BDS 5087 Retention and Stability PDF

BDS5087 RETENTION AND STABILITY What is Retention? It is the ability of the denture to resist vertical tissue away movement What is Stability? It is the quality of the denture to be firm and steady, when functional forces are applied. (Resistance to horizontal and rotational forces). BIOLOGI...

BDS5087 RETENTION AND STABILITY What is Retention? It is the ability of the denture to resist vertical tissue away movement What is Stability? It is the quality of the denture to be firm and steady, when functional forces are applied. (Resistance to horizontal and rotational forces). BIOLOGICAL FACTORS PHYSICAL FACTORS MECHANICAL FACTORS RETENTION PSHYCOLOGIC COMFORT STABILITY SUPPORT PHYSIOLOGIC COMFORT LONGEVITY Prosthesis Success Factors affecting Retention Physical Mechanical Psychological Retention Retentive aids Anatomical Surgical Physical factors 1. 2. 3. 4. 5. 6. Adhesion Cohesion Interfacial surface tension Atmospheric pressure Viscosity Gravity 1- ADHESION • Physical attraction between unlike molecules (Denture-saliva-mucosa) 2- COHESION • Physical attraction between similar molecules (Salivary molecules) 3-INTERFACIAL SURFACE TENSION and CAPILLARY ATTRACTION • Interfacial surface tension is the resistance to separation possessed by a film of liquid between two welladapted surfaces • Results from the attractive forces between surface molecules • It depends on the ability of the fluid to wet the surrounding surfaces or to spread out in a thin film • surface tension → contact spread out in thin film Surface tension and capillary attraction: • The space between the denture base and the mucosa (degree of adaptation) affects retention due to capillary attraction When salivary film is very thin + good adaptation of denture base to mucosa → the space filled with the thin film of saliva acts like a capillary tube and retains the denture 4- ATMOSPHERIC PRESSURE When you seat the denture, air escapes from underneath the fitting surface, forming a partial vacuum between the mucosa and the denture, resulting in trapped reduced pressure. Atmospheric pressure is larger, thus seats the denture. The effectiveness of atmospheric pressure depends on: 1. Surface area covered 2. Peripheral seal 5- VISCOSITY • The resistance of part of the fluid to move over another. The greater the viscosity of saliva the better the retention. 6- GRAVITY • Is considered retentive to the lower denture and displacing to the upper denture. ALL THE FACTORS WORKING TOGETHER. ADHESION COHESION INTERFACIAL SURFACE TENSION Remember! • The physical factors of retention are directly proportional to the surface area covered. • Maxillary dentures are mainly retained with physical factors. • Mandibular dentures usually are less retentive due to the smaller surface area, and may need more factors to enhance retention Mechanical factors 1. Shape of the polished surface 2. Undercuts 3. Neutral zone 1-SHAPE OF POLISHED SURFACE 2-PRESENCE OF UNDERCUTS 3-Setting teeth in the Neutral Zone • Neutral Zone is the potential space where forces from the lips & cheeks on one side are neutralized by those of the tongue on the other side Anatomical Factors 1. 2. 3. 4. 5. Ridge height Soft palate anatomy Arch relationship Tongue size Saliva 1-RIDGE HEIGHT Well developed ridge Severely resorbed ridge 2-SOFT PALATE ANATOMY • Depending on the degree of flexure the soft palate makes with the hard palate • Class I allows greater area for coverage for the post dam area 3- ARCH RELATIONSHIP • Class II and III arch relationship compromise retention and stability. 4- TONGUE SIZE • Moderately large tongue will enhance retention as it permits excellent peripheral seal for the lower denture 5- VISCOSITY OF SALIVA Surgical factors 1. Ridge augmentation 2. Vestibuloplasty 3. Dental implants 1- RIDGE AUGMENTATION • Increasing the size of the ridge using natural bone or artificial material 2- VESTIBULOPLASTY DEEPENING OF THE VESTIBULE TO GAIN RIDGE HEIGHT. 3- DENTAL IMPLANTS Retentive Aids 1. Adhesives 2. Micro-suction discs 3. Dental implants 1- ADHESIVES • CREAMS USED AS ADHESIVE IN THE FITTING SURFACE OF THE DENTURE. 2- MICRO SUCTION DISCS Obsolete 3- DENTAL IMPLANTS Psychological 1. 2. 3. 4. Intelligence Expectations Apprehension Acquired muscle control - adaptation Some patients have the neuromuscular and psychological ability, to cope and use the denture. Factors affecting Retention Physical Mechanical Psychological Retention Retentive aids Anatomical Surgical FACTORS AFFECTING STABILITY • Retention • Balanced occlusion • Height of occlusal plane • Position of posterior teeth • Proper relief • Ridge form • Palatal vault • Width of occlusal surface • Shape and size of the tongue • Shape of the polished surface 1. Retention For a denture to be stable it should be retentive first 2. Balanced Occlusion • Harmonious contact between upper and lower teeth during jaw movement 3. Height of the occlusal plane The further away the occlusal plane , from the ridge, the less the stability. WHICH IS MORE STABLE? 4. Position of posterior teeth Placing the posterior teeth slightly lingual to the crest of the ridge, the more stable. The forces falling on the teeth becomes more centralized. This is known as “ lever balance”. INCLINED PLANE ACTION 5. Proper relief FIRST ROCKING THEN MIDLINE FRACTURE 6. Ridge form and height • Well developed ridge with high vertical walls will resist lateral forces 7. Palatal vault V- shaped palate helps resist lateral loads, but retention is less as it is more difficult to maintain the seal U- shaped palate provides the most favorable retention and stability 8. Width of the occlusal table The occlusal width is less than the natural, thus decreasing the amount of load falling on the denture. 9. Shape and size of the tongue Large and medium sized tongues help stabilize the lower denture 10. Shape of the polished surface The cheek and the tongue seat the dentures in place Reading material • Prosthodontic Treatment for Edentulous Patients 13th Edition George Zarb ,John Hobkirk ,Steven Eckert and Rhonda Jacob • A Colour Atlas of Complete Dentures: John A. Hobkirk • Essentials of Complete Denture Prosthodontics by Sheldon Winkler