Physiology of tooth movement and appliances overview Flashcards

1
Q

What is the Physiological basis of orthodontics?

A
  • If external force applied to tooth, tooth will move as bone around it remodels
  • Bony remodelling is mediated by periodontal ligament
  • If tooth has no PDL or is ankylosed will not move
  • Cementum more resistant to resorption than bone
  • Some degree of root resorption after orthodontics should be expected
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2
Q

What are the 3 theories for orthodontic tooth movement?

A
  • Piezo-electric theory
  • Differential pressure theory
  • Mechano-chemical theory
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3
Q

What is the differential pressure theory?

A
  • Coronal part of tooth undergoes a force
  • Root undergoes compression and tension
  • In areas of compression bone is resorbed
  • In areas of tension bone is deposited
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4
Q

What is the mechano-chemical theory?

A
  • Occurs at cellular level
  • Cell shape changes occur within periodontal ligament and adjacent alveolar bone
  • Inititiates signalling interactions between cells e.g. Production and release of cytokines
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5
Q

What are cytokines?

A
  • Low molecular weight proteins
  • Regulate action of target cells
  • May cause target cells to secrete mediators
  • Lots of cytokines within PDL
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6
Q

What is the mechano-chemical theory?

A
  • Occurs at cellular level
  • Cell shape changes occur within periodontal ligament and adjacent alveolar bone
  • Initiates signalling interactions between cells e.g. Production and release of cytokines
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7
Q

Histologically how is the periodontal space maintained?

A
  • On root surface the cementum covered by cementoblasts
  • Sharpey’s fibres (collagen fibres) penetrate cementoblasts and attach to cementum
  • In PDL epithelial cells islands form 3D network around root (called Epithelial Rests of Malassez)
  • Epithelial Rests of Malassez constantly release Epithelial Growth Factor (EGF)
  • EGF diffuse through cells in extracellular matrix and stimulate osteoclasia on periodontal bone surface
  • Promotes maintenance of periodontal space
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8
Q

What is the mechanism for bone resorption in the mechano-chemical theory?

A
  • Mechanical loading
  • Fluid movement, stretching and compression of fibres within PDL ; lead to 1,2,3,4
    • Adjacent bone distorted
      - Fluid flow within bone canaliculi is altered
      - Osteocytes within bone detect distortion
      - Osteocytes produce cytokines
      - Cytokines activate osteoblasts to recruit osteoclasts
      - Bone resorption
  1. Macrophages increase production of IL-1
    - Bone resorption
  2. Osteoblasts produce prostaglandins and leukotrienes
    - Bones resorption
  3. Fibroblasts produce Matrix metalloproteinases
    - Bone resorption
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9
Q

What is the cascade of cytokines within the periodontal ligament leads to bone resoprtion?

A
  • Cytokines activate osteoblasts to produce Prostaglandins (PGE-2) and leukotrienes
  • PGE-2 and leukotrienes causes osteoblasts to produce intracellular messenger (secondary messenger)
  • Intracellular secondary messengers initiate production of Receptor Activator of Nuclear factor Kappa-B-Ligand (RANKL) and CSF and IL-1
  • IL-1 increases production of RANKL
  • RANKL and CSF cause blood monocytes to fuse and form multinucleated osteoclasts
  • RANKL stimulates osteoclast to become active and resorb the bone
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10
Q

How are osteoblasts involved in areas of compression?

A
  • Osteoblasts bunch together
  • They expose the osteoid layer giving osteoclasts access to resorb the bone
  • Osteoblasts send signals to osteoclasts (e.g. RANKL) to recruit and activate osteoclasts to resorb bone
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11
Q

How are osteoblasts involved in areas of tension?

A
  • Osteoblasts are flattened covering the osteoid layer
  • Prevents osteoclasts from gaining access to the bone
  • Osteoblasts secrete collagen and other proteins forming the organic matrix
  • Secrete Hydroxyapatite crystals which form new bone into the organic matrix
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12
Q

What two components are viral in regulating bone remodelling?

A
  • Osteoblasts release another protein called Osteoprotegerin (OPG) which prevents osteoclastic differentiation and suppresses their activity
  • Balance between RANKL and OPG produced regulates bone remodelling
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13
Q

How do orthodontists use this knowledge to their advantage?

A
  • Utilise the inflammatory response which occurs in PDL when a force is placed on teeth
  • Use appliances to transmit force to PDL and bone
  • Manages patients carefully through periods of resorption and repair of their alveolar bone
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14
Q

What are the types of orthodontic appliances?

A
  • Removable (URA)
  • Functionals
  • Fixed
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15
Q

What are the types of tooth movement?

A
  • Tipping
  • Bodily movement
  • Intrusion
  • Extrusion
  • Rotation
  • Torque
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16
Q

What are the effects of functional applicance on Class II case?

A
  • Restrict maxillary growth
  • Promote mandibular growth
  • Remodel the glenoid fossa
17
Q

What are the dental changes that occur in functional applicance Class II case?

A
  • Lower incisors procline
  • Upper incisors retrocline
  • Twin block therapy for 6-12 months
  • Reduce overjet
18
Q

What are the mode of actions of functional appliances? (Twin blocks)

A
  • Skeletal change (30%) lead to growth of mandible, restraint of mandible
  • Dentoalevolar change (70%) lead to retroclination of upper teeth, proclination of lower teeth
  • Mesial migration of lower teeth
  • Distal migration of upper teeth
  • Combo of above achieve class I
19
Q

How is bodily movement acheived?

A
  • Fixed appliance
  • Frontal resorption
  • Bony deposition on opposiute side so bone remodels around tooth
  • Need 150-200grams of force
  • In order for PDL to retain normal width and stability then secondary remodelling occurs
20
Q

What occurs histologically during frontal resorption?

A
  • Occurs on side of pressure
  • Hyperaemia of blood vessels
  • Increased osteoclastic activity, resorption of lamina dura
  • Slow tooth movement which is why it takes years
  • PDL reorganises
21
Q

What occurs histologically during deposition?

A
  • Occurs on tension side
  • Hyperaemia of blood vessels
  • Increased osteoblastic activity
  • Deposition of osteoid
22
Q

What are Matrix Metalloproteinases?

A
  • Enzymes that break down the extracellular matrix
23
Q

What is apical root torque?

A
  • Rotation of root at apex
  • Uses force couple in opposite directions
  • Need 50-100grams
24
Q

What is the optimum force for tipping movement?

25
What is the optimum force for bodily movement?
150-200g
26
What is the optimum force for intrusion?
10-20g
27
What is the optimum force for extrusion?
35-60g
28
What is the optimum force for rotation?
35-60g
29
What is the optimum force for torque?
50-100g
30
What are the histological events that occur during light forces applied to tooth?
- Hyperaemia or increase in blood flow throughout PDL - Osteoclasts appear on pressure side - Osteoblasts on tension side - Osteoclasts resorb the lamina dura on pressure side - Osteoblasts lay down osteoid in increased PDL space on tension side - AKA frontal resorption - Over time PD fibres reorganise - Supracrestal gingival fibres don't - Shows why rotations and spacing most likely to relapse following correction
31
What are the histological events that occurs in moderate forces?
- Increased forces lead to occlusion of blood vessels on pressure side - Hyperaemia of vessels on tension side - Due to increased pressure on pressure side there are cell free areas, process called hyalinsation - Tooth does not move (stasis) - Anchor units or teeth can still move leading to loss of space - Increased vascularity on underside of bone supporting tooth, with increase in osteoclasts lead to undermining resorption - Resorption continues until tooth moves in desired direction - Healing of PDL occurs and process repeats
32
What are the histological events that occur in heavy forces?
- Excessive forces associated with occlusion of blood vessels, areas of hyalinisation, undermining resorption, areas of necrosis of bone and areas of resorption of root surface - Pt may experience pain and loss of vitality of tooth - Adjacent alveolar bone also undergoes extensive remodelling -
33
What are some unwanted side effects of excessive forces?
- Pain - Necrosis of bone - Anchorage loss - Root resorption - Possible loss of tooth vitality
34
What are some factors that affect the response to orthodontic forces?
- Magnitude - Duration - Age - Anatomy
35
What are some anatological features that affect response to ortho appliances?
- No bone perhaps if wasting or cleft pt - Soft tissues like anterior open bite - Mid-palatal suture - Teeth that have been root treated - Thin bone (has lots of dense cortical plate)
36
What are some negative effects of orthodontic forces?
- Pain and mobility - Pulpal changes - Root resorption - Loss of alveolar bone support - Relapse
37
What is the ideal tooth movement per month for ortho appliances?
- 1mm per month
38
What is the treatment time for fixed appliances?
24 months