Ideal occlusion and Selecting Equipment Flashcards
What is the ideal occlusion?
Distribution of load in the most favourable way
RCP = ICP - when closed posterior teeth contact and anterior teeth have light contact only
Forces directed through the long axis of the teeth
Posterior disclusion in eccentric positions
Mutual protection
Why do we want RCP to equal ICP?
When closed the posterior teeth contact and anteriors have light contacts
Occlusal load is directed through the long axis of te teeth
Condyles are positioned to distribute load into the bone with minimal muscular movement
What happens when RCP does NOT equal ICP?
Functioning in ICP requires more muscular activity to position the condyle and intraarticular disc
80-90% of population have RCP not equal to ICP
Bruxists may function on the RCP contact
- Damage vulnerable restorations
- Create wear facets on sound teeth
Bruxists may also grind in/from ICP
- Muscular activity increased
Why are forces down the long axis of the teeth favourable?
Distributes occlusal forces favourably Contacts on inclines result in horizontal forces - Wear - Tooth movement - Bone loss - Fracture of restorations
If restoring tooth with RCP not equal to ICP think about..?
Where RCP contact is
Tougher restorations
Multiple contact points
Minimise difference between RCP and ICP
What occurs in posterior disclusion? What happens if posterior contacts occur?
Anterior teeth disclude (separate) the posterior teeth Avoids lateral forces on posterior teeth Working side: group function NWS interference (undesirable) and protrusive interference (undesirable)
Anterior guidance?
Palatal surfaces of upper anteriors dictate the movement - interference occurs on mesial of lower and distal of upper teeth
How do teeth protect each other?
In ICP posterior teeth protect the anterior teeth
In excursions anterior teeth protect the posteriors
What allows canine guidance - why is canine guidance favoured?
Morphology of the canine Crown:Root Distant from the hinge Distant from the muscle Highly innervated
What occurs in group function?
Multiple contacts on working side
Define class I incisors
Lower incisor occludes at or below the upper incisor cingulum plateau
Define class II div I incisors
Lower incisor occludes behind the upper incisor cingulum plateau
Define class II div II incisors
Lower incisor occludes behind the upper incisor cingulum plateau
Upper central incisors are retroclined
Be careful with labial surface of lower incisor and palatal surface of upper incisor if restoring
Define class III incisors
Lower incisors occlude infront of the upper incisor cingulum plateau
Take care with occlusion when restoring - reproduce contacts or change them for the better
When restoring a tooth what should you do regarding occlusion?
Analyse existing occlusion - know the tooth contacts
Conforming - don’t introduce unfavourable contacts
Reorganising - work to the ideal occlusion
= Know RCP and ICP contacts pre and post op
What dictates the movement of the mandible?
Position of the condyle in the fossae
Condylar pathway along the articular eminence
Teeth interfere with this border movement
What is the only position where the mandible can rotate about a hinge without using the lateral pterygoid muscles to brace the closing muscles?
CR
What do deprogramming methods depend on?
Operator ability
Tooth mobility
Edentulous areas
Difficulty of pt
Methods for deprogramming?
Bilateral manual manipulation (dawson technique) Cotton wool rolls Anterior jigs Gothic arch tracing Flat plane splint
Methods to record CR?
Manual manipulation into wax or silicone
Anterior jig with silicone
GAT with silicone
Functions of articulators?
Hold models in ICP
- Limit of simple hinge articulators
- They do not mimic opening movement as hinge is in the wrong place
Galetti articulator
Do not mimic opening movement as hinge in wrong place
Anatomical articulators
Replicate jaw movements = hinge is in the correct place in relation to the teeth. All movements are rotational around an axis. Necessary to mount models in CR Average value 30 degree condylar angle Straight condylar pathway
Semi-adjustable:
Condylar path can be adjusted between 0 and 60 degrees - condylar path is still flat
Fully adjustable:
Custom made condylar pathways
Mechanically replicate the movements of the condyles
How to record the relationship
Facebow e.g. earbow - external auditory canal used for convenience
Records relationship between condyles and maxillary teeth
How to position the models on an articulator?
Average relationship
Bonwill triangle
Denar automark or combi articulator - used in CCDH - what is the fixed condylar angle?
Fixed 20 degree condylar angle
What does the equipment depend on?
Occlusal scheme
Objectives of tx
Clinician’s skill
CD - what is wanted with occlusion? How is this done?
Balanced occlusion RCP - ICP Working side contacts Balancing (non-working) side contacts Protrusive contacts on incisors and posterior teeth
Facebow transfer (as models moving) Models mounted in CR Reproduction of condylar movement - condylar angle, intercondylar width, bennett movement
Anterior guided dentition?
Discluding teeth:
- Contact in ICP
- dISCLUSION ELSEWHERE
- Rely on anterior guidance rather than the condyle to create disclusion
Facebow transfer
Models mounted in ICP
20 degree condylar angle
Use average bennett movement and intercondylar width
Can also use an average intercondylar width
Anterior guided dentition (guiding teeth)
Guiding surface on tooth is very important on guiding teeth
Either:
- check in mouth
- copy existing guidance on to articulator
- change guidance
Facebow transfer Mount models in ICP 20 degree condylar angle Use average bennett movement and intercondylar width Record anterior guidance
How to reorganise the occlusion?
Facebow transfer
Mount models in CR
20 degree condylar angle
Use average bennett movement and intercondylar width
What dentitions require more attention? Why?
When posteriors are contacting in protrusive excursions, non-working side excursions
Careful as guidance is on posterior teeth, extensive group function and extreme wear cases
What to think about with RPDs?
Acceptable OVD
Stable ICP - if no stable icp or ovd mount in CR to reorganise
Large edentulous area - look to see if anterior guidance is possible, if not default to balance occlusion for denture stability
What do to with splints?
Establish ideal occlusion on splint Facebow transfer Mount models in CR 20 degree condylar angle Use average bennett movement and intercondylar width
Facebow uses?
To ensure incisal plane angle is correct
Ensure correct model height on articulator = has a relative effect on the condylar angle
