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denture base considerations



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