2. INTRODUCTION
• Orthodontic tooth movement is a complex biomechanical process
which is initiated by the clinician with the application of a force.
The applied force moves the tooth beyond its range of
physiologic tooth movement.
• Tooth movement is also noticed following trauma, in certain
pathologic condition, or at the time of extracting a tooth.
• Tooth movements can be broadly divided into three types:
(1) Physiologic
(2) Pathologic/(Pathologic migration)
(3) Orthodontic
3. PHYSIOLOGIC
• The term physiologic tooth movement designates, primarily, the slight
tipping of the functioning tooth in its socket & secondarily, the
changes in tooth position that occur in young persons during & after
tooth eruption.
• These are normal or routine in nature.
4. PATHOLOGIC
• The minor changes in tooth position observed in growing persons &
adults are usually called tooth migration.
• These are associated with periodontal breakdown or altered force
levels in the dental arches.
5. ORTHODONTIC
• The orthodontic tooth movement is based on the simple premise that
whenever pressure is applied to a healthy tooth for a sufficient long
duration of time, its surrounding bone remodels.
6. THEORIES OF ORTHODONTIC TOOTH MOVEMENT
• Pressure tension theory
• Blood flow theory
• Piezoelectric theory
7. PRESSURE TENSION THEORY
• This is the simplest & the most widely accepted theory.
• Schwartz proposed the pressure tension theory in 1932.
• According to this theory:
• Whenever a tooth is subjected to an orthodontic force, it results in
areas of pressure & tension.
• The alveolar bone is resorbed, for a certain length of time, causes
compression of the periodontal ligament, i.e. the pressure side.
• New alveolar bone is deposited whenever there is a stretching force
acting on the periodontal ligament fibers, i.e. the tension side.
8.
9. BLOOD FLOW THEORY
• Also known as fluid dynamic theory.
• This theory was proposed by Bien in 1966.
• According to this theory:
• Tooth movement occurs as a result of alterations in fluid dynamics in the
periodontal ligament.
• Bien characterized three distinct but interacting fluid systems in the
periodontal ligament:
1. Vascular system
2. Cellular system
3. Interstitial fluid system.
10. Force
Compression of PDL
Occlusion of blood vessels
Stenosis of blood vessels
Formation of aneurysms
Blood gases escape into local
environment
Favorable environment for
bone resorption
11. PIEZOELECTRIC THEORY
• It is also known as bone bending or bioelectric theory.
• According to this theory the deformation of the crystal structure
produces a flow of electric current as electrons are displaced from
one part of the crystal lattice to another.
PIEZOELECTRIC SIGNALS
Piezoelectric signals have two unique characteristics:
1. A quick decay rate &
2. The production of an equivalent signal opposite in direction,
when the force is released
In simple words, the piezoelectric signal is created in response to the
force, but it quickly reaches zero even though the force is maintained.
The piezoelectric signal is again produced, this time in the opposite
direction, when the force is removed.
12. • Not only is bone mineral a crystal structure with piezoelectric
properties but so is collagen. Hence, the possible sources of electric
current are:
1. Collagen
2. Hydroxyapatite
3. Collagen hydroxyapatite interface
4. The mucopolysaccharide fraction of the ground substance.
13. • When the force is applied on a tooth, the adjacent alveolar bone
bends.
• Areas of concavity are associated with negative charge & cause bone
deposition.
• Areas of convexity are associated with positive charge & cause bone
resorption.
14. PHASES OF TOOTH MOVEMENT
• Burstone categorized three distinct yet overlapping stages of tooth
movement:
1. Initial phase
2. Lag phase
3. Post-lag phase
15. INITIAL PHASE
• The initial phase of tooth movement is immediately seen following
the application of a force on a tooth.
• The phase is characterized by a sudden displacement of the tooth
within its socket.
• The movement of the tooth into the periodontal space & the bending
of the alveolar bone probably cause it.
16. LAG PHASE
• The lag phase is characterized by very little or no tooth movement.
• It is the phase where the cellular components around the area of
interest get activated to cause tooth movement.
• The lag phase is longer if high forces are applied & vice versa, as the
area of hyalinization created is large & the resorption is rearward.
17. POST-LAG PHASE
• This phase is characterized by the removal of the hyalinized tissue &
tooth movement.
• The movement is mediated by osteoclasts & there is either direct
resorption of the bony surface facing the periodontal ligament or
rearward bone resorption.
18.
19. BONE RESORPTION
• Bone resorption means that the bone is being removed by the various
cellular changes at the site of pressure.
• Two types of bone resorption are seen:
1. Direct/frontal
2. Undermining/rearward
20. DIRECT/FRONTAL RESORPTION
• The term frontal resorption implies that osteoclasts are formed
directly along the bone surface.
• If such resorption is to be obtained, the periodontal fibres must be
compressed to a certain extent.
• This is only possible when the forces are close to the capillary pulse
pressure, i.e. 20-26 gm/sq cm of root surface area.
• Oppenheim & Schwarz have been given credit for discovering the
optimum orthodontic force levels.
• Optimum force are adequate force which move teeth rapidly in the
desired direction with least possible damage to surrounding tissues.
21. UNDERMINING/REARWARD BONE RESORPTION
• Undermining bone resorption is seen when heavy forces are used for
the purpose of tooth movement.
• The use of heavy forces causes the blockade of blood vessels in the
pressure areas due to compression between the root & alveolar
bone.
22. Compression of PDL
Shrinkage & disappearance of cell nuclei
Exchange of degraded capillaries & fibrils
Osteoclasts form in marrow spaces & adjacent areas (20-30 hrs)
Osteoclasts remove the bone adjacent to the necrotic PDL
Undermining resorption occurs
23. ORTHODONTIC FORCE
Orthodontic force is classified according to the duration of decay as:
CONTINUOUS: A force whose magnitude doesn’t decrease over a
period of time. Continuous forces are maintained between activations.
INTERMITTENT: Intermittent forces fall to zero intermittently when the
appliance is taken out & resume when the appliance is reinserted into
the mouth.
INTERRUPTED: Interrupted forces drop to zero between activations.
24. BONE FORMATION
• Bone formation is the result of deposition of osteoid by osteoblasts.
• The number of fibroblasts & osteoblasts increase on the tension side.
• The increase in number occurs by mitotic cell division.
• After this, the osteoid gets deposited along the stretched fiber bundles,
resulting in formation of bone lamellae.
• Calcification of deepest layer of osteoid starts as the new tissue increases
in thickness & the superficial layers remain uncalcified.
• The newly calcified tissue along with that of already deposited layer is
called bundle bone.
• When the new bundle bone attains a certain thickness, it reorganizes into
lamellated bone.
26. EFFECT OF DRUGS/MEDICATIONS ON TOOTH
MOVEMENT
• Orthodontic tooth movement enhancers:
- Vitamin D administration
- Direct injection of prostaglandin into the PDL
• Orthodontic tooth movement depressors:
- Bisphosphonates
- Prostaglandin inhibitors.
