Retention of complete dentures


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Retention of complete dentures

  1. 1.  Introduction  Definition  Factors affecting retention - Classification - Interfacial force - Adhesion -Cohesion -Oral & facial musculature
  2. 2. -Atmospheric Pressure -Undercuts, Rotational insertion paths, Parallel walls -Gravity  Denture Adhesives  Conclusion  Bibliography
  3. 3.  Success of treatment with CD  Integration of oral functions + psychological acceptance  Perception of the dentures as stationary during function
  4. 4.  ‘That quality inherent in the prosthesis which resists the force of gravity, adhesiveness of foods, and the forces associated with the opening of jaws’ - GPT  The resistance of removal in a direction opposite that of insertion - Boucher
  5. 5.  The resistance of the movement of a denture from its basal seat, especially in a vertical direction - Winkler  The resistance it poses to withdrawal from its planned position in the mouth -Grant & Johnson
  6. 6.  Atmospheric pressure  Surface tension  Viscosity of saliva  Physical retention: area of the denture adaptation of denture viscosity of saliva volume of saliva wettability of the denture base resin
  7. 7. RETENTION ANATOMICAL Size of the denture bearing area Quality of the denture bearing area Parallel ridge walls PHYSIOLOGICAL Saliva PHYSICAL Adhesion Cohesion Interfacial surface tension Capillarity Atmospheric pressure Gravity MECHANICAL Undercuts Retentive springs Magnetic forces Denture adhesives Suction chambers & discs Palatal implants MUSCULAR Oral musculature Facial musculature
  8. 8.  Primary retention -physical means -mechanical means  Secondary retention - surrounding musculature - shape of the denture borders & flanges - psychological factors - proper instructions
  9. 9.  Mastication  Adhesive food  Gravity (upper)  Surrounding musculature  Occlusal prematurities  Parafunctional habits
  10. 10.  ‘The tension or resistance to separation possessed by the film of liquid between two well-adapted surfaces’ - GPT  ‘The resistance to separation of two parallel surfaces that is imparted by a film of liquid between them’
  11. 11.  Interfacial surface tension  Viscous tension
  12. 12. INTERFACIAL SURFACE TENSION  Thin layer of fluid that is present between two parallel planes of rigid material  Ability of the fluid to wet the rigid surrounding material  Low surface tension : maximize contact- spread out in thin film  High surface tension : minimize its contact – formation of beads on the material’s surface
  13. 13.  Processed denture base materials- higher wettability  High surface tension reduced on coating by the salivary pellicle › Retention by virtue of the tendency of the fluid to maximize the contact between the denture base & mucosa
  14. 14. Capillarity ‘That quality or state, because of surface tension causes elevation or depression of the surface of a liquid that is in contact with a solid’ - GPT
  15. 15.  Close adaptation between denture base & mucosa- thin film of saliva in the space › Retention- Capillary tube in which the liquid seeks to increase its contact
  16. 16.  Important in maxilla  If two plates with interposed fluid immersed in the same fluid- no resistance  External borders of mandibular denture awash in saliva
  17. 17. INTERFACIAL VISCOUS TENSION  Force holding two parallel plates together that is due to viscosity of the interposed liquid
  18. 18.  Stefan’s law: For two parallel, circular plates of radius (r) that are separated by a newtonian (incompressible) liquid of viscosity (k), & thickness (h), the force (F) necessary to pull the plates apart at a velocity(V) in a direction perpendicular to the radius will be F=(3/2)πkr4 V h3
  19. 19.  Viscous force viscosity of the fluid  Viscous force thickness of the medium  Viscous force opposing surface area
  20. 20.  Optimal adaptation- minimal ‘h’  Maximizing denture bearing area- maximum ‘r’  Increasing the viscosity of the medium  Slow steady displacing action-small ‘V’ effective at removing the denture than a large ‘V’  Enhanced by ionic forces- adhesion & cohesion
  21. 21.  ‘Physical attraction of unlike molecules for each other’ IONIC FORCES Salivary glycoproteins Acrylic resin in denture base Surface epithelium of the mucous membrane
  22. 22.  Xerostomia :Adhesion between denture base & the dry mucosa  Not very effective- mucosal abrasions & lacerations  Ethanol free rinse with aloe or lanolin  Saliva substitute with carboxymethylcellulose/ mammalian mucin  Sjogren’s syndrome: 5-10mg oral pilocarpine tds
  23. 23.  Retention by adhesion with area covered by denture  Mandibular dentures , small jaws, very flat alveolar ridges- less adhesion  Dentures extended to limits of the health & function of oral tissues  Preserve the alveolar height
  24. 24.  ‘Physical attraction of like molecules for each other’  Within the layer of interposed saliva & maintains its integrity  Normal saliva not very cohesive unless modified  High mucinous saliva- though more cohesive, less retentive
  25. 25.  Supplement retention if:  Teeth are positioned in the neutral zone  Polished surfaces of the denture are properly shaped  Buccal & lingual flanges should be so shaped that the musculature fits automatically
  26. 26. Buccal flange  Buccinators tend to retain both  Tongue perfect the border seal if: lingual surfaces of the lingual flanges slope toward the centre of the mouth MAXILLA: Slope up & out from the occlusal plane MANDIBLE: Slope down & out from the occlusal plane
  27. 27.  Lingual side of the distal end of the lingual flange:  Guides the base of the tongue on top of the lingual flange  Ensures the border seal at the back end of mandibular denture  Base of tongue: emergency retentive force
  28. 28.  Most effective in retention when:  The denture bases are properly extended to cover the maximum area possible  The occlusal plane is at the correct level  The arch form of the teeth is in the neutral zone
  29. 29.  Resist dislodging forces to dentures with an effective seal  Called Suction: resistance to removal from the basal seat  No suction unless another force is applied  Suction alone applied: serious damage to the health of the soft tissues
  30. 30.  Force exerted perpendicular to & away from the basal seat of a properly extended & fully seated denture  Pressure between the tissues & the denture drops below the atmospheric pressure: resists displacement  Retention area covered by the denture
  31. 31.  Most effective in retention when:  Denture has a perfect seal around its entire border  Proper border molding with physiological, selective pressure techniques is carried out
  32. 32.  Modest undercuts enhance retention: resiliency of the mucosa & submucosa  Exaggerated bony undercuts: compromise retention  Less severe ones: extremely helpful  Lateral tuberosities  Maxillary premolar areas  Distolingual areas  Lingual mandibular midbody areas
  33. 33.  Undercuts necessitate adopting a rotational path of insertion: resists vertical displacement  Inferior to the retromolar pad: posterior end placed first, from the superior & posterior before rotating the anterior segment down
  34. 34.  Anterior alveolus: anterior part inserted in a posterior & superior direction & posterior border rotated over the tuberosities  More important when other retentive mechanisms are weak:  Loss of normal anatomical contours  Surgically created undercuts
  35. 35.  Prominent alveolar ridges with parallel buccal & lingual walls increase the surface area maximize interfacial & atmospheric forces  Limit the range of displacive force directions  Flat ridges resist displacing forces perpendicular to the basal seat, but susceptible to movement parallel to it
  36. 36.  Retentive force for the mandibular & displacive for the maxillary- when the person is upright  Weight of the prosthesis- gravitational force insignificant  Heavy maxillary prosthesis unseat if the other retentive forces – suboptimal
  37. 37.  Increasing the weight of the mandibular denture- beneficial when other retentive factors are marginal  Xerostomia patients prefer heavier maxillary prostheses
  38. 38.  Commercially available nontoxic, soluble material that is applied to the tissue surface of the denture to enhance retention, stability& performance  Products which enhance the treatment outcome  US: 33% of denture wearers use adhesive products  Sale exceeded 200 million$ in 2001
  39. 39. Dentists should:  Educate all denture wearing patients about the advantages, disadvantages& uses of adhesives  Identify those patients for whom such a product is advisable and/or necessary for a satisfactory denture wearing experience
  40. 40. STRICTLY INADVISABLE FORMS OF ADHESIVES  Home reliner/repair kits  Paper/cloth pads  Self applied cushions  Thin wafers of water soluble material: adherent to denture & basal tissue- don’t flow
  41. 41. Possible sequelae:  Soft tissue damage  Alterations in occlusal relations & VD  Exacerbation alveolar bone destruction
  42. 42.  Augment the already operating retentive mechanisms  Enhance retention through optimizing interfacial forces by: 1. Increasing the adhesive & cohesive properties & viscosity of the interposed medium 2. Eliminating the voids between the denture base & its basal seat
  43. 43.  Hydrated material formed by adhesives- stick readily to the tissue surface & the mucosal surface of the denture  More cohesive than saliva- resists displacing pull  Increases viscosity of saliva  Hydrated material swells up in the presence of saliva/water: obliterates voids
  44. 44.  Before early 1960’s: VEGETABLE GUMS  Karaya  Tragacanth  Xanthan  Acacia  Modest nonionic adhesion to denture & mucosa
  45. 45. Drawbacks  Very little cohesive strength  Highly water soluble(particularly in hot): washed out readily  Allergic reactions- Karaya & methyl paraben(preservative)  Acetic acid odor  Short-lived & unsatisfactory adhesive performance
  46. 46.  Presently : SYNTHETIC MATERIALS  Mixtures of the salts of short acting Carboxymethylcellulose (CMC) long acting (polyvinyl methyl ether maleate) ‘gantrez’ polymers
  47. 47.  CMC hydrates & displays quick-onset ionic adherence to both dentures& mucous epithelium  Original fluid increases its viscosity & CMC increases in volume- eliminates voids between prosthesis & basal seat  Enhance the interfacial forces acting on the denture
  48. 48.  Polyvinylpyrrolidone (‘povidone’) behaves like CMC  Gantrez salts: More protracted time course than necessary for the onset of hydration than CMC, hydrate & increase adherence & viscosity
  49. 49.  Display molecular cross-linking more pronounced & longer lived in Calcium- Zinc gantrez than in Calcium- Sodium gantrez  All polymers fully solubilised & washed out by saliva : hastened by the presence of hot liquid
  50. 50. OTHER COMPONENTS:  Petrolatum, Mineral oil, Polyethylene oxide : bind the materials & make placement easier  Silicone oxide, Calcium stearate: powders to minimize clumping  Menthol, Peppermint oils: flavoring  Red dye: Coloring  Sodium borate, Methylparaben, Polyparaben: Preservatives
  51. 51.  No reports of tissue reactions excepting uncommon allergic reactons to karaya/ methyl paraben  Earlier formulations had benzene- carcinogen  Lessened inflammation of the underlying tissues if dental hygiene is maintained
  52. 52.  Incisal bite force in well fitting dentures over well- keratinized ridges with favorable anatomical features  Can be improved for well fitting dentures over inferior basal tissues
  53. 53.  Frequency of dislodgement - chewing  Increased confidence & security in chewing- but no improvement in chewing performance  Improvement in chewing efficiency during adjustment to new dentures
  54. 54. OBJECTIONS:  Grainy/ gritty texture of the powder  Taste or sensation of semidissolved adhesive material that escapes from the posterior & other peripheries  Difficulties in removing adhesives from the oral tissues & denture  The cost of the material
  55. 55.  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
  56. 56.  Salivary dysfunction  Xerostomia- medications, irradiation, systemic disease, disease of salivary glands  Need to be educated- deliberately moisten the adhesive bearing denture
  57. 57.  Neurological disorders  CVA- oral cavity insensitive to tactile stimulation/ paralysis of oral musculature  Help to accommodate to new dentures  Dentures fabricated before stroke
  58. 58.  Orofacial Dyskinesia/ Tardive Dyskinesia  Exaggerated, uncontrollable muscular actions of tongue, lips, cheeks & mandible  Side effect of: - phenothiazines - neuroleptics - GI medications -Dopamine blocking drugs
  59. 59.  Resective surgical/ traumatic modifications of the oral cavity  Oral neoplasia  Loss of integrity of intraoral structures  Even in the presence of surgically created rotational undercuts
  60. 60.  Poorly fitting or improperly fabricated prosthesis  Hypersensitivity to any of the components
  61. 61.  Major information source to the patient- dentist  Effects of powder formulations do not last long compared to cream formulations  Initial ‘hold’ is better for them compared to creams  Easier to clean out  The least amount of the material that is effective should be used: 0.5-1g/denture unit
  62. 62. POWDERS:  Clean prosthesis moistened- thin even coat of adhesive sprayed onto the tissue surface of the denture  Excess is shaken off & it is firmly seated  Sprayed denture slightly moistened with water before insertion- inadequate salivation
  63. 63. CREAMS 2 approaches 1. Placement of thin beads of adhesive in the depth of the dried denture in the incisor & molar regions  Anteroposterior bead in the midpalate- maxillary
  64. 64. 2. Small spots of cream placed at 5mm intervals throughout the fitting surface of the dried denture- even distribution  Denture then seated & inserted firmly  Requires moistening before placement in cases of xerostomia
  65. 65.  Daily removal of the adhesive- soaking prosthesis in water / soaking solution overnight  If not possible, running hot water over the tissue surface & scrubbing with a suitable hard bristle brush
  66. 66.  Adhesive adherent to alveolar ridges & palate – rinsing with warm/ hot water- firmly wiping the area with gauze/washcloth saturated with hot water  Discomfort will not be resolved by placing a ‘cushioning layer’ of adhesive under the denture
  67. 67.  Professional management required:  Pain /soreness  Gradual increase in the quantity of adhesive required  Patients recalled annually for mucosal evaluation& prosthesis assessment
  68. 68.  Frequently regarded as unesthetic, impedes dentist’s ability to appraise the health of oral tissues & the true adaptation  Use of denture adhesive & residual ridge resorption- believed to be correlated: no scientific basis  Reduce the amount of lateral movements that denture undergoes while in contact with basal tissues
  69. 69.  Patient may ignore the need for professional help when dentures actually become ill fitting  Integral part of a professional service & their adjunctive benefits must be recognised
  70. 70.  Irrespective of the underlying reasons for the patient’s dissatisfaction with the prosthesis, dentist must realize that a patient’s judgement of the treatment outcome is what defines prosthodontic success  Though complete denture retention is a complex phenomenon, it is every patient’s invariable need that the prosthesis stays firm & stable during function & hence every possible attempt should be made by the dentist to achieve it
  71. 71.  Prosthodontic Treatment for Edentulous Patients- Zarb & Bolender,Twelfth edition  Essentials of CompleteDenture Prosthodontics- Sheldon Winkler,Second edition  Textbook of Prosthodontics- Deepak Nallaswamy  Complete Denture Prosthodontics- John Joy Manappallil