biology of tooth movement

Question 1

how to move teeth

Answer 1

1) bonded brackets with archwire
2) elastic force

Question 2

what is needed

Answer 2

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

turnover: bone biology

Question 3

tooth

Answer 3

1) site of force application

Question 4

PDL

Answer 4

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

Question 5

bone

Answer 5

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

Question 6

fibroblasts

Answer 6

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

Question 7

osteoblasts

Answer 7

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

Question 8

osteoclast

Answer 8

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

Question 9

PDL and normal function

Answer 9

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

Question 10

bone- local control

Answer 10

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

Question 11

bioelectric theory

Answer 11

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

Question 12

piezoelectric current

Answer 12

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

Question 13

sustained force of orthodontic tooth movement

Answer 13

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

Question 14

pressure tension theory

Answer 14

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

Question 15

alterations in blood flow

Answer 15

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

Question 16

tooth movement occurs in 3 stages

Answer 16

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

Question 17

modeling of socket

Answer 17

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

Question 18

areas of tension and pressure in the PDL

Answer 18

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

Question 19

light force

Answer 19

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

Question 20

heavy force

Answer 20

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

Question 21

how much force is optimal

Answer 21

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

Question 22

effects of force duration

Answer 22

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

Question 23

physiologic response to light sustained pressure

Answer 23

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

Question 24

physiologic response to heavy pressure

Answer 24

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

Question 25

drug effects

Answer 25

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

Question 26

ortho Applicance can control

Answer 26

1) level, duration, and distribution of force

Question 27

biologic responses in clinical tx

Answer 27

1) root resorption
2)

Question 28

root resorption

Answer 28

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

Question 29

what to do when root resorption occurs

Answer 29

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

Question 30

longeivity of short rooted teeth

Answer 30

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

Question 31

take home message

Answer 31

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

Question 32

orthodontic relapse

Answer 32

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

Question 33

retention is needed

Answer 33

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

Question 34

remodeling of surrounding tissues

Answer 34

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

Question 35

hawley retainer

Answer 35

1) plastic and wire

Question 36

clear retainer

Answer 36

1) can lose shape over time

Question 37

bonded retainer

Answer 37

1) with more likelihood of relapse

Question 38

later mandibular growth

Answer 38

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