biology of orthodontictooth movement
DESCRIPTION
Widescreen 16:9TRANSCRIPT
JM 1
BIOLOGY OF ORTHODONTIC TOOTH MOVEMENT
Prepared By
JEAN MICHAELFinal Year - RDC
Guided By
Dr. Hariprasad MDSDr. Sarath MDSDr. Shaji MDSDr. Yohan Varghese MDS, PhD
Widescreen (16:9)
JM 2
Physiologic Tooth Movement
It is the naturally occurring tooth movementsthat take place during and after tooth eruption
1. Tooth eruption2. Migration or drift of teeth3. Changes in tooth position during mastication
JM 3
Tooth Eruption
Axial or occlusal movement of the tooth from its developmental position within the jaw to its functional position in the occlusal plane
JM 4
Theories Of Tooth Eruption
• Vascular pressure theory• Root formation• Bone Remodeling• Periodontal ligament traction
This theory states that the periodontal ligament is rich in fibroblaststhat contain contractile tissue. The contraction of these periodontal fibers (mainly the oblique group) result in tooth eruption.
JM 5
Migration Or Drift Of Teeth• Teeth have the ability to drift through the alveolar
bone • Human teeth have a tendency to migrate in mesial or
occlusal direction • This maintains the inter-proximal and occlusal contact • Aided by bone resorption and deposition by
osteoclasts and osteoblasts respectively
JM 6
• Mesial - due to proximal caries (loss of tooth structure)
• Occlusal - Due to premature exfoliation or absence of opposing tooth (supra-eruption)
JM 7
Tooth Movement During Mastication• Normal force of mastication – 1 to 50 kg• It occurs in cycles of 1 second duration• Teeth exhibit slight movement within the socket and
return to their original position on withdrawal of the force
• Whenever the force is sustained for more than 1 second, periodontal fluid is squeezed out & pain is felt as the tooth is displaced within the periodontal space
JM 8
PERIODONTIUM
JM 9
JM 10
• Thickness of normal PDL – 0.5 mm• Collagenous fibres of PDL connects
the cementum and lamina dura• The fibers run at an angle attaching
farther apically on the tooth than on the adjacent alveolar bone
• PDL space is filled with fluid derived from vascular system
JM 11
Periodontal Ligament
JM 12
Cellular Elements in the PDL• Fibroblasts – produce and destroys collagen fibers• Osteoblasts –produce new bone• Osteoclasts – aids in bone resorption• Cementoblasts – forms new cementum• Cementoclasts – removes cementum• PDL is vascular and contains nerve endings which
aid in proprioception
JM 13
JM 14
FIBROBLAST
JM 15
OSTEOCYTE
JM 16
OSTEOBLASTS
JM 17
OSTEOCLASTS
JM 18
• Is orthodontic movement possible for a tooth that has undergone endodontic treatment ?
YES (the PDL is intact in this case)
• Is it possible to move an ankylosed tooth ?
NO (here there is complete absence of the PDL)
JM 19
Piezoelectric Effect• When a force is applied to a
crystalline structure (like bone or collagen), a flow of current is produced that quickly dies away
• When the force is released, an opposite current flow is observed
• The piezoelectric effect results from migration of electrons within the crystal lattice
JM 20
Response to Normal Function• Teeth and periodontal structures are subjected to
forces up to 50 kg during mastication• Force is transmitted to the alveolar bone which
bends in response• Generation of piezoelectric currents• It acts as an important stimulus to skeletal
regeneration and repair resulting in adaptation of bony architecture to functional demands
JM 21
Response to Continuous Pressure• < 1 second: Fluid in the PDL is incompressible
• 1 – 2 seconds: PDL fluid expressed, Tooth moves within PDL space
• 3 – 5 seconds: PDL fluid squeezed out, Tissue compressed and immediate pain is felt if force is heavy
JM 22
Force for Orthodontic Tooth Movement• Forces that bring about orthodontic tooth movement
are continuous and should have a minimum magnitude (threshold)
• Below this threshold limit, the PDL has the ability to stabilize the tooth by active metabolism
• The minimum pressure required is 5 to 10 gm/cm2 (current concept)
JM 23
Resting Pressure from Lip & Tongue• Upper Anteriors
Force exerted by LIP > Tongue• Lower Anteriors
Force exerted by TONGUE > LIP• Teeth remain stable in their position as the
unbalanced forces acting on them, are below the threshold limit tolerated by the metabolism in PDL
JM 24
Magnitude of Force VS Tooth Movement
JM 25
ORTHODONTIC TOOTH MOVEMENT
JM 26
Modes of Orthodontic Tooth Movement
Forces created by orthodontic appliances bring about tooth movement by 2 mechanisms.
• FRONTAL Resorption• UNDERMINING Resorption
JM 27
Frontal Resorption
• Accomplished by Light Orthodontic Forces• least painful • least harmful to the periodontium• Most desirable
JM 28
• Caused by Heavy Orthodontic Forces• Painful• More harmful to the periodontium• Occurs in a small scale even in the most careful
orthodontic treatment• The dentist should always try to minimize this
Undermining Resorption
JM 29
Role of Piezoelectric Current • Piezoelectric currents produced on application of force
on tooth and alveolar bone dies off quickly and play little role in orthodontic tooth movement
• Orthodontic tooth movement requires sustained forces which does not produce continuous piezoelectric current
• But these signals which are produced while normal chewing are required for proper maintenance of normal bony architecture
JM 30
The Pressure – Tension Theory• When force is applied on the tooth, PDL is
compressed on one side and stretched on the other side
• Blood flow is decreased on the pressure side where PDL is compressed
• Blood flow is increased on the tension side where PDL is stretched
JM 31
• The process of initiation of tooth movement has 3 stages1. Alternation of blood flow associated with
pressure within the PDL2. The formation and release of chemical
messengers3. Activation of cells which causes deposition and
resorption of bone
JM 32
• BONE RESORPTION (osteoclastic activity) takes place at the side of the PDL where there is PRESSURE
• BONE FORMATION (osteoblastic activity) takes place at the side where there is TENSION
JM 33
Maintenance of Thickness of Alveolar Bone• In an ideal treatment, the attachment level is
maintained • Resorption and deposition of bone maintains its
thickness in the facial and lingual side irrespective of the type of movement the tooth has undergone on the alveolar bone
JM 34
Chemical Regulation of OTM• Within the 1st hour
Increase in Prostaglandin E & Interleukin – 1Increase in Cytokines & Nitric oxide (NO)
• After 4 hours of pressure applicationIncrease in cAMP (chemical mediator for differentiation)
PROSTAGLADINS can stimulate formation of both OSTEOBLAST & OSTEOCLAST
JM 35
• It takes a minimum of 4 to 6 hours of continuous force to initiate orthodontic tooth movement
• So removable appliance worn for less than this minimum period of time is of no use
Maximum efficiency is obtained if the appliance is worn for 24/7
JM 36
Types of Orthodonic Forces
• LIGHT Force – Frontal resorption• HEAVY Force – undermining resorption
JM 37
Effect of Magnitude of Force on PDL
JM 38
Application Of Continuous Light Force• < 1 second: PDL fluid is incompressible, alveolar bone
bends, piezoelectric signal generated
• 1 – 3 seconds: PDL fluid expressed & tooth moves within the socket
• 3 – 5 seconds: Blood vessels within PDL partially compressed on pressure side & dilated on tension side. PDL fibers and cells are mechanically distorted
JM 39
• Minutes: Blood flow altered & oxygen tension begins to change. Prostaglandins and cytokines released
• Hours: Metabolic changes ocures. Chemical messengers affects cellular activity. Enzyme levels change
• 4 Hours: Iincreased cAMP levels are detectable & cellular differentiation begins within PDL
• 2 Days: Tooth movement begins as osteoclasts & osteoblasts remodel bony socket
JM 40
No pressure – Normal perfusion of blood vessels
JM 41
Light pressure – blood vessels constricted
JM 42
Tension side – Fibers stretched & Vessels open wide
JM 43
Result of Continuous Light Force• Osteoclasts initiates resorption of lamina dura from
the side of PDL• The osteoclasts arrive in 2 waves
1st wave derived from the PDL itself2nd wave (larger) from distant areas via blood flow
• All these events lead to FRONTAL RESORPTION
JM 44
Application of Continuous Heavy Force• < 1 second: PDL fluid is incompressible, alveolar bone
bends, piezoelectric signal generated
• 1 – 3 seconds: PDL fluid expressed & tooth moves within the socket
• 3 – 5 seconds: Blood vessels with in PDL occlude on the pressure side
JM 45
• Minutes: Blood flow gets cut off to compressed PDL area
• Hours: Cell death in compressed area• 3 to 5 days: Cell differentiation in adjacent marrow
spaces; undermining resorption begins• 7 to 14 days: Undermining resorption removes
lamina dura adjacent to compressed PDL & tooth movement occurs
JM 46
Heavy Pressure – Blood flow totally cut off
JM 47
Compressed PDL after Sterile Necrosis
JM 48
Cellular Changes• Loss of blood flow causes sterile necrosis of the PDL• A “Hyalinized” area devoid of cells and vasculature
develops• Osteoclasts appear within the adjacent bone marrow
spaces and begins an attack on the underside of the bone immediately adjacent to the necrotic PDL area
• An initial delay in tooth movement ocures
JM 49
• This delay is due to 2 reasons• The delay in stimulating differentiation of cells
within the marrow space • A considerable thickness of bone has to be
removed from the underside before any tooth movement can take place
JM 50
Undermining Resorption
JM 51
Frontal Resorption VS Undermining Resorption
JM 52
Centre Of Resistance
• It is the point on the tooth when a single force is passed through it, would bring about its translation along the line of action of the force
JM 53
• Factors affecting Centre of Resistance1. Number of roots2. Degree of Alveolar Bone loss3. Degree of Root Resorption
JM 54
ANCHORAGE• It is the Resistance to Unwanted Tooth Movement
Or
• It is the nature and degree of resistance to displacement offered by an anatomic unit for the purpose of effecting tooth movement
JM 55
Absolute Anchorage
1. Appliances gaining anchorage from extraoral structures – Extraoral appliances (eg – Head Gear)
JM 56
2. Titanium screws implanted into the alveolar bone through the gingiva to act as anchorage
JM 57
Intraoral Anchorage
• Anchorage value of a tooth is proportional to the surface area of the root
• The tooth with larger root surface area requires greater force to move
JM 58
Anchorage Value Of Each Tooth
JM 59
• Teeth that are ANKYLOSED or DILACERATED are very good sources of anchorage
JM 60
Different Types of OTM
CONTROLLED TIPPING
UNCONTROLLED TIPPING
BODILY MOVEMENT
JM 61
ROTATION ROOTUPRIGHTING
JM 62
EXTRUSIONINTRUSION
JM 63
Optimum Forces For OTMsTYPE OF MOVEMENT FORCE REQUIRED (gm)
Tipping 35-60 Bodily movement (translation) 70-120Root uprighting 50-100Rotation 35-60 Extrusion 35-60Intrusion 10-20
JM 64
Forces Delivered by Appliances
• Continuous Force (ideal spring)• Interrupted Force (removable active plates)• Intermittent Force (removable appliances)
JM 65
Continuous Force
JM 66
Interrupted Force
JM 67
Intermittent Force
JM 68
Deleterious Effects of Orthodontic Force• Pain• Allergic reactions• Mobility • Gingival Inflammation• Loss of vitality of pulp• Root Resorption
JM 69
Pain• If appropriate force (not heavy) is applied, the patient
feels little pain immediately• Pain develops after several hours• The patient feels mild aching sensation and the teeth
are quite sensitive to pressure• The pain usually lasts for 2 – 4 days and disappears
until the appliance is reactivated
JM 70
• For most of the patients, the pain associated with the initial activation of the appliance is most severe
• Pain is due to the development of ischemic areas in the PDL
• The pain is directly proportional to the area of PDL that has undergone sterile necrosis (hyalinization)
• So heavier forces produce larger areas of hyalinization and greater pain
• Pain can be managed using analgesics like ACETAMINOPHEN
JM 71
Allergic Reactions• Some patients may develop allergic reactions
to Stainless steel which contains NICKEL• Allergic reactions manifest as widespread
erythema and swelling of oral tissue which develops 1 – 2 days after starting the treatment
• In such patients, Stainless steel appliances (brackets, bands, wires etc) should be substituted with TITANIUM appliances
JM 72
Mobility• Mobility is due to–Widening of PDL space during orthodontic
treatment– Temporary disorganization of the fibers in the PDL
• Moderate increase in mobility is an expected response of orthodontic treatment
JM 73
• Heavier Force causes greater degree of Undermining Resorption which leads to Excessive mobility
• Excessive mobility indicates that there is heavy force acting on the tooth
• If the tooth becomes extremely mobile, force should be discontinued until the mobility decreases to moderate levels
• Excessive mobility will usually correct itself without permanent damage
JM 74
Insults to the Pulp• There will be a modest inflammatory response
within the pulp at the beginning of the treatment• It may cause an initial mild pulpitis which has no
long term significance
JM 75
Loss of Vitality of Pulp• Loss of vitality may be encountered if there is– History of previous trauma to the tooth – Poor control of orthodontic forces
• Heavy forces cause abrupt movement of root apex causing obstruction of the blood flow to the pulp
• Relatively heavy forces applied for intrusion can also give rise to the same situation
JM 76
Root Resorption• Cementum adjacent to the hayalinized PDL undergo
resorption by cementoclast cells• This can progress to the extend of dentin destruction• Once orthodontic forces are removed, repair occurs
by the deposition of new cementum in the area of previous destruction
• Dentin once lost will not be replaced
JM 77
Craters of Root Resorption in Dentin
JM 78
Types of Resorption• Slight Blunting• Moderate resorption – up to ¼ of the root length• Severe resorption – more than ¼ of the root length• Moderate Generalized Resorption• Severe Generalized Resorption • Severe Localized Resorption
JM 79
Slight Blunting
JM 80
Moderate Resorption
JM 81
Severe Resorption
JM 82
Moderate Generalized Resorption• Most of the teeth show some loss of root length • Greater in patients whose treatment duration
was longer• Shortening of root length is more for maxillary
incisors • In most cases, this type of resorption is clinically
insignificant
JM 83
Severe Generalized Resorption• This is mostly of unknown etiology• In case of patients with thyroid deficiency, chances
of developing severe generalized resorption is high• To prevent this, thyroid supplementation is
indicated
JM 84
Severe Localized Resorption
• Caused by excessive forces and prolonged duration of treatment
• Risk of severe resorption is much greater for maxillary incisors
• Very high risk is noted if roots of maxillary incisors are forced against the lingual cortical plate
JM 85
Effect of DRUGS on OTM
JM 86
Drugs which Enhance OTM
• Vitamin D administration
• Direct injection of Prostaglandin into PDL(disadvantage – It is very painful)
JM 87
Synthesis of Prostaglandins
PHOSPHOLIPIDS ARACHIDONIC ACID PROSTAGLADINS
CORTICOSTEROIDS NSAIDS
JM 88
Drugs which Impede OMT• BISPHOSPHONATES – for Osteoporosis– Alendronate
• PROSTAGLADIN INHIBITORS– Indomethacin
• TETRACYCLINES– Doxycycline
JM 89
• TRICYCLIC ANTIDEPRESSANTS– Doxepine– Imipramine
• ANTIARRHYTHMIC agents– Procaine
• ANTIMALARIALS Drugs–Quinine– Chloroquine
JM 90
Patient with Osteoporosis• This condition is encountered in case of post-
menopausal females• The patient may be using BISPHOSPHONATES which
binds to Hydroxyapatite in bone and inhibits Osteoclast mediated Bone Resorption
• BEFORE ORTHODONTIC TREATMENT,– Consult the patient’s physician and temporarily
switch to estrogen therapy (Evista)
JM 91
Pain killers – Do they Inhibit OTM ?• Common analgesics used during treatment– IBUPROFEN– ASPIRIN
• At the dose level used during orthodontic treatment, they do not impede tooth movement
• Acetaminophen is a better option as it is a centrally acting agent which does not reduce inflammation
NSAIDS
JM 92
Prostaglandin Inhibitors in Microspheres• If Prostaglandin Inhibitors were placed in mini-
spheres and could be maintained in the sulcus around tooth (like antibiotics in periodontal therapy) which has to serve as anchorage, the efficiency of the orthodontic treatment can be improved.
JM 93
Conclusion• A dentist should thoroughly understand the biological
factors and principles behind Orthodontic Tooth Movement. He should achieve the desired aesthetic and functional result using the optimum amount of force. He should also give consideration to the health of the periodontium and thus try to minimize the deleterious effects of the treatment.
JM 94
REFERENCE
• Contemporary Orthodontics 4/e• Orban’s Oral Histology and Embryology 11/e• Ten Cate’s Oral Histology 7/e• Orthodontics – The Art and Science 4/e
THANK YOU