Biomechanics of Othodontic Tooth Movement_ 1 Dr. Nabil Al-Zubair

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Biomechanics of Othodontic Tooth Movement_ 1 Dr. Nabil Al-Zubair

  1. 1. BiomechanicsofOrthodonticTooth Movement_1Dr. Nabil Al-Zubair
  2. 2. OverviewPhysiology/Anatomy Movement/Forces Orthodontic force Appliances
  3. 3. What is needed?
  4. 4. What is needed?• Tooth• Healthy periodontal ligament• Bone• Applied force Tooth movement is dependant upon physiology of the Periodontal ligament and Bone – i.e. Turnover
  5. 5. Tooth• Means of force application/delivery• Otherwise ‘inactive’
  6. 6. Periodontal Ligament• Fibres transmit forces applied to the tooth• Viscostatic damping of force• Cells within PDL - Fibroblasts - Osteoblasts - Osteoclasts - Undifferentiated cells
  7. 7. Bone• Role of Bone in the body - Structural - Metabolic
  8. 8. BoneStructural: Metabolic:Cortical bone • Trabecular boneslow turnover constant turnover
  9. 9. Bone Turnover Control is by systemic and local factors• Osteclasts • Osteblasts derived from perivascular cells derived from monocytes
  10. 10. Bone – Metabolic Role (systemic control) Kidney – PO4 excretion Ca++ resorption PTHCa++ Gut – Ca++Serum Ca binding Serum Ca absorption Vit D (1,25 DHCC) Bone – short term: Ca++ from bone fluid long term: Resorption Deposition
  11. 11. Local control• Biologic electricity• Blood flow• Microfractures
  12. 12. Local control• Biologic electricity 1. Pietzoelectric effect (V. short duration)• Blood flow Bending of collagen and bone results in -’s moving within crystal lattice• 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. 13. Local control• Biologic electricity• Blood flow Sustained pressure• Microfractures Alters blood flow in PDL flow in tension flow in compression Affects biochemical environment
  14. 14. Local control• Biologic electricity• Blood flow• Microfractures Microfractures Occur within bond, these accumulate affecting the microenivironment
  15. 15. Local control• Biologic electricity• Blood flow• Microfractures Prostaglandins Cytokines Cyclic amp Osteblasts Osteoclasts
  16. 16. Local control (+systemic)• Biologic electricity• Blood flow• Microfractures Prostaglandins Cytokines Cyclic amp Osteblasts Osteoclasts PTH Systemic Control Vit D Calcitonin
  17. 17. Force Tooth movement Tooth PDL/Bone Biological electricity Blood flow Microfractures Osteoblasts (tension) Osteoclasts (compression) Resorption and Deposition of bone
  18. 18. What happens depends on: • Level of force • Duration of force
  19. 19. What happens depends on: • Level of force Heavy force/short duration • Duration of force 1-50Kg / less than 1 sec Force absorbed by bone bending = Pain (Pietzoelectric effect)
  20. 20. What happens depends on: • Level of force Heavy force/short duration • 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 – PDL fluid displaced 2-3 secs – PDL tissues compressed = pain Hours-days – cellular necrosis within bone = hyalanised (acellular layer) Removed by osteoclasts, tooth movement in ‘steps’ – Undermining Resorption
  21. 21. What happens depends on: • Level of force Light force/short duration • Duration of force less than 1Kg / less than 1 sec Force absorbed by PDL = no effect (PDL is actively stable – 5-10g)
  22. 22. What happens depends on: • Level of force Light force/short duration • Duration of force less than 1Kg / less than 1 sec Force absorbed by PDL = no effect (PDL is actively stable – 5-10g) Light force/long duration less than 1Kg / continuous Progressive tooth movement occurs
  23. 23. What happens depends on: • Level of force Orthodontic forces • Duration of force Excessive = pain + undermining resorption Ideal = socket remodeling In reality – some undermining resorption occurs
  24. 24. Orthodontic force• Tipping Simplest orthodontic movement• Translation Occurs about centre of resistance (1/3 from root apex)• Rotation Forces are high at apex and alveolar crest,• Extrusion reduce to zero at centre of resistance• Intrusion
  25. 25. Orthodontic force• Tipping Simplest orthodontic movement• Translation Occurs about centre of resistance (1/3 from root apex)• Rotation Forces are high at apex and alveolar crest,• Extrusion reduce to zero at centre of resistance• Intrusion Force – 50-75g
  26. 26. Orthodontic force• Tipping Bodily movement• Translation All of PDL is uniformly loaded• Rotation• Extrusion• Intrusion
  27. 27. Orthodontic force• Tipping Bodily movement• Translation All of PDL is uniformly loaded• Rotation• Extrusion• Intrusion Force – 100-150g
  28. 28. Orthodontic force• Tipping Rotary movement• Translation Theoretically need high force• Rotation• Extrusion• Intrusion
  29. 29. Orthodontic force• Tipping Rotary movement• Translation BUT Theoretically need high force• Rotation Tipping occurs = excessive compression of PDL• Extrusion• Intrusion Force – 50-100g
  30. 30. Orthodontic force• Tipping Vertical movement• Translation Need to produced tension in fibres of PDL• Rotation• Extrusion• Intrusion
  31. 31. Orthodontic force• Tipping Vertical movement• Translation Need to produced tension in fibres of PDL• Rotation• Extrusion• Intrusion Force – 50g
  32. 32. Orthodontic force• Tipping Vertical movement• Translation Forces concentrated at root apex• Rotation• Extrusion• Intrusion
  33. 33. Orthodontic force• Tipping Vertical movement• Translation Forces concentrated at root apex• Rotation• Extrusion• Intrusion Force – 15-25g
  34. 34. Orthodontic force duration• Ideal• Intermittent• Interrupted
  35. 35. Orthodontic force duration• Ideal Light continuous force• Intermittent Achievable with fixed appliances• Interrupted
  36. 36. Orthodontic force duration• Ideal• Intermittent Force decays between adjustments• 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. 37. Orthodontic force duration• Ideal• Intermittent• 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
  38. 38. Orthodontic adverse affects• Pulp• Root• PDL• Bone
  39. 39. Orthodontic adverse affects• Pulp Minimal effect• Root transient inflammatory response can cause loss of vitality:• PDL compromised teeth excessive force• Bone inappropriate movement
  40. 40. Orthodontic adverse affects• Pulp• Root Some resorption of root occurs• PDL usually repaired by cementum Repairs occur during ‘rest’ periods• 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
  41. 41. Orthodontic adverse affects• Pulp• Root• PDL Minimal transient damage Unless:• Bone excess force maintained existing periodontal disease
  42. 42. Orthodontic adverse affects• Pulp• Root• PDL• Bone Minimal transient damage BUT : loose ½ -1mm of alveolar crest
  43. 43. When to use what appliance…. TippingBodily movement Rotation Intrusion Extrusion
  44. 44. When to use what appliance…. Springs / Screws Tipping (Individual or groups of teeth)Bodily movement Rotation Removable Accidental!! Intrusion Extrusion FABP (Groups of teeth)
  45. 45. When to use what appliance…. TippingBodily movement Rotation Fixed Intrusion Extrusion
  46. 46. Adv / DisadvRemovable: Fixed:Adv: Adv:• Cheap • All tooth movements possible• Oral hygiene• Anchorage Disadv:• ‘Simple to use’ ? • Patient co-operation• Patient co-operation ? • Oral hygiene• Better tolerated ? • AnchorageDisadv: • Require skilled operator• Limited tooth movements (tipping) • Cost ?• NOT ‘simple to use’
  47. 47. Summary• Physiology of tooth movement• Biomechanics of achieving tooth movement• ‘Review’ of available appliances
  48. 48. Dr. Nabil Al-Zubair

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