Principles of occlusion Flashcards
Class I
Most people
Why bother with occlusion
Unstable occlusion–>
- tooth wear
- fractured cusps/ restorations
- localised periodontitis
- pulpitis
- drifting teeth
- failure of crowns and bridges
- failure of endodontic treatment
- cracked cusp syndrome
When restoring dentition your aim should be to achieve
- contacts on all teeth in ICP
- anterior guidance will create posterior disclusion
- use canine guidance where possible to provide lateral guidance (otherwise group function)
- if occlusion acceptable, restore at existing height (OVD) and position (ICP) = conformative
- if ICP unacceptable you have to use centric relation = reorganised
When restoring dentition your aim should be to achieve
- contacts on all teeth in ICP
- anterior guidance will create posterior disclusion
- use canine guidance where possible to provide lateral guidance (otherwise group function)
- if occlusion acceptable, restore at existing height (OVD) and position (ICP) = conformative
- if ICP unacceptable, unavailable, unreproducible you have to use centric relation = reorganised
ICP
Intercuspal position
Position of mandible in relation to maxilaa when teeth are maximally intercuspated
Centric relation
Relationship between mandible and maxilla, when properly aligned condyle-disc assemblies are in most superior position against eminenta
Allows approx 25mm opening of pure hinge movement.
Terminal hinge axis or retruded hinge axis
Imaginary line between mandibular condyles around which mandible rotates when mandible is in CR
Allows an opening of approx 25mm before condyles move down eminentia, when opening
Terminal hinge axis or retruded hinge axis
Imaginary line between mandibular condyles around which mandible rotates when mandible is in CR
Allows an opening of approx 25mm before condyles move down eminentia, when opening
Retruded contact position
RCP is first tooth contact when mandible is closed in CR
One point within CR arc
Significance of RCP
RCP often involves only 2 opposing teeth - these carry all the load of occlusion when px slides from RCP to ICP or from ICP to RCP
If these are un-restored sound teeth, there is uaully no problem, however if heavily restored or root treated, then failure of restorations likely
Border movements in a sagittal plane
Posselt described envelope of border movement in sagittal plane
These envelopes of movement are tools which may be used to help diagnose or describe problems of TMJ dysfunction
Forward (protrusive) movement
Anterior guidance (mandible)
Pathway taken by lower teeth is guided anteriorly by teeth and condyles
Normally involves anterior teeth but may involve posterior teeth, e.g. anterior open bite or edge to edge class III
Determined by amount of overjet and overbite
Condyles in forward movement
Move forwards and downwards on eminentia
Gives rise to condylar angle: angle between occlusal plane and path taken by condyles during protrusion
Average value 30degrees
Working and non-working sides
Working side: side to which mandible moves during chewing. As mandible moves to left, left canines function or work, therefore this is working side (and vice versa)
Non-working side: opposite side. As mandible moves to left, no teeth function on right therefore this is non-working side (and vice versa)
Lateral excursions
Can be guided by canines or group function
Restoring palatal surface of canine involved in canine guidance can alter guidance and increase load on tooth
The ideal occlusion
Forces through axis of teeth-cusp to fossae
Disclusion of posterior teeth in eccentric excursions
Mutual protection
RCP = ICP
Forces on teeth
Contact - cusp tip to fossa results in axial forces
Contact on incline results in destructive horizontal forces
Posterior disclusion
Any movement away from ICP should ideally result in disclusion of posterior teeth
This results in avoidance of destructive forces on inclines of teeth
Why should we have canine guidance in lateral excursions?
Morphology - very strongh tooth with long roots
High degree of proprioception to prevent excessive loading
Distant from hinge of mandible
Distant from powerful muscles of mastication
Mutual protection
In ICP all teeth should be in contact, posteriors should contact firmly but anterior teeth should only contact lightly
Most force of occlusion is carried and distributed by posterior teeth in axial direction thus: the posterior teeth protect the anterior teeth
In protrusive excursion, anterior teeth protect posterior teeth
Why can anterior teeth take reduced load during protrusive excursion?
Furthest away from hinge of mandible and so force exerted is limited
Distant from masseter and therefore force exerted is limited
Highly innervated resulting in brain limiting force exerted on teeth
Why RCP = ICP best?
Optimum position for muscles
If not, we want as many contacts in RCP as possible to share occlusal load
Minimal slide RCP - ICP
Earliest contacts should be balanced or at least be on strong teeth, so occlusal load can be tolerated by teeth involved
