biology of tooth movement Flashcards by Eileen Xue

how to move teeth

1) bonded brackets with archwire
2) elastic force

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what is needed

1) tooth
2) healthy PDL
3) bone
4) applied force

turnover: bone biology

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tooth

1) site of force application

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PDL

1) fibers transmit forves
2) cells
- fibroblasts, osteoblasts, osteoclasts
- undifferentiated pluripotent cells
- cells of vascular and neural
- fluid

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bone

1) bone turnover
- systemic factors
- local factors
2) osteoclasts
- derived from perivascular cells
3) osteoblasts
- derive from local mesenchymal cells

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fibroblasts

1) mesenchymally derived
2) multiple functions in tissues
3) primary function in periodontium is making ECM and collagen

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osteoblasts

1) mesenchymal in origin
2) produce bone
3) matrix is called osteoid (type I collagen)

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osteoclast

1) derived from hematopoietic stem cells
2) differentiation pathway is common to macrophages and dendritic cells
3) main function is to dissolve mineral and degrade underlying organic matrix

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PDL and normal function

1) during mastication, teeth and PDL are subjected to heavy intermittent force
<1 sec: PDL fluid is incompressible and alveolar bone bends (piezoelectric signal)
1-2 sec: PDL fluid expressed, tooth moves in the PDL space
3-5 sec: PDL fluid squeeze out, tissue compressed, immediate pain if pressure is heavy
2) the PDL is designed to resist forces of short duration

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bone- local control

1) bioelectric theory
2) pressure tension theory
- both plan a role in biologic control of tooth movement

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bioelectric theory

1) pressure causes deformation of cell and bone structures
- piezoelectricity
2) electric signals causes changes in bone metabolism
- piezoelectric bursts
- cell membrane allows ionic migration
- fluid flow and streaming potentials

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piezoelectric current

1) maintenance of the skeleton
2) mechanism by which bony architecture is adapted to functional demand

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sustained force of orthodontic tooth movement

1) does not produce sustained electric signal
2) vibrating application of pressure => no advantage
3) stress-generated signals (piezoelectricity) has little to do with ortho tooth movement

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pressure tension theory

1) cellular changes produced by chemical messengers generated by alterations in blood flow through the PDL
2) pressure side: less blood flow => bone resorption by OC
and vice versa for tension side

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alterations in blood flow

1) changes local chemical environment (O2 and metabolites)
2) stimulate bio active agents
3 )stimulate cellular differentiation

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tooth movement occurs in 3 stages

1) alteration in blood flow
2) formation/release of chemical messengers
3) activation of cells

modeling of socket

1 )prolonged pressure => tooth movement
2) cells in PDL responds to pressure
3 )bone is selectively resorbed and laid down
4) PDL is reorganized

areas of tension and pressure in the PDL

1) osteoblasts
- respond to tension
- build bone
2) osteoclast
- respond to pressure
- resorb bone

light force

1 )differentiation of OC within the PDL (and from blood vessels)
2) OC attach the adjacent lamina dura and remove bone
- frontal resorption
3) tooth movement begins

heavy force

1) total shut off blood flow
2) cells disappear => avascular areas in PDL
3) sterile necrosis : hyalization
4) differentiation of OC within PDL is not possible
- bone modeling of necrotic PDL must be done by cells derived from adjacent undamaged areas
- delay in tooth movement
5) after a delay of several days
- osteoclasts within the adjacent area attach the underside of the lamina dura => undermining resorption
6) once bone is resorbed, rapid tooth movement
7) painful, possible damage to PDL and root

how much force is optimal

1) level of pressure depends ondistribution of pressure
P = F/A

effects of force duration

1) sustained force is important
2) only after 4 hrs of force do cyclic nucleotide levels in PDL increase
- stimulate cellular differentiation
3) clinically, threshold for tooth movement for force duration is 4-8 hours

physiologic response to light sustained pressure

1) light pressure
- 3-5 seconds: blood vessels compress on pressure side and dilate on tension side
- minutes: blood flow altered, O2, prostaglandins and cytokines
- hours: metabolic changes
- > 4hours: increased cAMP causes cellular differentiation within PDL
- >2 days: tooth movement beginning as osteoclasts/osteoblasts remodel bone socket

physiologic response to heavy pressure

1) 3-5 sec: blood vessels within PDL occluded on pressure side
2) minutes: blood flow cut off to compressed PDL
3) hours: cell death in compressed
4) 3-5 days: cell differentiation in adjacent marrow spaces, undermining resorption
5) 7-14 days: undermining resorption removes lamina dura to compressed PDL, tooth movement

drug effects

1) chemical mediators are critical for ortho 2) inhibitors directly to chemical mediators inhibit tooth movement - COX inhibitors: aspirin, ibuprofen, etc - chronic steroid therapy: reduces movement - bisphosphonates: inhibit OC

ortho Applicance can control

1) level, duration, and distribution of force

biologic responses in clinical tx

1) root resorption 2)

root resorption

1) root is remodeled just like bone 2) typically, cementum can regenerate after tooth movement 3) cementum next to hyaline areas are targets for resorption 4) if the attack produced large defects at the apex, the tip will eventually be separated from the root - why the resorption occurs there

what to do when root resorption occurs

1 )take progress x rays 2) pano xray 9-14 mo - make sure crowns and roots are straight - see if root resorption is occurring

longeivity of short rooted teeth

1 )RR associated with ortho ceases after active treatment 2) even severe RR does not affect functional longevity of teeth 3) in the absence of bone loss, an incisor with 5 mm shortening will still have 75% PDL attachment 4) patients with severe RR were recalled 5-15 yrs and not teeth with mobility score more than 1

take home message

1) ortho does not affect the pulp unless severe or extreme force 2) RR is multifactorial with some genetics 3) upper lateral > upper canines > upper centrals > lower canines > lower lateral > lower centrals (most likely to be short) 4) no occlusal relationship but 4 premolars are higher risk for RR 5) treatment duration and apical displacement are associate with RR

orthodontic relapse

1) teeth will migrate back to their original position 2) factors - force duration, distance of movement, and functional problems - gingival and periodontal fiber (esp, transseptal fiber) - time period of bone modeling following orthodontic tooth movement

retention is needed

1) teeth return to the original position 2) gingival fibers may take years to reorganize 3) occlusal and soft tissue pressure may be present --- 1) remodeling of surrounding structures 2) late mandibular growth

remodeling of surrounding tissues

1) periodontal fibers : 90 days 2) gingival fibers remodeling 232 days 3) bone remodeling 6 months - soft unorganized osteoid matrix in tension side - lamellar bone

hawley retainer

1) plastic and wire

clear retainer

1) can lose shape over time

bonded retainer

1) with more likelihood of relapse

later mandibular growth

1) males who do not wear retainer, the lip will push up against the teeth during late mandibular growth