OB P9 + 10 : Tooth movements Flashcards
where are occlusal forces greater?
greater between molars than incisors
what are the physiological chewing forces?
– 70-150N dentate (between molars)
– Edentulous 4-55N
what are the maximum clenching forces?
– 500-700N between molars
– Up to 1500N – Inuits
what is the load applied in the horizontal and vertical plane in tooth movement?
- Greater movement in horizontal plane (~100μm)
- Lesser movement in the vertical plane (~10μm)
what are the tooth support components?
- bone
- PDL fibres
- PDL fluids
what is responsible for the drag response on the movement/time graph?
Visco-elastic system
Describe the viscosity of the Visco-elastic tooth support.
-extracellular matrix - aggregates at rest-therefore less mobility
-Periodontal fluids:
>interstitial
>blood
Describe the elasticity of the Visco-elastic tooth support.
- collagen
- bone
- osseointegrated implants (“pure” elastic support)
what is the difference between teeth and osseous-integrated implant?
Tooth: -PDL and bone -Viscoelastic support Osseointegrated implant : -no PDL -Elastic support-bone -much less movement
what are the 4 types of post -eruptive movements?
- vertical
- buccal
- mesial
- orthodontic
Describe vertical movements.
Continued eruption:
- compensation for wear (occlusal and incisal)
- bone deposition (apically and cervically)
- Cementum deposition (increased cementum thickness)
Describe the buccal movements.
- growth of jaws
- bone remodelling
when does medial drift occur?
throughout life
what is mesial drift?
teeth drift in medial direction -towards arch midline
what is the result of medial drift?
– Compensates for approximal wear – Incisal crowding – Shortening of dental arch – may make space for 8’s – Orthodontic relapse – Space closure following tooth loss • Positive • Negative
what is approximal surface wear?
teeth rub against each other
What are the measurements of medial drift?
From 6-18 years : 3-4mm
With hard diet : 7mm
what are the mechanisms for medial drift extrinsic to periodontium?
- Occlusal forces
- Muscular soft tissue forces
- Erupting molars
what are the mechanisms for medial drift intrinsic to periodontium?
- Bone remodeling
- PDL fibres
> Transeptal fibres
what is the evidence for occlusal forces?
- Vertical occlusal load applied:
> Horizontal vector of force
> Occlusal load of 9Kg results in a horizontal load of
• 2.25Kg against the molars
• 5Kg against the canines - Approximal tooth wear must require a force pushing teeth together
what is the evidence against occlusal forces?
occlusal loads transient
what type of force is medial drift?
anterior vector to closing force
How was medial drift visualised?
contact points opened up with cutting disk
what was the result from extracting opposing teeth?
medial drift was faster
what was the result of flattened cusps?
medial drift was faster
What was the result of reshape cusps ?
one side favoured medial drift and other side opposed it
what is the conclusion for occlusal forces?
– occlusal forces partly involved in mesial drift
– but not the most important factor
what are the soft tissue forces?
forces from cheeks (buccinator ) and tongue
what experiment was used to tests soft tissue forces effect on medial drift?
– Cover teeth with acrylic dome
– No opposing teeth
– Still get mesial drift
what was the conclusion for soft tissues forces?
not likely to play a role
what is the evidence for forces from erupting molars?
Extraction of premolars:
– Spaces close more rapidly when molars erupting
what is the evidence against forces from erupting molars?
> Mesial drift occurs throughout life – Even after molars erupted > Still get mesial drift: – If no adjacent tooth contacts – Anterior to an ankylosed tooth
what is the evidence for bone remodelling?
Get remodelling at same time as mesial drift
what is the evidence against bone remodelling?
- Marker experiments show that bone fills in
- Effect, not cause
Describe the PDL fibres : transeptal fibres affect on medial drift.
- Transeptal fibres maintain tooth contact
- Stabilise tooth position
- Less orthodontic relapse if cut
- mesial drift slows down when fibres are cut
what is the summary of the cause of medial drift?
- multifactorial:
>Greatest factor: PDL -transeptal fibres
>Other factor: occlusal forces
(not likely erupting molars)
what is the result of orthodontics applying small continuous forces?
– Bone remodel
– PDL remodel
– Tooth movement
what are the 3 types of orthodontic tooth movement?
– Tipping
– Bodily
– rotational
During tipping movements , where is the force greatest?
Movements and hence forces greater the further away from the fulcrum
How much force?
> Ideally close to naturally occurring forces (e.g. mesial drift)
Ideally less than the PDL capillary pressure:
– If < capillary pressure – PDL remains normal
– If > capillary pressure - ischaemia
Depends on type of movement and size of tooth
what are the forces (g) for different tooth movements?
tipping - 30-60g
bodily - 60-120g
rotational - 30-60g
intrusion - 10-20g
what is the result of light forces?
- Compression : frontal resorption by osteoclasts
- Tension : deposition by osteoblasts
what is the result of heavy forces?
- Compression ++ (capillary pressure exceeded) : undermining endosteal resorption by osteoclasts
- Tension : deposition by osteoblasts
What are the possible effects of excessive forces?
> Pain – Ischaemic – Inflammatory - necrosis > Unrepaired hyalinisation > Pulp death – strangulation of vessels at apex > Root resorption – Odontoclasts – Can self repair – new cementum infill
Describe remodelling of principle collagen fibres.
– Rapid below alveolar crest
– Slower above alveolar crest • Supralaveolar
• Especially transeptal
• Rotations
what is the need for retention?
– Long term / permanent e.g.: • Large space closure
• Correction of severe rotations
