RETENTION IN COMPLETE

DENTURES

INTRODUCTION

Optimal outcome of complete denture treatment depends on the successful integration of the prosthesis with the patients oral function plus psychological acceptance of the dentures by the patients. These parameters requires that patient perceive their dentures as a stationary or well retained during function.

DEFINITIONS

GLOSSARY OF PROSTHODONTIC TERMS; It’s the quality inherent in the prosthesis acting to resist the forces of dislodgement.

BOUCHER;It’s the resistance to removal in a direction opposite to that of its insertion. It’s the quality in a denture that resists the forces of gravity, the adhesiveness of foods, and the forces associated with the opening of the jaws.

Fish was among the Ist to discuss the determinants of retention and differentiate between the tissue, polished and occlusal surfaces of a complete dentures.

The proper design of the tissue, polished and occlusal surfaces of the complete denture permits the dentist to incorporate the mechanical, biological, and physical factors of denture retention.

FACTORS IN THE RETENTION OF DENTURES

PHYSICAL PHYSIOLOGICAL MECHANICAL PSYCHOLOGICAL

PHYSICAL Adhesion

Cohesion

Interfacial surface

tension

Capillarity

Atmospheric pressure

Gravity

FACTORS AFFECTING THE RETENTION

PHYSIOLOGICAL Orofacial musculature

Neuromuscular

control Intimate

tissue contact

Consistency of saliva

Ridge

characteristics

Condition of mucosa

and submucosa

FACTORS PROVIDING RETENTION

MECHANICAL Undercut Balanced occlusion Springs Denture adhesives Suction chambers Rubber suction discs Magnets

SURGICAL

Vestibuloplasty Ridge augmentation procedureImplants

PSYCHOLOGICAL

ADHESION

Its the attraction of unlike molecules for each other .

Adhesion of saliva to the mucous membrane and denture is achieved through ionic forces between charged salivary glycoproteins and surface epithelium or acrylic resin.

In case of Xerostomia adhesion is observed between denture base and mucous membrane.

Retention provided by adhesion is proportionate to the area covered by the denture.

Therefore dentures should be extended to the limits of the health and function of the oral tissues.

COHESION

It’s the attraction of like molecules for each other.

It’s a retentive force because it occurs within the layer of

saliva that is present between the denture base and the mucosa and maintains the integrity of the saliva.

INTERFACIAL FORCES

It’s the resistance to separation of two surfaces that is imparted by a film of liquid between them. It can be discussed under

Interfacial surface Viscous tension tension

INTERFACIAL SURFACE TENSION

It results from a thin layer of fluid that is present between

two parallel planes of material.

It depends on the ability of the fluid to wet the rigid

surrounding material-WETABILITY

If the material has low surface tension fluid will maximize its

contact with the material.

CAPILLARITY-Is what causes a liquid to rise in a capillary

tube. The space between the denture base and the

mucosa ,when its sufficiently close acts like a capillary tube

in which the saliva tends to maximize contact and aid in

retention

Interfacial surface tension plays a important role in the retention of maxillary denture.

Its totally dependant on the presence of air at the margins of liquid and solid interface.

GLASS SLAB MODEL

When two glass slab is interposed with a thin film of water its

difficult to separate them. But when the glass slabs are

placed under water, it can be easily separated.

This is because, there is no liquid-air interface under water

and hence no surface tension

VISCOUS TENSION – STEFAN’S LAW

(3/2) πkr4

F = x V

h3

F – Force necessary pull the circular plates

r – The radius of the circular plates

k – Viscosity of the liquid between the plates

h – Thickness of the liquid

V – Velocity in a direction perpendicular to radius

ATMOSPHERIC PRESSURE

Its an emergency retentive factor. Its due to the pressure of atmosphere on the earth surface.

At sea level its 14.7lb/in2. Atmospheric pressure resists dislodging forces applied to the

denture if the dentures have an effective seal around their borders.

This resisting force is called suction. But there no suction , or negative pressure ,unless a dislodging force is applied.

BORDER SEAL The contact of the denture border with the underlying or adjacent

tissue to prevent the passage of air or other substances.

Border seal is achieved by border molding.

Posterior palatal seal area is important in getting a proper border seal.

This maintains the tissue contact during soft palate function and compensates for processing changes.

This area extends between the hamular notches along the flexural line of soft palate

A region that often causes problem in maintaining border

seal is the retrozygomatic space.

The remaining border of denture can be recorded by

draping effect of the lips and cheek and is not a problem

when overextension is avoided

The mandibular denture presents a major problem with regard to retention.

Reasons for this are - - Movable floor of the mouth. - Lack of ideal ridge height and conformation.

Border seal - facial flanges

- retromolar pad

- lingual flange

Lingual flange –

Distolingual flange-Adequate seal can be obtained by gently compressing the lateral wall of the retromylohyoid fossa lingual to the retromolar pad and tucking the distolingual flange laterally against the mucosa.

The contour and inferior extension of the lingual flange are dependent on anatomy of the mylohyoid muscle.

GRAVITY

It’s the force exerted by the earth on all objects towards its centre.

It helps in retaining the mandibular denture in position.

When its difficult to bring other factors of retention into play, gravity aids in retention of mandibular retention.

SALIVA All the physical factors of retention comes into play

when saliva is interposed between mucosa and denture.

Many studies have been conducted to determine the role of saliva in denture retention.

According to Stefan’s law the saliva should be viscous enough to aid in retention.

Camphell observed that decrease in a fluid film thickness increases denture retention.

Wilhelm H.W. showed that minor salivary glands had great importance for denture retention.

The saliva should have optimum viscosity to incorporate the physical factors of retention.

OROFACIAL MUSCULATURE

They provide supplementary retentive forces.

The teeth should be positioned in the neutral

zone and the polished surface should be properly

shaped.

The buccal flanges -

The lingual

flanges -

The base of the tongue serves as a emergency

retentive force in maxillary denture.

NEUTRAL ZONE

NEUROMUSCULAR CONTROL

Neuromuscular forces refers to the functional forces

exerted by the musculature of the patient that can affect the

retention.

This is primarily a learned biological phenomenon.

Certain patients have the ability to wear their dentures and

function without complaint despite the fact that they may be

extremely ill-fitting, unstable or even broken.

The biological factor of neuromuscular control gradually

becomes a major determinant in complete denture

retention as experienced patients learn to alter their

muscular function to harmonize with the prosthesis.

INTIMATE TISSUE CONTACT

It’s the biological factor that refers to the close adaptation of the denture base to the underlying soft tissue.

The impression technique will determine the degree of intimate tissues contact.

The impression material should have adequate flow properties, accuracy and dimensional stability to provide intimate tissue contact.

RIDGE CHARACTERISTS

ELASTICITY OF THE TISSUES

Elasticity is the property of a body, which enables it to return to its original form after being distorted or deformed

Reasons for elasticity of tissues are their cellular structure and the presence of elastic fibers.

If the submucous membrane are soft and flabby and are displaced during impression making, the tendency will be for them to resume their rest position , unseating the denture.

MECHANICAL FACTORS

UNDERCUTS

Undercut acts as a mechanical locking system in the retention of the denture.

Undercut - Unilateral

- Bilateral

BALANCED OCCLUSION

It’s the bilateral, simultaneous, anterior and posterior

occlusal contact of teeth in centric and eccentric

position.

Balanced functional occlusion is critical in promoting

denture retention. The occlusion must be free of

interference within functional range of movement of the

patient to avoid dislodging forces.

SPRINGS

Springs are attached to the premolar region on both sides of

upper and lower dentures. The dentures are thus permanently

attached to each other and are held in occlusion for insertion

into the mouth. As soon as they are released the dentures are

forced apart by the action of springs and held in place.

Disadvantages

- Lateral movements are restricted

- Soreness of mucosa due to irritation

- Excessive alveolar resoption

- Unhygienic

MAGNETS Small magnets are fixed on the maxillary and

mandibular dentures with like pole facing each other.

The repulsive forces developing between like poles, forces the denture to press against the basal seat. This aids in retention

Magnets can be surgically embedded in the edentulous ridge

DENTURE ADHESIVES

Refers to commercially available non- toxic, soluble material that is applied to the tissue surface of the denture to enhance denture retention, stability & performance

Ingredients Mechanism of action Indications: - Xerostomia - Lack of neuromuscular control - Cerebro-vascular accidents - Neuro epileptic patients - Patients under gone resective surgery

It is emphasized denture adhesives is not indicated forretention of improperly fabricated or poorly fitting

prosthesis

SUCTION CHAMBERS

A relief chamber with definite margin is made on the palatal aspect of the denture.Such denture creates a partial vacuum & aids in retention

Disadvantage:

Irritation & proliferation of the soft tissue into the chamber

RUBBER SUCTION DISCS

It consists of a rubber disc which is buttoned onto a stud into the fitting surface of the maxillary denture

Disadvantage; It causes constant irritation & damage to soft tissue & even epithelioma

On prolonged use causes perforation of palate

SURGICAL METHODS

VESTIBULOPLASTY: It is any series of surgical procedure described to restore alveolar ridge height or width by lowering mucosal attachments & unattached mucosa form the ridge crest to a position deeper into the labial, buccal, lingual sulcus.

Objectives:

- To extend the denture bearing area

- To reposition muscle attachments

- To provide better foundation for the prosthesis

IMPLANTS

In case of resorbtion of the residual alveolar ridge &

deformities of the jaws, where other surgical procedures

cannot be used to correct the defect, implants are used

to aid in retention of the prosthesis

RIDGE AUGMENTATION PROCEDURE

It’s a surgical procedure, where in the width & height of the residual ridge is increased by placing the bone material or alloplast material or combination of both

Materials used:

Bone & Cartilage

Alloplastic materials: Proplast

Hydroxyappatite

Tricalcium phosphate

SUMMARY AND CONCLUSION

Several factors have been described as determining the relationship of the tissue surface of the denture base to the underlying soft tissues that will provide optimal retention.

It’s the understanding and incorporation of these determinants that may ultimately govern the success or failure.

THANK YOU

Primary impression making

With alginate (Maxillary)

(Mandibular impression with alginate)

Preliminary impressions using impression compound (Maxillary)

(Mandibular)

Making of special tray

Special trays

Border molding

Secondary impression

Mandibular border molding

Mandibular secondary impression