Forces moving teeth Flashcards
What are the 2 types of tooth movement?
Physiological tooth movement (eruption)
Orthodontic from externally generated forces
What are the stages in tooth eruption?
- pre-eruptive tooth movement (small, random)
- intra-osseous eruption (after crown forms, slow) aka erupting through the bone
- mucosal penetration (fast)
- pre-occlusal eruption (slow)
- post occlusal eruption (very slow)
Why is the dental follicle important for tooth eruption?
Its important for bone resoprtion
What other factors are important for eruption?
Deciduous tooth resorption
Apical blood flow
How can interceptive ortho treatment help ectopic canines?
Interceptive extraction of the deciduous canines at the correct stage
When is the right time/correct stage to interceptively extract deciduous canines to help treat ectopic canines?
When the permanent has 1/2-2/3rds of roots development
Pateint will be between 10-12
When should GPD’s be looking for ectopic canines? Why is it important to refer then?
Around age 9 and refer
Because if dont extract on time will need surgery to move them
What is the physiological basis of orthodontics? e.g. how does the tooth move
If an external force is applied to a tooth, the tooth will move as the bone around it remodels
The bony remodelling in orthodontic tooth movement is mediated by what?
The PDL
When will a tooth note move?
If it doesnt have a PDL or is ankylosed
What role does cementum play in tooth movement? (how is it affected?)
Cementum is muchmore resisitant to resorption than bone, although some degree of root resorption after orthodontics should be expected
If there was no cementum then teeth would exfoliate post treatment
Appliances transmit forces to the PDL and bone and osteoclasts ‘herd’. What happens if there is an osteoclast that isnt working optiminally?
Macrophage will phagocytose
What are the different theries for how orthodontic tooth movement occurs?
- differential pressure theory
- piezo-electric theory
- mechano-chemical theory
Describe the differential pressure theory.
You get tension on one side where there is bone deposition
Get compression on other side/parts and get resorption from osteoclasts here
Describe the piezoelectric current theory.
-piezoelectric currents are generated when crystalline structure, such as bone, are defomed
These currents have been suggested as the prime mechanism by which tooth movement is modulated
Describe the mechano-chemical pressure theory.
mechanical stress
- release of neuropeptides from nerve endings
- stimulate fibroblasts, endothelial cells and alveolar bone
- fibroblasts also communicate with osteoblasts and osteoclasts
- alveolar bone and PDL remodelling
- tooth movement
What are the diff types of ortho appliances? (3)
- removables
- functional
- fixed
What are the different types of tooth movement?
- tipping
- bodily movement
- intrusion
- extrusion
- rotation
- torque (is like tipping but moving the root instead of the crown)
What is the ideal force tot tip a tooth? (exam Q)
35-60 grams
What are functional orthodontic appliances used to treat?
To correct class II occlusions (bring the mandible forward)
How do functional appliances work?
- The mandible is postured away from its normal rest position
- the facial musculature is stretched which generated forces transmitted to the teeth and alveolus
- there may be an effect on facial growth
Give an example of how a functional appliacne may work with a Class II.
- restrict maxillary growth
- promote mandibular growth
- remodel the glenoid fossa
Describe the skeleton changes that occur with functional appliance.
Mandible is postured away from its normal rest position
Describe the dental changes that occur with a functional appliance.
- upper teeth tip back (maxillary restriction of growth)
- lower teeth tip forward (wouldnt do on patient with lowers tipped forward)
How long do you tend to wear a functional appliance for?
6 months full time then 6 months just at night
Summarise the mode of action of functional appliances and the changes that they cause. (4 main points)
These changes together achives what?
- skeletal change (30%)
- Growth of mandible
- Restriction of maxilla
- dentoalveolar change (70%)
- retroclination of the upper teeth
- proclination of the lower teeth
- Mesial migration of the lower teeth
- Distal migration of the upper teeth
Achieves Class I
What kind of tooth movement can fixed applianced facilitate?
All types (tipping, bodily movement, intrusion, extrusion, rotation, torque)
What is the ideal force for bodily movement of a tooth?
150-200grams
What does bodily movement of a tooth mean?
Moving the tooth at the same angle it is at
What type of wire is needed for bodily movement?
rigid stainless steel wire that can bend
Describe what happens in bodily movement of a tooth. (bone remodelling etc)
- Apply force to a tooth (150-200g)
- Get bone resorption on side of tooth that is moving
- Get deposition of bone on the opposite side of the tooth
There is co-ordinated bone modelling and remodellling in response to the applied force.
Osteoclasts and osteoblasts play a big role in this
What is the ideal force to intrude a tooth?
10-20grams
Describe how an orthodontic appliance is used to intrude a tooth.
Gentle small force and the tooth will intrude
-pressure on the supporting structures is evenly distributed, and bone resorption is necessary, particularly at the apical area and alveolar crest
What is the ideal force to extrude a tooth?
35-65grams
How are teeth extruded with orthodontic appliances?
Tension is induced in the supporting structures and bone deposition happens to maintain tooth support
What is the ideal force for rotation of a tooth?
35-60grams
How do teeth rotate from ortho appliances?
Need a force couple
FOrces going in different directions and will have a centre of rotation
What is the ideal force for apical root torque?
50-100grams
How is apical root torque achiveed with ortho appliances?
- is really difficult on any fixed appliance
- is like a force couple
- the crown doesnt move much but root does
Summarise the optimum forces for different types of tooth movements.
- Tipping = 30-60g
- Bodily movement = 150-200g
- Intrusion = 10-20g
- Extrusion = 35-60g
- Rotation = 30-60g
- Torque = 50-100g
How would you describe the kind of force in orthodontics generally?
Light force
We use light forces as we want what to happen?
Frontal resorption
Describe what histologically changes happen during orthodontics when light/ideal forces are used. (7 points)
- hyperaemia within the PDL
- appearance of osteoclasts and osteoblasts
- resorption of lamina dura from pressure side (osteoblasts)
- Apposition of osteoid on tension side (osteoblasts(
- remodelling of socket ‘frontal resorption’
- Periodontal fibres reorganise
- gingival fibres appear not to become reorgnaised ut remain distorted
What would happen if moderate force was applied to try and move a tooth?
- Would have occlusion of vessels of PDL on pressure side
- Leads to cell free areas (hylinsation)
- Isnt dead but cant resorb the bone anymore
- Hyperaemia of vessels of PDL on tension side
- Period of stasis (bone is just there and no tooth movement)
- Increased endsteal vascularity
- UNDERMINING RESORPTION (bad)
- Osteoclasts underneath the area causing this
- Relatively rapid movement on tooth with bone deposition on the tension side
- Tooth may become slightly loose
- HEaling of PDL - reorganisation and remodelling
The teeth dont move efficiently
What would happen if you tried to move a tooth with excessive force?
- necrosis
- undermining resorption
- pain
- permanent change
Would get no movement then a ‘clunk’
What are the 4 factors affecting the response to orthodontic force? (is really only 3)
- age
- magnitude
- duration
- anatomy
How does duration affect the response to ortho force?
Get bettwe results when worn 24hours a day
What anatomical factors can effect the response to ortho forces?
- bone wasting/cleft
- alveolar necking
- soft tissues
- mid-palatal suturre
What is alveolar necking and how does it affect ortho?
Tooth removed and the two alveolar plates are very close together
Almost impossible to move teeth through here
Are teeth that have been root treated a problem?
If there is no pathology then no
What are the deleterious effects/side effects of using orthodontic force?
- Pain and mobility
- Pulpal changes
- Root resorption
- Loss of alveolar bone support
- Relapse
What amount of tooth movement is though to be ideal?
1mm per month
It takes time!!
What is the treatment time for fixed appliances?
24 months
