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ICP - 4th year > Occlusion > Flashcards

Occlusion Flashcards

1
Q

What is ICP?

A

It is the position of the mandible when there is maximum intercuspation of the teeth.

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2
Q

What is RCP?

A

It is the first tooth contact when condyles are fully seated in the glenoid fossa.

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3
Q

What is centric relation?

A

It is the relationship of the mandible to the maxilla when the condyles are seated in the midmost uppermost position in the glenoid fossa and the most superior position against the eminentia. It is the optimum position for the neuromuscular system. In this position the muscles of mastication can fully contract and relax. This leads to efficient and pain free muscular function. The range of movement within centric relation is a hinge movement. There is about 25mm of movement still in centric relation. It is a jaw relationship and has nothing to do with the teeth.

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4
Q

What is the terminal hinge axis?

A

It is a horizontal line through the condyles. The condyles hinge about horizontal axis when in centric relation. The lateral pterygoids can relax in this position as they are not required to brace against closing muscles.

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5
Q

Are RCP and ICP the same?

A

RCP and ICP positions usually do not coincide. We can close to RCP and then slide to ICP. This can be described as Vh or vH. When they are different the muscles may be in conflict, causing trigger sites of pain/inflammation.

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6
Q

What are the contacts in protrusive excursions determined by?

A

The occlusive relationship. In class I there is guidance on anterior teeth. In class II there is guidance on anterior teeth but it is shallower/steeper. In class III there is no anterior guidance from upper incisors and the guidance is from posterior teeth. In an anterior open bite there is no guidance from upper incisors and the guidance is from posterior teeth.

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7
Q

If there is posterior guidance in protrusive excursions what is the relevance with crowns?

A

If a crown is placed on posterior teeth, remember that this tooth will probably be involved in protrusive movements so need to make sure it is in harmony with ICP/lateral/protrusive excursions, it won’t matter what is done to anterior teeth as they do not contact.

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8
Q

What happens to the condyles in protrusive movements?

A

The condyles move downwards and forwards on the articular eminence and this depends on the condylar angle. This is the angle formed by a horizontal line and the condylar path down the articular eminence. The average angle is 25 degrees but everyone is different. Condylar guidance is one of the factors that determines how quickly the lower teeth disclude from the upper teeth (shallow angle less disclusion, steep angle fast disclusion).

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9
Q

How do the posterior teeth contact in lateral excursions?

A

Lateral excursions are the teeth moving side to side. The working side is the side the jaw is moving towards. On the working side you can have canine guidance or group function. The non-working side is the side opposite to which the jaw is moving. Posterior teeth on the non-working side should ideally separate in order to avoid destructive forces on the inclines of the teeth. If there are non-working side contacts these are known as interferences and they can lead to failed restorations and occlusal disharmony. This is because it is very destructive on the inclines of teeth so restorations placed on these contacts are likely to fail.

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10
Q

What is Bennet’s movement?

A

It is a bodily shift of the mandible towards the working side during lateral excursion, followed by rotation around the vertical axis (average of about 1mm) but will move more if the patient has slacker TMJ ligaments. The non-working side condyle moves down, forwards and inwards and the working condyle moves laterally and rotates around a vertical axis.

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11
Q

What is Bennet’s angle?

A

Bennetts angle is the angle formed as the non-working side condyle moves downwards, inwards and forwards. It is the angle between the sagittal plane and the downward, inward and forward path of the non-working condyle. The mean Bennet angle is 7.5 degrees.

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12
Q

What is the muscle activity in centric relation?

A

As there are no tooth interferences the condyle-disc assembly can slide all the way up the eminentia until stopped by bone. The lateral pterygoid muscles can relax as there is no stimulus for muscle hyperactivity - the condyles are braced by bone. Centric relation is the only position where the mandible can rotate about a hinge without using the lateral pterygoid muscles to brace the closing muscles.

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13
Q

How can you find centric relation using the Dawson technique?

A

It is easily learned, consistently repeatable and you can verify the position. You firmly stabilise the head and place fingers on the lower border of the mandible and thumbs on the symphysis. Then gentle but firm pressure rotating back and forwards on the hinge movement then close into first contact in RCP. To verify, once the mandible is freely hinging, apply firm upward pressure with the little fingers. Only assume centric relation is obtained if there is no discomfort. This position should be consistently repeatable.

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14
Q

What are the methods of deprogramming and finding centric relation?

A

It can be difficult to position the mandible in centric relation, particularly in dentate patients as the neuromuscular system is programmed to close to ICP. It can be difficult to deprogramme and allow neuromuscular release.

  • Bilateral manual manipulation (Dawson technique)
  • Cotton wool rolls
  • Anterior/lucier jig
  • Gothic arch tracing
  • Flat plane splint
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15
Q

What do deprogramming methods depend on for CR?

A
  • Operator ability
  • Tooth mobility
  • Edentulous areas
  • Difficulty of patient
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16
Q

How can a lucier jig be used to find centric relation?

A

It is a flat anterior stop which separates the posterior teeth. It allows the elevator muscles to seat the condyles. It deprogrammes the TMJ and the brain forgets how the condyles seat normally so the patient can get into centric relation. Once in place you can inject stone bite so the lab has a record of the teeth in CR.

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17
Q

What are the uses of centric relation?

A
  • Routine restorations - assess preoperatively, if RCP contact is on tooth to be restored, consider changing the type of restoration or contact point
  • Occlusal reorganisation - complex restorative cases, ICP=RCP
  • Diagnosis of TMJ dysfunction - construct splint in centric relation, neuromuscular dissociation
  • Occlusal analysis and equilibrium - changing ICP to equal RCP
  • Complete denture construction - complete dentures are made so that ICP=RCP as this is reproducible and comfortable for the patient
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18
Q

What is Posselts diagram?

A

It represents jaw movement as the tips of the lower anteriors move in protrusive mandibular movements. Look at picture.

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19
Q

What are the different occlusal schemes?

A
  • Ideal occlusion - distribution of load in the most favourable way
  • Group function
  • Gnathological occlusion - highly engineered
  • Balanced occlusion
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20
Q

What are the principles and features of an ideal occlusion?

A
  • RCP = ICP
  • Forces directed through the long axis of teeth
  • Anterior guidance in protrusion
  • Canine guidance in lateral excursions
  • Mutual protection
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21
Q

Why does RCP = ICP in an ideal occlusion?

A

When closed the posterior teeth contact and the anterior teeth are in light contact. The occlusal load is directed through the long axis of the teeth. The condyles are positioned to distribute load into the bone with minimal muscular involvement. The condyle is braced against the articular eminence with the disc in between.
This is best as it is the optimum position for the muscles and forces can be distributed through the avascular part of the joint.

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22
Q

Why is it ideal for occlusal forces to be directed through the long axis of teeth?

A

Contacts between opposing teeth should have a cusp tip to fossa arrangement. This distributes occlusal loads favourably down the long axis of the tooth then distributed by the roots into the bone.
Contacts on inclines result in horizontal forces leading to wear, tooth movement, bone loss, fracture of restorations, tooth mobility, cusp fracture and periodontal problems.

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23
Q

Why is anterior guidance part of an ideal occlusion?

A

Any movement of the mandible away from ICP should result in disclusion of the posterior teeth. The palatal surfaces of the upper anterior teeth dictate the movement and separate/disclude the posterior teeth. This avoids lateral forces on posterior teeth. An interference would occur on the mesial surface of lower teeth and the distal surface of upper teeth and this is undesirable.

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24
Q

What is canine guidance and the alternatives?

A

This allows separation of all other teeth during lateral movements and avoids destructive forces on the inclines of posterior teeth. Group function is multiple contacts on the molars and premolars of the working side (difficult to engineer). Non-working side interference is undesirable.

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25
Q

Why is canine guidance ideal?

A
  • The morphology of the canine, ideal strong shape - long and triangular
  • The crown to root ratio as the root is long and it resists tipping movement
  • The canine is distant from the hinge of the mandible
  • The canine is distant from the powerful muscles of mastication
  • Highly innervated so high degree of proprioception to prevent excessive loading
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26
Q

Is posterior disclusion in eccentric positions easy to engineer?

A

It is simple to engineer. There is often only one tooth contact in eccentric positions, three contacts between the mandible and the skull.

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27
Q

What is mutual protection?

A

In ICP all teeth should contact but the posterior teeth contact firmly and the anterior teeth contact lightly. Occlusal force is distributed in an axial direction by the posterior teeth so they protect the anterior teeth. o In protrusive and lateral excursions the anterior protect the posterior teeth.

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28
Q

Why are anterior teeth capable of taking a reduced load in protrusive excursions?

A
  • They are furthest from the hinge of the mandible so the force exerted is limited
  • They are distant from the masseter so force exerted is limited
  • They are highly innervated and this results in the brain limiting the force exerted on these teeth
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29
Q

Why is RCP not equalling ICP not ideal?

A

80-90% of the population have RCP and ICP as unequal and most people function perfectly well. However, functioning in ICP requires muscular activity to position the condyle and intra articular disc. Bruxists may function on the RCP contact leading to damage on vulnerable restorations and the creation of wear facets on teeth. Bruxists may also grind in/from ICP which increases muscular activity. Large loads may be incurred by the RCP contact so you need tough restorations, multiple contacts, minimise difference between RCP and ICP, know where RCP contact is.

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30
Q

What is the definition of the different classes of incisor relationship?

A
  • Class I is when the lower incisor occludes at or below the upper incisor cingulum plateau
  • Class II div I is when the lower incisor occludes behind the upper incisor cingulum plateau (no anterior guidance)
  • Class II div II - lower incisor occludes behind the upper incisor cingulum plateau and the upper central incisors are retroclined
  • Class III is when the lower incisors occlude in front of the upper incisor cingulum plateau
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31
Q

What is movement of the mandible dictated by?

A
  • Position of condyle in the fossae
  • Condylar pathway along the articular eminence
  • Teeth interferences with the border movement
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32
Q

How can condylar movement in the transverse and sagittal plane be shown?

A

Sagittal plane with Posselts diagram. Transverse plane with gothic arch tracing.

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33
Q

What is the function of an articulator?

A

To hold models in ICP.

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34
Q

What is a simple hinge articulator?

A

Holding models in ICP is the limit of simple hinge articulators. They travel on a different arc to that of the teeth in the mouth because the hinge is in the wrong place in comparison to the patient’s condyle. Therefore they do not replicate the opening movement of the mandible.

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35
Q

What is the Galetti articulator?

A

It doesn’t mimic opening as the condyle is in an unrelated position to that of the patient. You don’t need plaster to mount.

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36
Q

What is an anatomical articulator?

A

To replicate jaw movements an anatomically correct articulator is required. An anatomical articulator has the hinge in the right place in relation to the teeth so it replicates patients jaw movements. The types of anatomical articulator are:

  • Average value - 30 degree condylar angle, straight condylar pathway
  • Semi-adjustable - condylar path can be adjusted between 0-60 degrees to mimic patient, condylar path is still flat, intercondylar width and Bennet movement may also be adjusted on some models
  • Full adjustable - record all condylar pathways, custom made condylar pathways, use a pantograph or stereograph to record condylar movements
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37
Q

What is a Denar Automark articulator?

A

It is non-adjustable, ARCON. It has a fixed 20 degree condylar angle.

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38
Q

What is ARCON and non-ARCON?

A

ARCON or NON-ARCON is used to describe the condylar arrangement of the articulator. ARCON has the condyle on the mandibular member of the articulator (e.g. Denar). The non-arcon has the condyle on the maxillary member.

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39
Q

How are models mounted in centric relation?

A

Anatomically correct articulators are necessary to mount models in centric relation. Centric relation records are taken at an increased OVD and require ‘closing’ on the articulator.

40
Q

How are models positioned on an articulator?

A

An average relationship can be used by using a Bonwill triangle. You can record the relationship using a facebow. A facebow records the relationship between condyles and maxillary teeth. Some record the relationship between the condyles and mandibular teeth. An ‘earbow’ can use the external auditory meatus as this is easier to locate than the condyle. Pantographic facebows record all border movements of the mandible for use with a fully adjustable articulator.
Selecting equipment depends on the occlusal scheme, objectives of the treatment and the clinicians skill.

41
Q

What are the features of the occlusion for complete dentures?

A
  • Balanced occlusion
  • RCP = ICP
  • Working side contacts
  • Balancing (non-working) side contacts
  • Protrusive contacts on incisors and posterior teeth
42
Q

Ideally how should an articulator be used for complete dentures?

A
  • Facebow transfer
  • Models mounted in CR
  • Reproduction of condylar movement - condylar angle, intercondylar width, Bennet movement
43
Q

What questions should you ask about occlusion when doing restorative work?

A
  • Is the occlusal scheme anterior guided?
  • Are we conforming or reorganising the occlusion?
  • Are we restoring a guiding or discluding tooth?
44
Q

What occlusal investigation should be done when restoring a discluding tooth?

A

Posterior teeth contact in ICP and disclude elsewhere. Here we can rely on anterior guidance rather than the condyle to create disclusion.

  • Facebow transfer
  • Models mounted in ICP (conforming)
  • 20 degree condylar angle
  • Use average Bennet movement (20 degrees) and intercondylar width (120mm)
  • Don’t need to worry about the patient’s condylar angle in this dentition because posterior teeth disclude and will disclude more in mouth than on articulator as articular has shallower angle
45
Q

What occlusal investigation should be done when restoring a guiding tooth?

A

The guiding surface of the tooth is very important to not change as it will alter the whole dentition. This is usually the palatal side of the upper anteriors.

  • Check carefully in the mouth
  • Or copy existing guidance on to the articulator
  • Or change guidance
  • Facebow transfer
  • Mount models in ICP
  • 20 degree condylar angle
  • Use average bennet movement and intercondylar width
  • Record anterior guidance
46
Q

What occlusal investigations should be done when reorganising the occlusion?

A
  • Facebow transfer
  • Mount models in CR
  • 20 degree condylar angle
  • Use average bennet movement and intercondylar width
47
Q

What are the uses of a facebow?

A
  • To ensure incisal plane angle is correct

- To ensure correct model ‘height’ on articulator. This has a relative effect on the condylar angle.

48
Q

What is the reason for assessing the occlusion?

A
  • Assessment of current occlusal scheme
  • Diagnose any current occlusal problems
  • Be aware of potential future problem areas
  • Preoperative assessment prior to undertaking restorative work in order to conform with current occlusion if desired or alter any occlusal problems before treatment
49
Q

What features might you see in the history of a patient with occlusal problems?

A
  • Pain – muscles, joints, movement, face
  • Clicking
  • Awareness of clenching or bruxing
  • Difficulties in chewing
  • Not definitely an indication of occlusal problems but indicates further investigation is required (there are many causes of TMJ dysfunction)
    Read notes on dental history, medical and general.
50
Q

What would you look at in a general examination for occlusal problems?

A
  • Palpation of the muscles of mastication
  • TMJ
  • Angles/incisor classification
  • Overbite
  • Overjet
  • Skeletal pattern
  • Crossbite
  • Overerupted teeth
51
Q

What types of paper can be used for occlusal analysis?

A
  • Shimstock foil - 8 microns thick

- GHM paper - 19 microns thick

52
Q

What is involved in a detailed occlusal analysis?

A
  • ICP contacts - check contacts using shimstock +/- GHM paper
  • RCP contacts - manipulate to centric relation and note first contact with GHM paper
  • Slide from RCP to ICP – is it a big movement? Vh or Hv?
  • Anterior guidance – which teeth guide? Use shimstock +/- GHM paper with very slow movement. Are there any posterior contacts during protrusive excursion? Crossover interferences – some people can overlap the upper teeth with the lower incisors. Think about incisor class.
  • Lateral excursions – canine guidance or group function? Use shimstock +/- GHM. Ask patient to move jaw very slowly. Check for non-working side contacts (esp palatal cusps of upper molars)
53
Q

What are the signs and symptoms of loss of occlusal disharmony?

A
  • Mandibular dysfunction
  • Mobility of teeth
  • Drifting of teeth
  • Fracture of restorations
  • Fracture of cusps or teeth
  • Faceting of teeth
  • Fremitus
  • Parafunction
    Other effects:
  • Loss of tooth vitality
  • Localised periodontitis
  • Facial pain
  • Asymptomatic
54
Q

What are terms for splint therapy?

A
  • Occlusal splint
  • Michigan splint (upper)
  • Tanner appliance (lower)
  • Stabilisation splint
  • Interocclusal appliance
  • Can be made from hard or soft acrylic - hard acrylic is much more effective
55
Q

What is an occlusal splint?

A

It is a removable device made of acrylic resin which fits between the maxillary and mandibular teeth.

56
Q

What are the indications for an occlusal splint?

A
  • TMJ dysfunction and pain
  • Diagnosis of occlusal disharmony
  • Establish centric relation prior to extensive rehabilitation
  • Severe bruxism
  • Protection of extensive dental work
57
Q

What are the goals of splint therapy?

A
  • Isolate the contact relations of teeth from masticatory system
  • To allow condyles to seat as optimally as possible thus stabilising and improving the function of the TMJs
  • To allow optimal function of the neuromuscular system
  • Protect teeth from attrition and adverse loading
58
Q

What is the effectiveness of occlusal splints?

A

They are effective in muscle pain reduction in 70-90% of cases. They are most effective for pain of muscular origin. There can be pain relief after a few days or weeks though some require several months of wearing. It is important to adjust splint periodically to centric relation and eliminate grooves due to bruxism.

59
Q

What are the features of occlusal splints?

A
  • Uniform contact in centric relation
  • Canine guidance to separate posterior teeth in eccentric excursions
  • Anterior guidance to separate posterior teeth in protrusion
  • Full coverage
  • I.e. the splint creates an artificial ideal occlusion
60
Q

What are the clinical stages of splint provision?

A 
Visit 1:
- Upper and lower alginate impressions
- Jaw registration in centric relation
- Facebow
Visit 2:
- Fit splint - fitting the splint can be very tedious. Splint seated and checked for retention and even contact. Check ICP=RCP. 
Subsequent visits:
- Review and adjust as necessary
61
Q

How is a splint made?

A

They are made in the lab by mounting the casts and incisal pin opened to give 2-3mm of space. Then an outline is drawn on the cast. Two thicknesses wax is adapted to cast and then shaped. Check disclusion in lateral and protrusive excursions. Finished wax up showing contacts and anterior guidance.

62
Q

What is a bilaminate splint?

A

They have soft acrylic against the teeth but hard acrylic on the biting surfaces.

63
Q

What are the positive aspects of soft splints?

A
  • Sometimes tolerated better by patients
  • Easily constructed
  • Cheap
  • Useful for protection from trauma
64
Q

What are the disadvantages of soft splints?

A
  • Difficult to adjust
  • Can encourage patient to brux
  • Research has shown that muscle pain either did not change, or in 26% of cases it increased
65
Q

What is occlusal adjustment?

A

Adjusting the occlusion to remove unwanted/interfering contacts, especially prior to restorative treatment.

66
Q

What are the uses of occlusal adjustment?

A
  • Eliminating fremitus in a periodontally involved/drifted tooth
  • Reducing a cusp from an overerupted tooth prior to restoring the opposing tooth e.g. plunging palatal cusp of upper molar
  • Reducing load on a compromised tooth e.g. non-working side interferences, RCP contact etc
67
Q

What should you be careful not to do in occlusal adjustment?

A

Be very careful and do not remove excessive tooth tissue. You must have an accurate record of the occlusion prior to treatment. It is much better to do it before restorative work – otherwise it looks like an excuse. You must get informed consent.

68
Q

What is occlusal equilibtration?

A

Reorganising the occlusion to give an ideal occlusion by selectively adjusting tooth tissue. It can be useful as a last resort for patients with TMD symptoms who have tried all other less invasive treatment modalities. Not advocated for this as limited evidence. It should only be undertaken with the patient’s informed consent by a suitably trained and experienced clinician.

69
Q

What is the dahl concept?

A

It was originally devised as a partial coverage bite plane made of cobalt chromium. It created space through a combination of over-eruption and intrusion. The concept has since evolved mainly due to its success to describe any procedure where restorations are placed in supra-occlusion with the intention for the dentition to adapt to the altered occlusal scheme in order to achieve even occlusal contact in ICP through over-eruption/intrusion.

70
Q

What are the indications for the dahl concept?

A

It is highly applicable to anterior tooth wear cases due to the loss of vertical tooth height. Teeth can be restored to normal contour by increasing the vertical dimension of selected teeth without necessarily requiring restoration of all teeth in both arches.

71
Q

What are the myths about the Dahl concept?

A
  • You need to check freeway space prior to restoring teeth
  • Restorations will fail due to the occlusal forces
  • It is a new technique with no evidence to back it up
72
Q

How do you plan a case using the Dahl concept?

A
  • Impressions, facebow and occlusal records (RCP)
  • Diagnostic wax up on articulated casts
  • Patient information and consent – will feel strange at first only biting on front teeth, soup only etc
  • Consider using a hard splint at the increased vertical dimension to check patient tolerance although this isn’t really done
  • Undertake restorative procedures using the wax up as your guide
73
Q

What are the practical aspects of the Dahl concept?

A
  • Warn patients regarding functional problems for a number of weeks
  • Movement often occurs quickly with occlusal contact being achieved in 6-8 weeks however it can take months
  • Keep a record of occlusal changes and review the patient regularly
  • Even very large increases in OVD can usually be tolerated
74
Q

What are the problems with the Dahl concept?

A
  • Most patients adapt very quickly but some may not adapt however this is very rare
  • In a very small number of patients tooth movement does not occur and therefore these patients may require restorative intervention for the posterior teeth such as onlays or crowns
75
Q

What are the situations where you may wish to change the occlusion following a simple restoration?

A
  • To avoid avoid excursive contacts on a restored cusp
  • To change an RCP contact point from a restored surface to natural tooth structure
  • To move an ICP contact point away from a restoration interface
  • To remove a non-working side interference
  • To reintroduce canine guidance
76
Q

Why is it ideal to restore canine guidance?

A

Loss of canine guidance usually as a result of tooth wear can transfer guidance posteriorly. This can result in non-ideal forces on the lingual cusps of lower molars resulting in fracture of the cusp. Simply restoring the posterior tooth again will likely result in repeated restoration fracture. Canine guidance should be reintroduced first.

77
Q

How can canines be restored?

A

There will usually be an ICP contact on the canine which will need to be maintained. However, the form of the canine is altered to restore this tooth as the only one involved in the working side excursion. This can be achieved using indirect restorations or more commonly nowadays direct composite.

78
Q

When would you conform and reorganise the occlusion with indirect restorations?

A

Conformative:

  • Usually for a smaller number of units
  • Easier case - 1-2 units, no guiding teeth involved and no interferences. A facebow is not usually necessary.
  • Complex case - 3+ units and any unit if guiding, difficult cases especially class II div II if restoring anterior teeth or class III/AOB if restoring posterior teeth. Facebow is recommended

Reorganised is always complex:

  • Done for multiple units
  • Increase in OVD
  • Full mouth rehab
79
Q

When conforming to the occlusion in easier cases, how should you assess the occlusion before preparation for indirect restorations?

A
  • Assess contacts in ICP - shimstock or GHM - adjacent teeth and contralateral side
  • Assess RCP contacts
  • Assess guidance in excursions
  • Study casts
80
Q

When conforming to the occlusion in easier cases, what should you assess during preparation for indirect restorations?

A
  • Ensure sufficient space for restorative material

- Check in ICP and excursions

81
Q

When conforming to the occlusion in easier cases, what should you assess during fit for indirect restorations?

A
  • Check ICP and lateral/protrusive excursion and adjust as necessary
  • ICP - ensure tooth can hold shimstock paper but also that all teeth with previous ICP contacts can also hold shimstock
  • Excursions - check excursions are the same as previous and no interferences have been introduced
82
Q

What can happen when preparing the last tooth in the arch?

A

This can be referred to as ‘last tooth in the arch syndrome’. It develops occasionally when preparing the last tooth in the arch. When you have prepared the tooth, the patient bites together and the teeth maintain contact and the space is lost. It occurs particularly if the last tooth is lone standing. It possibly occurs due to shift in the condyles following tooth preparation.

83
Q

How is ‘last tooth in the arch syndrome’ prevented?

A

The ICP contact point should be maintained following preparation with an occlusal stop. This is removed by the technician when fabricating the crown. This will then need to be removed on the tooth prior to fit. Do not allow the patient to bite down following removal of the stop as the patient will immediately adapt and the space will be lost.

84
Q

When conforming to the occlusion in difficult cases, how should you assess the occlusion before preparation for indirect restorations?

A
  • Undertake full occlusal analysis
  • Upper and lower impressions and facebow
  • Have casts mounted on articulator using facebow
  • Analyse mounted casts and check occlusal analysis
  • Decide if there are any aspects of the occlusion you wish to modify or adjust
  • Get a wax up of the intended restorations
85
Q

Why is a facebow used when conforming in difficult cases?

A
  • It records the spatial orientation of the upper teeth relative to the condyles
  • Allows correct positioning of the upper model. Lower model is mounted to the upper using interocclusal record
    Therefore:
  • Allows you to assess the casts in occlusion with ICP, RCP, protrusive and lateral excursions as close as possible to the patient’s natural occlusion
  • Allows the lab to construct a crown/bridge taking into account the above factors - less adjustment on clinic
  • Can customise guidance
86
Q

When conforming to the occlusion in difficult cases, how should you assess the occlusion during preparation for indirect restorations?

A
  • Ensure sufficient space for restorative materials

- Check ICP and excursions

87
Q

When conforming to the occlusion in difficult cases, how should you assess the occlusion during fit for indirect restorations?

A
  • Check ICP and lateral/protrusive excursion and adjust as necessary
  • Ensure occlusion in ICP and excursions is as intended i.e.:
    • ICP - all teeth able to hold shimstock as intended?
    • Protrusive - guidance on appropriate anterior teeth with posterior disclusion if possible?
    • Lateral excursions - canine guidance/group function>no non-working side interferences
88
Q

What makes teeth suitable to be involved in guidance?

A
  • Suitable root structure
  • Enough remaining tooth structure
  • Ideally no endodontic post
89
Q

What contacts and guidance should be present with bridgework?

A
  • Contact in ICP on the abutment tooth
  • Light contact in ICP on the pontic (shimstock just pulls through)
  • Avoid guidance on the pontic, especially if cantilevered
90
Q

What indirect materials can be use for guidance and which cannot?

A
  • Gold is generally suitable to be used in guidance
  • PFM - try to avoid ICP contacts on the interface between metal and porcelain, consider having metal on the guiding surface and occlusally for patients with heavy bites
  • Dentine bonded crowns gain strength from bonding to underlying tooth structure, try to avoid heavy/grinding contacts on individual teeth
  • High strength porcelain crown - should be able to withstand occlusal forces due to strength, however if a veneering porcelain has been layered on top this is liable to fracturing off
91
Q

What is customised guidance?

A

If you want to replicate guidance from the current teeth or sometimes the provisional restorations you can use a customised incisal guidance table. This will replicate the guidance with minimal adjustment at fit required. The patient will therefore find adapting to the new restorations much easier.

92
Q

What is the technique for customised guidance?

A
  • Take an impression of the upper arch once you are happy with guidance
  • Have the models mounted on an articular using a facebow
  • Ask the technician to construct a customised incisal guidance table
    Prepare the teeth, take a working impression, construct Provisionals. The lab can then construct the definitive restorations using the customised incisal guidance table. Fit the definitive restorations and check ICP and lateral/protrusive excursions to ensure these are as intended.
93
Q

In what cases do you reorganise the occlusion?

A
  • Multiple restorations in multiple quadrants
  • When increasing OVD
  • Full mouth rehab cases
    These cases are obviously complex and should be planned thoroughly using the principles from the complex conformative cases.
94
Q

What is the usual aim of reorganising the occlusion?

A

To change the occlusion to a new scheme, usually conforming to the concept of an ideal occlusion.

95
Q

What are the features of an ideal occlusion?

A
  • ICP = RCP
  • Forces directed through long axis of teeth
  • Canine guidance in lateral excursions (canine guidance on working side and no non-working side contacts)
  • Anterior guidance in protrusive excursions (anterior teeth contact and posterior teeth disclude)
  • Mutual protection

ICP - 4th year (9 decks)

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