1-Biology of tooth movement Flashcards
The periodontium consists of?
1-The periodontal ligament
2-The alveolar bone
3-The cementum
4-The gingiva
The function of the periodontium?
1-one of them is to distribute and absorbs the force during mastication
2-it provides active stabilization of the teeth against surrounding forces, therefore, it implies a threshold for orthodontic tooth movement
What is the thickness of the pdl?
Normal thickness is 0.5
What are the major components of the PDL
1-Collagenous fibers (connects the cementum to the lamina dura
2-Cellular elements (B.V, nerves)
3-Tissue fluids
What is the Alveolar bone?
The portion of the mandible and maxilla the houses the teeth
-and it is renewed in response to functional demand
What are the cellular elements of the pdl?
1-Fibroblasts—Produce and destroys collagen fibres.
2-Osteoblasts—Produce new bone.
3- Osteoclasts– aids in bone resorption.
4- Cementoblasts– Forms new cementum.
5- Cementoclasts– Removes cementum.
- The PDL is vascular and contains nerve endings which aid in proprioception
Why it is impossible to move an ankylosed tooth?
due to the absence of PDL
Types of tooth movement (not orthodntic)
1-eruption
2-physiologic tooth movement
3-orthodontic tooth movement
Define tooth eruption?
It is axial or occlusal movement of the tooth from its developmental position within the jaw, to its functional position in the occlusal plane
What are the theories of tooth eruption?
1-Vascular pressure theory (vascular pressure causes the axial movement)
2-root formation(the apical growth of the tooth causes the axial movement) = it was rejected
3-periodontal ligament traction (since the pdl is rich in fibroblasts the contain contracting tissues, the contraction of these fibers (mainly oblique fibers) aid in axial movement.
What is the physiologic tooth movement
it is the naturally occurring tooth movement that take place during and after tooth eruption.
examples of physiologic tooth movement
1-migration of drifting or teeth
2-changes in tooth position during mastication
What is the normal force of mastication?
1to 50 kg
it occurs in cycles of 1 second duration.
how does teeth move during mastication?
they exhibit slight movement within the socket and return to their original position on withdrawal of the force
what happens if the force of mastication is sustained for more the 1 second?
periodontal fluid is squeezed out and pain is felt
What are the theories of orthodontic tooth movement?
1-Bone bending piezo electric theory by Farrar
2-Blood flow theory by Bien
3-pressure tension theory by schwarz
How does the bone bending piezoelectric theory explains orthodontic tooth movement?
The force application will result in bone flexing and bending, which will cause a distortion of the crystalline structure, and generation of electric signals causing remodeling.
What is Piezoelectricity ?
Piezoelectricity is a phenomenon
observed in many crystalline materials
in which a deformation of the crystal
structure produces a flow of electric
current as a result of displacement of
electrons from one part of the crystal
lattice to the other
How is the piezoelectricity theory is applied?
On application of force on tooth, adjacent bone bends.
- Area of concavity :negative charged evoke bone deposition
- Area of convexity :positive charge evoke bone resorption
How does the pressure tension thoery explains orthodontic tooth movement?
The force will cause pdl compression, and it will decrease the blood flow, therefore, chemical messenger will be released, and they will cause cellular differentiation (resorption and deposition)
what does the Pressure tension theory relies on?
Relies on chemical signals as
the stimulus for remodeling
What is the Response to Continuous Pressure
*less than 1 sec = fluid in the pdl is incompressible
*1-2 sec=pdl fluid expressed, the tooth moves within pdl space
*3 - 5 sec=pdl fluid is squeezed out, tissue is compressed and immediate pain is felt.
the ideal force for orthodontic movement?
minimum continuous force
what is the minimum pressure to cause movement?
5 to 10 gm/cm2
- if less than that, the pdl has the ability to stabilize the tooth with active stabilization.
How does the fluid dynamics theory explains tooth movement?
alteration in fluid dynamics in the PDL.
what is the squeezed film effect by bien?
when a force of greater magnitude and duration is
applied such as during orthodontic tooth movement
the interstitial fluid in the periodontal space gets
squeezed out and move toward the apex and
cervical margins and results in decreased tooth
movement .
what is the Pressure-Tension Theory
When a tooth is moved due to application of orthodontic
force , there is bone resorption on the pressure side and new
bone formation on the tension side.
what is the osteoid?
the unmineralized, organic portion of the bone
The process of initiation of tooth movement
has 3 stages, what are they? -pressure tension theory-
1- Alternation of blood flow associated with pressure within the PDL
2-The formation and release of chemical messengers
3-Activation of cells which causes resorption and deposition of bone
which cell control the remodelling?
osteoblast, through RANKL
Describe osteoblasts
Bone forming cellss, that are ovoid cells with basophilic cytoplasm
and have an oval nucleus.
The bone formed during orthodontic tooth movement passes through 3 stages, what are they?
1-Osteoid (bone formed by osteoblasts)
2-Bundle bone (when the osteoid is calcified it forms bundle bone & the fibers of periodontal apparatus that are attached to it.
3-The lamellated bone
(when the bundle bone reaches certain maturity, part of it gets re-organized into mature lamellated bone).
What are osteoclasts?
1-multinucleated giant cells and may have 12 or more nuclei .
2-They are irregularly oval or club shaped with branching processes.
3-they have prominent mitochondria, lysosomes and vacuoles
4-each of their nuclei has a single nucleous.
where does osteoclasts lay?
in howships lacunae
what is special about the osteoclasts that in contact with the resorbing bone?
they have ruffled border
The histologic changes of tooth movement vary according to:
1.The amount of force applied.
2.The duration of force app
what happens during light force application?
1-light force cause minimal compression of the pdl
2-blood vessels are NOT occluded
3-then cells arrive to cause frontal or direct bone resorption
what happens on the pressure side during heavy force application?
1-crushing or total compression of the PDL
2-on the compression side the blood vessels will be completely occluded and hyalinization occur
3-Bone resorption occurs in the adjacent marrow spaces and in
the alveolar plate below, behind and above the hyalinized
zones this kind of resorption is called undermining resorption.
what happens on the tension side during heavy force application?
1-pdl gets over-stretched, leading to tearing of the blood vessels and ischemia.
2-thus leading to increased osteoclastic activity
what are hyalinized area?
they are areas where cellular death has occurred
the delay in tooth movement after heavy force is due to :
1-The delay in stimulating differentiation of cells
within the marrow space
2-A considerable thickness of bone has to be
removed from the underside before any tooth
movement can take place
WHAT IS THE OPTIMUM ORTHODONTIC FORCE?
It has following characteristics:
1-Produces rapid tooth movement
2-Minimal patient discomfort
3-The lag phase of tooth movement is minimal
4- No marked mobility of the teeth being moved.
-AND IT IS Equivalent to capillary pulse pressure which is 20-25 gm/sq. cm
From a histologic point of view the use of optimum force has the
following characteristics
1-vitality of teeth and pdl is maintained
2-it initiates maximum cellular response
3-it produces direct or frontal resorption
what is the simplest orthodontic movement?
tipping, can be controlled or un-controlled tipping.
where does controlled tipping occur?
around the tooth apex
where does un-controlled tipping occur?
center of resistance
amount of force needed in tipping
50 – 75 gm
The location and extent of hyalinization differ with tooth movement, so it tipping hyalinization will be
closer to alveolar crest
The location and extent of hyalinization differ with tooth movement, so it bodily movement hyalinization will be
closer to the middle portion of the root
When excessive forces are applied during tipping tooth movement , it can result In
2 areas of hyalinization, what are they?
one in the apical region and other one on the marginal area.
amount of force needed in translation (bodily movement
100-150gm
amount of force needed in rotation
50-100 gm
amount of force needed in extrusion?
50 gm
amount of force needed in intrusion?
15-25 gm
What are the Types of orthodontic forces acc. to Duration
1-Continuous Force (fixed orthodontics)
-They never decline to zero
2-Interrupted Force (removable appliances)
-Starts heavy then decline until it reaches zero
3-Intermittent Force (Extraoral appliances)
-Very high force (250-500gn)
-needs to be worn for at least 12h to be effective
side effect of interrupted force?
Produces some kind of undermining resorption .
What are the phases of tooth movement?
1-Initial phase (tooth is displced within pdl)
-at this phase both light and heavy force move the tooth to the same extent
2-Lag phase (little to no tooth movement, extent up to 2-3weeks)
3-post lag phase (tooth movement progress
what are the side effects of orthodontic forces?
- Mobility and pain
- Effects on the pulp
- Effects on the root structure
- Effects on alveolar bone height
- Effects on the TMJ
- Effect on Enamel
and of course periodontal problems
Risk factors for root resorption with ortho ttt
1-evidence of previous resorption
2-conical roots
3-dilacerated roots
4-teeth with history of trauma
What are the types of root resorption?
1-Slight Blunting
2-Moderate resorption – up to ¼ of the root length
3-Severe resorption – more than ¼ of the root length
4-Moderate Generalized Resorption
5-Severe Generalized Resorption
6-Severe Localized Resorption
Cause of severe localized resorption
excessive force and prolonged duration of treatment
-p.s, common in maxillary incisors, and if they are forced against lingual cortical plate
Cause of severe generalized resorption?
-unknown etiology
-patients with thyroid hormons deficiency have higher chances.
Excessive loss of crestal bone height is rarely seen.
Why?
Because the position of the teeth determines the position
of the alveolar bone.
As the tooth moves it brings its alveolar attachment and
bone with it.
loss of crestal bone is rare, but where is it mostly seen
with active PD disease
Why does orthodontic treatment cause TMJ pain?
-in case of poor occlusion and excessive occlusal shift.
what to do if tmj problem arise during treatment?
treatment should be discontinued (just remove the wire not the brackets)
for a period of time to monitor the problem.
What are the periodontal problems occuring during orthodontic treatment?
increase chance or gingival disease due to increased plaqye accumulation, and also hyperplasia of the gingiva
when does gingival hyperplasia develop after ortho ttt? and what is the solution?
1-2 months.
solution is oral health care and gingivectomy.
Common Banding error results in what?
tooth height and root torque errors
Treatment for gingival recession?
gingival grafting
