Retention and Stability of Complete Dentures PDF

‫ب‬ Dr : Sherin Donia  Retention: Is the resistance of the prosthesis to displacement in a vertical tissue away direction. It resist: - Force of gravity in upper denture. - The adhesiveness of food. - The jaw opening force(muscle pull). Factors affecting Complete Dent...

‫ب‬ Dr : Sherin Donia  Retention: Is the resistance of the prosthesis to displacement in a vertical tissue away direction. It resist: - Force of gravity in upper denture. - The adhesiveness of food. - The jaw opening force(muscle pull). Factors affecting Complete Denture Retention ; Physical Mechanical Anatomical Retentive Surgical Psychological aids Adhesion Cohesion Interfacial surface tension Capillary action Atmospheric pressure. Gravity.  A: Physical factors: 1-Adhesion: Is physical attraction between unlike molecules. Denture Saliva Mucosa It maintains the wetting of denture and mucosa by saliva. 2-Cohesion: Is physical attraction between similar molecules(saliva). Saliva film should be thin to be effective.  Adhesion and Cohesion Adhesive failure refers to the interface between two bodies; cohesive failure to within a material itself. Note: the cohesive strength of saliva is much greater than the adhesion of mucosa to denture Retention supplied by Adhesion and cohesion depends on : 1. The surface area covered by the denture. 2. the close adaptation of the denture to the supporting tissues. 3. good peripheral seal. 4. cleanliness of the fitting surface. 5. The fluidity of saliva.  3- Interfacial surface tension: It is attributed to the attractive forces of cohesion and adhesion at the surface molecules of the liquid. It is the resistance to separation – possessed by the film of liquid – between two well-adapted surfaces. Significance: Interfacial surface tension occurs in the thin film of saliva between the denture base and the mucosa of the basal seat.  Simplified cross-section to illustrate the seal arising from compliant tissue,flow restriction in narrow spaces, and the effect of surface tension in a well- fitting denture. Retention of maxillary complete denture. A. Atmospheric pressure (high). B. Fitting surface with low pressure, C. Peripheral seal. For atmospheric pressure to be effective, the denture must have a perfect seal around its entire border.  capillary attraction: Force that cause a surface of liquid to become elevated or depressed in a capillary tube. When is interfacial surface tension most effective? A. -When the salivary film is B. -When there is a of the denture base. C. -When the soft tissues are to underlying bone. -The space filled with the thin film of saliva acts like a capillary tube and helps to retain the denture; this force is directly proportional to the area covered by the denture.  4- Atmospheric pressure: When maxillary denture is in the patient’s mouth, air is expelled out from the area between the fitting surface of the denture and the mucous membrane, the pressure on the polished surface of the denture is more than that on the fitting surface. The difference between the two forces gives a positive force which will retain the denture in place. Effectiveness of Atmospheric pressure: -Denture must have a perfect seal around its borders. -The surface area covered by the denture should be at its maximum.  5-Viscosity of saliva: Is the resistance by one part of a liquid in moving over another part. Very thin watery saliva give the least retention does not seal the denture well and the seal can be easily broken The effect of viscosity of saliva on retention depends on : - Good denture base adaptation - Surface area covered by the denture. This may be relevant to the maxillary denture. The mandibular denture are bathed in saliva, surface tension, viscosity and film thickness may not play a role in lower denture retention  6- Gravity: It act as a retentive force in lower denture and displacing in upper denture when the patient is sitting upright. Mechanical factors (denture factors) : I. Shape of the polished surface. II. Presence of undercut. III. Denture foundation surface area. IV. Denture extension. V. Placing teeth on the neutral zone. Anatomical factors : 1- Ridge form A high well developed ridge with round crest gives good support, retention and stability more than flat ridge or knife edge ridges Anatomical factors : 2- Arch form The arch may be square, tapering or ovoid; square arch form is more favorable for denture retention than the tapered and ovoid Square form is favorable than tapered and ovoid 3-Palatal vault form U- Shaped palatal vault is the most favorable for retention and stability of complete denture as it resists vertical and horizontal forces. V- Shaped vault resists the lateral shift well but not the vertical displacing forces (break the seal) Flat vault resists vertical displacement but not the lateral forces.  4- Soft palate curvature There are three classifications for the configuration of the soft palate based on the degree of flexure the soft palate makes with the hard palate. Class I soft palate has a gentle curvature and demonstrates little muscular movement, hence it is the most favorable, as it allows more tissue coverage for producing the palatal seal 5-Arch relationship Retention and stability problem is expected with smaller arch  6-Interarch distance Small interarch space increase retention because the tongue fills the oral cavity. Tongue has tight contact with lingual and palatal surfaces of the denture, providing an excellent seal. 7- Tongue moderate size provide excellent seal for lower denture 8-Mucosa healthy mucosa. 9-Saliva medium.  D: Retentive Aids: 1- Adhesives: powder or cream applied on the fitting surface of the denture. 2- Vacuum devices(obsolete):either suction chambers or rubber suction disc. 3- Magnets: 4- Ball and socket attachment:( over denture).  E: Surgical Aids to improve retention: I. Ridge augmentation. II. Vistibuloplasty III. Implants. : 1- Intelligence. 2- Expectations 3-Apprehension. 4- Gagging. 5-Acquired muscle control and adaptation.