4. What is needed?
ā¢ Tooth
ā¢ Healthy periodontal ligament
ā¢ Bone
ā¢ Applied force
Tooth movement is dependant upon physiology of the
Periodontal ligament and Bone ā i.e. Turnover
5. Tooth
ā¢ Means of force application/delivery
ā¢ Otherwise āinactiveā
6. Periodontal Ligament
ā¢ Fibres transmit forces applied to the tooth
ā¢ Viscostatic damping of force
ā¢ Cells within PDL - Fibroblasts
- Osteoblasts
- Osteoclasts
- Undifferentiated cells
8. Bone
Structural: Metabolic:
Cortical bone ā¢ Trabecular bone
slow turnover constant turnover
9. Bone Turnover
Control is by systemic and local factors
ā¢ Osteclasts ā¢ Osteblasts
derived from perivascular cells derived from monocytes
10. Bone ā Metabolic Role (systemic control)
Kidney ā
PO4 excretion
Ca++ resorption
PTH
Ca++ Gut ā Ca++
Serum Ca binding Serum
Ca absorption
Vit D
(1,25 DHCC) Bone ā
short term:
Ca++ from bone fluid
long term:
Resorption
Deposition
12. Local control
ā¢ Biologic electricity
1. Pietzoelectric effect (V. short duration)
ā¢ Blood flow Bending of collagen and bone results in
-ās moving within crystal lattice
ā¢ Microfractures e
No signal = bone atrophy
2. Streaming potential
Movement of ground substance
results in a potential difference
+ve on compression
-ve on tension
Affects cell permeability
13. Local control
ā¢ Biologic electricity
ā¢ Blood flow
Sustained pressure
ā¢ Microfractures Alters blood flow in PDL
flow in tension
flow in compression
Affects biochemical environment
14. Local control
ā¢ Biologic electricity
ā¢ Blood flow
ā¢ Microfractures
Microfractures
Occur within bond, these accumulate
affecting the microenivironment
15. Local control
ā¢ Biologic electricity
ā¢ Blood flow
ā¢ Microfractures
Prostaglandins
Cytokines
Cyclic amp
Osteblasts Osteoclasts
16. Local control (+systemic)
ā¢ Biologic electricity
ā¢ Blood flow
ā¢ Microfractures
Prostaglandins
Cytokines
Cyclic amp
Osteblasts Osteoclasts
PTH
Systemic Control Vit D
Calcitonin
17. Force
Tooth movement
Tooth
PDL/Bone
Biological electricity
Blood flow
Microfractures
Osteoblasts (tension)
Osteoclasts (compression)
Resorption and Deposition
of bone
19. What happens depends on:
ā¢ Level of force
Heavy force/short duration
ā¢ Duration of force 1-50Kg / less than 1 sec
Force absorbed by bone bending = Pain
(Pietzoelectric effect)
20. What happens depends on:
ā¢ Level of force
Heavy force/short duration
ā¢ Duration of force 1-50Kg / less than 1 sec
Force absorbed by bone bending = Pain
(Pietzoelectric effect)
Heavy force/long duration
1-50Kg / continuous
1-2 secs ā PDL fluid displaced
2-3 secs ā PDL tissues compressed = pain
Hours-days ā cellular necrosis within bone
= hyalanised (acellular layer)
Removed by osteoclasts, tooth movement in
āstepsā ā Undermining Resorption
21. What happens depends on:
ā¢ Level of force
Light force/short duration
ā¢ Duration of force less than 1Kg / less than 1 sec
Force absorbed by PDL = no effect
(PDL is actively stable ā 5-10g)
22. What happens depends on:
ā¢ Level of force
Light force/short duration
ā¢ Duration of force less than 1Kg / less than 1 sec
Force absorbed by PDL = no effect
(PDL is actively stable ā 5-10g)
Light force/long duration
less than 1Kg / continuous
Progressive tooth movement occurs
23. What happens depends on:
ā¢ Level of force
Orthodontic forces
ā¢ Duration of force Excessive = pain + undermining resorption
Ideal = socket remodeling
In reality ā some undermining
resorption occurs
24. Orthodontic force
ā¢ Tipping Simplest orthodontic movement
ā¢ Translation Occurs about centre of resistance
(1/3 from root apex)
ā¢ Rotation Forces are high at apex and alveolar crest,
ā¢ Extrusion reduce to zero at centre of resistance
ā¢ Intrusion
25. Orthodontic force
ā¢ Tipping Simplest orthodontic movement
ā¢ Translation Occurs about centre of resistance
(1/3 from root apex)
ā¢ Rotation Forces are high at apex and alveolar crest,
ā¢ Extrusion reduce to zero at centre of resistance
ā¢ Intrusion
Force ā 50-75g
26. Orthodontic force
ā¢ Tipping Bodily movement
ā¢ Translation All of PDL is uniformly loaded
ā¢ Rotation
ā¢ Extrusion
ā¢ Intrusion
27. Orthodontic force
ā¢ Tipping Bodily movement
ā¢ Translation All of PDL is uniformly loaded
ā¢ Rotation
ā¢ Extrusion
ā¢ Intrusion
Force ā 100-150g
28. Orthodontic force
ā¢ Tipping Rotary movement
ā¢ Translation Theoretically need high force
ā¢ Rotation
ā¢ Extrusion
ā¢ Intrusion
29. Orthodontic force
ā¢ Tipping Rotary movement
ā¢ Translation BUT
Theoretically need high force
ā¢ Rotation Tipping occurs
= excessive compression of PDL
ā¢ Extrusion
ā¢ Intrusion
Force ā 50-100g
30. Orthodontic force
ā¢ Tipping Vertical movement
ā¢ Translation Need to produced tension in fibres
of PDL
ā¢ Rotation
ā¢ Extrusion
ā¢ Intrusion
31. Orthodontic force
ā¢ Tipping Vertical movement
ā¢ Translation Need to produced tension in fibres
of PDL
ā¢ Rotation
ā¢ Extrusion
ā¢ Intrusion
Force ā 50g
32. Orthodontic force
ā¢ Tipping Vertical movement
ā¢ Translation Forces concentrated at root apex
ā¢ Rotation
ā¢ Extrusion
ā¢ Intrusion
33. Orthodontic force
ā¢ Tipping Vertical movement
ā¢ Translation Forces concentrated at root apex
ā¢ Rotation
ā¢ Extrusion
ā¢ Intrusion
Force ā 15-25g
35. Orthodontic force duration
ā¢ Ideal Light continuous force
ā¢ Intermittent Achievable with fixed appliances
ā¢ Interrupted
36. Orthodontic force duration
ā¢ Ideal
ā¢ Intermittent Force decays between adjustments
ā¢ Interrupted e.g. Removable appliance springs
Initially force is too high, decays to ideal,
then to zero
Results in undermining resorption, which
repairs between visits
37. Orthodontic force duration
ā¢ Ideal
ā¢ Intermittent
ā¢ Interrupted Force only present when appliance
worn
e.g. Headgear
Heavy force used, needs at least 12hours/day for
tooth movement to occur.
Optimal 14-16 hours/day
250g/side for anchorage
450g/side for distal movement
39. Orthodontic adverse affects
ā¢ Pulp Minimal effect
ā¢ Root transient inflammatory response
can cause loss of vitality:
ā¢ PDL compromised teeth
excessive force
ā¢ Bone inappropriate movement
40. Orthodontic adverse affects
ā¢ Pulp
ā¢ Root Some resorption of root occurs
ā¢ PDL usually repaired by cementum
Repairs occur during ārestā periods
ā¢ Bone BUT permanent damage occurs to root apex
commonly lose 1-2mm root length
At risk: distorted apices
thin roots
compromised teeth
excess force
history of previous idiopathic resorption
42. Orthodontic adverse affects
ā¢ Pulp
ā¢ Root
ā¢ PDL
ā¢ Bone Minimal transient damage
BUT : loose Ā½ -1mm of alveolar crest
43. When to use what applianceā¦.
Tipping
Bodily movement Rotation
Intrusion Extrusion
44. When to use what applianceā¦.
Springs / Screws
Tipping (Individual or groups of teeth)
Bodily movement Rotation
Removable Accidental!!
Intrusion Extrusion
FABP
(Groups of teeth)
45. When to use what applianceā¦.
Tipping
Bodily movement Rotation
Fixed
Intrusion Extrusion