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Dental waxes by Dr. Jagadeesh kodityala


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Dental waxes by Dr. Jagadeesh kodityala

  1. 1. P.G 3rd year Dr.Jagadeesh. K
  2. 2. Contents • Introduction • Classification • Desirable properties of waxes • Physical properties • Factors affecting dimensional changes • Other materials used for making patterns • Methods of softening wax • Waxing instruments • Wax patterns • Conclusion • References
  3. 3. INTRODUCTION • WAXES are thermoplastic materials which are normally solids at room temp. but melt, without decomposition, to form mobile liquids. • They are essentially, soft substances with poor mechanical properties. • Primarily used in dentistry to form patterns of appliances prior to casting. • Other uses: impression making, bite registration, and in processing of laboratory procedures.
  4. 4. DEFINITION A thermoplastic molding material that is solid at room temperature and when subjected to moderate temperatures becomes low viscosity liquid. Waxes are esters of fatty acid, alcohol, or hydrocarbons. They are insoluble in water but soluble in most organic solvents.
  5. 5. Dental wax • A low molecular weight ester of fatty acids derived from natural or synthetic components, such as petroleum derivatives, that soften to a plastic state at relatively low temperature. • A mixture of two or more waxes and additives used as an aid for the production of gypsum casts, productions of nonmetallic denture bases, registering jaw relations, and laboratory work. - Phillip’s science of dental materials, 12th ed
  6. 6. Waxes Pattern waxes Impression waxes Processing waxes Corrective wax Biteplate wax Soft impression wax Disclosing wax
  7. 7. Sources of wax Carnauba wax – Copernica cerifera Candelila wax – E. cerifera, E. Antisyphilitica Japan wax - Rhus sp., Toxicodendron sp. Ouricury wax - Syagrus coronata Castor wax - Castor oil
  8. 8. • Bees Wax – honey bees • Shellac wax – kerria lacca • Chinese wax – ceroplastis ceriferus
  9. 9. • Animal wax – Lanolin Spermaciti • Petrolium waxes- Paraffin wax Microcrystalline wax • Mineral wax – Ozokerite Ceresin Montan wax • Synthetic waxes – Polyethylene Polyoxyethylene glycol
  10. 10. Desirable properties of waxes • When softened, the wax should be uniform. • The color should be contrast with die material. • No flakiness or surface roughening. • Wax should burnout completely -leave no residue. • Completely rigid and dimensionally stable. • Allow careful handling-show less distortion.
  11. 11. Important properties of waxes 1. Melting range 2. Flow 3. Coefficient of thermal expansion 4. Residual stress 5. Ductility
  12. 12. Melting range • Waxes do not melt at a single temperature • Do not have a melting point, they have a melting range. • The lower limit of melting range controls the applicability. • As the number of carbon atoms increases, the density and melting temp. increase. • Paraffin wax – 500 C-700 C • Bees wax - 600 C-700 C • Carnauba wax - 650 C-900 C • Microcrystalline waxes - 650 C-900 C
  13. 13. 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.
  14. 14. Coefficient of thermal expansion • Thermal expansion is the tendency of matter to change in volume in response to a change in temperature, through heat transfer. • Linear coefficient of expansion – change in length per unit of the original length of a material when its temp. is raised by 1 k (10C). • For most solid materials, the volumetric CTE can be considered to be thrice to that of linear CTE.
  15. 15. • Waxes have very high CTE, particularly around the melting range, and very high residual stress; they have the highest CTE as compared to all other materials used in dentistry. • CTE of typical pattern wax is 323 x 10-6/0C but that of dental porcelain is 20 times less 14 x 10-6/0C. • Small changes in temp. can cause a sufficient change in dimension to make the pattern inaccurate.
  16. 16. Thermal conductivity • The thermal conductivity of the waxes is low, and sufficient time must be allowed both to heat them uniformly throughout and to cool them to body or room temp.
  17. 17. Mechanical properties • Modulus of elasticity, proportional limit & compressive strength are less for waxes. • All these factors depend on temperature.
  18. 18. Flow • Viscoelastic properties. • Slippage of molecules over each other. • Flow of waxes is desirable as a part of molding process but becomes undesirable after the wax pattern or impression has been made. • Mineral waxes – Paraffin, ceresin – 50% flow at mouth temp. • Yellow Bees wax – No flow at 32°c. 70% flow at 40°c.
  19. 19. Residual stress • It is the stress remaining in a wax as a result of manipulation during heating, cooling, bending, carving or other manipulation. • The release of residual stress at higher temp. causes an irreversible deformation that can destroy the fit of a wax pattern. • The warpage is due to the residual stresses which result from the heating of wax specimens formed under compression or tension.
  20. 20. • It will result in dimensional inaccuracy and is undesirable. The longer the wax pattern is left before being invested, the greater the distortion that must be result. • Crystalline waxes develop more internal stresses when manipulated below the transition temp. • Extent of change in thermal expansion depends upon • Magnitude of residual stresses • Time & • Temp. of storage specimen.
  21. 21. Minimizing the warpage • Use higher temp. at the time of formation – less force to shape – less residual stresses. • Soften the wax uniformly at 500 C for 15 min. • Warmed carving instruments & die. • Adding wax to die in small increments.
  22. 22. Ductility • It is the ability of a material to be plastically deformed; it is indicated by plastic strain. • The ductility of a material represents its ability to be drawn into wire under a force of tension. • It is a property related to the workability of a material in the mouth (It is related to burnishability of margins of pattern or casting). • Highly refined waxes are quite brittle. • Wide melting ranges – greater ductility. eg : Microcrystalline mineral waxes.
  23. 23. Factors affecting dimensional changes 1. Cooling the wax under pressure increases expansion. 2. Retention of gas or solvent which may often expand within the wax on reheating, causing pronounced expansion. 3. Temperature of the die. 4. Method used for applying pressure to the wax as it solidifies.
  24. 24. INLAY CASTING WAX • A specialized dental wax that can be applied to dies to form direct or indirect patterns for the lost wax technique, which is used for the casting of meals or hot pressing ceramics. • ADA specification no: 4 • Blue, green, ivory, or deep purple colors. • Pellets and sticks • Type I – Medium wax – direct pattern • Type II – Soft wax – indirect technique
  25. 25. Composition Ingredient Percentage Base Paraffin (and microcrystalline) wax 60 Modifier Carnauba (and candelila) wax Ceresin Bees wax Gum dammar 25 10 5 1 colorants _ <1
  26. 26. Paraffin wax Paraffin that is used for Type I waxes has higher Melting point than the Paraffin used for type II waxes
  27. 27. • Paraffin wax is likely to flake when it is trimmed, and it does not produce a smooth, glossy surface, which is a desirable requisite for an inlay wax. Thus, other waxes and natural resins must be added as modifying agents.
  28. 28. Gum dammar • Gum dammar, or dammar resin, is a natural resin. It is added to the paraffin to improve the smoothness in molding and to render it more resistant to cracking and flaking. It also increases the toughness of the wax and enhances the smoothness and luster of the surface.
  29. 29. Carnauba wax • This wax is very hard, and it has a relatively high melting point and it has an agreeable odor. It is combined with the paraffin to decrease flow at mouth temperature. Carnauba wax contributes greater glossiness to the wax surface than dammar resin.
  30. 30. Candelila wax • Candelilla wax can also be added partially or entirely to replace carnauba wax. Candelilla wax provides the same general qualities as carnauba wax but its melting point is lower and it is not as hard as carnauba wax.
  31. 31. ceresin • Ceresin may replace part of the paraffin to modify the toughness and carving characteristics of the wax. • Ceresin is typically a white wax extracted from ozokerite, a waxy mineral mixture of hydrocarbons that is colorless or white when pure, but it has a somewhat unpleasant odor.
  32. 32. Ideal requirements • It must be able to closely adapt to the prepared portions • Should have low CTE • Must have good cohesion, but should not adhere to the cavity walls. • Must permit detailed carving without flaking or chipping. • Must not leave any residue when the wax is eliminated from the mold (max. of 0.1% residue) • It should harden at oral temp., remain plastic at temp. slightly above oral temp.
  33. 33. • At oral temp., type I inlay wax must have essentially limited flow to minimize the possibility of distortion of the pattern during removal from the tooth cavity. • Its color should contrast with the colors of teeth and oral tissues to facilitate carving.
  34. 34. Properties • Thermal properties • CTE : The average linear CTE 350 X 10-6 / 0 C . • Paraffin has the highest CTE, addition of modifier waxes such as bees wax and carnauba wax decreases the CTE of the inlay wax. • A maximum of 0.6% linear change in dimension when they are heated from 250 C to 370 C is permitted for type I waxes. • They may contract as much as 0.35% when it is cooled from 370 C to 250 C.
  35. 35. Physical properties • Good homogeneity • Contact angle • FLOW : the maximum permitted flow (acc. to ADA sp. No 4) for type I inlay wax should be 1% at 370 C (oral temp.) • The flow is restricted for type I wax, since it is used for fabrication of direct wax pattern. This permits carving and removal of the pattern from the prepared cavity at oral temp. with out distortion.
  36. 36. • Ductility • Residual stresses: most important cause of wax distortion • This can be minimized by working the wax at high temp. or by preheating the dies. • In order to maximize flow and minimize the residual stresses, molding of wax should be carried out slightly above the melting point or at least above the transitional temp. • CHEMICAL PROPERTIES • Oxidation: no residue is left.
  37. 37. Manipulation • Bunsen burner • In order to achieve even heating, the wax should be held in the warm rising air above the flame and not in the flame itself. • If the surface becomes shiny it indicates that the wax is becoming too hot and the outer layers are begining to melt.
  38. 38. • Warm water Advantages: More regular softening Disadvantages: May leach out some constituents Small quantities of water may become incorporated causing an alteration in the properties.
  39. 39. • Infra red lamp • 250 W • Method of softening used in standardization testing of waxes • Distance of the wax from the lamp must be carefully controlled in order to cause softening but not melting.
  40. 40. • Wax annealer • Ideal method for softening wax • Thermostatically controlled oven - constant temp. • Just above softening point, ready for use. • The annealer is most useful for inlay waxes.
  41. 41. Waxing instruments
  42. 42. • Volland 1922 – frahams 90° carver & wards carver • G.V.Black 1954 – blunt end, right angle burnisher semisharp ward carver sheperd’s crook burnishing instrument no 23
  43. 43. Wax adders • #7 Spatula • PKT #1 (Larger) • PKT #2 (Smaller)
  44. 44. Wax Carvers • ½ Hollenback • PKT #3 • Discoid Cleoid • Tanner Carver • #3 Hollenback Carver
  45. 45. PKT Instruments • Dr.Peter K Thomas introduced hand instruments for waxing procedures. • Among the popular instruments are PKT’s from No 1-5. • No 1 and 2 – wax addition instruments • No 3 - burnisher for refining occlusal anatomy • No 4 and 5 – wax carvers
  46. 46. • PKT No 1 : large increments of wax • PKT No 2 : small additions of wax • PKT No 3 : burnish and carve occlusal surface • PKT No 4 : designed as an all purpose carver • PKT No 5 : to refine triangular ridges and occlusal grooves
  47. 47. Electronic PKT
  48. 48. Discoid Cleoid • Discoid (rounded) – Concave surfaces • Cleoid (pointed) - grooves
  49. 49. Wax is added by heating the instrument in the bunsen flame, touching it to the wax, and quickly reheating its shank in the flame. Wax flow away from the hottest part of the instrument.
  50. 50. so that if the shank is heated, a bead of wax will flow off the tip, However if the tip is heated, the wax will flow up the shank of the instrument (to the considerable annoyance of inexperienced operators).
  51. 51. Tips for carving / usage of instrument 1) Wax carvers should be kept sharp and never heated. 2) When carving wax light pressure should be used to obtain the desired smooth surface. 3) Burnishing is an alternative to carving for obtaining a smooth wax pattern of the desired contour. 4) Digital manipulation-when working unimanually all 10fingers must be coordinated to perform their respective tasks-less force is transmitted from finger tips.
  52. 52. Wax pattern There are two methods of obtaining wax counterparts of prepared cavities: 1. Direct technique a) Open technique b) Closed technique 2. Indirect technique
  53. 53. Direct technique • Wax is inserted into the cavity and carved in the mouth to the form of the final restoration. • Advantages: • The pattern is carved on the tooth and not on a model; • Possible inaccuracies in many stages of indirect technique are avoided. • Less laboratory work comparatively.
  54. 54. • Disadvantages: • Great skill & patience to carve patterns in the mouth. • Stereoscopic judgement is lost. • Pattern in a compound cavity without a supporting tooth – pattern will move. • Discrepancies at cervical margin – difficult to carve. • If the inlay fails to cast – multiple visits. • More chair side time.
  55. 55. Direct open technique – Volland’s technique (1922)
  56. 56. Direct closed technique – Sturrock’s technique (1953)
  57. 57. Direct wax patterns
  58. 58. Sprue positioning & angulation
  59. 59. CASTING WAX • Composition: ingredients similar to those of inlay wax • Max. Flow at 350 C is 10% • Min. Flow at 380C is 60% • Vaporizes at 5000C, leaving no residue. • Used for the pattern of metallic frame work removable cast partial dentures.
  60. 60. Baseplate wax or modelling wax • Composition : paraffin, ceresin, beeswax, carnauba wax, and coloring matter. • Type I: Soft wax – building contours and veneers • Type II: Medium wax – fabrication of patterns in the mouth – temperate conditions. • Type III: Hard wax - fabrication of patterns in the mouth – hot weather conditions.
  61. 61. • Uses • Making occlusion rims and registering the vertical dimension • Holding artificial teeth to base plates • Extension of the impression tray • Patterns for orthodontic appliances • Spacer in custom tray for complete dentures • Checking the occlusal clearance after crown preparation
  62. 62. Sticky wax • It is composed of yellow bees wax, paraffin, and rosin. • It holds the broken pieces of a denture together and assembles the components of FPDs and wrought partial dentures in preparation for soldering. • Disclosing wax • Identify unequal pressure points in a denture – pressure indicator wax.
  63. 63. • Boxing wax • Consists of low melting point hydrocarbons and bees wax, fillers are added to increase the rigidity. • Used to form a box or a wall around impressions, this gives more uniform cast. • Low fusing impression wax • It can be made to flow when it is subjected to controlled pressure. Hence it, can be used to reline or rebase dentures
  64. 64. Bite registration wax • Uses: • Registration of bite both in mouth & dies • To accurately articulate certain models of opposing quadrants
  65. 65. Conclusion Few procedures in restorative dentistry like forming an inlay pattern, registration of occlusal bite relationships, boxing an impression & other processing steps, each requires a specially formulated wax. These examples display how the tasks these waxes perform & therefore their properties, vary greatly. “Accuracy is a requisite for successful restoration”.
  66. 66. References • Art & science of operative dentistry Sturdevent 4th ed • Principles & practice of operative dentistry Charbeneau 3rd ed • Restorative dental materials Craig 11th ed • Science of dental materials Phillips12th ed • Materials used in dentistry S.Mahalaxmi 1st ed