Dental Waxes

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Dental Waxes

  1. 1. DENTAL WAXES IT IS RECOMMENDED TO FOLLOW McCABE APPLIED DENTAL MATERIALS ALONG WITH THIS LECTURE PERSENTATION REFERENCES FOR THIS LECTURE: RESTORATIVE DENTAL MATERIALS, CRAIG NOTES ON DENTAL MATERIALS, COMBE’S DENTAL MATERIALS, PHILLIPS
  2. 2. DEFINITION Waxes are thermoplastic materials which are solids at room temperature but melt without decomposition to form mobile liquids* *Applied Dental Materials, McCabe
  3. 3. CLASSIFICATION OF DENTAL WAXES  According to use/application: Restorative Dental Materials, Craig
  4. 4. COMPONENTS OF DENTAL WAXES Restorative Dental Materials, Craig
  5. 5. Type Example Source Structure Properties a. Mineral Paraffin wax Distillation of crude petroleum Straight chain hydrocarbon, Polycrystalline Brittle at ambient temperature Microcrystalline / ceresin Distillation of crude petroleum Branched chain hydrocarbon, polycrystalline Less brittle than paraffin due to their oil content b. Insect Bees wax Honeycombs Less crystalline than paraffin wax, more amorphous When with paraffin wax: -at room temp. makes it less brittle -at high temp (e.g. mouth temp) reduces the flow of wax c. Vegetable Carnuaba wax South America palm tree - Hard, lustrous, tough wax. Blended with paraffin to harden it and raise it’s solid -solid transition temperature Candella wax Plants - Same as above Resins and gums Trees - Used to add adhesive qualities to wax
  6. 6. PROPERTIES OF DENTAL WAXES THERMAL PROPERTIES: 1. Solid-Solid transition temperature: (Tg) Temperature at which a sharp increase in coefficient of thermal expansion occurs indicating increased molecular mobility.* Also called softening temperature or glass transition temperature.  In waxes, at this temperature, transition from a stable crystal lattice (orthorhombic) to hexagonal form occurs which is present below the melting point of wax and thus it allows the wax to be manipulated easily without flaking or tearing. Wax is soft (not melted) at this temperature.. * Dental materials, Phillips
  7. 7. 2. Coefficient of thermal expansion: HIGHER COTE than any other dental material.. Value: 350x10-6/˚C This will cause the wax to expand n heating and appreciably shrink on cooling from solidification temp to room temp. On heating, may expand 0.7% when temp is increased 20 ˚C On cooling from 37˚C to 25 ˚C , a linear shrinkage of 0.35% occurs May cause distortion of wax patterns
  8. 8. 3. Melting range: Because waxes may contain several types of molecules, each having a range of molecular weights, they have melting ranges rather than melting points Paraffin: 40-70 ˚C Microcrystalline: 60-90 ˚C Bees wax: 65-70 ˚C 4. Thermal conductivity: Low thermal conductivity
  9. 9. MECHANICAL PROPERTIES Low compressive strength Low modulus of elasticity RHEOLOGICAL PROPERTIES 1. Flow: The property of flow results from the slippage of molecules over each other. Waxes show deformation when subjected to constant load for a period of time. Amount of flow depends upon: 1. temperature of the wax 2. the force bringing about the deformation, and 3. the time the force is applied Waxes will have a low flow below Tg temp. Flow greatly increases as the melting point of the wax is approached
  10. 10. It is important for inlay wax that is to be used in a DIRECT technique to have: 1. A large flow about 5˚C above mouth temperature so that good details of cavity can be attained 2. A negligible flow at 37 ˚C so that no distortion occurs upon removal of wax pattern from oral cavity INTERNAL STRESSES Waxes have low thermal conductivity making it difficult to achieve uniform heating. If a wax is adapted to shape without adequate heating to above Tg temperature, considerable stresses will develop in the wax. If then the wax is warmed, relief of stresses will occur resulting in distortion or WARPAGE of wax pattern. Also warpage occurs b/c waxes have high C.O.T.E
  11. 11. MODELLING WAX  A type of pattern wax  Pink Color  Available in sheet form USES: Making wax pattern of complete and partial dentures Making wax pattern of orthodontic appliances Making occlusal rims for recording maxilla-mandibular (jaw) relation COMPOSITION: Paraffin wax: 70-80% Bees wax: 12% Carnuaba wax: 2.5% Resins: 3% Synthetic waxes: 2.5% METLING RANGE: 44 ˚C-62 ˚C
  12. 12. TYPES For more images, click: http://ourdentalmaterials.webs.com/apps/photos/album?albumid=15488889
  13. 13. INLAY WAX  Type of pattern wax  Various colors (Blue, green, purple)  Available in sticks, cakes, blocks USES: Preparation of wax pattern for cast metal restorations like inlays, onlays, crowns, bridges COMPOSITION: Paraffin wax: 60% Carnuaba wax: 20% Ceresin wax: 10% Bees wax: 5% Gum Dammar: 5% TYPES: Type I (soft) For indirect technique Type II (Hard) For direct technique For more images, click: http://ourdentalmaterials.webs.com/apps/photos/album?albumid=15488889
  14. 14. CASTING WAX  The pattern for the metallic framework of removable partial dentures and other similar structures is fabricated from casting waxes.  These waxes are available in the form of sheets, usually of 28- and 30-gauge (0.40 and 0.32 mm) thickness, ready-made shapes, and in bulk  For more images, click: http://ourdentalmaterials.webs.com/apps/photos/album?albumid=15488889
  15. 15. BOXING WAX  A type of processing wax  Available in thin sheet and sticks  Mouldable at room temp  To form a plaster or stone cast from an impression of the edentulous arch, first a wax box must be formed around the impression, into which the freshly mixed plaster or stone is poured and vibrated.  This boxing procedure is also necessary for some other types of impressions.  The boxing operation usually consists of first adapting a long, narrow stick or strip of wax around the impression below its peripheral height, followed by a wide strip of wax, producing a form around the entire impression,
  16. 16. Sticky wax  A type of processing wax  Adhesive and brittle at room temp  Bright yellow/orange sticks USES: used to assemble metallic or resin pieces in a fixed temporary position during soldering or repair procedures MELTING RANGE: 60-65˚C COMPOSITION Yellow bees wax: 60% Resin: 17% Gum dammar: 17% This wax doesnot flow at room temperature
  17. 17. Utility wax USES:  a standard perforated tray for use with hydrocolloids may easily be brought to a more desirable contour by utility wax, This is done to prevent a sag and distortion of the impression material.  May be used on the lingual portion of a bridge pontic to stabilize it while a labial plaster splint is poured The utility wax is usually supplied in both stick and sheet form in dark red or orange color
  18. 18. Desirable Properties Modelling wax:  Easy to mould when softened and NOT tear or flake  Easy to carve  Capable of being melted and solidified a number of times without change in properties  No residue to be left after lost wax technique Inlay wax  Should have low thermal contraction  Correct flow properties  Good color contrast with oral tissues  Easy to carve without chipping  Burn out of mould without any residue  Should fracture rather than deform upon removal from cavity in case of an undercut
  19. 19. Methods of softening a wax  Water Bath  Flame of Bunsen burner  Infrared lamp  Wax annealer
  20. 20.  Direct technique: Wax pattern is made directly in the oral cavity  Indirect technique: Wax pattern is made on a cast/die in lab outside the oral cavity
  21. 21. THANKS !  For more on dental materials, Visit: ourdentalmaterials.webs.com

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