Principles of Occlusal Principles of Occlusal Practice In Simple Practice In Simple

Restorative DentistryRestorative Dentistry

Dr Wael AL-Dr Wael AL-OmariOmari

BDS;MDent.Sci.;Ph.BDS;MDent.Sci.;Ph.DD..

Why Clinical occlusion Why Clinical occlusion should be studiedshould be studied??

- Most dental treatments involve Most dental treatments involve occlusal surfaces of teeth.occlusal surfaces of teeth.

- Avoid either over or under Avoid either over or under treatment.treatment.

- Provide therapeutic and Provide therapeutic and successful dental treatment for successful dental treatment for patients.patients.

- Reduce the risk of failureReduce the risk of failure

The masticatory system is The masticatory system is made up of:made up of:

Teeth.Teeth. Periodontal tissuesPeriodontal tissues Articluatory systemArticluatory system

What is occlusion?

The Articulatory System:

-TMJ as the hinge

- Masticatory muscles as

the motor

- Dental occlusion as the

contacts

- Interdependent

elements make a system

Articulatrory system and masticatory system are very interrelated and interdependent systems

Analysis of Occlusion

-Occlusion is defined as : Contacts between the teeth when mandible is closed and when is moving.

-Static Occlusion:

I- Centric Occlusion:

-Maximum intercuspation

-It is how unarticualted models fit together

- It is the habitual bite

- Significance : Occlusal forces directed axially.

II- Centric Relation:

- It is not an occlusion but a jaw relation that is reproducible with or without teeth present.

- Described Anatomically, conceptionally and geometrically -Defined as- The position of manidble to the maxilla with the intra-articular disc in position, and during closure on its hinge axis, that is with the condyles maximally seated in their fossa (uppermost and foremost) and the muscles are at their most relaxed and least strained position.

Significance of CR record:

1- it is reproducible position with or without teeth present

2- If CR involves tooth to be prepared, better remove

deflective contacts prior to preparation

3- When re-organizing occlusion at new vertical dimension

4- To distalize mandible to create space lingually for

anterior crowns

5- If restoring anterior teeth and CR contact results in strong

anterior thrust against teeth to be prepared

Sliding from CR to COFreedom in Centric (Long Centric)

Dynamic Dynamic OcclusionOcclusion

Def.: Occlusal contacts during the Def.: Occlusal contacts during the mandibular movements relative to the mandibular movements relative to the maxilla.maxilla.

Mandible movements are guided by Mandible movements are guided by muscles, teeth, and TMJ.muscles, teeth, and TMJ.

Posterior guidance = TMJ Posterior guidance = TMJ Determined by intra-articular disc and Determined by intra-articular disc and

articulatory articulatory surfaces of glenoid fossasurfaces of glenoid fossa Anterior guidance = Teeth.Anterior guidance = Teeth. Any teeth contacts during eccentric Any teeth contacts during eccentric

movements.movements.

Anterior Anterior GuidanceGuidance

Classified intoClassified into::

I- Canine guidanceI- Canine guidance

II- Group function (contacts are II- Group function (contacts are shared by several teeth on the shared by several teeth on the working side)working side) Group function vs working side Group function vs working side

interferences.interferences. More Ideal if anterior guidance on More Ideal if anterior guidance on

front teeth.front teeth.

Canine Guidance

Group function

The Mandibular Movements are influenced by:

1- Neuromuscular control: Neuromuscular control: muscles and nervous system muscles and nervous system2- Guidance system: TMJ and teeth2- Guidance system: TMJ and teeth

Function:• Elevation (closing) of the mandible : Temporslis muscle (anterior fibers), masseter muscle & medial pterygoid muscle.• Retrusion of the mandible: Temporalis muscle (posterior fibers).• Protrusion: Right and left lateral pterygoid acts together, medial pterygoid• Opening the mandible: Digastric and Inferior pterygoid.

Neural Pathways

-Mandible is controlled by voluntary movements and reflexes.

- Jaw-closing reflex: protects mandible and associated structures during violent whole body movement.

- Jaw-opening reflex: protects the teeth during sudden mastication of a hard object and protects lips, cheeks and tongue during mastication.

- Central and autonomic nervous systems receive input from peripheral receptors, higher centres and propioceptors.

- Propioceptors are located in deep muscles and periodontal ligaments

- Any occlusal changes are sensed by the nervous system via the propioceptors

The head of the condyle on the non-working side moves: forwards, downwards and medially. The angle of downwards movement is known as the ‘condylar angle’ The angle of medial movement is known as the ‘Bennet angle’. Immediate side shift = Bennet movement

Direction of mandibular movement

Balancing side.Condyle has downward path

Working side.Condyle pivots

Occulsal Interferences

Any tooth to tooth contact which hamper or hinder smooth guidance in excursions or closure into CO.

- Working side and non-working side and CR interfernces.

Significance:

-May result in destructive oblique forces

-May interfere with TMJ guidance

Occulsal Interferences in Centric Relation

Non Working Side Occulsal Non Working Side Occulsal InterferencesInterferences

Protrusive occlusal interferenceProtrusive occlusal interference

Ideal Occlusion:

1- The coincidence of CO

and CR,with freedom in CO

2- When mandible moves

there is immediate and lasting posterior disocclusion

Significance:

1- Pretreatment record

2- Treatment of TMD

3- Conformative versus

reorganized approach.

Requirements of Stable Occlusion

1- Stable stops on all the teeth when the condyles are in Centric Relation (CR).

Centric Stops

Point contacts are onlingual cusp tips ofmaxillary posterior teeth, buccal cusp tips of mandibular posteriorteeth, central pits ormarginal ridges onposterior teeth, incisalsof lower anteriors andlinguals of upperanteriors.

Brian Palmer, 2004

Ideal bite• Should have point contacts of the maxillary posterior lingual cusp tips and the mandibular posterior buccal cusp tips to the central fossa or marginal ridges of opposing posterior teeth.• Forces exerted on the posterior teeth should be directed through the long axis of the teeth.• ‘Normal’ buccal positioning of the maxillary buccalcusps should be ‘outside’ or buccal to the mandibularteeth.

(Brian Palmer, 2004)

2- Disocclusion of posterior teeth in protrusive mandibular movements

3- Disocclusion of posterior teeth on the working side during lateral excursive movement.

4- Disocclusion of posterior teeth on the non-working side during excursive lateral movements

5- Coincidence between Centric occlusion and centric relation

Correct Excursive Contacts Marked in Green

(Brian Palmer, 2004)

Possible signs of non ideal occlusion:

• Giggling and loosening of teeth.• Migration and drifting with resultant open contacts.• Excessive tooth wear.• Non carious cervical notching (abfraction).• Misalignment of affected teeth.• Sensitive or tender teeth.• Fracture and cracking.• Recurrent fracture of restorations.• Bone loss.• Deviation of mandible on closure.• TMJ dysfunction symptoms ????• Tori could develop.

Recording of the occlusion Two dimensional records of

the patient’s occlusion:These rely on marking the

static and dynamic occlusal contacts between the teeth and then describing those marks in writing, by diagram or by photograph.

Using of articulating paper, foil, floss or shimstock

The T-scan uses a computer program to analyse the relative hardness of the contacts between the teeth.

Maintain the pre-existing occlusion

General General RecommendationsRecommendations

EDEC (examine design, execute, check) EDEC (examine design, execute, check) Rule.Rule.

Examine and record occlusion at Examine and record occlusion at preoperative stage.preoperative stage.

Design where to place the point contacts Design where to place the point contacts on the restoration (tripodal)on the restoration (tripodal)

Remove heavy point contacts on the Remove heavy point contacts on the inclines and restoration marginsinclines and restoration margins

Re-establish the preoperative occlusal Re-establish the preoperative occlusal contacts at the same intensity and contacts at the same intensity and poitions.poitions.

Avoid both static and dynamic Avoid both static and dynamic occlusal contacts with the occlusal contacts with the margins of the restorationmargins of the restoration

• Weakening of tooth by deep or wide (>1/3 occl.surface) filling may indicate a provision of cast restoration