PHYSIOLOGY OF TOOTH MOVEMENT & APPLIANCE OVERVIEW Flashcards
What are the different types of tooth movement?
- physiological (tooth eruption & mesial drift)
- orthodontic (from externally generated forces)
what is the physiological basis of orthodontic appliances?
if an external force is applied to a tooth (ortho appliance), the tooth will move as the bone around it remodels
what is bone remodelling around a tooth mediated by?
The PDL
- if a tooth has no PDL or is ankylosed the tooth will NOT move
what is meant by ankylosed?
tooth fused to bone
what are the different theories for orthodontic tooth movement?
- piezo-electric theory
- differentials pressure theory
- mechano-chemical theory
what is the differential pressure theory?
In areas of compression bone is resorbed and in areas of tension bone is deposited
what is the mechano-chemical theory?
Cell mediated interactions take place.
- cell shape changes in the PDL & adjacent alveolar bone
- initiates signalling between cells (production of cytokines)
- cytokines activate osteoblasts
- osteoblasts produce prostaglandins & leukotriene which initiates production of RANKL
- RANKL & CSF cause formation of osteoclasts (which resorbs bone)
how do osteoblasts act in areas of compression?
- osteoblasts bunch up together & expose the osteoid layer giving osteoclasts access to resorb bone
- osteoblasts send RANKL signals to osteoclasts to activate resorption of bone
how do osteoblasts act in areas of tension?
- osteoblasts are flattened covering the osteoid layer and prevent osteoclasts from gaining access to the bone
- osteoblasts secrete collagen and other proteins forming the organic matrix into which they secrete hydroxyapatite crystals which forms new bone
the balance between which two proteins mediates the bone remodelling?
balance between RANKL & OPG regulates bone remodelling
what are the different types of orthodontic appliances?
- removable (URA)
- functionals
- fixed
in order for a functional appliance to work, what must the patient be?
patient must be growing!
what are the different types of tooth movement?
- tipping
- bodily movement
- intrusion
- extrusion
- rotation
- torque
what occurs when a tooth undergoes bodily movement?
crown and root move together
how do functional appliances work?
- the mandible is postured away from its normal rest position
- the facial musculature is stretched which generates forces transmitted to the teeth and alveolus
- may be an effect on facial growth
what is the mode of action of functionals?
Skeletal change (30%) = growth of mandible restraint of maxilla
Dentoalveolar change (70%) = retroclination of upper teeth & proclination of lower teeth
what is the optimal force applied to cause tipping of tooth?
35-60g
what is the optimal force applied to cause bodily movement of tooth?
150-200g
what is the optimal force applied to cause intrusion of tooth?
10-20g
what is the optimal force applied to cause extrusion of tooth?
35-60g
what is the optimal force applied to cause rotation of tooth?
35-60g
what is the optimal force applied to cause torque of tooth?
50-100g
what histological changes occur in orthodontics when a light force is applied?
- hyperaemia within the PDL
- appearance of osteoclasts & osteoblasts
- resorption of lamina dura from pressure side
- apposition of osteoid on tension side
- remodelling of socket
- PDL fibres reorganise
- gingival fibres appear not to become reorganised but remain distorted
what is frontal resorption of a tooth?
remodelling of socket
what are some unwanted side effects of excessive forces applied to a tooth?
- pain
- root resorption
- anchorage loss
- possible loss of tooth vitality
what are some factors that affect the response to orthodontic force?
- magnitude of force applied
- duration force is applied
- age of patient
- anatomy of patient
what anatomical factors can effect the response of a tooth to force?
- no bone (wasting/cleft)
- soft tissues
- mid-palatal suture
how much movement of tooth should occur per month when using orthodontics?
1mm of tooth movement per month
What is the usual treatment time for fixed appliances?
24 months
