Impression materials 2


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Applied Dental Material
Second Year

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Impression materials 2

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  2. 2. Non-elastic Impression Materials Definition: They are impression materials which fracture or distort upon removal from the undercut area after setting. They can’t record the undercut area.  Better to use them in completely edentulous patients.  Types: 1. Impression wax.[Historical] 2. Impression compound. 3. Plaster. 4. Zinc oxide & eugenol. 2
  3. 3. Impression Compound Supplied form: -Sheets -Cakes -Sticks -Cones  3
  4. 4. Impression Compound Types: Type I Low fusing compound [soften at5060ºC] -1ry impression +Stock tray -Single impression + Copper band Type II High fusing compound [soften at70ºC] Tray material to hold 2ndry impression material. Peripheral seal 4
  5. 5. Impression Compound Composition: 1.Thermoplastic waxes & resins Thermoplastic polymers 2.Fillers body. 3.Gum adhesive to the tray. 4. Plasticizers. 5. Pigments.  Setting reaction: Being thermoplastic, it sets by physical setting reaction.[Reversible] Impression compound[Hard] ~45ºC Impression compound [Soft]  5
  6. 6. Impression Compound Manipulation: 1.As impression compound is of low thermal conductivity, [Type of bonding] adequate time should be given for uniform heating Flow during impression taking.   Soaking in warm water-bath .[Sheets or cakes]  Over a flame.[Sticks]  Dry kneading with fingers. 6
  7. 7. Impression Materials Manipulation:  Application as:  1ry impression material + stock tray. Single impression + copper band. Peripheral seal. Tray material for 2ndry impression. 2. As impression compound is of low thermal conductivity, adequate time should be given for uniform cooling. Distortion on removal from the mouth. 7
  8. 8. Impression Compound Manipulation: 1.Kneading 3.Insertion into completely edentulous patient 2.Filling the stock tray 4.Lower impression after removal 8
  9. 9. Impression Compound  1. 2. 3. Properties: Viscous material Low flow.[Mucocompressive technique] .·.It can not record the fine details. High coefficient of thermal expansion & contraction [Due to weak intermolecular 2ry bonds] Contraction during cooling from mouth-to room temperature 0.3-0.4%. Rigid material: .·.It is used only in minimum undercut.[Completely edentulous patient] 4. Self adhesive to the tray (has gum). 9
  10. 10. Impression Compound  4. 5. 7. Properties: Non-elastic on removal from undercut distortion. Not dimensional stable during storage due to release of internal stresses Time + Temperature distortion. .·. Immediate pouring of the model is recommended. Compatible with the model material: a. The gypsum mix can adapt & fill the impression. b. No separating medium is required. c. Being thermoplastic ,the assembly [Tray + impression + model] is immersed in warm water-bath to soften the impression compound for easy separation from the model. d. The single impression can be copper electroplated. 10
  11. 11. Zinc Oxide & Eugenol ZOE  Supplied form: Two pastes of contrast colors in metallic collapsible tubes. 11
  12. 12. Zinc Oxide & Eugenol Composition: Base paste:   Zinc oxide. Inert oil Plasticizers. Retarders. Catalyst paste: Eugenol or oil of cloves.  Fillers.  Gum.  Accelerators MgCl2. Moisture  12
  13. 13. Zinc Oxide & Eugenol  1. 2. Types: Eugenol free impression material for sensitive patients: Other type of oil of cloves instead of eugenol. Regarding setting time: [According to the amount of accelerators & retarders] Type I Hard S.T. 10 minutes. Type II Soft S.T.15 minutes. 13
  14. 14. Zinc Oxide & Eugenol Setting reaction:  It is acid base reaction. Zinc oxide + water  Zinc hydroxide +2 Eugenol [ZO+2Eugenol Zinc hydroxide Zinc eugenolate Chelate [Salt]+H2O Zinc Eugenolate] 14
  15. 15. Zinc Oxide & Eugenol Setting reaction:  Chelation reaction:  It is the attachment of molecule or ion to metal ion at more than one point. The term Chelation is derived from the Greek word meaning crab’s claw indicating2 projecting attachments. A central zinc atom is held by 2 adjacent eugenol. 15
  16. 16. Zinc Oxide & Eugenol    1. 2. 3.  Manipulation: Armamentarium: - Oil resistant paper pad or glass slab & Stainless Steel spatula. - Special tray. Steps: Two equal lengths of the two pastes. Mix until homogeneous mix without streaks is obtained. Factors affecting setting time: High temperature & humidity: accelerate the setting reaction. Cool glass slab & spatula: retard the setting reaction. Application: 2ndry impression for completely edentulous patient + Special tray. 16
  17. 17. Zinc Oxide & Eugenol  Manipulation: 1 2 3 4 17
  18. 18. Zinc Oxide & Eugenol  1. 2. 3. 4. 5. 6. 7. 8. Properties: High flow Record the fine details. Slight contraction during setting.[0.1%] Rigid Use in minimum undercut. [completely edentulous patient] Self adhesive to the tray. Non-elastic Can’t record the undercut. Distortion on removal. Can be disinfected. Dimensional stable during storage. Compatibility with model materials: a. The gypsum mix can adapt & fill the impression. b. No separating medium is required. c. Immerse the assembly in warm water-bath for easy separation. d. Can not be electroplated. 18
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  20. 20. Elastic Impression Materials  Definition: Elastic impression materials are able to record the undercut area in the dental arch on removal from the patient’s mouth. They are able after setting to compress at the undercut area facilitating their removal from the patient’s mouth. This is known as flexibility. Then they return back to the original recorded dimensions. This is known as elasticity. But these materials are not purely elastic, they are viscoelastic. 20
  21. 21. Elastic Impression Materials What is viscoelasticity? Viscoelasticity is a strain time relationship. It is a combination of : Elastic • On stress application :Immediate strain , which remains constant during stress application. • On stress removal: Immediate recovery. Anelastic • On stress application: Gradual increasing strain during stress application.. • On stress removal: Gradual recovery till reaching zero. Viscous • On stress application: Gradual increasing strain during stress application. • On stress removal: No recovery Permanent strain. 21
  22. 22. Elastic Impression Materials Strain Permanent deformation Time Strain rate sensitive material Rate = Quickly Time Permanent Deformation Rate = Slowly Time Permanent Deformation 22
  23. 23. Elastic Impression Materials       1. 2. What is the influence of viscoelasticity on the impression material? Don’t exert pressure on the tray after insertion. Don’t move the tray. Rapid snap removal of the impression in a direction as nearly // as possible to the long axes of the teeth. - Permanent deformation. Tear strength. Time is required to allow for the gradual recovery of the anelastic recovery. Types: Hydrocolloids.[Aqueous elastic impression materials] Rubbers [Elastomers][ Non aqueous elastic impression materials] 23
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  25. 25. Hydrocolloids[Aqueous Elastic Impression Materials]    Definition: Hydrocolloids are considered type of 2 phase system. -Dispersed phase [Solute] & Dispersion medium.[Solvent] Water Hydrocolloids Difference between : 25
  26. 26. Hydrocolloids [Aqueous Elastic Impression Materials]   States of hydrocolloids: Sol [Viscous liquid] Gelation Gel [Jelly like material] Types of hydrocolloids: Reduction in temperature reaction Agar [Reversible hydrocolloid] Chemical Alginate [Irreversible hydrocolloid] Both are introduced in the sol form intra-orally. They are removed in the gel form from the patient’s mouth. 26
  27. 27. Hydrocolloids[Aqueous Elastic Impression Materials]  Structure of hydrocolloid gel: Gelation occurs by the agglomeration of the dispersed phase [Solute] to form fibrils in a network pattern enclosing water in-between.[Brush heap structure] This is accompanied by slight shrinkage. Filler Fibrils H2O 27
  28. 28. Hydrocolloids [Aqueous Elastic Impression Materials]  1. 2. 3.  Factors affecting gel strength: Concentration of fibrils. Concentration of fillers. Temperature. N.B. Hydrocolloids are of poor tear strength. .·. - Use in thick section.[4-6mm] - Rapid snap removal. 28
  29. 29. Hydrocolloids [Aqueous Elastic Impression Materials]  Dimensional stability:  Being hydrocolloid Dry condition Wet condition Loss of water SYNERSIS Gain of water IMBIBITION Shrinkage Expansion Poor dimensional stability 29
  30. 30. Agar[Reversible] Supplied form:[Gel] 1. Sealed container. 2. Metallic collapsible tubes. [ High viscosity Flow] 3. Syringe material.[ Low viscosity Flow] It is packaged -In plastic or glass cartridges that fit a syringe. - Preloaded syringe.  30
  31. 31. Agar[Reversible] Composition: The gel is composed of:  Agar 12% Dispersed phase.[Natural polymer]  Water 8o% Dispersion medium. Viscosity.  Borax Filler to control Strength  but acts as retarder for the setting of gypsum model.  Potassium sulfate Accelerator for the setting of gypsum model. 31
  32. 32. Agar[Reversible]    Gelation reaction: It is a physical reaction.[Reversible] Sol 70 - 100ºC Gel. 37 -45ºC Hysteresis: It is the temperature lag between the liquefaction & gelation temperature, otherwise - Gelation will be rapid. - There will be thermal injury to the patient’s tissues. 32
  33. 33. Agar[Reversible] Manipulation:  Agar needs special armamentarium.  1.Heating & Conditioning Bath: 1st Compartment:[Boiling] Gel Sol. 2nd Compartment:[Storage] Store in the sol state. 3rd Compartment:[Tempering] to avoid thermal injury of the patient. 33
  34. 34. Agar[Reversible]  2. Manipulation: Use of water cooling system tray with means of retention. [Looped wire] Avoid – 3. ◦ ◦ Exerting pressure on the tray after insertion. ◦  Iced water Moving the tray during gelation. Application as Concentration of stresses. -Full & quadrant impression for partially or completely edentulous patients. - Duplication material. 34
  35. 35. Alginate[Irreversible]  Supplied form: Powder in -Bulk container. -Preweighed package for individual impression.  N.B. Preweighed package is preferable than large container, because alginate is very sensitive to storage temperature & moisture contamination.[Poor shelf life]  Precautions during storage: 1. Stock only for 1 year. 2. Store in cool dry place. 35
  36. 36. Alginate[Irreversible] Composition : Action:  Sodium or Potassium alginate    12% Calcium sulfate dihydrate 12% Soluble salt.[Natural polymer]  Trisodium phosphate 2% Filler  Fluoride  Glycol Chemical indicators   To release Ca++ to react with alginate. [Reactor]  Retarder . Viscosity  To control Strength  Accelerator for the setting of gypsum model.  Decrease dust formation.  To indicate the pH changes during manipulation. 36
  37. 37. Alginate[Irreversible]  Gelation reaction: It occurs by chemical reaction.[Irreversible] It occurs in 2 steps: - Retardation reaction:[To prolong the working time] Trisodium phosphate + Calcium sulphate dihydrate +H2O Calcium phosphate + Sodium sulphate. - Gelation reaction: Potassium alginate + Calcium sulphate dihydrate +H2O Calcium alginate [gel] + Potassium sulphate 37
  38. 38. Alginate[Irreversible]  The gel structure: The final structure sodium alginate cross-linked with calcium ions.  Types: According to the amount of Trisodium phosphate [Retarder] -Regular set -Fast set Cross-linking of Sodium alginate
  39. 39. Alginate[Irreversible]    1. 2. 3. 4. Manipulation: Armamentarium: -Rubber bowl & stiff wide bladed Stainless Steel spatula. - Perforated stock tray for retention. Steps: Proportioning for powder & water. Vigorous mixing against the sides of the rubber bowl [Sol] Mixing time: 1 minute [Regular set] 45 seconds [Fast set] Gelation time: 1.5-5 minutes from the start of the mix till the material looses tackiness.[Sol Gel] Avoid -Iced water for mixing. -Exerting pressure on the tray after mixing. -Moving the tray during gelation. 39
  40. 40. Alginate [Irreversible] Manipulation:  The pH changes during gelation 40
  41. 41. Alginate [Irreversible] Manipulation:  Application: Alginate is the most frequently used impression material: 1. Easy to use & to mix. 2. Does not require special equipment. 3. Fast setting. 4. Acceptable by the patient. 5. Low price.  41
  42. 42. Agar & Alginate       Properties: High flow, since the dispersion medium is water. .·. Excellent in recording fine details. Slight shrinkage during gelation due to agglomeration of the dispersed phase. Flexible. Agar< Alginate[most flexible elastic impression material] Not adhesive to the tray. Need for mechanical retention. e.g. Perforations. Viscoelastic. Record the undercut. .·. No torque or twist during removal of the impression. Rapid snap removal Permanent deformation [Agar<Alginate] Allow for gradual recovery before pouring the model. 42
  43. 43. Agar & Alginate     Properties: Low tear strength. .·. –Use thick section. [4-6mm] - Rapid snap removal. Can be disinfected only by spraying . During storage they are subjected to synersis & imbibition. .·.- Pour the model as soon as possible. - Keep the impression in a humidor .[100%relative humidity] - Wrap the impression in wet paper towel. 43
  44. 44. Agar & Alginate   1. 2. 3. 4. Properties: Compatibility with model materials: Being hydrophilic , the gypsum model can be poured without air pockets. No need for separating medium. .·. Easy separation if the impression is not left overnight. Retarding effect on the model surface Chalky soft surface. Therefore an accelerator for the setting of the gypsum model is included in the material. Can not be electroplated. 44