Balanced occlusion Department of Removable Prosthodontics 2nd



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Balanced occlusion
Department of Removable Prosthodontics

2nd year

DIFFERNCES BETWEEN NATURAL AND ARTIFICIAL OCCLUSION:

To understand the complete denture balanced occlusion one must know the differences between complete denture occlusion and natural occlusion.


Artificial occlusion

Natural occlusion

1. Supported by a denture base placed on slippery mucosa

Supported by roots which are firmly anchored to the bone

2. Moves as a unit on their base

Moves independently in their socket

3. Malocclusion evokes immediate instability and pain

Malocclusion may remain uneventful for years

4. Forces acting on complete denture affect the whole base

Occlusal forces affect only the concerned teeth

5. Non-vertical forces are usually not well tolerated

Non-vertical forces are tolerated much better

6. The second premplar area is preferred for mastication.( it is the anteroposterior center of the occlusal table); mastication in the second molar region can cause shifting of the bases

Mastication is usually done in the second molar region

7. Bilateral balance is usually considered necessary for denture stability

Bilateral balance is not naturally found and is considered detrimental

FUNCTIONS OF COMPLETE DENTURE OCCLUSION:

A complete denture occlusion should:



  • Improve masticatory function

  • Minimize harmful non vertical or lateral forces

  • Contribute to the stability of the denture bases

  • Contribute to the health and preservation of the alveolar bone and soft tissues

  • Maintainance of the comfort and well-being of the patient

IDEAL REQUIREMENTS OF THE COMPLETE DENTURE OCCLUSION:

  • Stability of the denture and its occlusion when the mandible is in both centric and eccentric relations

  • Balanced occlusal contacts(tripod contact) during all eccentric movements

  • Unlocking (removing interferences) the cusps mesiodistally so that the denture can settle when there is a ridge resorption.

  • The cuspal height should be reduced to control the horizontal forces.

  • Functional lever balance should be obtained by vertical tooth to ridge crest relatioship. ( lever balance is a balance against leverage forces acting on the denture. Presence of positive contact on the opposing side provides lever balance.).

  • Cutting, penetrating and shearing efficiency of the occlusal surface equivalent to that of natural dentition.

  • Incisal clearance during posterior functions like chewing.

  • Minimal area of contact to reduce pressure while crushing food

  • Sharp ridges, cusps and slice ways to increase masticatory effieciency.


BALANCED OCCLUSION:

The balanced occlusal scheme has gained wide spread acceptance as the ideal occlusal scheme for complete dentures. The term ‘balanced articulation’ is also used.

Definition acc. To GPT-8: Is the ‘bilateral, simulataneous, anterior and posterior occlusal contact of teeth in centric and eccentric positions’.

Or ‘the simultaneous contacting of the maxillary and mandibular teeth on the right and left and in the posterior and anterior occlusal areas in centric and eccentric positions, developed to lessen or limit tipping or rotating of the denture bases in relation to the supporting structures’.

MECHANICS OF BALANCED OCCLUSION:

In natural teeth or in unbalanced occlusion, when the mandible is protruded so that the incisal edges of the upper and lower teeth contact, there is a gap between the upper and lower teeth in the posterior region ( also referred to as Christensen’s phenomenon ). Such an occlusion in complete dentures could cause tipping or instability of the dentures in the posterior section. Thus the stability of the denture can be improved if there are simultaneous anterior and posterior contacts when the mandible is protruded (protrusive balance).

In the same way, when the mandible is moved to one side (working side) with the teeth in contact on that side, a space may be observed on the opposing side ( balancing side). This again can lead to instability because of the uneven contacts. Giving simultaneous occlusal contacts on both sides of the arch ( working and balancing sides ) would improve stability of the denture. This is known as lever balance.

Inferences: when the patient moves his lower denture from centric occlusion to eccentric occlusion, the occlusal surfaces glide along each other. Any obstruction to this movement is known as interference. Interference may be the result of an obstructing cusp or ridge.

OBJECTIVES OF THE BALANCED OCCLUSION:


  1. Create simultaneous bilateral contacts from the centric to eccentric occlusal positions –thus reducing tipping forces.

  2. when gliding from centric to eccentric positions these contacts should be free of interferences.

  3. these movements and contacts should be in harmony with the temporomandibular joints and neuromuscular activity.

Advantages of balanced occlusion:

Some feel that balanced occlusion was not necessary or possible especially during mastication with food in the mouth. Thus came the statement-“Enter bolus, exit balance”



  • However it was shown that teeth do not contact occasionally during mastication.

  • Teeth contact occurs through the day even when there is no food in the mouth. Eccentric tooth contacts are increased in bruxism.

Thus it can be seen that balanced occlusion

    1. improves the stability and retention of the denture bases

    2. reduces soreness and resorption caused by the denture base movement

    3. Dentures more comfortable to the patient.

Achieving balanced occlusion: by

  • Careful teeth arrangement in a programmed articulator ( semi adjustable or fully adjustable ) in harmony with the factors affecting the balanced occlusion.

  • A programmed articulator is one in which the articulator movements are programmed to stimulate the patients mandibular movements.

  • Initially the teeth are arranged tentatively.

  • Final balance is achieved by selective grinding of interferences.

TYPES OF BALANCED OCCLUSION: Occlusal balance or balanced occlusion can be classified as follows:

  • Unilateral balanced occlusion

  • Bilateral balanced occlusion

  • Protrusive balanced occlusion

  • Lateral balanced occlusion

Unilateral balanced occlusion:

This is a type of occlusion seen on occlusal surfaces of the teeth on one side when they occlude simultaneously with a smooth, uninterrupted glide. This is not followed during complete denture construction. It is more pertained to fixed partial dentures.

Bilateral balanced occlusion:

This is a type of occlusion that is seen when simultaneous contact occurs on both the sides in centric and eccentric positions. Bilateral balanced occlusion helps to distribute the load evenly across the arch and therefore helps to improve the stability of the denture during centric, eccentric or parafunctional movements.

For minimal occlusal balance, there should be at least three points of contact on the occlusal plane. More the no. of contacts, better the balance. Bilateral balanced occlusion(B.O.) can be protrusive or lateral balance.

Protrusive balanced occlusion : This type of balanced occlusion is present when mandible moves in a forward direction and the occlusal contacts are smooth and simultaneous anteriorly and posteriorly. There should be at least three points of contact in the occlusal plane. Two of these should be located posteriorly and one should be located in the anterior region. This is absent in natural dentition.

Posterior contact during protrusion to maintain balance.


Lateral balanced occlusion : In lateral balance, there will be a minimal simultaneous three point contact (one anterior, two posterior) present using lateral movement of the mandible.

Lateral balanced occlusion is absent in normal dentition. When a dentulous person with canine guided occlusion moves his mandible to the right, there will be canine guided disocclusion of all his teeth. That is, the canine will be the only tooth that contacts the opposing tooth. Even the canine on the opposite side will not have contact .

If this relationship is followed during teeth arrangement, then the denture will loose stability due to lever action.

To prevent this the teeth should be arrange such that there is simultaneous tooth contact in the balancing and working sides. (working side is the side to which the mandible moves; here right. Balancing side is opposite to the working side; here left).


Fig. a: Canine guided dis occlusion. This relationship is seen in natural dentition.



Fig. b: Anterior and posterior tooth contact during-laterotrusion seen on the working side.




(a).shallow cusp teeth allow the opposing members to slide through the mastication. (b) teeth with higher cusp angle tend to lock the opposing teeth during movement.(c.d.) dentures with steep incisal guidance tend to get displaced during protrusion. (e.g) dentures with shallow incisal guidance produce lesser interference during protrusion. However, the amount of anterior interference depends on other factors like condylar guidance, etc,

An increase in any of the above factors will affect balanced occlusion leading to compromised stability in the denture.

If the vertical overlap of the anterior teeth is increased for aesthetic and phonetic reasons, then the horizontal overlap should be adjusted to reduce the incisal guidance angle.

This adjustment provides space for free movement of the anterior teeth. Without this adjustment, there will be increased anterior interference leading to initial instability of the denture base during protrusion. In the long run, this may lead to resorption of the residual alveolar ridge in the anterior region.

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FACTORS AFFECTING BALANCED OCCLUSION;


  • Condylar guidance

  • Incisal guidance

  • Plane of occlusion

  • Compensating curves

  • Cuspal inclination

Except for the condylar guidance, all factors can be altered by the dentist in the denture. The condylar guidance is obtained from the patient.

What are the compensating curves?

The compensating curves are artificial curves introduced into the complete denture occlusion in order to achieve a balanced occlusion. They are called compensating curves because they compensate for the space (Christensen’s phenomenon ) formed between the posterior portions of the upper and lower occlusal surfaces during eccentric movements of the mandible.

It is determined by the inclination of the posterior teeth and their vertical relationship to the occlusal plane so that the occlusal surface results in a curve that is in harmony with the movement of the mandible as guided posteriorly by the condylar path.

The curvatures in the natural dentitions are:



  • Curve of Spee

  • Curve of Wilson

  • Pleasure curves



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