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Impression materials part 1

Impression compound, Zinc oxide eugenol, Alginate

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Impression materials part 1

  1. 1. Impression materials 1
  2. 2. 2 INTRODUCTION Items to be covered 1. Definitions 2. Indications 3. Requirements 4. Classification
  3. 3. 3 Definitions  Impression: negative replica (reproduction) of the oral tissues.  Primary impression * Impression taken for the first time. * Does not register (reproduce, record) the fine details.  Secondary impression * Impression taken for the second time. * Register (reproduce, record) the fine details. * More accurate than primary impression
  4. 4. 4 Definitions  Cast (model): positive replica (reproduction) of the oral tissues.  Die: positive replica of single tooth.
  5. 5. 5 Definitions  Tray: a container that is used to hold (carry) the impression material into the patient mouth.  Stock tray * Universal tray * Ready-made * Use: make primary impression * Material: metal or plastic  Special tray * Custom tray * Use: make secondary impression * Material: usually acrylic resin
  6. 6. 6 Stock trays
  7. 7. 7 Special trays
  8. 8. 8 Indications  Any impression is poured to form a cast (primary or secondary cast).  Functions of primary cast (diagnostic cast) * Diagnosis & treatment planning * Fabrication (making) of special tray  Function of secondary cast (master cast) * Fabrication (construction) of indirect restoration, such as crown & bridge
  9. 9. 9 Pouring the impression with gypsum products → cast
  10. 10. 10 Notes Stock tray → Primary impression → Primary cast (model) → Special tray → Secondary impression (more accurate ….) → Secondary cast (more accurate ….) → Construction of crown, bridge or denture …..
  11. 11. 11 Crown Bridge
  12. 12. 12 Complete denture
  13. 13. 13 Requirements of impression materials  Acceptable odor & taste, not toxic & not irritant  Suitable working & setting times and shelf life  Low cost and easy to use (with minimum equipment)  Easy to disinfect (without distortion)
  14. 14. 14 Requirements (continued)  Accurate (record fine details): by high flow & good wetting to the oral tissues  Dimensional stability = no dimensional changes: * No expansion or contraction * No absorption or loss of water or fluids * Not release byproduct
  15. 15. 15 Requirements (continued)  Elastic: to record undercuts * Can be used with dentulous patient (having teeth) * And good elastic recovery  Flexible: to be easily removed from undercuts
  16. 16. 16 Requirements (continued)  High tear strength: to resist tearing during removal from undercuts  Compatible with gypsum products (cast material): * Not need separating medium * Not release byproducts that affect the model surface
  17. 17. 17 Classification of impression materials According to elasticity after setting Rigid (non-elastic) Elastic Impression plaster Impression wax Impression compound Zinc oxide eugenol Hydrocolloids Elastomers Alginate Agar Polysulfide Condensation silicone Addition silicone Polyether
  18. 18. 18 Classification of impression materials According to the nature of setting reaction Physical reaction (reversible) Impression plaster Impression wax Impression compound Zinc oxide eugenol Elastomers Alginate Agar Chemical reaction (irreversible)
  19. 19. 19 Impression compound
  20. 20. 20  Definition  Form  Types & uses Composition  Reaction Manipulation Properties Items to be covered
  21. 21. Thermoplastic material: * Soften by heating * Harden by cooling Non-elastic → not record undercut Used for making primary impression for edentulous patient (without teeth) 21 Definition
  22. 22. Cakes Sticks 22 Form
  23. 23. Impression compound, low fusing type 45-55°C Uses: * Primary impression for edentulous patient * Tracing (border molding) of special tray Tray compound, high fusing type 70°C Use: Tray material which is rigid enough to support other impression materials 23 Types & uses Type I Type II
  24. 24. 24 Green compound sticks
  25. 25. 25 Special trays Border molding
  26. 26. Thermopastic materials Fillers Plasticizer Coloring agent 26 Composition
  27. 27. Thermopastic materials * To give thermoplasticity, flow and cohesion. e.g. natural resins & waxes. Fillers * To give body and suitable working consistency. e.g. talc. 27 Composition (continued)
  28. 28. Plasticizer * To act as lubricants & control consistency (with fillers), e.g., stearic acid or stearin. Coloring agent * To give characteristic color, e.g., rouge 28 Composition (continued)
  29. 29. Physical reaction Reversible Thermoplastic: * Soften by heating (45-55°C) * Harden by cooling (37°C) 29 Reaction
  30. 30. The compound has low thermal conductivity, so  Soften the compound in thermostatically controlled water bath at 45°C (just above the mouth temperature) for sufficient (adequate) time  Kneading by fingers Until complete (homogenous, uniform) softening 30 Manipulation
  31. 31. Loading the perforated stock tray Insertion in the patient mouth Cooling by water spray: * To accelerate hardening * For sufficient time → to ensure complete hardening 31 Manipulation (continued)
  32. 32. 32 Compound impression
  33. 33. 33 Properties  Non-elastic  Not record fine details  Flow  Thermal conductivity  Thermal contraction * Precautions to avoid contraction  Distortion (warpage)  Compatibility with model materials
  34. 34. Not record undercuts Used only for edentulous patient (without teeth) 34 Properties Non-elastic Not record fine details Used for making primary impression
  35. 35. At 45°C, type I has higher flow than type II: Records better fine details than type II. = More accurate than type II. 35 Properties Flow
  36. 36. Impression compound is a bad thermal conductor. During softening, the outside (surface) soften first before the inside.  Softening must be done for sufficient time To ensure complete softening To avoid the internal stresses 36 Thermal conductivity Why?
  37. 37. High coefficient of thermal expansion & contraction Contraction (0.3–0.5%) occurs from the mouth temperature (37°C) to room temperature (25°C) 37 Thermal contraction
  38. 38. Cooling the impression in the patient mouth by water spray equal to room temperature Heating the set impression surface & remaking the impression Pouring the impression immediately 38 Precautions to avoid contraction
  39. 39. Causes of distortion Incomplete softening Incomplete hardening Delayed pouring of the impression 39 Distortion (warpage)
  40. 40. Compatible with model & die materials Not need separating medium To separate the impression from the cast → use warm water 40 Compatibility with model materials
  41. 41. Can be added & reused after sterilization Low cost & easy to use (ease of use) Non-toxic & non-irritant Compatible with model & die materials * Not need separating medium 41 Advantages
  42. 42. Transfer infection (non hygienic) Non-elastic → so ……. Not record fine details Dimensional changes due to: Thermal contraction Relief of internal stresses 42 Disadvantages
  43. 43. 43 Zinc oxide eugenol (ZOE)
  44. 44. 44  Definition  Uses  Form Composition  Reaction Manipulation Properties Items to be covered
  45. 45. Non-elastic Used for making secondary impression for edentulous patient (without teeth) 45 Definition
  46. 46. Final (secondary) impression for edentulous patient Wash impression over the compound Impression in old denture for relining 46 uses
  47. 47. Two pastes in tubes  Base paste: white  Catalyst paste = accelerator = reactor: red or brown 47 Forms
  48. 48. Zinc oxide (80–85%): reactive ingredient Inert oils (15–20%): * Form paste * Act as plasticizer 48 Composition Base
  49. 49. Oil of cloves or eugenol (15%): oil of cloves, which contains 75% eugenol, is preferred than eugenol, because it produces less burning sensation. Filler (16%): form paste Gum rosin & oils (65%): softened in hot water → facilitate removal of the impression from the cast MgCl2 or CaCl2: accelerator Water 49 Composition (continued) Catalyst
  50. 50. Chemical reaction: called chelation reaction Irreversible Two steps 1. Hydrolysis ZnO + H2O → Zn(OH)2 2. Formation of chelate Zn(OH)2 + 2HE (eugenol) → ZnE2 (Zinc eugenolate)+ 2H2O 50 Reaction
  51. 51. Water: * Initiate the reaction * A byproduct of the reaction 51 Reaction (continued)
  52. 52. = ↓ setting time by Increasing the catalyst Drop of water & ↑ humidity ↑ Mixing time Accelerator: zinc acetate 52 Factors affecting setting time of ZOE Accelerate the reaction by
  53. 53. = ↑ setting time by ↑ Base Cooling the glass slab Waxes & oils 53 Factors affecting setting time of ZOE (continued) Retard the reaction by
  54. 54. Two equal lengths of the base & catalyst are mixed  On a waxed paper pad or glass slab  Using a flexible stainless steel spatula  In a sweeping motion  Until a uniform (homogenous) color is obtained 54 Manipulation
  55. 55. Loading the acrylic special tray (with border tracing by green compound). Note: the tray should be dry  Because ZOE does not adhere well to wet surfaces. Paint the patient lips with Vaseline before impression  To avoid sticking (adhering) of ZOE to the lips. 55 Manipulation (continued) Why? Why?
  56. 56.  Non-toxic (but it is irritant & causes burning sensation)  High flow → can record fine details → secondary impression  High dimensional stability  Accurate  Compatible with model & die materials:  Not need separating medium  Not retard (affect) setting of gypsum 56 Properties Advantages
  57. 57. To separate the ZOE impression from the cast  Use warm water at 60°C  Gum rosin: softened in hot water → facilitate removal of the impression from the cast 57 Note
  58. 58. Non-elastic:  Not record undercuts  Used only for edentulous patient (without teeth) Eugenol may cause burning sensation (irritation)  Eugenol-free zinc oxide can be used Stick to dry skin (lips)  Paint the lips with Vaseline before impression 58 Disadvantages
  59. 59. Ethoxy benzoic acid is used instead of eugenol  To avoid burning sensation of eugenol Irreversible chemical reaction called  Saponification reaction (instead of chelation reaction) The reaction is less affected by water & humidity 59 Non-eugenol zinc oxide (eugenol-free) Why? Composition Reaction
  60. 60. Two pastes in tubes  Base: white color  Catalyst: blue color (not red or brown) 60 Non-eugenol zinc oxide (eugenol-free) Form
  61. 61. 61
  62. 62. 62
  63. 63. 63
  64. 64. 64 Hydrocolloids
  65. 65. 65  Introduction  Solution, suspension, emulsion & colloids  Hydrocolloids  Sol-gel transformation  Types of hydrocolloids: alginate & agar Items to be covered
  66. 66. 66 Solution Colloids Suspension Homogenous (one phase) Heterogenous (more than one phase) Heterogenous Particle size: 0.01-1 nm. Atoms, ions or molecules. Particle size: 1-1000 nm. Intermediate in size between those of solution & suspension. Large molecules or aggregates. Particle size: over 1000 nm. Large particles or aggregates. Often seen with naked eye. Do not separate on standing. Cannot be separated by filtration. Do not separate on standing. Cannot be separated by filtration. Particles settle out. Can be separated by filtration. Do not scatter light Scatter light (Tyndall effect) May either scatter light or be opaque Sugar in water Alginate in water Paint Sand in water
  67. 67. 67 Tyndall effect
  68. 68. The dispersed particles are intermediate in size between those of solution & suspension. 68 Colloids Emulsions Liquid in a liquid Such as oil in water
  69. 69. Colloids are called hydrocolloids when the dispersion medium is water. Used for making impression Exist in sol & gel state Inserted in the mouth in sol state, which is sufficiently fluid to record details Removed after the gel is formed, which has elastic properties 69 Hydrocolloids
  70. 70. Sol (colloidal solution) → molecules agglomerate → fibrils → network pattern → brush heap structure (gel) 70 Sol-gel transformation (gelation)
  71. 71. Primary bond between fibrils Irreversible Sol ––chemical reaction→ Gel 71 Types of hydrocolloids Alginate Agar Secondary bond between fibrils Reversible Gel ––heating→ Sol Sol ––cooling→ Gel
  72. 72. 72  Definition  Uses  Form Composition  Reaction Manipulation Properties Alginate
  73. 73. Visco-elastic impression material → can record undercut Used for making primary impression → less accurate than rubber impression Irreversibe chemical reaction (sol → gel). 73 Definition
  74. 74. Used for making primary impression  Which is used for making diagnostic (primary) casts  Functions of primary cast (diagnostic cast) * Diagnosis & treatment planning * Fabrication (making) of special tray * N.B: Not used for crown & bridge fabrication - Because it does not produce fine details. - Higher dimensional changes & lower tear strength than rubber impression materials 74 Uses Why?
  75. 75. Powder in container or individual packets  Packets are preferred, - Less chance for contamination during storage 75 Form Why?
  76. 76. Potassium or sodium alginate (soluble)  The main reactant  Reacts with calcium sulfate to form calcium alginate (insoluble) Calcium sulfate dihydrate (CaSO4.2H2O)  Source of calcium for cross-linking of alginate chains 76 Composition
  77. 77. Sodium phosphate (Na3PO4): retarder  React with calcium to delay (retard) calcium reaction (cross-linking) with alginate  According to its amount: alginate may be - Regular set (3–4 min) - Fast set (1–2 min) Potassium titanium fluoride (K.Ti.fluoride)  Gypsum accelerator 77 Composition (continued)
  78. 78. Fillers: such as diatomaceous earth or silicate powder  Strengthen the gel Glycol: make the alginate dustless (dust-free) Coloring & flavoring agents Disinfecting agent: such as chlorhexidine 78 Composition (continued)
  79. 79. Irreversible chemical reaction Called gelation reaction (sol → gel) When the powder is mixed with water, a retardation reaction occurs by reaction of calcium with phosphate (retarder). After the retarder is consumed, a gelation reaction occurs by reaction of calcium with alginate to form calcium alginate gel. 79 Reaction
  80. 80. Retardation reaction  Calcium + Phosphate (retarder)  Until the retarder is consumed Gelation reaction  Calcium + Alginate → Calcium alginate gel 80 Reaction (simplified)
  81. 81. ↑ Water temperature → accelerate the reaction  ↑ P/L ratio (within limits) → accelerate the reaction  ↑ Mixing rate → accelerate the reaction  ↓ Particle size of the powder → accelerate the reaction  ↓ Amount of retarder → accelerate the reaction  Note: - ↑: increase - ↓: decrease 81 Factors affecting the setting time (reaction)
  82. 82. Shake the alginate container The powder is mixed with water against the wall of rubber bowl until homogenous (uniform) creamy mix is obtained. Perforated tray Snap (rapid, sudden) removal Pouring immediately 82 Manipulation Why? Why? Why? Why?
  83. 83. 83 Manipulation
  84. 84. 84
  85. 85. Visco-elastic impression material → can record undercut Used for making primary impression → less accurate than rubber impression 85 Properties
  86. 86.  Dimensional changes (instability) on storage  Due to syneresis or imbibition.  Syneresis: loss of fluid exudate → contraction (shrinkage)  Imbibition: uptake of water → expansion 86 Properties (continued) Dimensional stability Why?
  87. 87.  How to reduce (decrease) dimensional changes?  Pouring the alginate impression immediately (within 10 min)  Or storing in sealed plastic bag 87 Dimensional stability (continued) Reference: Ritter AV, Boushell LW, Walter R. Sturdevant's art and science of operative dentistry. 7th ed. St. Louis, Elsevier; 2019. p. 485
  88. 88. 88 Storing in sealed plastic bag
  89. 89.  Viscoelastic  Can record undercut  Elastic recovery: 97.3%  Significance (importance)  Snap (sudden, rapid) removal of alginate impression from the mouth → ↓ permanent deformation 89 Elasticity Permanent deformation
  90. 90.  Flexible → easy to be removed from undercut 90 Flexibility Means: with low force (low stress) Will produce large elastic deformation (elastic strain)
  91. 91.  Low tear strength  How to increase tear strength?  Snap removal  ↑ Thickness of alginate impression (at least 4 mm)  Proper (correct) powder / water ratio Note: ↑ Powder / water ratio → ↑ tear strength, but this will ↑ viscosity & ↓ flow 91 Tear strength
  92. 92.  Don’t need separating medium  Affect the setting & surface of gypsum  The water content of alginate inhibits (delays, retards) the setting of gypsum surface.  Alginate is hydrophilic → absorbs water from the gypsum surface → chalky appearance.  Note: potassium sulfate (2%) is a gypsum accelerator. 92 Compatibility with gypsum
  93. 93.  Non-toxic  But inhalation of airborne particles from alginate powder can result in pulmonary hypersensitivity  Glycol coat the alginate particles → to make the alginate dustless (dust- free). 93 Biocompatibility How to avoid?
  94. 94.  Alginate is hydrophilic  Good wetting to oral tissues  Good wetting by gypsum  Imbibition (water uptake) → expansion (dimensional changes)  Cannot be electroplated 94 Hydrophilicity Advantages Disadvantages
  95. 95.  Low cost & ease of use  Can record undercut  Stock tray  Hydrophilic → good wetting to oral tissues & by gypsum 95 Advantages of alginate
  96. 96.  Dimensional changes: syneresis & imbibition  Low tear strength  Less accurate than rubber impression → primary impression  High permanent deformation  Hydrophilic → imbibition → cannot be electroplated 96 Disadvantages of alginate How to avoid? How to overcome? How to overcome?
  97. 97.  Dust-free alginate (dustless)  Chromatic alginate 97 Modified alginate
  98. 98.  Glycol → coats the alginate particles → dustless 98 Dust-free (dustless) alginate Chromatic alginate  pH indicator → change the alginate color during manipulation.  Different colors during mixing, loading the tray & insertion.
  99. 99.  Compound & alginate are primary impressions.  ZOE & rubber (elastomers) are secondary impressions. 99 Notes

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