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Biologic basis of Orthodontic Treatment

INDIAN DENTAL ACADEMY Leader in continuing dental education www.indiandentalacademy.com www.indiandentalacademy.com


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 www.indiandentalacademy.com


ď ś

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.

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THE BASIS OF ORTHODONTIC TOOTH MOVEMENT ORTHODONTIC TREATMENT IS BASED ON THE PRINCIPLE THAT 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.

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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.

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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.

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Theories of tooth movement ď ś Pressure-tension

theory ď ś Piezo-electric theory

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Theories of tooth movement ď ś 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

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Theories of tooth movement ď ś

a) b) c)

Pressure-tension theory: Can be divided into three overlapping stages which include – Alterations in Blood flow associated with pressure Formation and /or release of chemical mediators Activation of cells www.indiandentalacademy.com


Theories of tooth movement 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

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Theories of tooth movement ď ś 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 www.indiandentalacademy.com


After a delay of several days, cellular elements from 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 the Bone immediately adjacent to PDL—undermining Resorption, since the attack is from the underside Of lamina dura. www.indiandentalacademy.com


These osteoclasts arrive in two waves -First wave-derived from local cell population -Larger second wave-are brought in from distant Areas via blood flow. These cells attack the adjacent lamina dura removing bone in the process of Frontal resorption. Tooth movement begins thereafter.At the same time,osteoblasts recruited from PDL form bone on the tension side & begin remodeling activity. www.indiandentalacademy.com


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Pressure-tension theory ď ś

a) b)

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

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Pressure-tension theory a) Frontal Resorption: This is a favourable resorption pattern which depends on: -- Magnitude of force -- Duration of force In this type of resorption, Howship lacunae are seen adjacent to the PDL in the frontal aspect of the lamina dura. www.indiandentalacademy.com


Pressure-tension theory 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. www.indiandentalacademy.com


Pressure-tension theory 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

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The Piezo-electric theory ď ś ď ś

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

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The Piezo-electric theory ď ś a) b)

Limitations: Does not explain how the chemical mediators act Piezo-electricity exists only for a short period.

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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 ď ś

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

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Classification of Orthodontic forces 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) ď ś

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Classification of Orthodontic forces According to Schwarz : 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. ď ś

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Classification of Orthodontic forces ď ś a) b) c)

According to Proffitt : Continuous Forces Interrupted forces Intermittent forces

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Factors affecting tooth movement a) b) c)

Age of the patient and in turn, the viability of supporting structures Magnitude, duration and type of forces applied Chemical agents – action of certain drugs

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THE ORTHODONTIC FORCE DURATION IS CLASSIFIED1) CONTINUOUS – 2 ) INTERRUPTED3 ) INTERMITTENT-

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

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Factors affecting tooth movement a) b) c)

Age of the patient and in turn, the viability of supporting structures Magnitude, duration and type of forces applied Chemical agents

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Types of Orthodontic tooth movement a) b) c) d) e)

Tipping Translation (Sagittal) Intrusion Extrusion Rotation www.indiandentalacademy.com


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EFFECTS OF FORCE MAGNITUDE THE HEAVIER THE SUSTAINED PRESSURE,GREATER SHOULD BE THE REDUCTION IN BLOOD FLOW THROUGH COMPRESSED AREAS OF PDL,VESSELS ARE TOTALLY COLLAPSED NO FURTHER BLOOD FLOWS. WHEN LIGHT BUT PROLONGED FORCE IS APPLIED-

•Blood flow decreases •Partially compressed PDL •Tooth moves in the socket www.indiandentalacademy.com


Harmful effects of Orthodontic Forces Heavy forces often result in extensive damage to the PDL as well as root surfaces. a) Crushing of the PDL – causing pain as well as mobility b) Reversible resorption of bone c) Apical Root Resorption

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

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