Physical and Mechanical Factors Affecting Complete Denture Retention and Stability PDF

Physical and mechanical factors affecting the retention and stability of complete dentures Dr. Azize Demir Success of treatment with Complete Dentures Integration of oral functions & physhological acceptance Perception of the dentures as stationary during function...

Physical and mechanical factors affecting the retention and stability of complete dentures Dr. Azize Demir Success of treatment with Complete Dentures Integration of oral functions & physhological acceptance Perception of the dentures as stationary during function  Retention \ rĭ-tĕn΄shun \ n (15c): that quality inherent in the dental prosthesis acting to resist the forces of dislodgment along the path of placement Denture retention \ dĕn΄churrĭ-tĕn΄shun \ : 1. the resistance in the movement of a denture away from its tissue foundation especially in a vertical direction; 2. a quality of a denture that holds it to the tissue foundation and / or abutment teeth Denture stability \ dĕn΄chursta-bĭl΄ĭ-te\: 1. the resistance of a denture to movement on its tissue foundation, especially to lateral (horizontal) forces as opposed to vertical displacement (termed denture retention); 2. a quality of a denture that permits it to maintain a state of equilibrium in relation to its tissue foundation and/or abutment teeth THE GLOSSARY OF PROSTHODONTIC TERMS Ferro, K. J., Morgano, S. M., Driscoll, C. F., Freilich, M. A., Guckes, A. D., Knoernschild, K. L.,... & Twain, M. (2017). The glossary of prosthodontic terms.  ANATOMICAL PHYSIOLOGICAL Size of the denture bearing area Saliva Quality of the denture bearing area Parallel ridge walls PHYSICAL RETENTION Adhesion Cohesion Interfacial surface tension MECHANICAL Capillarity Undercuts Atmospheric pressure Retentive springs Gravity Magnetic forces Denture adhesives MUSCULAR Suction chambers & discs Oral musculature Palatal implants Facial musculature FACTORS AFFECTING DEGREE OF RETENTION Primary retention Physical means; adhesion,cohesion,interfacial surface tension Mechanical means; undercuts, denture adhesives Secondary retention Surrounding musculature Shape of the denture borders & flanges Pyschological factors Proper instructions Dislodging Forces Mastication Adhesive foods Gravity (for maxillary complete dentures) Surrounding musculature Premature occlusal contacts Parafunctional habits  Physiological factors The amount and consistency of saliva affects retention Thin, watery saliva affords best retention Excessive saliva that is thick and ropy, accumulates between tissue surface of the denture and the palate leading to loss of retention The absence of saliva i.e. Xerostomia affects retention and can also cause irritation and soreness of the denture bearing tissues. https://news.mit.edu/sites/default/files/styles/news_article__image_gallery/public/images/201008/20100722100357-0_0.jpg?itok=bAEcMSmU  Surface tension \ sûr΄fastĕn΄shun\: a property of liquids in which the exposed surface tends to contract to the smallest possible area, as in the spherical formation of drops; a phenomenon attributed to the attractive forces, or cohesion, between the molecules of the liquid. THE GLOSSARY OF PROSTHODONTIC TERMS Ferro, K. J., Morgano, S. M., Driscoll, C. F., Freilich, M. A., Guckes, A. D., Knoernschild, K. L.,... & Twain, M. (2017). The glossary of prosthodontic terms.  Low surface tension liquid: maximize contact- spread out in thin film High surface tension liquid: minimize its contact- formation of beads on the material’s surface https://www.mdpi.com/symmetry/symmetry-13-01265/article_deploy/html/images/symmetry-13-01265-g001.png  INTERFACIAL SURFACE TENSION Defined as tension or resistance to separation possessed by a film of liquid between two well adapted parallel surfaces. Dependant on the ability of the liquid to wet the rigid surrounding material The oral mucosa has low surface tension and hence the saliva wets it well spreading out in a thin film thus wetting the denture surface aiding in retention To obtain maximum interfacial surface tension thin and even layer of saliva adequate adhesion and cohesion  The denture base must be precisely fitted to the tissue surface in order for saliva to create a thin film in the gap and increase the interfacial force.  PHYSICAL FACTORS ADHESION ‘Physical attraction of unlike molecules for each other’ Acrylic resin in denture base Salivary glycoprotein's Surface epithelium of the mucous membrane  COHESION ‘Physical attraction of like molecules for each other’ Occurs within the film of interposed saliva which aids in retention Normal saliva is not very cohesive so retention from mucosa is dependant on adhesion and surface tension As viscosity of saliva increases, greater is the cohesion but more thicker the saliva it can physically push the denture out resulting in loss of retention. Capillarity ‘That quality or state, which because of surface tension causes elevation or depression of the surface of a liquid that is in contact with a solid’ Capillarity causes the thin film of saliva to rise and increases its contact with the denture base and the mucosa Close adaptation between denture base & mucosa is important for the capillarity to provide effective retention Capillarity: The rising or collapsing of a fluid surface in contact with a solid object, as in capillary tubes. Meniscus: The concave or convex shape of the surface of a fluid column due to the effect of capillarity. When the prosthesis base plate is well adapted to the mucosa, a very thin space remains around the prosthesis and between the mucosa and the base plate. This gap acts like capillary tubes in physics. However, this capillary tube is not vertical and straight, but curved and horizontal. The liquid in between is saliva. Since the total prosthesis is located in the middle of mobile tissues and sits on resilient mucosal tissue, it cannot be expected to be completely stable, especially during function. During function, the following physical events occur as the total prosthesis tries to move away from the tissues; There is a capillary space (capillary tube) between the prosthesis base plate and the surrounding tissues. The meniscus formed at the end of this capillary space, which coincides with the edge of the prosthesis, surrounds the prosthesis like a spring. The meniscus resists the tendency of the prosthesis to move away from the tissues during function. In total prostheses, this force is a factor that increases retention through surface tension.  Capillarity Surface tension, meniscus In order for the retention created by the surface tension force to be large, the saliva film between the denture base plate and the tissues must be thin and continuous. The fit of the denture base plate to the tissues should be very good and there should be a minimum gap between them.  Xerostomia Adhesion between denture base & the dry mucosa Not very effective- mucosal abrasions & lacerations Ethanol free rinse with aloe or lanolin(wool wax) Saliva substitute with carboxymethylcellulose/ mammalian mucin Due to lack of saliva causes difficulties in oral function-causes difficulty in eating, speaking and swallowing and denture retention is compromised. Adhesion is not there due to lack of saliva https://dimensionsofdentalhygiene.com/wp-content/uploads/2019/07/AC-featured-450x300.jpg https://www.cancer.org/cancer/salivary-gland-cancer/about/what-is-salivary-gland-cancer/_jcr_content/par/textimage/image.img.jpg/1518039133881.jpg  Xerostomic patients who experience a quantitative or qualitative reduction in saliva may have reduced complete denture retention due to decreased interfacial surface tension.  Retention by adhesion increases with area covered by denture. Mandibular dentures, small jaws, very flat alveolar ridges means less adhesion. Dentures extended to limits of the health and function of oral tissues means adequate adhesion.  Atmospheric pressure Resist dislodging forces to dentures with an effective seal called suction; creates negative pressure in palatal surfaces of maxillary denture enhancing retention. Avoided because they cause serious damage to the health of the soft tissues- papillary hyperplasia. A precancerous condition is a condition or lesion involving abnormal cells which are associated with an increased risk of developing into cancer! https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcSLA5Q8gMFQEhC_QtmIM6tx19LsNfCGCYHmVuNcLrH-x5RbgymIBmYsJavZvJ4P20zXHlU&usqp=CAU  Atmospheric pressure is most effective in retention when: Denture has a perfect seal around its entire border Proper border molding with physiological, selective pressure techniques carried out https://youtu.be/N2Eg5wXkSj8  GRAVITY Retentive force for the mandibular and displacive for the maxillary- when the person is upright. The displacement of a heavy maxillary prosthesis is possible if the other retentive forces are suboptimal. When other retentive variables are insignificant, it may be advantageous to make the mandibular denture heavier. MECHANICAL FACTORS Undercuts Undercuts enhance retention because of resiliency of the mucosa & submucosa eg; unilateral tuberiosity undercuts, undercuts in maxillary premolar area, distolingual areas and lingual to the midline of the mandible Severe undercuts covered within the mucosa compromises retention and need to be surgically eliminated  Denture adhesives This are commercially available products that enhances retention by increasing the adhesive and cohesive properties and by eliminating voids between denture base and basal seat tissues https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcTme7_I3sAeTnxo48OGFz0ZLDKyDWAv4h6Imw&usqp=CAU  Dentists should educate all patients who wear dentures about the advantages and disadvantages of the denture adhesives as well as the correct way to apply them. Additionally, dentists must determine whether individuals require such a product for a positive experience wearing dentures. INDICATIONS OF DENTURE ADHESIVES Well made complete dentures do not satisfy a patient’s perceived retention & stability expectations Candidates for implant supported prosthesis , precluded by health, financial or other restraints Salivary dysfunction Xerostomia- medications, irradiation, systemic disease, disease of salivary glands Need to be educated- deliberately moisten the adhesive bearing denture CONTRAINDICATIONS OF DENTURE ADHESIVES Poorly fitting or improperly fabricated prosthesis Hypersensitivity to any of the components