENT

ORTHODONTIC TREATMENT IS BASED ON THE PRINCIPLETHAT IF PROLONGED PRESSURE IS APPLIED TO A TOOTH,

TOOTH MOVEMENT WILL OCCUR AS THE BONE REMODELS.

BONE IS SELECTIVELY REMOVED IN SOME AREAS AND ADDED IN OTHERS.


THE TOOTH MOVES THROUGH THE BONE CARRYING ITS ATTACHMENT APPARATUS WITH IT,AS THE SOCKET OF THE TOOTH MIGRATES.

THIS BONY RESPONSE IS MEDIATED BY THE

PERIODONTAL LIGAMENT, TOOTH MOVEMENT IS

PRIMARILY A PERIODONTAL PHENOMENON.


Forces applied to the teeth can also affect the pattern of bone apposition and resorption at sites distant from the teeth, viz sutures of the maxilla and bony surfaces of the TMJ

Thus, the biologic response to orthodontic treatment includes not only the response of the PDL, but also the growing areas distant from the dentition.


Theories of tooth movement

Pressure-tension theory Piezo-electric theory



Pressure-tension theory: This is the most accepted theory. According to this theory, whenever pressure and tension zones exist, chemical messengers are released which will bring about recruitment of osteoblasts and osteoclasts



Pressure-tension theory: Can be divided into three overlapping stages which include –

a) Alterations in Blood flow associated with pressure

b) Formation and /or release of chemical mediators

c) Activation of cells



Alterations in Blood flow associated with pressure

a) Increasing pressure on the tooth results in reduction of blood flow.

If the force application continues, a zone of sterile necrosis results – Zone of Hyalinization



The second stage involves the release of chemical messengers

--- Primary messengers: Cytokines, Prostaglandins

---- Secondary messengers: Cyclic AMP

Prostaglandin E2 has the property of stimulating both osteoblastic as well as osteoclastic activity


After a delay of several days, cellular elementsfrom adjacent undamaged areas of PDL begin to

invade the necrosed area.Osteoclasts appear within adjacent bone marrow

Spaces & begin an attack on the underside of theBone immediately adjacent to PDL—underminingResorption, since the attack is from the underside

Of lamina dura.


These osteoclasts arrive in two waves

-First wave-derived from local cell population-Larger second wave-are brought in from distantAreas via blood flow. These cells attack the adjacent lamina dura removing bone in the process ofFrontal resorption.Tooth movement begins thereafter.At the sametime,osteoblasts recruited from PDL form bone on the tension side & begin remodeling activity.


Pressure-tension theory

Two types of resorption patterns are seen whenever forces are applied to move teeth.

a) Frontal Resorption

b) Undermining resorption



a) Frontal Resorption: This is a favourable resorption pattern which depends on:

-- Magnitude of force -- Duration of forceIn this type of resorption, Howship lacunae are seen

adjacent to the PDL in the frontal aspect of the lamina dura.



b) Undermining resorption : This is a resorption pattern seen whenever heavy forces are applied, which compress the PDL beyond half its original size.

Due to obstruction of the blood flow, osteoclasts cannot be recruited onto the frontal aspect of the lamina dura.



b) Undermining resorption :

Instead, a resorption wave is initiated from the underside of the Lamina dura – known as ‘Undermining resorption’

Responsible for ‘jumpy’ pattern of tooth movement, often seen with fixed appliances


The Piezo-electric theory

According to this theory, whenever stresses are applied to bone, it deforms and bends.

Charges are produced on the inside and outside, which stimulate either deposition or resorption


The Piezo-electric theory

Limitations:

a) Does not explain how the chemical mediators act

b) Piezo-electricity exists only for a short period.


Classification of Orthodontic forces

According to Schwarz :

a) First degree of efficiency:These are forces lower than the threshold of stimulation to activate Orthodontic tooth movement.

---Short duration and low force balanced by the compensatory mechanisms




c) Third degree of Efficiency: The forces in this category tend to interrupt circulation in the PDL (20-50 gm/sq.cm)



According to Schwarz :b) Second degree of efficiency:This refers to force

levels most effective in achieving Orthodontic tooth movement. (Optimum Orhtodontic force). Characterised by low but continuous forces (roughly 15-20 gm/sq.cm over the compressed PDL)




d) Fourth degree of Efficiency: The force levels in this group are so excessive that they crush the PDL between the tooth and the alveolar bone in the areas of pressure. If continuous, they can cause extensive, irreparable damage.



According to Proffitt :

a) Continuous Forces

b) Interrupted forces

c) Intermittent forces


Factors affecting tooth movement

a) Age of the patient and in turn, the viability of supporting structures

b) Magnitude, duration and type of forces applied

c) Chemical agents – action of certain drugs


THE ORTHODONTIC FORCE DURATION IS CLASSIFIED-

1) CONTINUOUS –

2 ) INTERRUPTED-

3 ) INTERMITTENT-

Continuous and interrupted forces are produced by Fixed appliances, while the intermittent forces are produced by removable appliances


Factors affecting tooth movement

a) Age of the patient and in turn, the viability of supporting structures

b) Magnitude, duration and type of forces applied

c) Chemical agents


Types of Orthodontic tooth movement

a) Tipping

b) Translation (Sagittal)

c) Intrusion

d) Extrusion

e) Rotation


EFFECTS OF FORCE MAGNITUDE

THE HEAVIER THE SUSTAINED PRESSURE,GREATER SHOULD BE THE REDUCTION IN BLOOD FLOW THROUGH COMPRESSED AREAS OF PDL,VESSELS ARE TOTALLYCOLLAPSED NO FURTHER BLOOD FLOWS.

WHEN LIGHT BUT PROLONGED FORCE IS APPLIED-•Blood flow decreases•Partially compressed PDL•Tooth moves in the socket


Harmful effects of Orthodontic ForcesHeavy forces often result in extensive damage to the PDL

as well as root surfaces.

a) Crushing of the PDL – causing pain as well as mobilityb) Reversible resorption of bone c) Apical Root Resorption


Orthopedic forces and their effectsa) On the maxilla – Maxillary growth stimulation or restraint is facilitated because of the presence of suturesin the naso-maxillary complex.


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copy of biologic basis tooth movement /certified fixed orthodontic courses by indian dental academy

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