denture base considerations


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denture base considerations

  2. 2. <ul><li>Definition </li></ul><ul><li>Requirements </li></ul><ul><li>Functions </li></ul><ul><li>Types </li></ul><ul><li>a,Plastic </li></ul><ul><li>b,Metal </li></ul><ul><li>Tooth supported partial denture base </li></ul><ul><li>Distal extension denture base </li></ul><ul><li>Methods of attaching denture base </li></ul><ul><li>Methods of attaching artificial teeth </li></ul><ul><li>Relining </li></ul><ul><li>Stress breakers </li></ul>
  3. 3. <ul><li>Definition – </li></ul><ul><li>Is that part of the removable partial denture which rests on oral mucosa and to which teeth are attached. </li></ul>
  4. 4. <ul><li>Accuracy of Adaptation To Tissues With Low Volume Change </li></ul><ul><li>Dense non irritating surface capable of receiving & </li></ul><ul><li>maintaining a good finish. </li></ul><ul><li>Thermal conductivity </li></ul><ul><li>Low specific gravity – Lightness in mouth </li></ul><ul><li>Esthetics </li></ul><ul><li>Biologically Compactable with tissues </li></ul>
  5. 5. <ul><li>Dimensional stability </li></ul><ul><li>Resist deformation </li></ul><ul><li>Low Cost </li></ul><ul><li>Self cleansing </li></ul><ul><li>Potential for future relining </li></ul><ul><li>Sufficient strength – Resistance to fracture /distortion </li></ul>
  6. 6. <ul><li>Functions – </li></ul><ul><li>Esthetics </li></ul><ul><li>Support and retain artificial teeth </li></ul><ul><li>Assist in transfer of occlusal forces directly to abutment teeth thru rests. </li></ul><ul><li>Prevent vertical and horizontal migration of remaining natural teeth. </li></ul><ul><li>Eliminate undesirable food traps. </li></ul><ul><li>Stimulates the underlying tissue. </li></ul>
  7. 7. <ul><li>Types – </li></ul><ul><li>Plastic </li></ul><ul><li>Acrylic </li></ul><ul><li>Polystyrene </li></ul><ul><li>Valplast </li></ul><ul><li>Metal </li></ul><ul><li>Gold </li></ul><ul><li>Co-Cr </li></ul><ul><li>Titanium </li></ul><ul><li>Vitallium </li></ul>
  8. 9. Tooth supported partial dentures Inadequate interarch space Structural details Designed with optimum extension Thinner base than plastic resin Avoid sharp margins
  9. 10. <ul><li>Accuracy & performance of form </li></ul><ul><li>Comparative tissue response </li></ul><ul><li>Thermal conductivity </li></ul><ul><li>Weight & Bulk </li></ul>
  10. 11. <ul><li>Accuracy and permanence of form- </li></ul><ul><li>Cast more accurately than denture resins and maintain their accuracy of form without change in mouth. </li></ul><ul><li>Internal strains released later to cause distortion not present. </li></ul><ul><li>Need for an additional pps eliminated entirely. </li></ul><ul><li>Accuracy –metal base provides intimacy of contact-retention of denture prostheses. </li></ul><ul><li>Such intimacy-not acrylic resin bases. </li></ul>
  11. 12. <ul><li>Comparitive tissue response- </li></ul><ul><li>Inherent cleanliness of cast metal base contributes to health of oral tissue. </li></ul><ul><li>Bacteriostatic activity – ionization and oxidization of metal base. </li></ul><ul><li>Metal base naturally cleaner than an acrylic resin base. </li></ul>
  12. 13. <ul><li>Thermal conductivity- </li></ul><ul><li>Temperature changes transmitted though metal to the underlying help to maintain health of that tissue. </li></ul><ul><li>Pts acceptance. </li></ul><ul><li>Denture resins – insulating property </li></ul>
  13. 14. <ul><li>Weight and bulk- </li></ul><ul><li>Metal alloy may be cast thinner than acrylic resin and still have adequate strength. </li></ul><ul><li>Certain situations demands use of acrylic denture base- </li></ul><ul><li>Xtreme loss of residual alveolar bone-fullness to denturebase to restore facial contours. </li></ul><ul><li>To provide fullness to fill a max vestibule </li></ul><ul><li>Esthetics </li></ul>
  14. 15. <ul><li>Esthetics </li></ul><ul><li>Enhancement of retention not possible – lack of weight </li></ul><ul><li>of metal base </li></ul><ul><li>Relining difficult </li></ul><ul><li>Restoration of normal facial contour can not be achieved </li></ul>
  15. 17. Acrylic denture base- Indications Extension base partial denture Long span edentulous ridges Relining Contour restoration
  16. 18. Adequate bulk & strength - junction of base & minor connector Tissue stops at extension base frame work Placement of Base – Placement over crest ridge- Resin breakage Buccal/lingual of crest ridge
  17. 19. <ul><li>1950,s </li></ul><ul><li>Valplast – flexible base resin ideal for partial dentures. </li></ul><ul><li>Esthetic yet fully functional alternative to traditional cast metal based removable partial dentures. </li></ul>
  18. 20. <ul><li>Biocompatible nylon and thermoplastic resin-flexibility and stability. </li></ul><ul><li>Color, shape and design of valplast partials blend seamlessly with natural appearance of gingiva making prostheses nearly invisible. </li></ul><ul><li>Strenght of valplast resin doesn’t require a metal framework-eliminates metallic taste. </li></ul><ul><li>Enables partial to be fabricated thin enough with non metallic clasps. </li></ul>
  19. 21. <ul><li>Adequate occlusal clearance b/w arches for tooth placement. </li></ul><ul><li>No tooth preparation required. </li></ul><ul><li>Vitallium combination-better support and clasp esthetics </li></ul>
  20. 22. TYPES <ul><li>Tooth Supported Partial Denture Base </li></ul><ul><li>Distal Extension Partial Denture Base </li></ul>
  21. 23. <ul><li>In tooth supported prostheses denture base is primarily a span b/w 2 abutments supporting artificial teeth. </li></ul><ul><li>Occlusal forces transferred to abutments-Rests. </li></ul><ul><li>Prevent horizontal migration of all abutment teeth in partially edentulous arch and vertical migration of teeth in opposing arch. </li></ul>
  22. 24. <ul><li>Support of the denture. </li></ul><ul><li>Support critical to goal of minimizing functional movt and improving prostheses stability. </li></ul><ul><li>Max support obtained – broad accurate denture bases-occlusal load equitably. </li></ul><ul><li>Support – gross size and cellular characteristics of residual alveolar ridge. </li></ul><ul><li>Snow shoe principle-broad coverage furnishes the best support with least load per unit area is principle choice for providing max support. </li></ul><ul><li>Support –primary consideration </li></ul>
  23. 25. <ul><li>Esthetics,stimulation of underlying tissue,and oral cleanliness-secondary importance. </li></ul><ul><li>Relining necessary in tooth supported denture base. </li></ul><ul><li>Tooth – supported bases made soon after xn should be of material that permits relining. </li></ul><ul><li>Primary retention for RPD –mechanically by placing retaining elements on abutment teeth. </li></ul><ul><li>Secondary retention-intimate relationship of denture base and major connectors. </li></ul>
  24. 26. <ul><li>Retention of denture bases as a result of following forces- </li></ul><ul><li>Adhesion –attraction of saliva to denture and tissue. </li></ul><ul><li>Cohesion –attraction of molecules of saliva for each other. </li></ul><ul><li>Atmospheric pressure-border seal. </li></ul><ul><li>Physiological molding of tissue around polished surface of the denture. </li></ul><ul><li>Effect of gravity on mandibular denture. </li></ul>
  25. 27. <ul><li>Acrylic resin bases-attached to partial denture frame work-minor connector designed b/w framework and underlying tissue. </li></ul><ul><li>Relief 20 guage thickness-basal seat. </li></ul><ul><li>Plastic mesh patterns in forming retentive framework less satisfactory than open pattern. </li></ul>
  26. 28. <ul><li>12-14 guage half round wax and 18 guage round wax-ladder like framework rather than mesh pattern. </li></ul><ul><li>Designing retentive framework –bucally lingually- </li></ul><ul><li>strengthen acrylic resin base-minimize distortion of base-stress </li></ul><ul><li>Not interfere with teeth arrangement-future adjustment </li></ul>
  27. 29. <ul><li>Metal bases –cast as integral parts of partial denture framework. </li></ul><ul><li>May also be assembled and attached to framework with acrylic resin. </li></ul>
  28. 30. Plastic Mesh Pattern Open Lattice
  29. 31. BEADS & NAIL HEADS
  30. 32. <ul><li>Porcelain/ Resin Artificial Teeth with Resin </li></ul><ul><li>Porcelain/ Resin Tube Teeth & Facings Cemented Directly to Metal Bases </li></ul><ul><li>Resin Teeth Processed Directly To Metal Bases </li></ul><ul><li>Metal Teeth Cast With Frame Work </li></ul><ul><li>Chemical Bond </li></ul>
  31. 33. <ul><li>Mechanically retained. </li></ul><ul><li>Posterior teeth retained by acrylic resin in their diatoric holes. </li></ul><ul><li>Ant teeth retained by acrylic surrounding their lingually placed retention pins. </li></ul><ul><li>Acrylic resin teeth retained by chemical union with acrylic resin of denture base. </li></ul>
  32. 34. <ul><li>Attachment of acrylic resin to metal base – nail head retention,retention loops or diagonal spurs. </li></ul><ul><li>Any junction of acrylic resin with metal should be at an undercut finish line.(mech retention) </li></ul><ul><li>Every attempt should be made to prevent separation and seepage which results in discoloration and uncleanliness. </li></ul><ul><li>Denture odors are frequently caused by accretions at the junction of acrylic resin with metal. </li></ul><ul><li>Separation occurring b/w acrylic resin and metal can eventually lead to some loosening of acrylic resin base. </li></ul>
  33. 35. <ul><li>Some disadv of this type of attachment are- </li></ul><ul><li>Difficulties in obtaining satisfactory occlusion. </li></ul><ul><li>Lack of adequate contours for functional tongue and cheek contact. </li></ul><ul><li>Unesthetic display of metal at gingival margins. </li></ul>
  34. 36. <ul><li>Modification of this method is attachment of ready made acrylic resin teeth to the metal base with acrylic resin of same shade(pressing). </li></ul><ul><li>Particularly applicable for ant replacements. </li></ul>
  35. 37. <ul><li>Procedure- </li></ul><ul><li>Labial index of the position of teeth is made. </li></ul><ul><li>Lingual portion cut away or post hole prepared. </li></ul><ul><li>Subsequently tooth is attached to denture with acrylic resin of same shade. </li></ul><ul><li>For best occlusal relation jaw relation records made with denture casting in mouth. </li></ul><ul><li>Tube teeth preferred. </li></ul><ul><li>Teeth are ground to fit the ridge with sufficient clearance beneath for metal base. </li></ul><ul><li>Casting completed and tried. </li></ul><ul><li>Teeth ground to harmonious occlusion. </li></ul>
  36. 38. <ul><li>Occlusal relation established in mouth and transferred to articulator. </li></ul><ul><li>Teeth can be carved or processed in acrylic resin of proper shade. </li></ul><ul><li>Long,short,wide or narrow teeth may be created when necessary to fill spaces. </li></ul><ul><li>Occlusion on acrylic resin teeth may be restablished to compensate for wear or settling by reprocessing new acrylic resin or using light activated acrylic resin. </li></ul>
  37. 39. <ul><li>Occasionally a second molar tooth may be replaced as part of partial denture casting. </li></ul><ul><li>Space too limited for attachment of an artificial tooth. </li></ul><ul><li>Because metal particularly a chrome alloy is abrasion resistant area of occlusal contact should be held to min to prevent damage to peridontium of opposing tooth. </li></ul><ul><li>Should be used only to fill a space and to prevent tooth extrusion. </li></ul>
  38. 40. <ul><li>Recent developments-direct chemical bonding of acrylic resin to metal frame works. </li></ul><ul><li>Investing alveolar and gingival tissue replacement components can be attached without the use of loops,mesh or surface mechanical locks. </li></ul><ul><li>Section of metal framework-roughned with abrasives-treated with vaoporized silica. </li></ul><ul><li>Acrylic resin bonding agent applied-thin layer of acrylic resin. </li></ul>
  39. 41. <ul><li>Triochemical coating accomplishes a second method of fusing a microscopic layer of ceramic to metal. </li></ul><ul><li>Sandblasting metal framework with silica particle (Rocatec-plus). </li></ul><ul><li>Silane added to ceramic-chemical bond b/w silicate layer and denture base acrylic resin. </li></ul><ul><li>Denture base acrylic resins formulated with 4-Meta are also available and provide mechanism of bonding acrylic resin to metal. </li></ul>
  40. 42. <ul><li>Distal extension base differs from toothsupported base-made of material-relined. </li></ul><ul><li>Acrylic resin denture base materials that can be relined are generally used. </li></ul>
  41. 43. <ul><li>Loss of support - distal extension bases- changes in residual ridge-loss of occlusion-heavy occlusal contact b/w remaining natural teeth. </li></ul><ul><li>Relining necessary. </li></ul><ul><li>Rotation of fulcrum line with indirect retainers lifting from their seats as distal extension base is pressed against ridge tissue-relining </li></ul>
  42. 44. <ul><li>Loss of occlusal contact and rotation-relining. </li></ul><ul><li>Loss of occlusal contact with no evidence of rotation -restablish occlusion. </li></ul><ul><li>Loss of support assessed clinically-hydrocolloid, wax,tissue conditioning material. </li></ul>
  43. 45. <ul><li>Acrylic resin bases – distal extensions </li></ul><ul><li>Min and harmonious occlusion,and accuracy with which base fits the underlying tissue influences trauma occuring under function. </li></ul><ul><li>Absence of trauma-ridge integrity. </li></ul>
  44. 46. <ul><li>Best indication for metal distal extension bases-ridge that supported a previous partial denture. </li></ul><ul><li>Tissues remain healthier beneath a metal base than a acrylic resin base –thorough Rx planning-pt education-care of denture bases. </li></ul><ul><li>Highest pressure was on the residual ridge crest. The pressure distribution varied along with the design of the occlusal rest. </li></ul><ul><li>“ Development of in vivo measuring system of the pressure distribution under the denture base of removable partial denture. J Prosthodont Res. 2009 Jan;53(1):15-21” </li></ul>
  45. 47. <ul><li>In distal extension situations-rigid connection b/w denture base and supporting teeth account for the base movt without causing tooth or tissue damage. </li></ul><ul><li>Stress on abutment teeth and residual ridge minimised-broad coverage,harmonious occlusion,direct retainers. </li></ul>
  46. 48. <ul><li>2 types of clasp assembly-distal extensions-stress breaking design. </li></ul><ul><li>Retentive clasp arms-engage undercuts on abutment tooth-tissueward movt- min leverage to abutment. </li></ul><ul><li>Tapered,wrought wire retentive clasp-flexibility. </li></ul><ul><li>Act as stressbreaker b/w denture base and abutment tooth. </li></ul><ul><li>Another concept of stress breaking-separating action of retaining elements from denture base </li></ul>
  47. 49. <ul><li>Stress breakers effectively dissipate vertical stresses. </li></ul><ul><li>It is the rigid nature of conventional RPD that allows satisfaction of requirements of support,stability and retention. </li></ul>
  48. 50. <ul><li>Carr A B, Mc Givney G P, Brown D T, Major connector in McCraken’s Removable partial Prothodontics. 11 th ed, st louis: Mosby; 2008 </li></ul><ul><li>Stewart K L, Rudd K D, Kuebker W A, Major connector in Stewart’s Clinical Removable Partial Prosthodontics. 2 nd , Chennai; 2004 </li></ul><ul><li>Miller E L, Grasso J E, Major connector in Removable Partial Prosthodontics. 2 nd ed, Baltimore: Williams & Wilkins; 1979 </li></ul><ul><li>Development of in vivo measuring system of the pressure distribution under the denture base of removable partial denture. J Prosthodont Res. 2009 Jan;53(1):15-21 </li></ul>