Physiology of tooth movement Flashcards
what are the types of tooth movement?
Physiological
- tooth eruption
- mesial drift
orthodontic
- from externally generated forces
Briefly outline the physiological basis of orthodontics
if an external force is applied to a tooth, the tooth will move as the bone around it remodel
What structure mediates the remodelling of bone during orthodontic tooth movement?
the periodontal ligament
Give the 3 different theories for orthodontic tooth movement
- differential pressure theory
- mechano-chemical theory
- piezo-electric theory
Briefly describe the differential pressure theory
- in areas of compression, bone is resorbed
- in areas of tension bone is deposited
What are the types of orthodontic tooth movement?
- tipping
- bodily movement
- extrusion
- intrusion
- rotation
- torque
What effects do moderate forces have when applied to a tooth?
- occlusion of vessels of PDL on pressure side
- hyperaemia of vessels of PDL on tension side
- cell free areas on pressure side
- relatively rapid movement of tooth with bone deposition on tension side
- tooth may become slightly loose
- healing of PDL leading to reorganisation and remodelling
What effects do excessive orthodontic forces have on a tooth?
- pain
- necrosis
- root resorption
- anchorage loss
- possible loss of tooth vitality
What factors affect the response a tooth may have to an orthodontic force?
- magnitude
- duration
- age
- anatomy
briefly outline the piezo-electric theory of orthodontic tooth movement
- piezo-electric currents are generated when crystalline structures, such as bone, are deformed
= currents are relatively short lived so unlikely to play a major role in bone remodelling
briefly outline the pressure-tension theory of orthodontic tooth movement
- alterations in blood flow in the PDL and/or release of chemical messengers from damaged cells leads to remodelling of the alveolar bone and tooth movement
- areas of compression bone is resorbed
- areas of tension bone is deposited
types of orthodontic appliances
- removable (URA)
- functionals
- fixed
What type of active tooth movement is achievable with an upper removable appliance?
tipping
How do functional appliances work?
- mandible is postured away from its normal rest position
- the facial muscles are then stretched which generates forces to the teeth and alveolar bone
What are functional appliances usually used to treat?
Class 2 div 1 maloclussion
Skeletal changes from a functional appliance
- restricted maxillary growth
- promotion of mandibular growth
- remodelling of glenoid fossa
dentoalveolar changes from use of twin block functional appliances
- mesial migration of lower teeth
- distal migration of upper teeth
- retroclination of upper teeth
- proclination of lower teeth
Amount of force required on a tooth to create bodily movement
150-200 grams
Amount of force required on a tooth to cause intrusion
10-20 grams
Amount of force required on a tooth to cause extrusion
35 - 60 grams
Amount of force required on a tooth to rotate a tooth
35 - 60 grams
effect of torque
to upright roots
Amount of force required on a tooth to create torque
50-100 grams
factors affecting the response to orthodontic force
- magnitude
- duration
- age
- anatomy
- drugs/medication
effects of light orthodontic forces on a tooth and PDL
- hyperaemia within PDL
- appliance of osteoclasts and osteoblasts
resorption of lamina dura from pressure side - deposition of bone on tension side
- remodelling of socket
- PDL fibres reorganise
- gingival fibres appear not to become reorganised but remain distorted
Anatomical factors affecting response to orthodontic forces
- alveolar necking
- soft tissues e.g. tongue thrust, digit sucking habit
- mid-palatal suture
drugs which affect response to orthodontic forces
prostaglandin inhibitors for pain control - corticosteroids and NSAIDs
bisphosphonates
deleterious effects of orthodontic force
- pain and mobility
- root resorption
- loss of alveolar bone support
- relapse
