Physiology of tooth movement and appliances overview Flashcards
What is the Physiological basis of orthodontics?
- 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
What are the 3 theories for orthodontic tooth movement?
- Piezo-electric theory
- Differential pressure theory
- Mechano-chemical theory
What is the differential pressure theory?
- 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
What is the mechano-chemical theory?
- 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
What are cytokines?
- Low molecular weight proteins
- Regulate action of target cells
- May cause target cells to secrete mediators
- Lots of cytokines within PDL
What is the mechano-chemical theory?
- 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
Histologically how is the periodontal space maintained?
- 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
What is the mechanism for bone resorption in the mechano-chemical theory?
- 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
- Adjacent bone distorted
- Macrophages increase production of IL-1
- Bone resorption - Osteoblasts produce prostaglandins and leukotrienes
- Bones resorption - Fibroblasts produce Matrix metalloproteinases
- Bone resorption
What is the cascade of cytokines within the periodontal ligament leads to bone resoprtion?
- 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
How are osteoblasts involved in areas of compression?
- 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
How are osteoblasts involved in areas of tension?
- 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
What two components are viral in regulating bone remodelling?
- Osteoblasts release another protein called Osteoprotegerin (OPG) which prevents osteoclastic differentiation and suppresses their activity
- Balance between RANKL and OPG produced regulates bone remodelling
How do orthodontists use this knowledge to their advantage?
- 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
What are the types of orthodontic appliances?
- Removable (URA)
- Functionals
- Fixed
What are the types of tooth movement?
- Tipping
- Bodily movement
- Intrusion
- Extrusion
- Rotation
- Torque
What are the effects of functional applicance on Class II case?
- Restrict maxillary growth
- Promote mandibular growth
- Remodel the glenoid fossa
What are the dental changes that occur in functional applicance Class II case?
- Lower incisors procline
- Upper incisors retrocline
- Twin block therapy for 6-12 months
- Reduce overjet
What are the mode of actions of functional appliances? (Twin blocks)
- 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
How is bodily movement acheived?
- 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
What occurs histologically during frontal resorption?
- 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
What occurs histologically during deposition?
- Occurs on tension side
- Hyperaemia of blood vessels
- Increased osteoblastic activity
- Deposition of osteoid
What are Matrix Metalloproteinases?
- Enzymes that break down the extracellular matrix
What is apical root torque?
- Rotation of root at apex
- Uses force couple in opposite directions
- Need 50-100grams
What is the optimum force for tipping movement?
35-60g
What is the optimum force for bodily movement?
150-200g
What is the optimum force for intrusion?
10-20g
What is the optimum force for extrusion?
35-60g
What is the optimum force for rotation?
35-60g
What is the optimum force for torque?
50-100g
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
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
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
What are some unwanted side effects of excessive forces?
- Pain
- Necrosis of bone
- Anchorage loss
- Root resorption
- Possible loss of tooth vitality
What are some factors that affect the response to orthodontic forces?
- Magnitude
- Duration
- Age
- Anatomy
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)
What are some negative effects of orthodontic forces?
- Pain and mobility
- Pulpal changes
- Root resorption
- Loss of alveolar bone support
- Relapse
What is the ideal tooth movement per month for ortho appliances?
- 1mm per month
What is the treatment time for fixed appliances?
24 months
