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41 Cards in this Set
- Front
- Back
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Why study occlusion? |
- Failure of routine restorations - Fractured teeth and restorations - Fractured crowns - Worn teeth opposing porcelein crowns - Tx of complex restorative cases - Tx of tooth wear cases Other effects - Localised perio - Loss of teeth vitality - Facial pain due to parafunction |
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Terminology |
Mandibular positions - ICP - RCP Other terms associated with RCP - Centric relation - Terminal hinge axis (THA) Mandibular movements - Side to side (lateral excursions) - Forwards (protrusive excursions) - Working and non-working side |
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InterCuspal Position (ICP) |
The positions of the mandible when there is maximum intercuspation of the teeth |
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Centric Relation |
- Relation of mandible to maxilla when the condyles are seated in the midmost uppermost position in the glenoid fossa - It is a JAW relationship - nothing to do with teeth - optimum position for neuromuscular system - In this position, MOM are able to fully contract and relax - This leads to efficient, pain-free muscular function |
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Range of movement within centric relation (HINGE MOVEMENT) |
25mm |
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Terminal Hinge Axis |
- The condyles hinge about a horizontal axis when it is in CR. This is the Terminal Hinge Axis. - Lateral ptergoids can relax in this position. NOT required to brace against closing muscle. |
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Retruded Contact Position (RCP) |
- Related to teeth: the first tooth contact when condyles are fully seated in glenoid fossa |
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RCP vs ICP |
- Usually do not coincide - We can close to RCP and then slide to ICP - Vh or vH - When they are different, the muscles may be in conflict, causing trigger sites of pain/inflammation |
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Protrusive movements |
- When anterior teeth are in contact in ICP, the contacts in protrusive excursions are determined by occlusal relationship - Class 1 - anterior teeth - Class 2 - anterior teeth (shallower/steeper) - Class 3 - no overbite, no anterior guidance from upper incisors ---> guidance from posterior teeth - Anterior open bite - no overbite, no anterior guidance from upper incisors ---> guidance from posterior teeth What happens to condyles on protrusive movements? - Condyles move downwards and forwards, depend on condylar angle |
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Lateral excursions |
Working side - side that jaw is moving towards On working side guidance can be: - Canine guidance - Group function Non- working side - side opposite to which the jaw is moving - Posterior teeth on non-working side should ideally separate in order to avoid destructive forces on the inclines of the teeth - Non-working side contacts (interferences) can lead to failed restorations and occlusal disharmony |
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What happens to condyles on lateral excursions |
Bennetts movement (lateral shift): - Bodily shift of mandible towards working side during lateral excursions followed by rotation around the vertical axis - The slacker the TMJ ligaments, the greater the movement (0-4mm, av 1mm) - WS condyle moves laterally - NWS condyle moves down, forwards, inwards Bennett Angle: - The angle in the horizontal plane between the sagittal plane and the downward, inward and forward path of the NW condyle - Mean Bennett Angle = 7.5 |
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CENTRIC RELATION (AGAIN) |
- JAW relationship - Allows range of movements (~25mm) when condyles are fully seated in glenoid fossa - It is a hinge movement - Very useful for restorative dentist - Relationship of mandible to maxilla when the properly aligned condyle disc assemblies are in superior posisiton against eminentia |
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Muscle activity in CR |
- No tooth interferences mean condyle-disc assembly can slide all the way up the eminentia until stopped by bone - Lateral pterygoids can relax, because there is no stimulus for muscle hypersensitivity - condyles braced by bone |
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How to find CR? |
Dawson technique: - Easily learnt, repeatable, allows verification of the position - Firmly stabilise head - Position fingers on lower border of mandible - Thumbs on symphysis, no pressure yet - With very gentle touch, manipulate so that jaw hinges slowly open and close freely (gentle but firm guidance of condyles upwards with little fingers) Verify: - To verify, once mandible is freely hinging, apply firm upward pressure with little fingers. Only assume CR is obtained if there is no discomfort. - This position should be consistently repeatable. |
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Recording Centric Relation |
Anterior jig - Flat anterior stop separates posterior teeth, allowing elevator muscles to seat condyles - Manipulate using centric relation - Record using wax/silicone |
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When is CR useful for restorative dentist |
Routine restorations: - Assess pre-op: if RCP contact on tooth to be restored consider changing type of restoration or contact point Occlusal reorganisation - Complex restorative cases - ICP should = RCP Diagnosis of TMJ dysfunction - Construct splint in CR - neuromuscular dissociation Occlusal analysis & equilibrium - Changing ICP to = RCP - only for experts! Complete denture construction - Complete dentures made so RCP=ICP as this is reproducible and comfortable for the pt |
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Ideal occlusion |
- RCP=ICP - Forces directed through long axis of teeth - Posterior disclusion - Mutual protection |
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Why RCP=ICP? |
- Avoid large forces on RCP contact - Allow condyles to distribute forces into bone - Allows muscles to work favourably Most ppl dont have ICP=RCP --> 80-90% the neuromuscular system adapts, for some the system is overloaded. |
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If ICP does not = RCP |
- Don't alter prophylactically - Have as many contacts as possible - RCP contacts on strong teeth or rough restorations - Minimise the difference between RCP and ICP - Remember large forces can be transmitted through RCP contact |
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Forces through long-axis of tooth |
- Contacts on inclines alone result in horizontal forces --> fracture of restored teeth, tooth movement and bone loss |
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Posterior disclusion |
Lateral excursions: - NWS (no contacts) + WS (canine guidance) Protrusive excursions: - Anterior teeth contact Posterior disclusion - avoids lateral forces on post teeth. Only 3 contacts occur between mandible and the base of the skull. |
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Mutual protection |
- In ICP - posterior teeth transmit force, anteriors hae light contact only. Posteriors protect anteriors - In excursions - anterior teeth take load, seperating the vunerable posteriors. Anteriors protect the posteriors. |
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Why canine guidance? |
- Morphology of the tooth - Crown root ratio - Further from hinge - Further from muscle - More highly innervated |
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Practically |
- Be aware of tooth contacts - Look at existing occlusion - Conform to existing occlusion - Don't introduce unfavourable contacts - If changing the occlusion, work towards the ideal occlusion - Know where ICP and RCP contacts are pre-operatively - Know where the ICP and RCP contacts are post-operatively |
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Improving |
- What if tooth has no ICP contact preoperatively? - What tooth contact is on incline of cusp? - What if a tooth to be restored has an interference? - What if a tooth to be restored is an RCP contact? |
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Centric Relation |
- Skeletal relationship - Relationship between mandible and maxilla when the properly aligned condyl-disc assemblies are in the most superior position against the eminence , irrespective of tooth position - It is the only position where the mandible can rotate about a hinge without using lateral pterygoid muscles to brace the closing muscles (NOT the most retruded position, NOT an unstrained position) RELEVANCE? - The neuromuscular system can function optimally - Muscles can work antagonistically allowing periods of rest |
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When to use CR? |
- Complete dentures - Routine restorations - When re-organising the occlusion - Dx and Tx of TMJ dysfunction - Occlusal analysis and equilibrium Problem: - Dentate pts are programmed to close directly into ICP and can be difficult to deprogramme the neuromuscular system |
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Deprogramming |
Method chosen depends on: - operator ability - difficulty of pt - tooth mobility - edentulous area - occlusal interferences Methods: - Manual manipulation (Wax/silicone) - Cotton wool - Anterior jig (silicone) - Gothic Arch Tracing (silicone) - Splint (for difficult cases) |
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Verifying CR records |
- only way is to compare several - difficult as records can be taken anywhere on CR arc of opening |
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Equipment for occlusion |
Which articulator to use? Holding models in ICP: - Limit of simple hinge articulator Moving models correctly: - An anatomical articulator is required Mounting models in CR: - The mandible is opened (with jig?) to record CR Establish correct position: - use an average: Bonwill Triangle - Alternatively use facebow to record the relationship - This concerns all movements on the articulator Selecting equip depends on tx being carried out and desired occlusal scheme |
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Anatomical articulators |
Average value - 30 degree condylar angle - Straight condylar pathway Semi adjustable - Condylar path may be adjusted between 0 and 50 degrees - Condylar pathway still flat - Intercondylar width - Bennett movement - Anterior guidance Fully adjustable - Custom made condylar pathways - Mechanically reproduce movements - Pantograph or stereograph |
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ARCON or Non- ARCON |
- Mandibul(ar con)dyle |
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Denar Automark |
For restorative work we use fixed 20 degree condylar angle |
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Complete Dentures |
Objective: balanced occlusion - Centric relation = ICP - Working and balancing side contact To reproduce this: - Facebow transfer - Models are mounted in CR - Reproduction of condylar paths - Intercondylar width and Bennett movement |
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Restorative work |
- Is the occlusal scheme anterior guided? - Are we conforming or reorganising? - Are we restoring a guiding or discluding tooth? |
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Anterior guided dentition |
Discluding teeth: - Contact in ICP - Disclude elsewhere - Here we rely on the anterior tooth to guide the dentition, not the condyle To reproduce this: - Facebow transfer - Models are mounted in ICP - 20 deg condylar angle - Av Bennett movement Av intercondylar width Guiding teeth - this surface is very imp! To reproduce this: - Be careful, either - Copy existing surface - Change to improve the guidance How? - Facebow transfer - Mount models in ICP - 20 deg condylar angle - Record anterior guidance - Av intercondylar width and bennett movement |
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Reorganising |
- Facebow transfer - Mount models in CR - 20deg condylar angle - Record anterior guidance - Av intercondylar width and Bennett movement |
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Ideal occlusion |
- Allows simple techniques and equipment to be used |
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Limit of simplified articulators? |
If anterior guidance can not disclude the posterior teeth in either: - Protrusive excursions - NWS excursions |
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Things get tricky! |
- Extensive grp function - Severe wear cases |
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Occlusal analysis |
- Pts with occlusal plane problems - Mount study casts to assess extent of the interference - Condylar pathway reproduction is required* FACEBOW |
