Physiology of Tooth Movement Flashcards
What are the different types of tooth movement?
- physiological
- tooth eruption
- mesial drift
- orthodontic
- externally generated forces
What is the physiological basis of orthodontics?
- if external force is applied, tooth will move
- bone around tooth remodels
- mediated by PDL
Why does root resorption occur after orthodontics?
- only 1-2mm
- severe resorption not common
- cementum more resistant to resorption than bone
What is the differential pressure theory?
- in areas of compression bone is resorbed
- in areas of tension bone is deposited
What is the mechano-chemical theory?
- cell shape changes in PDL and adjacent alveolar bone
- fluid flow in bone canaliculi altered
- osteocytes detect distortion and produce cytokines
- signalling interactions between cells
- production and release of cytokines
- regulate action of target cells
- production and release of cytokines
- macrophages increase production of IL-1
- increases RANKL production
- osteoblasts produce prostaglandins and leukotrienes
- activated by cytokines
- PGE2 and leukotrienes act on osteoblasts
- production of secondary intracellular messengers - production of RANKL and CSF initiated
- cause blood monocytes to fuse and form osteoclasts - RANKL stimulates osteoclast activity
- fibroblasts produce MMPs
- breakdown extracellular matrix - in areas of compression osteoblasts bunch together
- exposure of osteoid layer
- osteoclasts allowed access to bone
- in areas of tension osteoblasts are flattened
- covering of osteoid layer
- osteoclasts cannot gain access to bone
- secretion of collagen and OPG to form organic matrix
What are the different ways in which teeth can move?
- tipping
- bodily movement
- crown and root move at same time
- intrusion
- extrusion
- rotation
- torque
- tipping movement of root within bone
- usually used in buccal-lingual fixed appliances
What is tipping movement?
- movement around a centre of rotation
- requires 35-60g force
What kind of tooth movement to upper removable appliances facilitate?
tipping
How do functional appliances work?
- mandible postures away from rest position
- occlusion corrected
- facial muscles stretched
- forces transmitted to teeth and alveolus
- facial growth altered
- restrained maxillary growth
- promoted mandibular growth
- remodel of the glenoid fossa
- appliance created with blocks
What are the clinical effects of a twinblock appliance?
- reduced overjet
- posterior open bite created
- appliance worn at night to allow continued eruption
- may require fixed appliance to restore buccal occlusion
What is bodily movement?
- movement of both the crown and root simultaneously
- resorption on one aspect
- deposition on the other
- 150-200g force required
- secondary remodelling
- allows tooth to retain normal PDL width and stability
What is intrusion in terms of tooth movement?
- movement of a tooth further into the alveolar bone
- pressure on supporting structs evenly distributed
- bone resorption occurs
- apical area
- alveolar crest
- 10-20g force required
- reduce risk of root resorption with light force
What is extrusion in terms of tooth movement?
- movement of a tooth further out of the alveolar bone
- tension induced in supporting structures
- bony deposition to maintain tooth support
- tension induced in supporting structures
- 35-60g required
What is rotation?
- rotation of a tooth in its socket
- wire bracket exerts force
- palatal or lingual surface attached to elastic chain
- 35-60g force required
What is torque?
- root uprighting
- force couple around bracket
- results in apical torque
- 50-100g force required
What are the histological changes during light orthodontic forces?
- hyperaemia of blood vessels in PDL
- allows cells into space
- osteoclasts and osteoblasts arrive
- osteoclasts resorb lamina dura on pressure side
- osteoblasts appose osteoid on tension side
- remodelling of socket through frontal resorption
- periodontal fibres reorganise
- gingival fibres remain distorted
- slow tooth movement
What is the histological reason for leaving several weeks between orthodontic visits?
to reactivate an appliance one the PDL has reorganised as a result of the force applied
What are the histological changes during moderate orthodontic forces?
- occlusion of vessels in PDL on pressure side
- no influx of cells
- hyperaemia of vessels in PDL on tension side
- cell free area on pressure side created
- hylinisation
- period of stasis
- 10-14 days for full resorption of hylinisation
- increased endosteal vascularity
- undermining resorption
- rapid tooth movement
- bone deposition on tension side
- tooth may become slightly mobile
- healing of PDL
- reorganising and remodelling
- no more force applied until fully healed
What are the histological changes during excessive orthodontic forces?
- necrosis and undermining resorption
- root resorption
- prognosis poor after 1/3 root length lost - anchorage loss
- possible loss of tooth vitality
- blood vessels constricted at apex
- rare
- root resorption
- painful
How does age affect the response of teeth to force?
- teeth can be moved at any age
- slower in older patients
- due to denser bone and lower cell turnover
What anatomy affects response to orthodontic forces?
- lack of bone
- wasting
- cleft
- soft tissues
- anterior open bite
- mid-palatal suture
What is alveolar necking
- movement of cortical plates closer together
- creation of dense cortical bone
- too dense for teeth to move through
- prosthetic restoration required
Can teeth that have been root treated be moved by orthodontics?
- yes
- in absence of periapical pathology
- in tact PDL
What are the deleterious effects of orthodontic force?
- pain and mobility
- pulpal changes
- root resorption
- loss of alveolar bone support
- relapse
How does relapse occur after orthodontic treatment?
- gingival fibres do not reorganise
- pull tooth back to original position
