Retention of Complete Denture

7/27/2019 Retention of Complete Denture

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Successfu l integration

of the prosthesis with

the patients oral

functions on dentureretention.

A retentive

denture

contributes

severely to

patient

acceptance ofthe finish

Importance of

retention

Successfulincorporation of the

denture with the

patients oral

functions depend

largely on dentureretention


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of the denture can be defined as:The resistance of the denture to

dislodgment.

The quality of the denture that holds it to the

tissue foundation.

The resistance in the movement of a denture

away from its tissue foundation especially in a

vertical direction .

The resistance to removal in a direction

opposite to that of insertion.


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>Retentive forces Displacing force

Denture stay in place if the retentive

forces acting on the dentures go overthe displacing forces.


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Occlussal

surface

Polished

surface

Impression

surface

Denture

surfaces


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Occlussal surface:

That portion of the surface of a

denture which makes contact or

near contact with thecorresponding surface of the

opposing denture or dentition.


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Polished surface:

It is that part of the denture base

which is usually polished, includes

the labial, buccal and lingualsurfaces of the teeth, and is in

contact with the lips, cheeks and

tongue.


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Impression surface:

That portion of the surface of a

denture that had its shapedetermined by the impression. It

includes the borders of the denture

and extends to the polished surface .

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The retentive forces that act upon

each of these surfaces are of twomain types,

muscular forces and

physical forces.


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(1) force of the muscles of mastication

acting through the occlussal surface;(2) muscular forces of lips, cheeks and

tongue acting through the polished surface;

(3) physical forces acting through the

impression surface.

Retaining forces acting on a denture


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Muscular forces.

These forces are exerted by the musclesof the lips, cheeks and tongue upon the

polished surface of the denture and by

the muscles of mastication indirectlythrough the occlussal surface. They

depends on two factors:

The design of the dentures.

patient's skill.


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The design of the dentures.

(1) the denture bases must beproperly extended to cover the

maximum area possible, without

interfering in the health and function

of the structures that surround the

denture.


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(2) the polished surfaces of the

dentures are properly shaped.

with the buccal and lingual surfaces

converging in an occlusal direction,this muscular force will seat the

dentures on the underlying mucosa


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(a) seating the dentures when the polished surfaces are

correctly shaped;

(b) displacing the dentures when the polished surfaces are incorrectly

shaped.

Influence of muscles forces on dentures:


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(3)The occlusal plane

must be at the correct level;externally should it be with the

relaxed lower lip level or with

commissars of lips and internallywith the lateral border of the tongue

and slightly below the superiorportion of the tongue.


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Occlusal plane


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(4) the arch form of the teethmust be in theneutral zone

between the tongue and the

cheeks.


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Patients skill

The patients ability to acquire thenecessary skills to control new

dentures is related to biologicalage. In general, the older the

patient, the longer the learning

period.


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Physical forces(1) Interfacial force is the resistance to

separation of two parallel surfaces

that is imparted by a film of liquid

between them. These forces act tokeep the denture inside the patients

mouth because of thin film of saliva

between the denture and mucosa.

interfacial surface tension

viscous tension


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Interfacial surface tension

andViscous tension.

Interfacial forces depends on:


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Interfacial surface tension

Is the tension or resistance to

separation possessed by the film ofliquid between two well adapted

surfaces. This acts with the air-liquid

interface acting between two surfaces

where a thin film of liquid holds the

surfaces on the either sides.


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Wett abilityis the ability of a liquid to

maintain contact with a solidsurface, resulting from

intermolecular interactions

when the two are broughttogether.
http://en.wikipedia.org/wiki/Liquidhttp://en.wikipedia.org/wiki/Solidhttp://en.wikipedia.org/wiki/Surfacehttp://en.wikipedia.org/wiki/Intermolecularhttp://en.wikipedia.org/wiki/Intermolecularhttp://en.wikipedia.org/wiki/Surfacehttp://en.wikipedia.org/wiki/Solidhttp://en.wikipedia.org/wiki/Liquid


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Wettebility


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Capillarity

Is what causes a liquid to rise in a

capillary tube, because in this

physical setting the liquid willmaximize its contact with the

walls of the capillary tube.
http://upload.wikimedia.org/wikipedia/commons/6/64/Capillarity.svghttp://upload.wikimedia.org/wikipedia/commons/6/64/Capillarity.svg


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Interfacial viscous tension refers tothe force holding two parallel platestogether that is due to the viscosity of

the interposed liquid. the viscous force

increases proportionally to increases inthe viscosity of the interposed fluid, and

decreases as the distance between the

plates (i.e., the thickness of the

interposed medium) increases.


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Thick, high-mucin saliva is moreviscous than thin, watery salivayet

thick secretions usually do not result

in increased retention for the

watery, serous saliva can be

interposed in a thinner film than themore cohesive mucin secretions.


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(2) Adhesion

Adhesion is the physical attraction of unlike

molecules for each other. Adhesion of saliva

to the mucous membrane and the denture

base is achieved through ionic forces between

charged salivary glycoproteins and surface

epithelium or acrylic resin. By promoting the

contact of saliva to both oral tissue and

denture base, adhesion works to enhance

further the retentive force of interfacial

surface tension.


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(3) Cohesion

Cohesion is the force of attraction

between like molecules, whichmaintains the integrity of the

saliva film.


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The chain of intermolecular forces

between the denture and the mucosa

contributing to retention.


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(4)Atmospheric

pressure Atmosphericpressure can act to resist

dislodging forces applied todentures, if the dentures have an

effective seal around theirborders.


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Obtaining optimum physical retention

The aspects of complete dentures that

influence the amount of physical

retention are:

border seal

area of impression surface

accuracy of fit.


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Border seal

Lateral extension of the buccal flange to

produce a facial seal


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Right: denture poorly retained

because the thin flanges failed to

create a facial seal


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Bony undercuts

If bony undercuts exist, retention may beenhanced by designing a denture that

utilises these undercut areas. In order to

achieve this without traumatising themucosa on insertion and removal of the

denture, special care is required in

planning the path of insertion


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Selection of path of insertion to improve retention byutilising undercuts: (a) single path of insertion to engage

labial undercut; (b) dual path of insertion to engage

unilateral undercut.


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GravityIn most cases, the weight of the

prosthesis constitutes a

gravitational force that is insignificant in comparison with

the other forces acting on thedenture.


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Surgical factors:

Usually we use these factors toincrease the retention of the

dentures through various

procedures, like vestibuloplasty,

ridge augmentation, frenectomy &

dental implants.


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Psychological factors:The role of psychological factor on denture

retention depends on several considerations

related to the patient himself which include:

Intelligence

Expectations

ApprehensionGagging reflex

Previous denture experience.


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Retention of Complete Denture