Retention & Stability PDF

Dr. Emad Amin Azmy Lecturer of Prosthodontic, BDs, MDs, DDs. (Cairo University) Faculty of Dentistry, Nahda university Denture Success  Retention Stability Support SUCCESS Retention, Stability and Support are important to succe...

Dr. Emad Amin Azmy Lecturer of Prosthodontic, BDs, MDs, DDs. (Cairo University) Faculty of Dentistry, Nahda university Denture Success  Retention Stability Support SUCCESS Retention, Stability and Support are important to success  Retention  The quality of a denture by which the denture resists vertical tissue away movement.  Resistance of the denture to dislodgment.  Support  The quality of the prosthesis to resist vertical tissue-ward force.  Resistance to tissue ward movement.  Transferring and distribute occlusal stresses to the supporting oral structures.  Stability  The quality of the prosthesis to be firm, steady, or constant, to resist displacement by functional horizontal or rotational forces (Tipping - Rocking).  Bracing: Resistance to lateral movement of the denture. I. Retention  Retention 1. Physical 2. Mechanical 3. Anatomical & Physiological 1. Undercuts 1. Physical condition 1. Adhesion 2. Occlusion 2. Physiologic molding of tissues 2. Cohesion around polished surfaces 3. Interfacial Surface 3. Leverage 3. Condition of mucosa and Tension 4. Contour of submucosa 4. Atmospheric pressure denture base 4. Ridge characteristics 5. Capillary action 5. Ridge relationship 6. Viscosity 6. Neuromuscular control 7. Gravity 7. Quality and quantity of saliva  Retention 4. Psychological Acceptance 6. Surgical factors 1. Psychological Acceptance 2. Expectation 1. Implant 3. Intelligence 5. Retentive aids 2. Ridge expansion 4. Gagging 3. Ridge augmentation 1. Adhesives 2. Springs 3. Suction cup 4. Magnet 1. Physical Factors  Physical Factors 1. Adhesion 2. Cohesion 3. Interfacial Surface Tension 4. Atmospheric pressure 5. Capillary action 6. Viscosity 7. Gravity  A. Adhesion Physical attraction between unlike molecules in presence of water creates retentive force (mucosa and acrylic denture base in presence of saliva).  Retention supplied by adhesion depend on: 1. Area covered by the denture 2. Close adaptation of the denture to the supporting tissues. 3. Fluidity of saliva  B. Cohesion Physical attraction between similar molecules creates retentive force (The force where molecules of the matter adhere to one another). Usually occurs within saliva that is present between the denture base and mucosa. Cohesion Force  Adhesive failure refers to the interface between two bodies. Cohesive failure to within a material itself.  Forces affect denture retention Adhesion Cohesive forces forces Influence the wetting of Maintain the the denture and the integrity of the saliva mucosal film  C. Interfacial Surface Tension Combination between adhesion and cohesion. It is attributed to the attractive forces of the surface molecules of the liquid.  D. Atmospheric pressure Hydrostatic pressure (force/unit area) due to the weight of atmosphere on the surface. When an upper denture is inserted; air is expelled from between it and mucous membrane. In the presence of perfect seal around its entire border no air can get in. Atmospheric pressure This means that the pressure acting on the fitting surface of the denture is less than that acting on the non-fitting surface. The difference between these two pressures gives a positive force holding the denture in place.  E. Capillary attraction Capillarity is what causes a liquid to rise in capillary tube. With intimate contact between mucosa and denture base they act as a capillary tube in which the saliva is present  seeks to increase the contact between denture and tissues.  F. Gravity It acts as retentive force for the mandibular denture and displacing one for the maxillary one. So, it is insignificant in comparison with other forces acting on CD.  G. Viscosity Resistance by one part of a liquid in moving over another part. Why Viscosity is Important ? Because it plays an important role in the sealing of CD. Which is better thin watery or thick ropy saliva for retention? Saliva should be of medium viscosity: Thin watery saliva does not seal the denture well and seal can be easily broken. Thick ropy saliva is likely to cause gagging but it is better than thin (excellent for sealing). Maxillary dentures usually more retentive than mandibular one…. why?? 1. Small area of contact. 2. Bathed in saliva.  N.B To achieve maximum benefits from physical factors: 1. Good basal adaptation to the underlying tissues. 2. Wide area of coverage. 3. Perfect border seal. 4. Fluidity of saliva. 5. Direction of displacing forces: Adhesion acts almost powerfully at right angles to the surface. Impression technique and subsequent denture base design and fabrication. Maxillary versus Mandibular denture. Surface area 2. Mechanical Factors  Mechanical Factors 1. Undercuts 2. Occlusion 3. Leverage 4. Contour of denture base  A. Undercuts Means mechanical locking. Common sites for undercuts: 1. Maxilla: Distobuccal vestibule and tuberosity. 2. Mandible: Distolingual vestibule. If it is bilateral, is that good ? Denture should be inserted into the undercut area first, and then rotate other side into place on the opposite side.  B. Occlusion Occlusion in CD to enhance retention and stability: For example: 1. Balanced occlusion. 2. Monoplane occlusion. Balanced occlusion  C. Leverage The height of occlusal plane should be near the base as possible.  D. Contour of denture base Accurate fitting surface by good impression. Highly polished and contoured polished surfaces. 3. Physiological Factors  1. Quality and quantity of saliva Absence of saliva (xerostomia), thick ropy or excessive saliva decrease the retention of CD.  2. Arch relationship Ideal jaw relation provide better retention. Severe retrognathic or prognathous ridge relationship can be compromised the prosthetic treatment.  3. Neuromuscular control Functional forces exerted by musculature of the patient that can affect retention (masseter muscle). Dentures when placed for the first time most muscular actions tend to expel them; it considered as foreign body. Positive muscular control of denture requires that their design must follow certain criteria: 1. Teeth should be in neutral zone. 2. Position of occlusal plane in relation to tongue. ?? 3. Shape of polished surface ??  Buccinator muscle in relation to CD Buccinators muscle run anteroposteriorly, so that dislodging force during mastication is minimal. Polished surface of the flanges should be concave so that the pressure falling on them help to retain, rather than dislodge, the denture.  Masseter muscle in relation to CD Denture base must be contoured at the Masseter muscle influencing area (Distobuccal area) to permit the contraction of Masseter muscle otherwise displacement of the denture.  Mylohyoid muscle in relation to CD  Mylohyoid muscles anatomically and functionally form the floor of the mouth so it acts to raise the tongue with the floor of the mouth. Contour and extension of lingual flange should be determined by the functional movement of the muscle providing seating force to the denture.  4. Habits Tongues habits (retracted or protruded positions). Bruxism, clenching. What are critical anatomic areas that influence maxillary denture retention, stability and support?  Anatomical landmarks affecting denture borders Hamular notches Retention. Soft palate Retention. Posterior palatal seal Retention.  Posterior border Hard palate Support, retention. and PPS are two Retromylohyoid space stability. of the most critical Retromolar pad Support. areas for maxillary Sublingual fold Stability. denture retention Buccal shelf Support. Buccal vestibule Retention, stability.  5. Arch and ridge form 1. Ridge height: Large, broad ridges offer a greater resistance to lateral forces than small, narrow ridges. 2. Arch form: Square or tapered arches tend to resist rotation of the prosthesis better than ovoid arches.  6. Soft palate  It is classified in: class I class II class III 4. Psychological Acceptance  Psychological Acceptance  Dentures should be meeting with patient concerning as esthetics.  Wearing dentures for the first time can be as hard as learning how to swim. 1. Patient Intelligence. 2. Patient Expectations. 3. Fear of dislodgement. 4. Gagging.  Intelligence of patient (Education of patient) Every patient should be informed regarding the care & proper use of his denture. 1. How to eat. 2. How to speak. 3. Adaptation period.  Management of CD patients 1. Building up patient's confidence in the dentist, regardless of the quality of final prosthesis. 2. Acceptance of denture limitations, patient must be educated to understand and accept the reduced efficiency of the artificial dentition. 3. Esthetic denture may be the turning point in patient acceptance. 5. Retentive aids  A. Springs Made of coiled stainless steel attached to premolar area on both sides of the upper and lower dentures. B. Rubber suction disc  C. Adhesive It just a glue that is applied to dentures to temporarily hold them in place. A nontoxic soluble material applied to tissue surface of the denture to enhance retention and stability. Supplied as Strips, Paste, Powder.  D. Magnets Usage of small magnets beneath molar and premolar teeth. Arranged with similar poles oppose each other.  Main disadvantages is the Corrosion of magnet.  To overcome this problem; magnets are encapsulated in stainless steel, titanium or palladium. 6. Surgical Factors  1. Vestibuloplasty Surgical procedure designed to restore alveolar height and/or width by lowering the muscles attached.  2. Ridge Augmentation To increase the height and width of the alveolar ridge. 1. Autogenous bone from rib. 2. Non-autogenous bone (donor). 3. Synthetic; Hydroxyapatite injected to build sufficient height of the residual ridge (nonresorbable).  3. Distraction Osteogenesis  Using distractor to pull the two pieces of bone apart slowly heightening the alveolar ridge. Advantages: 1. No need for donor site. 2. Simultaneous lengthening of surrounding soft tissues. Disadvantages: 1. Long treatment period. 2. Danger of infection.  4. Implant-supported Overdenture  Dental implants may be the only solution for some patients. I. Ball and socket. II. Bar and clip. III. Magnet II. Stability  Stability It is the quality of prosthesis to be firm, steady, or constant, to resist displacement by horizontal or rotational stresses which tend to alter the relationship between the denture base and its supporting structure.  Factors affecting CD stability 1. Retention. 2. Occlusion. 3. Leverage (Height of occlusal plane). 4. Position of posterior teeth. 5. Proper relief of hard area. 6. Ridge and the form of palate. 7. Shape of polished surface. 8. Shape and size of the tongue.  1. Retention Better retention  better stability and vice verse.  2. Occlusion Occlusion means the contact relationship of the upper and lower teeth during various mandibular movements. Balanced occlusion: The simultaneous contacting of the upper and lower teeth on both sides and in the anterior and posterior occlusal areas of the jaws. O C C L U S I O N  3. Height of Occlusal plane Occlusal plane should be as near as possible to the ridge to enhance denture stability. The higher the occlusal plane in relation to residual ridge, the greater will be the leverage action and the lesser will be the stability of the denture. Various anatomical landmarks can be used to determine acceptable level of the occlusal plane as: 1. Stensen's duct, retromolar pad and Linea alba. 2. Anteriorly parallel to ……… & posteriorly to ……...... ? 3. It should be parallel to the crest of residual ridge. 4. Relation to the tongue ………………….?  4. Proper position of posterior teeth Artificial posterior teeth should be placed as nearly as possible where the natural teeth were or placed on the crest (center) of the ridge. If more buccal or more lingual ?  Neutral zone Neutral zone concept is based on the buccal and lingual forces generated by the musculature of the lips and cheeks in one side and tongue in the other side are balanced on the entire polished surface.  5. Proper Relief of hard area Hard areas under the denture should be relieved otherwise denture instability and denture rocking. Examples of hard areas ………………..  6. Ridge and palatal form Residual ridges with high vertical walls resist lateral forces and so enhance denture stability.  7. Shape of the polished surfaces Polished surfaces of the denture should be concave so surrounding musculature act to stabilize the dentures. If it is convex, lower denture will tend to be displaced by the powerful muscles. It is sometimes difficult to achieve a concave surface in the maxillary labial region without affecting the appearance adversely ?????  8. Tongue size and position Normal tongue completely fills the floor of the mouth. Stability of the denture can be affected by the tongue  thick and broad tongue enhance stability. On other hand small narrow or extremely large tongue reduce denture stability. Tongue size III. Support  Snow shoe principle The Snowshoe principle refer to maximal extension of the denture base to provide better support. A broader denture-bearing area decreases the force/unit area under the denture base.  Effective support is obtained when: 1. Maximum surface coverage without impinging on movable tissues. 2. Selective loaded of primary stress bearing area (to resist bone resorption).  Methods to improve denture support Surgical methods Non Surgical methods  Surgical removal of flabby  Rest on primary upporting tissues. tissues.  Surgical reduction of sharp  Correction of occlusal and ridges. vertical dimension of old prosthesis.  Surgical enlargement of ridge.  Good nutrition.  Implant.  Conditioning of patient musculature. NOW***** THANK YOU  References 1. Allen AA, Heath JR, Mc Cord: Complete Prosthodontics; Problems, Diagnosis and Management. Mosby- Wolf, London, 1995. 2. Beresin, V.E. and Schiesser, F. J.: The neutral zone in complete and partial dentures. 2nd ed. St. Louis, The C.V. Mosby Company: 1978. 3. Coleman, R. D. and kaiser, W. B.: The Scientific Bases of Dentistry. Philadelphia, W. B. Sounders; 1966. 4. Craig, R.G.: Restorative Dental Materials. 8th ed. St. Louis, C. V. Mosby Company. 5. Fenn, H.R.B.; Liddelow, K.P. and Gemson, A.B.: Clinical Dental Prosthetics. 2 ed. London, Staples; 1974. 6. Geering AH, Kundert M , Kelesy C: Complete denture and overdenture Prosthetics. Theme medical publication Inc. New York, 1993. 7. Grant AR, Heath JR, Mc Cord JF: Complete Prosthodontics; Problems, Diagnosis and Management. Mosby-Wolf, London, 1996. 8. Heartwell, C.M. and Rhan, A.G.: Syllabus of Complete Dentures. 3rd ed. Philadelphia, Lea and Febiger; 1986. 9. Winkler, S.: Essential of complete Denture Prosthodontics. 2nd ed. PSG Publishing Company; 1988. 10. Zarb, G.A.; Bolender, C.L.; HicKey, J.C. and carlesson, G.E.: Boucher's Prothodontic Treatment for Edentulous Patients. 7th. Ed. St-Louis, The C.V.Mosby Company; 1990. N, B. All pictures in these slides are copied from the above references and from the internet.