OCCLUSION IN COMPLETE DENTURES

BALANCED OCCLUSION

{BY Dr. N.SWATHI, INTERN, 2K6 BATCH,

UNDER THE GUIDANCE OF

Dr. SRI RAMULU,

ASST. PROF. ,

DEPT. OF PROSTHODONTICS}

INTRODUCTION:

                                 Occlussion in Complete Dentures

Occlude means to ‘to close’.

Definition: ‘ Any contact between the incising or masticatory surfaces of the maxillary and mandibular teeth’ is termed as occlusion

Occlusion deals with the static relationship of the opposing teeth while articulation deals with the dynamic relationship of the opposing teeth.

Occlusion is an important factor that governs the stability and retention of the complete denture.

               Important differences between natural and artificial occlusion

Natural teeth function independently and each tooth disperses the occlusal load.

Proprioceptive impulses from peridontium avoid the occlusal prematurities

Malocclusion can be nonproblematic for yrs.

Non vertical forces are well tolerated.

Bilateral balance is not necessary & usually considered a hindrance

2nd molar favored for mastication owing to leverage & power.

Artificial teeth function as a group and occlusal loads are not individually managed.

There is no feedback & the denture rests in centric relation.Any prematuries can shift the base

Malocclusion pose immediate drastic problems.

Non vertical forces damage the supporting tissues.

Bilateral balance is mandatory to produce stability of the denture.

Heavy pressure on the 2nd molar will tilt the base on inclined foundation

                            General concepts of complete denture occlusion

   Spherical concept:

the anterioposterior & mesiodistal inclines of artificial teeth should be arranged

in harmony with a spherical surface.

   Organic concept:

Movement of the condyle determines the direction of the ridges and the grooves

& mandibular movement determines other factors like cusp height, depth of

fossa.

   Neutrocentric concept of occlusion

plane of occlusion should be flat & parallel to the residual alveolar ridges.

                          Ideal requirements of complete denture occlusion

1). Stability of the denture & its occlusion   when the mandible is in both centric & eccentric relations.

2).Balanced occlusal contacts.

3).Unlocking the cusps mesiodistaly so  that the denture can settle down when there is ridge resorption.

4).Functional lever balance should be obtained by vertical tooth to ridge crest relationship.

5)Cutting, penetrating and shearing efficiency of occlusal surface.

6). Minimal area of contact.

7). Incisal clearance during posterior functions.

8). Sharp ridges, cusps & sluiceways to increase masticatory efficiency.

                        Sears axioms of complete denture occlusion.

1. Smaller the area of the occlusion surface, the lesser is the amount of occlusal load transmitted to the supporting structures.

2. Vertical forces on a tilted occlusal surface will produce non-vertical forces on the denture.

3. Vertical forces on the denture base lying over the resilient tissues will produce lever forces on denture.

4. Vertical forces acting outside the ridge crest will produce tipping of the denture

Occlusal scheme requisites.

Occlusal scheme has three characteristics

1). Incising units

2). Working units

3). Balancing units

1). Incising units- includes all the four incisors.

a).sharp units for improved incising efficiency.

b). The unit should not contact during mastication except during protusion.

c). Shallow incisal guidance.

d). Increased horizontal overlap to avoid interference during settling.

2).Working units- includes the canine s & the posterior teeth of the side towards which the mandible moves.

(a). Cusps for good cutting.

(b). Smaller buccolingual width to decrease the occlusal load.

(c). Group function at the end of chewing cycle in eccentric positions.

(d). The  occlusal load should be

directed to the anterioposterior

center of the denture.

(e). Plane should be parallel to mean

foundation of the ridge.

3).Balancing Units- includes canines & posterior teeth opposing he working side.

(a). The second molars should be contact during protrusion.

(b). They should contact the working side at the end of chewing cycle.

(c). Smooth gliding contacts.

                              Types of Occlusion

                                           1). Balanced occlusion

                                           2). Monoplane occlusion

                                           3). Lingualised occlusion

1). BALANCED OCCLUSION

Reported by Brewer.

Definition: The simultaneous contacting of maxillary and mandibular teeth on right and left and in the posterior and anterior occlusal areas in centric and eccentric positions.

Significance:Normal individual makes masticatory tooth contact only for 10 mins in one day compared to 4hrs of total tooth contact during other functions. So, for these 4hrs of tooth contact, balanced occlusion is important to main denture stability.

Objectives of balanced occlusion

1).To improve the stability of denture.

2). To reduce resorption of the residual ridge and soreness.

3). To improve oral comfort  & well being of the patient.

General considerations for balanced occlusion

• The wider and larger the ridge & the teeth closer to the ridge, the greater

the lever balance.

• Wider the ridge &narrower the teeth buccolingually, greater the balance.

• The more lingual the teeth are placed in relation  to the ridge crest, the

greater the balance.

• The more centered the force of occlusion anteriopsosteriorly, the greater

the stability of the base.

Types of balanced occlusion

1).Unilateral balanced occlusion:

Type of occlusion when occusal surfaces of teeth on one side occlude simultaneously, as a group, with a smooth uninterrupted glide.

2). Bilateral occlusal balance type of occlusion seen when simultaneous contact occurs on both the sides in centric and eccentric positions.

For minimal occlusal balance,

there should be atleast

3 point contact on occlusal

plane (2 posterior & 1 anterior).

a). Protrusive occlusal balance

Usually seen during the protrusion of the mandible.

Factors governing protrusive balance:

• Inclination of condylar path

• Angle of incisal guidance.

• Angle of the plane of occlusion.

• Compensating curves.

• Cuspal height & inclination of the posterior teeth.

Shallow cusp teeth allow the opposing members to slide during

Mastication,

Higher cuspal angle lock the teeth

denture with steep incisal guidance tend to  get displaced,

denture with shallow incisal guidance produce less interference

b).Lateral occlusal balance :

Minimal 3 point contact during lateral moment of the mandible.

Absent in normal dentition.If allowed while tooth arrangement then the denture

would loose its stability due to lever action.

Factors :

• Angle of inclination of condylar path.

• Angle of incisal guidance.

• Angle of inclination of plane of occlusion

• Compensating curves.

• Buccal & lingual cusp height.

• The Benett side shift on the working side.

Concepts proposed to attain balanced occlusion

1). Gysi’s concept- for the use of 330 anatomic teeth under various movements of articulator.

2). Sear’s concept- Balanced occlusion for non-anatomical teeth with anterioposterior & lateral curvature.

3). Pleasure’s concept- Introduced the pleasure curve or the posterior reverse lateral curve

4).Frush’s concept- arranging teeth in 1-dimensional contact

5).Hanua’s Quint- Rudolph proposed nine factors that govern articulation of artificial teeth

Components:

Condylar guidance

Incisal guidance

Compensating curves

Relative cusp height

Plane of orientation

Nine factors governing the articulation are called as”Laws of articulation”

• Horizontal condylar guidance

• compensating curve

• Protrusive incisal guidance

• Plane of orientation

• Buccolingual inclination of the tooth axis

• Sagittal condylar pathway

• Sagittal incisal guidance

• tooth alignment

• Relative cusp height

6).Boucher’s concept-

Orientation of the occlusal plane, incisal guidance & the condylar guidance.

Anguation of the cusp.

Increase in the height of the cusp without changing the form of the teeth.

7). Lott’s concept

Mechanics of balanced occlusion

In natural teeth when the mandible is protuded so that the incisal edges of the

upper & the lower teeth contact, there is a gap between the upper & lower posterior teeth, this is termed as “Christensen’s phenomenon”.But this occlusion could cause tipping of  the denture in the posterior region. Thus simultaneous anterior & posterior contacts are required when mandible is protruded.

Factors influencing balanced occlusion

(1) Inclination of the condylar path.

(2). Incisal guidance.

(3). Orientation of the plane of occlusion

(4). Cuspal angulation.

(5). Compensating curve.

A balance of these five factors is required for balanced occlusion

When patients with steep incisal guidance brings his mandible forward, the movement is controlled by the lingual surface of upper anteriors thus leading to the lifting of the posterior part of denture . To prevent this other three components have to be modified

(1). CONDYLAR GUIDANCE

Recorded from the patient using protrusive registration.

The interocclusal records are transferred to the articulator and then accomodated to glide freely into position.

Mechanics: Increase in the condylar guidance will increase the jaw separation during protrusion. This factor cannot be modified. So in patients with steep condylar guidance incisal guidance is decreased to prevent the posterior jaw separation.

Components of condylar guidance

a).Horizontal condylar guidance-guides the forward movement for protrusive balance.

b).Lateral condylar guidance-guides the sideward or lateral movement of the mandible.

Posterior slope of the articulator eminence represented by the condylar tract of articulator

(2).INCISAL GUIDANCE

Defined as “The influence of the contacting surfaces of the mandibular and maxillary anterior teeth on mandibular movements”

Determined by the dentist & customized during anterior try-in

desired overjet &overbite are determined.

If overjet is increased, the inclination of incisal guidance is decreased

overjet  ~  1/ incisal guidance

overbite  ~  incisal guidance

• Incisal guidance has more influence on posterior teeth than condylar

guidance.

• During protrusive movements mandibular teeth move downward & forward

called as incisal guidance.

• If the incisal guidance is steep, steep cusps or occlusal plane or steep

compensatory curve is needed to balance occlusion.

• Incisal guide angle should be acute with suitable vertical overlap and

horizontal overlap to achieve vertical overlap and horizontal overlap to achieve balanced occlusion.

Component of incisal guidance:

1).  Horizontal component

2).  Vertical component

3). PLANE OF OCCLUSION OR OCCLUSAL PLANE-

Defined as “An imaginary surface which is related anatomically to the cranium and which theoretically touches the incisal edges of the incisors & the tips of the occluding surfaces of posterior teeth. It represents the mean curvature of the surface.

Established anteriorly by height of lower canine and posteriorly by height of retromolar pad.

Parallel to campher’s line & tilting of the plane >10o is not advisable

4). COMPENSATING CURVE

• “The anterioposterior and lateral curvatures in the alignment of the occluding surfaces and incisal edges of artificial teeth which are used to develop balanced occlusion”

• Determined by inclination of posterior teeth and their vertical relationship to occlusal plane.

2 types of curves

1). Anterioposterior compensating curve-

a). Curve of spee-

“ Anatomic curvature of the occlusal alignment of teeth beginning at the tip of lower canine and following the buccal cusps of the natural premolars  and the molars, continuing to the anterior border of the ramus” as described by Graf Von Spee.

Significance - when the patient moves his mandible forward, the posterior teeth set on this curve will continue to remain in contact.Thus avoiding disocclusion.

2).Lateral compensating curves

   a).Compensating curve for Monson curve

“ The curve of occlusion in which each cusp and incisal edge touches to a segment of the sphere of 8” in diameter with its center at glabella”

runs across the palatal & buccal cusps of maxillary molars.

b). Compensating curve for Wilson’s curve

“Curve of occlusion which is convex upwards”

it is followed when the 1st premolar are arranged to prevent their interference to lateral movements.

c). Pleasure’s curve

A curve of occlusion which in transverse cross-section conform to a line which is convex upward except for the last molar.

1st molar horzt, 2nd premolar buccally tilted & 2nd molar independently follows compensating curve& is lingually tilted

5). CUSPAL ANGULATION –

“Angle made by the average slope of a cusp with the Cuspal plane measured mesiodistally or buccolingually”.

It is an important factor that modify the effect of plane of occlusion & the compensating curves.

Mesiodistal cusps are reduced to prevent the locking of cusps

In shallow bite cases- cuspal angle should be reduced to balance the incisal guidance.

In Deep bite cases with steep incisal guidance , the jaw separation is more during protrusion .Teeth with high cuspal inclines are required for these cases

“ Occlusal reshaping is done after teeth arrangment to produce balanced occlusion.”

MONOPLANE Or NON-BALANCED OCCLUSION

Shepherd gave the statement “ Enter bolus and exit balance”

According to this multiple uniform contacts in centric relation was sufficient to avoid harmful lateral forces, non anatomic teeth were preferred

Following concepts developed

(ii)Spherical theory

(iii)Organic occlusion

(iv)Occlusal balance theory

Pound’s concept- proposed monoplane occlusion with sharp upper lingual & wide lower central fossa with buccal cusp reduced, thus suggesting lingualised

occlusion.

Cusp form gold occlusal concept - suggests the use of teeth with a 33o cusp form made on a gold surface.

Occlusal pivot by Sears

Kurth’s concept

Philip M. Jones Scheme of non-balanced occlusion

Neutrocentric concept-

a). Non-anatomic teeth

b). Plane of occlusion parallel to the residual ridge.

C).No compensating curves, teeth are set flat

d). Maxillary & mandibular teeth arranged without any vertical overlap.

(e). Complete intercuspation between the upper & lower posterior teeth except second molar.

(f).Narrow teeth selected to decrease occlusal forces.

3) LINGUALISED

First proposed by Alfred Gysi in 1927.

1941 Payne desired a modification of anatomic teeth.

Involves the use of a large upper palatal cusp against a wide lower central fossa.

Buccal cusps of upper & lower teeth do not contact each other.

Lingual contact occlusal scheme

Payne proposed the use of 30o anatomical teeth Myerson’s lingualised Integration (MLI).

Specialized tooth mould for arranging teeth in lingualized occlusion control contact (CC)

4)FUNCTIONALLY GENERATED OCCLUSION:

In this occlusion scheme, the maxillary teeth carve out a path in  the wax placed on the lower occlusal table. This is known as ‘functionally generated path’. Later the wax containing this path is replaced with cast gold or Cobalt alloy.

Used in amalgam inserts, cast gold occlusal.

TOOTH FORMS OF POSTERIOR TEETH

• ANATOMIC TEETH (30O)

• SEMI-ANATOMIC TEETH (<30O)

• CUSPLESS TEETH (ZERO DEGREE)

Teeth are selected according to the required occlusal scheme

Conclusion :

Many occlusal schemes have been proposed over the years. Most schemes when

correctly used gives satisfactory results. The result is satisfactory if the patient gets

better function, esthetics & comfort without any adverse changes in denture

foundation.

:::::::::::::::::::::::REFERENCES::::::::::::::::::::

Zarb and bolender 12th edition : pg no. 414

Boucher 11th edition : pg no. 313

Heartwell : pg no. 231-235

Winkler : pg no. 231

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THANK YOU