1. DENTURE STABILITY
1.1. Is the resistance to horizontal and rotational forces
1.2. Prevents lateral and anteroposterior shunting of denture base
1.3. Provides physiologic comfort
1.4. Factors Affecting Stability
1.4.1. Retention
1.4.1.1. Pre-requisite to stabilty
1.4.2. Residual ridge size and contour
1.4.2.1. greater resistance to horizontal forces for:
1.4.2.1.1. Large
1.4.2.1.2. Square
1.4.2.1.3. Broad
1.4.3. Residual ridge quality
1.4.3.1. Retrognathic and prognathic
1.4.4. Parallelism of the ridges
1.4.4.1. Parallel ridges prevents to skid the denture forward
1.4.5. Occlusal plane
1.4.5.1. Ideal is :
1.4.5.1.1. Inclined slightly posteriorly
1.4.5.1.2. parallel to anatomically oriented to the ridges
1.4.6. Form and Contour of the Polished Surfaces
1.4.6.1. External surfaces should be developed to harmonize with the musculature
1.4.7. Stability of denture material
1.4.7.1. Metal bases is preferres because dimensionally stable
1.4.8. Neutral Zone
1.4.9. Occlusal harmony
1.4.10. Neuromuscular control
2. DENTURE SUPPORT
2.1. Is the resistance to VERTICAL MOVEMENT of the denture base toward the ridge.
2.2. those forces directed the ridge at right angle to the occlusal surfaces
2.3. Requirements
2.3.1. Firm and resilient keratinized tissue
2.3.2. Uniform thickness
2.3.3. Resistant to bone resorption
2.3.4. At right angle to occlusal
2.4. Factors affecting Support
2.4.1. Surface area
2.4.2. Nature of supporting mucosa
2.4.3. Impression procedure
2.4.4. Accuracy of fit
2.4.5. Direct bone anchorage
3. Retention
3.1. It is the quality inherent in the prosthesis acting to resist the forces of dislodgement
3.2. resistance to vertical displacement
3.3. Provides psychological comfort
3.4. Factors affecting CD retention
3.4.1. PHYSICAL
3.4.1.1. Adhesion
3.4.1.1.1. attraction of unlike molecules”
3.4.1.1.2. Thin film of saliva is formed between the denture and the tissue surface
3.4.1.1.3. denture that covers the greatest area will have the (best adhesion)
3.4.1.1.4. Quality of retention depends on
3.4.1.2. Cohesion
3.4.1.2.1. attraction of like molecules”
3.4.1.2.2. act within the thin film of saliva
3.4.1.2.3. Low viscosity =
3.4.1.3. Surface tension
3.4.1.3.1. resistance to separation possessed by the film of liquid between two well adapted surfaces”
3.4.1.3.2. within the thin film of saliva
3.4.1.3.3. Dependent on the ability of the fluid to wet the surrounding the material
3.4.1.4. Atmospheric Pressure
3.4.1.4.1. Supplied by the weigh of atmosphere
3.4.1.4.2. Prevents air entry between
3.4.2. Factors Affecting the Physical Forces
3.4.2.1. Saliva
3.4.2.1.1. Serous
3.4.2.1.2. Mucous
3.4.2.1.3. Mixed Saliva
3.4.2.2. Surface area
3.4.2.2.1. greater the surface area the greater the retention
3.4.2.3. Intimacy of contact
3.4.2.3.1. the closer the contact the greater the retention
3.4.2.4. Border seal
3.4.2.4.1. prevent the entry of air
3.4.2.4.2. obtained by cutting a groove in the master cast known (Post dam)
3.4.2.5. Gravity
3.4.2.5.1. contributes to mandibular retention
3.4.2.5.2. The weight of lower denture should not exceed 40gm.
3.4.3. ANATOMIC
3.4.3.1. Shape of the ridge
3.4.3.1.1. Firm and regular and covered by firmly attached, dense mucoperiosteum
3.4.3.1.2. vertical and parallel sides
3.4.3.1.3. Square and ovoid upper arch and palatal vaults are favorable
3.4.3.2. undercut
3.4.3.2.1. Unilateral
3.4.3.2.2. Bilateral
3.4.3.2.3. Denture flange should extend providing 1mm engagement of undercut on one or both sides
3.4.3.3. Anatomy of the border tissues
3.4.4. PHYSIOLOGICAL
3.4.4.1. Neuro muscular control
3.4.4.1.1. Functional forces exerted by Muscles apply supplementary retention
3.4.4.1.2. balance between the buccal musculature and the tongue.
3.4.4.1.3. Dorsum of the tongue presses the ((distal border)) of the upper denture
3.4.4.2. Neutral zone
3.4.4.2.1. potential space between the lips and cheeks on one side and the tongue on the other
3.4.4.2.2. subject to equal and opposite forces from the surrounding musculature
3.4.4.3. Viscosity and volume of saliva
3.4.5. MECHANICAL
3.4.5.1. Balanced occlusion
3.4.5.1.1. Must be free of interferences to avoid dislodging forces
3.4.5.2. Contour of the polished surface
3.4.5.2.1. Must be shaped and properly positioned
3.4.5.3. Position of the Occlusal plane
3.4.5.3.1. Higher =
3.4.5.4. Position of the teeth in respect to alveolar Ridge
3.4.5.4.1. Set the posterior teeth over the crest of the ridge
3.4.5.5. Inclination of the teeth labiolingually at the incisal edge
3.4.5.5.1. Occlusal plane should be inclined upward slightly to the posterior
3.4.5.5.2. Rugae – prevent anterior movement
3.4.5.5.3. Retromolar pad – resist posterior movement
3.4.6. BIOLOGICAL
3.4.6.1. Intimate tissue contact
3.4.6.2. Peripheral seal
3.4.6.2.1. positive contact of the entire perimeter of the denture base that outline the basal seat
3.4.7. AIDS TO RETENTION
3.4.7.1. Springs
3.4.7.1.1. attached to the buccal flanges of upper and lower dentures
3.4.7.2. Magnets
3.4.7.2.1. Increase retention of highly resorb ridges
3.4.7.3. Denture chambers
3.4.7.3.1. Creates an area of negative pressure which increase retention
3.4.7.4. adhesives
3.4.7.5. microvalves
3.5. Tow physical factors under control of dentist
3.5.1. Maximal extension of the denture base
3.5.2. Maximal intimate contact of :
3.5.2.1. denture base
3.5.2.2. denture- supporting structures.