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Retention, stability and support for complete denture

Dept. of Prosthodontics
2017

C.D. is a mechanical object in a biological environment

to ensure success of C.D. dentist must understand

physical, mechanical and biological .

Treatment objectives :

Pt. education…..clean…expectation…

Restoration of esthetic…smiling, facial form,

lip, cheek, wrinkles.

Improvement of mastication…chewing (dif.)

Improvement of speech

Preservation of remaining oral structure….ill fitting denture…resorption

Maintenance of health and comfort of mouth…sharp borders od denture …injury…recall pt.

Health of TMJ …all above in general

Pattern of restoration in the maxilla and mandible.

Mandible: downward and outward.
In maxilla : upward and inward.

End result

Mandible : becomes wider
Maxilla : becomes smaller

Retention:

If the denture has to function well ………..it must be retentive.

Retention is the means by which the denture held in mouth if denture is easily dislodged during speech eating it would be very embarrassing

Retention : is the resistance to removal in direction opposite that of its insertion

Dislodging forces:

The act of chewing of foods
Adhesive nature of certain foods
Gravity
Surrounding musculature (cheek, tounge, soft palate)
Premature contact

Primary retention:

Physical means
Mechanical means


Secondary retention :
Factors contribute to stability indirectly also contributes to retention.

Physical forces in denture retention:

Two glass plates….not stick…at microscopic level there are imperfections between the two glass plates
Two glass plate with film of water between …difficult to separate …..

The physical forces involved are:

Adhesion
Cohesion
Interfacial surface tension
Atmospheric pressure
Capillary
Gravity

Adhesion:

Is the physical force involved in the attraction between two unlike molecules.

In case of denture

It is the attraction between the denture and saliva and between saliva and oral mucosa.

Cohesion:

It is the physical attraction of like molecules to each other …molecules of the same substance together .

In complete denture :

Saliva needs to be cohesive

Interfacial surface tension:

It is the tension or resistance to separation developed between two well adapted surface separated by thin film of fluid.

Molecules on the inside attract the surface molecules inward resulting in potential energy called surface tension

In the mouth:

prevent denture from separation at its borders.

Atmospheric pressure:

It is the pressure caused by the weight of the atmospheric on the earth surface.

Denture:

when an attempt is made to separate the denture, a –ve pressure develops between denture and base and surrounding mucosa .
This activates outside atmospheric pressure which pushes denture back toward to basal seat

Capillarity or capillary attraction:

Causes liquid to rise in a capillary tube:

Denture:

The space between the denture and the basal tissue acts as capillary with saliva as liquid

Gravity:

good or bad ??

Gold denture …weight ?

Factors affecting the physical forces:

Saliva:
Quantity/quality
Serous saliva/mucous saliva/mixed

Surface area:

Larger surface area …better….vestibuloplasty

Intimate contact

Good impression…good retention

Peripheral seal:
No air ….cheek tongue

Mechanical aids in denture retention:

Undercuts:
Is the depressed portion of the sides of a ridge that flanges of denture can engage and mechanically will retain denture.

within limit ….difficult insertion and removal

should be: unilateral undercut/mild bilateral undercuts

Overdenture attachments

Implants

Mucosal inserts
Magnetics

Rubber suction discs

Suction chambers

Secondary retention :

Factors contribute to stability indirectly also contributes to retention.

Surrounding musculture:

Should be in harmony with the denture……failure….…dislodge force
Cheek muscle:
Dislodgment if teeth placed to far buccally
flange over extended.

Lips:

unseat if teeth to far forward.

Tounge:

Teeth placed too far lingually.
Floor of the mouth:
Will raises during swallowing…instability of lower denture.

Soft palate:

If overextended or over postdammed
will cause unseating of upper denture

Neutral zone:

Is a potential space between lips and cheeks on one side and the tongue on the other side.

The area or position where the forces between lip , cheeks and tongue are equal teeth should be located in this space…..outside this zone will cause dislodge of denture

Over extended denture bordes:

Cause:
Dislodgment
Irritation of tissue
Prevent by accurate border moldeing of the spacial tray

Coronoid process:Dist bucca;l portion of upper denture….dislodge when mouth opened

Occlusal schemes:

Should be smooth and harmonious even during lateral movement.
(balanced occlusion)
any interference known as (premature contact).
Another occlusal scheme is use of (zero degree or monoplane teeth) to manimize horizontal force.

Stability:

Many of the factors affecting retention would affect stability the main difference between retention and stability ………………

is the direction in which the dislodging forces act.

retention: the denture resist dislodging force pulling the denture away from basal seat in a vertical direction.

The stability: denture resist forces acting in a horizontal or lateral direction

Factors affecting stability :

Intimate contact….with ridge…good impression
Residual ridge size and contour
Palatal vault
Neutral zone and surrounding muscle
Flange shape and contoured
Abnormal ridge relationship
Direct bone anchorage

Support :

Without support denture cannot maintain retention and stability.
Support is that property which resists vertical movement or displacement of the dentures toward the basal seat .

Importance of the support :

By preventing tissue ward movement.
Good support needed to improve masticatory force.
Good support needed to maintain occlusal relationship.

Requirements of the support:

Tissue capable of support should be firm resilient tissue covered by keratinized tissue and which is firmly attached to the underling bone.
Should be uniform thickness.
Underling bone should be resistant to bone restoration.
The support area should be at right angle or near as possible to occlusal force

All area of the denture bearing area should contribute to support except relief areas.

A greater area coverage puts less force per
unit area.Based on principle snow shoe

There are certain areas are capable of providing more support than others(primary stress bearing area).

Factors affecting support:

Surface area: larger…better
Nature of supporting mucosa: resilient firmly attached better
Impression procedure.
Accuracy of fit
Direct bone anchorage