Occlusion Flashcards
Consequences of bad occlusion
Fractured cusps, teeth, restorations Failed crowns and bridges Localised periodontal disease Drifting/overerupted teeth Loss of vitality of teeth TMD Muscle pain Parafunction
ICP
Mandible position when there is maximum cuspation of teeth
RCP
Mandible position when condyles are fully seated in glenoid fossa/in most superior position - first tooth contact in this position
CR
Jaw position when condyles are fully seated in glenoid fossa/in most superior position - best neuromuscular position because muscles don’t need to work as hard. Condyle braced by bone so muscles are doing less work.
Techniques to find CR/RCP
and when to use
Gothic arch tracing Manual positioning/Dawson technique Flat plane splint Anterior jig - Useful for when reorganising occlusion or if ICP is unstable or OVD needs to be increased e.g. CD, TMD
THA/terminal hinge axis
Hinge movement of condyles in CR
Lateral excursion details [4]
The working side is the side you’re moving to. Group function or canine guidance.
NWS - there shouldn’t be any contacts hee. If there are, they are called interfering contacts and lateral force on cusps can cause a fracture.
Bennett movement/angle
Horizontal plane
During lateral excursion
NWS Condyle moves down forward and rotates = Bennett’s movement
WS condyle rotates ~7.5 degrees = Bennett’s angle
Protrusive excursions
Anterior guidance or group function if class 3 or edge-to edge. Condyle moves down and forward
Condylar movement
Rotation movement in glenoid fossa first and then moves down articular eminence.
Rotation and translation
Occlusal schemes [4]
Ideal occlusion Balanced occlusion (For CD) Group function Gnathecial occlusion (all teeth working in all movements. Difficult)
Principles of ideal occlusion [4]
- ICP = RCP
- Mutual protection bw anterior and posterior teeth, heavier contacts on posterior teeth during ICP movements, lighter during eccentric.
- Posterior teeth disocclude on eccentric movents
- Forces down long axis of the molar teeth
Bruxists in ideal occlusion
Parafunction in RCP and destroy this contact
Grind in ICP and increase neuromuscular activity
- Good to know where RCP contact is and provide tougher restoration or make ICP = RCP
Why is canine guidance good
Good crown: root ratio
Highly innervated so can feel when too much force etc
Distance from TMJ muscles/hinge means less force through it
What is group function
Lots of teeth contacting on WS, NWS teeth disocclude
Class 2 div 1 protrusive movements
May have posterior contacts/less anterior guidance, esp if proclined.
Class 3 protrusive movements
Will have posterior contacts or group function e.g. if edge-to-edge
Different types of articulators [5]
Simple hinge articulator - just has the teeth in ICP, no eccentric movements.
Anatomical articulators - have the hinge in the same place as TMJ so models can be mounted in CR. Show eccentric movements
- Average value articulator = 30-degree condylar angle and flat/straight condylar pathway
- Semi-adjustable = adjustable condylar angle but a flat condylar pathway
- Fully adjustable = custom made condylar pathways
Denar Automark articulator = 20-degree condylar angle, which means that any posterior work will definitely have disocclusion on the model, and be more in real life bc IRL condylar angle is steeper.
What is a facebow used for/details
Used to record the relationship between condyles and teeth.
2 separate parts - earbow to record TMJ position, and one on the occlusal plane and then join them together and send to the lab.
Also useful for getting the correct height of the model.
Can get different ones for maxilla and mandible.
Complete denture - equipment and occlusal considerations
ICP = RCP
Facebow and models mounted in CR
To create balanced occlusion (ICP = RCP) and restore OVD
Restorative work on posterior disoccluding teeth - equipment and occlusal considerations
Facebow and mount models in ICP
Can use a 20-degree articulator to ensure no posterior interfering contacts
Or use a simple articulator and rely on the anterior guidance.
Restorative work on guiding anterior teeth- equipment and occlusal considerations
Facebow and mount in ICP
Record all eccentric movements and contacts on the anterior teeth on the articulator
Make sure not to change these movements
- If intending to change the movements, need to mount the models in CR
RPD - equipment and occlusal considerations
If OVD and ICP are stable - mount the models in ICP.
If unstable, facebow and mount models in CR and recreate ideal occlusion (ICP = RCP, eccentric movements, etc.)
Hard acrylic splints - equipment and occlusal considerations
Facebow and mount models in CR
20-degree articulator to ensure posterior disocclusion
How to carry out an occlusal assessment (before examination)
Occlusal history
- Pain during movements, facial or muscle pain
- TMD
- Parafunction
Dental history
- Failed crowns/bridges
- Signs of occlusal disharmony
- Fractured cusps and restorations
- TMD
- Patient’s expectations
Medical history
- Contraindications to long complex treatment
- Medications that cause clenching/bruxism
- Joint/bone conditions or previous h&n trauma/surgery
Social history
- Stress
- Contraindications to long complex tx
Occlusal assessment examination
- TMJ
- Muscles of Mastication
- ICP, RCP and the slide bw the 2
- Excursive movements and guidance and contacts inc interfering
- Skeletal, molar and incisor relationship
- Overjet, overbite, crossbite
- OVD
Occlusal treatment planning considerations for simple direct restorations
Check contacts before and after to make sure you’ve not changed anything.
If planning on changing things
- Excursive contacts not on restoration or cusps
- ICP contacts not on restoration interface
- Remove NWS interfering contacts
- Re-introduce canine guidance (will protect lingual cusps of lower posterior teeth)
Occlusal treatment planning considerations for indirect restorations - confirmative and simple
Non-guidance teeth - no facebow needed.
Study models to check contacts and guidance beforehand.
Need enough occlusal preparation depth so new restoration doesn’t affect contacts.
Check contacts after fitting.
Considerations for indirect restorations on the last tooth in the arch
Patient will bite down and adjust bite so all the space you just prepared is lost.
1) check ICP contact and don’t remove this (prepare whole tooth and leave this island)
2) Send imp to lab and they will remove this island and make the crown
3) Remove this island in the clinic and fit the crown - don’t let patient bite down until final restoration is in place
Occlusal treatment planning considerations for indirect confirmative complex
If 3+ unit bridge, guiding tooth or complex occlusion. - Facebow transfer and mount models on articulator.
- Can use a diagnostic wax up.
- Metal backing or high strength porcelain for guiding surfaces
- ICP contacts should be on abutment tooth, and no guidance contacts on pontic tooth esp if cantilever.
- Can get a customized incisal guide from the lab to replicate the guidance on the models.
Occlusal treatment planning considerations for complex reorganised cases
If changing OVD, multiple units, full mouth rehab
- Need diagnostic wax ups (can do a mock up using ProTemp)
- Models articulated in CR using facebow transfer
- Ideal occlusion principles.
Types of hard occlusal splints
Mitchigen Upper Tanner lower Interocclusal appliance Stabilisation splint Flat plane occlusal splint
Why use splints
TMD Bruxism Protect extensive restorative work Finding CR Diagnose occlusal problems - Splints can reprogramme neuromuscular system by separating teeth and allowing condyle to seat in most optimal position so protect teeth from parafunction/excessive forces
What occlusal plan do you try to achieve with hard splints
Ideal occlusion
in CR (facebow and articulate models on 20 degree adjustable articulator)
Full coverage to stop teeth overerupting
Dahl concept (old)
Cement a partial CoCr with an anterior bite plan that allows posterior teeth to disocclude.
- Posterior teeth overerupt
- Anterior teeth intrude
Creates FWS in new ICP and you can provide anterior restorations now
Dahl concept (new)
Restore anterior teeth first and the posterior teeth will over erupt (+ intrusion of anterior teeth) to create a new ICP.
New posterior contacts can from 6 weeks after anterior cons.
If the posterior teeth don’t over-erupt, may need to provide indirect restorations.
What occlusal planning needs to be done before Dahl concept
Models articulated using facebow
Wax up of proposed anterior cons
Occlusal RCP records
Regular reviews to get a record of the occlusal changes.
Security vs stability of dentures
Security = retention, ability to resist forces and displacement in an axial direction Stability = ability to resist forces in other non-axial directions
Retention of complete denture compromised by what
Lack of moisture/suction seal
Post dam = air gets in
Not fitting ridge
Unfavourable anatomy e.g. fibrous ride, atrophic ridge
What is the neutral zone
The balance between cheek/muscle forces pushing teeth in and tongue forces pushing teeth out
Teeth should be placed here
How to record the neutral zone
Get a wax registration block
Remove anterior wax and replace it with alginate
Take an impression and record all the movements and sounds made by the mouth
Send to the lab and ask them to place teeth here.
Rules for complete dentures wrt neutral zone
Teeth shouldn’t be placed too lingually = the tongue will displace them, trauma to the tongue, bad lip support, and tongue cramp.
7’s aren’t needed and if u do add them, need to make sure they don’t take away from the tongue’s space
Teeth shouldn’t be placed too buccally/labially bc will cause cheek trauma and lift on function
Problems when making a complete upper denture opposed by lower natural teeth
Fibrous upper ridge so needs combination impression tray and muco-static material/technique.
Careful recording of face height and OVD.
