Tooth Movement Flashcards
What problems are there when excessive force is placed on a tooth?
- delays tooth movement (10-14 days)
- increases change of anchorage loss
- more patient discomfort
- increased tooth mobility
- increased risk of root resorption
What do osteoclasts do?
Resorb bone
What do osteoblasts do?
Produce new bone
What do fibroblasts do?
Produce and destroy collagen fibres
What do cementoblasts do?
Form new cementum
What do cementoclasts do?
Removes cementum
What are the 3 types of forces?
- continuous force - force is maintained between activities
- intermittent - force drops to zero
- interrupted - force declines to zero
What are the effects of excessive force?
- delays movement of teeth
- increase chance of anchorage loss
- more patient discomfort
- increased tooth mobility
- increased risk of root resorption
- hyalinisation of the area
- undermining resorption
What is the ideal force for tipping movements?
Tipping - 35-60g
What is the ideal force for bodily movements?
Bodily movement - 70-120g
What is the ideal force for extrusion?
Extrusion - 35-60g
What is the ideal force for intrusion?
Intrusion - 10-20g
What is the ideal force for torque?
Torque - 50-100g
What is the ideal force for rotational movements?
Rotation - 35-60g
What happens on the pressure side when optimum force is applied to the tooth?
- PDL is compressed
- within seconds alveolar bone bends and blood supply is altered
- when pressure is continued over a period of hours there is a chemical reaction within the blood cells
- cytokines and prostaglandins are released which signals the need for osteoclasts to the area
- within two days osteoclasts migrate to the area and begin bone resorption = tooth can move
What happens on the tension side when optimum force is applied to the tooth?
- PDL is stretched
- blood supply alters and chemical reaction within blood cells
- signals are sent for the need of osteoblasts and fibroblasts to migrate to the area and lay down osteoid bone and new PDL fibres
How long does it take for osteoid to calcify?
6 weeks
What happens what excessive force is placed in the pressure side?
- force is above capillary pressure
- osteoclasts are not able to reach pressure area to resorb bone
- area becomes hyalinised and appears like ground glass as there are no cells
- once pressure is relieved osteoclasts can reach the area
- undermining resorption occurs, bone is resorped from back to front
- creates a lag time for movement of 10-14 days
What happens on the tension side when high force is applied to a tooth?
Blood vessels rupture
What factors can increase root resorption?
- torque on teeth
- excessive force
- nail biting
- previous orthodontic treatment
- previous trauma
- distance to move teeth
- root shape - blunt roots, pipette shape
- type of movement
How much root resorption occurs during orthodontic treatment?
1-2mm
What are the time frames with regards to tooth movement on the pressure side?
1-5 seconds - PDL compressed and change in cell shape
Minutes - O2 levels change, chemicals released
4 hours - osteoclasts differentiate
1-2 days - bone remodels
What are time frames with regards to tooth movement on the tension side?
1-5 seconds - PDL stretches, change in cell shape
Minutes - O2 levels change, chemicals released
4 hours - osteoblasts differentiate
1-2 days - bone remodels
The centre of rotation on a single rooted tooth is?
Approximately one third down the root from the apex
What is compression in regards to tooth movement?
The direction the tooth is moved into
What is tension in regards to tooth movement?
The areas behind which the tooth has been moved from
What is undermining resorption?
- osteoclasts need to remove dead bond before new bone is placed
- resorption occurs back to front
- lag phase of 10-14 days
What is tip?
The mesio disto angulation of a tooth
What is torque?
The labio palatal angulation of the tooth
What is the ideal force that should be used to move a tooth?
20-25g/cm2
How can root resorption be minimised?
- take careful history and examination
- take pre treatment X-rays
- light forces and mechanics
- minimise treatment length
- monitor susceptible patients
What can make a patient more prone to root resorption?
- root form - blunt, pipette roots are more susceptible
- ectopic canines
- trauma
- treatment mechanics - fixed appliance, class II elastics, torque, intrusion
- age
- gender
- length of treatment
- individual variety
- systemic problems
What effect does excessive force have on teeth?
Delayed movement Anchorage loss risks More discomfort Tooth mobility Root resorption risk
What is friction influenced by?
Arch wire factors
Bracket factors
Ligation factors
What is friction?
The force resisting the relative motion of surfaces sliding against each other
