retention in complete denture
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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
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