topic 11 Impression Materials final lectutre.pptx

Impression

1. Impression Impression Tray Impression Materials

2. Important Terms Hydrophilic: Strong affinity for water. Hydrophobic: Aversion to water. Setting Time: The time from the start of mixing until the material is firm enough to resist permanent deformation. Working Time: The time from the start of mixing until the impression is fully seated without any distortion. Syneresis : Contraction through loss of water. Imbibition: Expansion through water intake. Sol state: Molecules or aggregates of molecules dispersed in a liquid medium. Gel state: Formation of jelly like mass, when the suspended particles combine with a liquid vehicle. Solid state Gel state Gelation Temperature Liquefaction Temperature

3. Important Terms Addition reaction: A polymerization reaction in which each polymer chain grows to a maximum length in sequence and no reaction by-product is formed. Condensation reaction: A polymerization process in which a polymer chain grows simultaneously and a reaction by-product is formed.

4. Important Terms Elastic material: Elasticity is the ability of a material to return to its original size and shape on the removal of external forces and such a material is called an elastic material. Nonelastic /rigid material: The materials that do not return back to its original size and shape on the removal of external forces is called a nonelastic / rigid material.

5. INELASTIC Rigid Cannot be used with undercuts For edentulous or bite registration ELASTIC Flexible & “rubbery” Used with undercuts Generally used today Two subcategories: Hydrocolloids (Aqueous) Elastomers

6. Viscoelasticity Materials showing combination of viscous & elastic properties are called as viscoelastic . It can be explained by models: Spring Dashpot Maxwell (combination) Dental applications: Polymers like soft relining materials & denture base polymers exhibit viscoelastic behaviour Elastomeric impression materials agar-agar; alginate Creep of dental amalgam.

7. Viscoelasticity of Elastomers and Alginates A viscoelastic material has following characteristics If the stress is held constant the strain increases with time. If the strain is constant the stress decreases with time. The effective stiffness depends on the rate of application of the load. The faster the impression is removed i.e. stress is applied faster; lesser is the distortion. Permanent deformation is less if the set impression is removed from the mouth quickly (snapping action).

8. Viscoelasticity

9. Introduction An impression is the negative replica / reproduction of the oro - dental structures. The materials used to obtain the impression of the tooth structure and / or the surrounding oral tissues are called as impression materials ( Auxillary dental material). The impression material can be used to produce replicas of both intra-oral and extra-oral tissues.

10. Impression Impression Tray Image source: Steve Bayne, University of Michigan, 2008 Ideal properties of Impression Materials Biological properties Chemical properties Physical and Mechanical properties Other properties

11. Ideal properties of Impression Materials Biological Properties: No adverse effect on the health of the operator or patient. Non toxic. Non irritant.

12. Ideal properties of Impression Materials Chemical Properties: Should not react with other materials. e.g. model and die. Should not react with other materials during setting process. Should form bond with impression tray. Capable of being disinfected. Should not produce any by-product.

13. Ideal properties of Impression Materials Physical and Mechanical Properties: Thixotropic behavior ( the time-dependent pseudoplastic flow of polymers that is characterized by the gradual decrease of viscosity under a constant applied shear rate). Should have enough time for mixing, loading of tray and setting in patients mouth. Elastic enough to be withdrawn from the undercut areas without deterioration. Should not shrink (0.1% - 0.27%). Should have acceptable discrepancy (20 – 50µm). Should not deform permanently. Tear resistance. Neutral odor and taste. Acceptable color.

14. Ideal properties of Impression Materials Other properties: Radiopaque. Ease of handling. Require minimum equipment. Cost effective.

15. Impression Trays Three different types Stock trays Disposable trays Special trays

16. Impression Trays Stock Trays: Standard sizes. Can be smooth or perforated. Reusable. Made up either of plastic or metal.

17. Impression Trays Disposable trays: For single use only. Mostly perforated. Made up of polymeric materials. E.g. Nylon.

18. Impression Trays Special Trays: Also called as custom trays. Disposable. Made from self cure acrylic.

19. Impression Trays Difference in upper and lower Impression Trays

20. Classification of Impression Materials Classification can be on the basis of: Impression Techniques Setting properties / Elastic behavior Viscosity

21. Classification of Impression Materials Classification on the basis of Impression Techniques: Mucostatic and Mucocompressive Impression Technique

22. Classification of Impression Materials Mucostatic Impression Technique “It is the technique in which the impression material is fluid enough to flow and does not displaces the oral tissues.” It includes: Impression Plaster Agar Agar Impression material ZnO Eugenol Impression pastes Light body Elastomers

23. Classification of Impression Materials Mucocompressive Impression Technique “It is the technique in which the impression material is viscous and are able to compress the oral tissues on insertion in the patients mouth”. It includes: Impression Compound Viscous Alginate R,H,P consistencies of Elastomers

24. Classification of Impression Materials Classification on the basis of Setting properties / Elastic behavior

25. Classification of Impression Materials Classification on the basis of Viscosity (Agar) (Alginate)

26. Non Elastic Impression Materials Impression Plaster Impression Compound Zinc Oxide Eugenol Impression Pastes

27. Impression Plaster

28. Impression Plaster Current I.S.O standard for dental gypsum products identifies 5 types. Type I Dental plaster, Impression. Type II Dental plaster, model. Type III Dental stone, die and model. Type IV Dental stone, die, high strength, low expansion. Type V Dental stone, die, high strength, high expansion.

29. Impression Plaster Powder form Chemically: Calcinied β -calcium sulphate hemihydrate On reaction with water forms calcium sulphate dihydrate . Mixing with water or anti-expansion solution. Calcium sulphate hemihydrate* Main ingredient Potassium sulphate * Accelerator Borax* Retarder Alizarin red Coloring agent Gum tragacanth Improves cohesiveness starch Soluble plaster Composition: * Agents in anti-expansion solution

30. Impression Plaster Manipulation: Measure 50ml of room temperature in caliberated measuring beaker. Measure 100gm of plaster. Using a flat, wooden handled, stainless steel spatula, use the tip to initially mix the gypsum and water together. Place the rubber bowl on the laboratory vibrator and remove all the air bubbles from the mix. The final mix should appear as thick cream like consistency.

31. Impression Plaster Advantages Disadvantages Initially fluid state capable of recording soft tissues in uncompressed state. Dry sensation to patient due to absorption of water from tissue surface. Absorbs water from the tissue surface. No elasticity after setting. Useful in recording impressions of excessive mobile teeth and flabby ridges. Exothermic reaction. Indications Contraindications For use in edentulous patients In case of undercut areas

32. Impression Compound

33. Impression Compound “Impression compound is a muco -compressive, thermoplastic, non elastic impression material used to record the primary impression of the edentulous arches”. Available in the form of sheets, cakes, discs and sticks. Usually referred as “compo”. Other names (Dental compound, Model compound, Modelling compound). According to ISO, Impression Compound are classified as Type I (Low Fusing): Green stick compound (also called as tracing stick/tracing compound/border moulding compound). Type II (High Fusing): Tray compound

34. Impression Compound…Composition Components Function Thermoplastic materials (R esins & Waxes) (47%) Plasticity Workability Forms matrix Fillers (50%) Effect viscosity Decreases thermal conductivity Lubricants (2%) Flowability Coloring agents (traces) Coloring contrast

35. Impression Compound…Manipulation Softening of impression compound. Hot water bath method. Temperature range: 55 - 60ᴼC. Kneading is performed. Prolonged immersion or over heating not recommended. Constituents may leach out. Do not boil or ignite the material. Impression must be thoroughly cooled before withdrawal from the oral cavity. Cool water must be sprayed till the material becomes hard. Softening of the compound in warm water is recommended for removal from the cast. Dry kneading Wet kneading Improves plasticity

36. Impression Compound…Properties Undercut recording is poor. Dimensional stability is not good (1.5% shrinkage by volume on cooling). Impression may relax with an increase in room temperature. The temp. at which there is a definite reduction in plasticity of impression compound is known as Fusion temperature. (material looses its hardness or brittleness on heating or forms a rigid mass on cooling)

37. Impression Compound Advantages Disadvantages Biocompatible Poor dimensional stability Compatible with model and die materials Need water bath for softening Adequate shelf life Technique sensitive Fine details not recorded well. Indications Contraindications For taking primary / preliminary impression of complete denture. In case of undercuts For fabricating special tray.

38. Zinc Oxide Eugenol Impression Paste

39. Zinc Oxide Eugenol Impression Paste Non elastic Sets by chemical reaction 1. Zinc oxide ( ZnO ): Fine odorless white or yellowish powder. 2. Eugenol: A colorless liquid extracted from cloves. Pungent spicy taste. Antiseptic and analgesic properties. It is a 2 paste system (paste – paste formulation) Paste 1: Base paste (white in color) Paste 2: Accelerator paste (blue in color)

40. Zinc Oxide Eugenol Impression Paste Composition: Zinc oxide (87%) Main reactive agent Vegetable oil or mineral oil (13%) Inert compound Plasticizer Counteracts irritant action of eugenol Zinc acetate Accelerator Water Accelerator If absent, setting retards till contact with saliva Eugenol / clove oil (12%) Main reactive agent Less burning sensation from clove oil as compared to Eugenol. Fillers (wax, kaolin, talc) 20% Inert like Gives body to the set material. Canada Balsam / Peru Balsam (10%) Increases flow Improves working properties Gum or polymerized rosin (50%) Accelerator Provides a smooth mix Accelerator soln and color Facilitates reaction For coloring demarcation Base paste Eugenol / clove oil (12%) Main reactive agent Less burning sensation from clove oil as compared to Eugenol. Fillers (wax, kaolin, talc) 20% Inert like, Gives body to the set material. Canada Balsam / Peru Balsam (10%) Increases flow, Improves working properties Gum or polymerized rosin (50%) Accelerator, Provides a smooth mix Accelerator soln. and color Facilitates reaction, For coloring demarcation Accelerator paste

41. Zinc Oxide Eugenol Impression Paste Manipulation: Use an oil impervious paper pad / glass slab and a flexible stainless steel spatula. Take equal length of both the pastes extruded on to the mixing pad. Both pastes mixed together rapidly. Mixing completes when a homogeneous mix is attained. Load the mixed impression material on to the tray. Clean the spatula and the glass slab. Type I Zinc oxide Eugenol is hard type and sets in 10 minutes where as Type II Zinc oxide Eugenol is SOFT type and sets in 15 minutes.

42. Zinc Oxide Eugenol Impression Paste Setting reaction (Chelation reaction) The phenolic-OH of eugenol undergoes an acid base reaction with ZnO . Zn(OH) 2 + 2HE ZnE 2 + 2H 2 O Base + Acid Salt + Water Zinc eugenolate is formed. 2 molecules of eugenol react with 1 molecule of ZnO . Zinc eugenolate

43. Zinc Oxide Eugenol Impression Paste Advantages Disadvantages Adapts well to soft tissues Rigid when set Low viscosity Cannot record undercuts High accuracy: Dimensional stability satisfactory (shrinkage less than 0.1%). May have taste in patients mouth. Inexpensive May have slight burning sensation. Messy material Indications Contraindications For recording Secondary/final impression in complete denture making. In undercut areas

44. Eugenol free ZnO paste Zinc oxide reacts with carboxylic acid to form ZOE like material. Orthoethoxybenzoaic acid (E.B.A) Substitute of Eugenol Bactericidal and other medicaments can be added

45. Elastic Impression Materials

46. Solution : One small substance (solid) dissolved in another (liquid). Exists as a single phase. Suspension: Larger particles visible by a naked eye or on microscope dispersed in a medium. Exists as a two phase system. Colloids : Colloidal solution or Sol is between smaller molecules of solution and larger particles of a suspension. It is a two phase system. Dispersed particles phase Dispersed medium (the substance in which particles are suspended)

47. Colloids A solid, liquid or gaseous substance made up of large molecules or masses of smaller molecules that remain in suspension in a surrounding continuous medium of different matter. Types of colloids Aerosols------------- liquids or solids in air Lysosols ------------- gas or liquid or solid in liquid. Foams---------------- gases in solid Solid emulsion ----- liquids in solid Solid suspension -- solids in solid

48. Hydrocolloid A colloid that contains water as the dispersion phase

49. Colloid with liquid as dispersion medium can exist in two different forms “Sol” and “Gel” “Sol” Molecules or aggregates of molecules dispersed in a liquid medium.

50. Gel Formation of jelly like mass, when the suspended particles combine with a liquid vehicle. It is produced via gelation from “ S ol”. It is a network of fibrils that form a weak slightly elastic brush heap structure of hydrocolloid

51. Sol-gel Transformation Sol state Gel state. If a hydrocolloid contains an adequate concentration of dispersed phase, a sol under certain conditions, may change to a semisolid material known as gel . In the gel state the dispersed phase agglomerates to form a chain of fibrils called micelles . These fibrils may branch and intermesh to form a brush heap structure. The dispersion medium is held in the interstices between the fibrils by capillary attraction or adhesion. Gelation Temperature Liquefaction Temperature

52. Sol-gel Transformation For A gar secondary bonds hold the fibrils together. These bonds break at slightly elevated temperatures and become re-established as the hydrocolloid cools to room temperature. This process is reversible. In case of Alginate the fibrils are formed by chemical action and the transformation is not reversible.

53. Sol-gel Transformation The GEL form of the hydrocolloids is the material as it is “Set”. The SOL form is when it has flow and is in a liquid solution. Since hydrocolloids are mostly comprised of water, they are not dimensionally stable – they MUST be poured-up immediately in stone or plaster before the water has evaporated from the impression and changed the dimension.

54. Liquifaction temperature Temperature at which gel changes to sol. (70 -100°c) Gelation temperature Temperature at which sol changes to gel.(37-50°c) Hysteresis The difference between the liquefaction temperature and the gelation temperature is called Hysteresis Agar

55. Imbibition The process of water sorption i.e. the gel swells when placed in water. Syneresis Expression of fluid on to the surface of gel structure. Agar

56. Agar Also called as Agar-Agar. Agar is a galactose sulphate which forms a colloid with water. When heated hydrogen bonds are broken, helix is uncoiled and a viscous fluid is formed. The process is reversible. Thermoplastic material and therefore can be used repeatedly. Gelation Temperature Liquifaction Temperature

57. Agar Usually supplied in two forms: Syringe material Tray material Requires careful control and expensive equipment. Dimensionally unstable therefore model poring should be soon.

58. Agar Composition: Components Function Weight % Agar Gelling agent 13% - 17% Borate Strength 0.2% - 0.5% Sulphate Gypsum hardener 1.0% - 2.0% Wax Filler 0.5% - 1.0% Thermoplastic material Thickener 0.3% - 0.5% Water Reaction medium balance main component

59. Agar Setting reaction:

60. Agar Manipulation: There is no manipulation required for agar. A special conditioning unit is used. The water in the conditioning unit should not be contaminated. The difference between syringe material and tray material is both in their fluidity and color. At high altitude, Propylene glycol is added to water to get to a boiling temperature of 100 °C. The process of bringing down the temperature of agar sol to a level; which is tolerable in the oral cavity is known as tempering. The triple impression technique is used with Agar because of its low viscosity.in this technique the patients bits into the agar and the upper and the lower impression are recorded along with the occlusal record.

61. Agar Special water bath Handling Reversible Hydrocolloid: Special water baths with 3 chambers are used 1) Material is immersed in boiling tank (100 °C); for 10-20 minutes; turns from gel to sol. 2) Place in storage bath (65°C) in a sol condition; 10 minutes to few days; remains sol. 3) Load tray; immerse in the tempering bath (46°C); 5-10 minutes; lowers temp for pt. comfort.

62. Agar Advantages Disadvantages No mixing required Initial expanse Good surface details. Technique sensitive Inexpensive (after initial equipment) Poor tear strength Dimensionally unstable Indications Contraindications Full arch impressions Bulky trays Quadrant impressions

63. Alginate First presented in 1940s by Amalgamated dental company. ViScoelastic and mucostatic impression material.

64. Alginate Composition: The principal component of alginate impression material is Anhydro - β -d- manuronic acid Or alginic acid.

65. Alginate Setting reaction: Typical sol gel reaction. Soluble sodium alginate + calcium sulphate Insoluble calcium alginate (cross linked complex or polymer) Calcium ions replace sodium or potassium ions of soluble alginate The irreversible ch. reaction of the transformation of the sol to gel of alginate occurs due to the calcium ions replacing the sodium or potassium ions of soluble alginate. Structurally the calcium ions replace the sodium or potassium ions from two adjacent molecules to produce the cross linking H 2 O retarder Reaction 1 Reaction 2

66. Alginate Manipulation: Powder/water ratio is suggested by the manufacturer (normally equal parts are taken). Powder is added to water in a clean rubber bowl. If powder is added first, greater mixing time is required. Avoid incorporation of air in to the mix. Vigorous figure-8 motion of spatulation is best for thorough mixing. A smooth creamy mix is formed. Should not drip when the spatula is raised from the bowl. Mixing time; 45 sec – 1 min. Setting time: Fast setting ………………1.5 to 3 min. Regular setting………….3 to 4.5 min.

67. Alginate Properties: Easy to manipulate. Comfortable to the patient. Relatively inexpensive. Requires inexpensive instruments for manipulation.

68. Alginate Advantages Disadvantages Easy to manipulate Poor dimensional stability Elastic properties Satisfactory detail recording Inexpensive Room temperature and humidity can affect the working and setting time. Rapid setting Hydrophilic Indications Contraindications Study models Not accurate for fine detail Removable partial dentures Gag reflex Bleaching trays Mouth guards Fabrication of special / custom tray

69. Alginate The best way to influence the setting time of alginate is by altering the amount of retarder being added to the alginate during manufacturing. The most appropriate way for the clinician to influence the setting time is to alter the temperature of the water being used (cold water increases the setting time and hot water accelerates the setting time). The minimal thickness of alginate between the tray and the tissue should be 3mm . The best storage media to preserve the water content of hydrocolloid impression material is 1005 relative humidity.

70. Modified Alginates Alginates modified by the incorporation of silicone polymers (paste form). They show marginally Better fine detail reproduction Better tear resistance Poor dimensional stability (lose water at about the same rate as a conventional alginate, if allowed to stand). The material is considered as hybrid of alginate and silicone Elastomers but their properties are closely related to that of Alginates

71. Comparison of the requirements of reversible and irreversible hydrocolloid impression materials (ISO 1564 and ISO 1563)

72. Viscoelasticity of Elastomers and Alginates A viscoelastic material has following characteristics If the stress is held constant the strain increases with time. If the strain is constant the stress decreases with time. The effective stiffness depends on the rate of application of the load. The faster the impression is removed i.e. stress is applied faster; lesser is the distortion. Permanent deformation is less if the set impression is removed from the mouth quickly (snapping action).

73. Elastic Impression Materials

74. Non Aqueous Elastomers Also referred to as “Elastomeric Impression Materials” or simply “Elastomers”. Four types of elastomeric impression materials are available.

75. Non Aqueous Elastomers Polysulphide: Highest tear strength , it may distort rather than tear in thin sections. Highest permanent deformation among elastomers. Composition:

76. Non Aqueous Elastomers… Polysulphide Setting reaction: Mercaptan + lead dioxide polysulphide rubber + lead oxide + water Crosslinking by oxidation of pendant ---SH group Chain lengthening by oxidation of terminal ---SH group .

77. Non Aqueous Elastomers… Polysulphide Advantages Disadvantages Viscoelastic High flexibility (elongation to break,500%) Poor dimensional stability Water is a by-product Pour within 1 hour Setting contraction 0.3% - 0.4% in first 24 hrs. Lower cost Lowest cell cytotoxicity Custom trays (it supports the less stiff material and as less material is used so minimal polymerization shrinkage ). Long working time Lead allergy Long shelf life Long setting time Good detail production Messy Paste-paste mix Bad color May stain clothes Highest tear strength By product i.e. water Only radiopaque impression material as Lead dioxide. Hydrophobic

78. Effect of filler on some properties of Polysulphide Polysulphide impression material exhibit “Pseudoplasticity” If sufficient speed and force is used for spatulation, the material will seem easier to handle

79. Non Aqueous Elastomers Condensation cured Silicone: (Polydimethylsiloxane) Composition: Base paste Catalyst paste Silicone polymer with terminal 0H group Tetra-ethyl silicate (cross linking agent) Inert Fillers Stannous octoate (activator)

80. Non Aqueous Elastomers…… Condensation cured Silicone Setting reaction: Polymerization occurs as a result of crosslinking between the orthoethyl silicate and the terminal hydroxyl group of dimethyl siloxane.

81. Non Aqueous Elastomers…… Condensation cured Silicone Advantages Disadvantages Better dimensional stability than alginates. Poor dimensional stability (0.3% to 0.5% shrinkage in 24hrs). More elastic than polysulphides and polyethers . Hydrophobic Adequate tear strength Limited shelf life Adequate elongation to break. Byproduct i.e. Ethanol

82. Non Aqueous Elastomers Addition Silicone: Composition: Base paste Catalyst paste Poly (methyl hydrogen siloxane) Divinyl Poly siloxane Other siloxane prepolymers Other siloxane prepolymers Fillers Fillers Palladium (hydrogen absorber) Platinium salt-catalyst ( chloroplatinic acid) Hybrid silicone Retarders Coloring agents

83. Non Aqueous Elastomers… Addition Silicone Setting reaction: Vinyl silozane + Silane siloxane Silicone rubber Pt salt There are no by products as long as, there is balance between the reactants. If unbalanced, moisture and residual hydrides react n hydrogen gas is produced causing air bubbles in the stone model. To avoid this palladium is added to absorb Hydrogen.

84. Non Aqueous Elastomers… Addition Silicone ( best dimensional stability as can be removed from severe undercuts with virtually no distortion) Advantages Disadvantages Accurate Temperature and humidity effects setting Easy to manipulate Effect of latex gloves i.e. Sulphur which retardes setting. Hydrophilic addition silicone having contact angle of 30 – 35 is available because of the addition of surfactant. Hydrophobic (Makes them compatible with epoxy resin and hence more accurate casts and dies). Range of viscosities ( Pseudoplasticity makes them useful for automated devices) Rapid setting No by product

85. Non Aqueous Elastomers Polyethers : Composition: Base paste Catalyst paste Polyether polymer. Alkyl aromatic sulphonate . Fillers (silicates) Fillers Plasticizer (a glycol, either high or low viscosity) Plasticizer. Pigments Pigments. Flavorings

86. Non Aqueous Elastomers…… Polyethers Setting reaction: Polyether + Sulfonic ester Crosslinked Rubber

87. Non Aqueous Elastomers…… Polyethers Advantages Disadvantages Reliable material. Very stiff material. Good dimensional stability. Due to high stiffness, tearing on withdrawal. Clean to handle. On prolonged contact with water, dimensional stability is not good as absorbs water and fluids with simultaneous leaching out of water soluble plasticizer (immersion in disinfectants for 4hrs should be avoided). Odorless Working time was short Hydrophilic –best compatibility with stone Highest cell cytotoxicity

88. Non Aqueous Elastomers Consistencies: Supplied in various consistencies (viscosities) Polysulphides are supplied in various consistencies Low (syringe or wash) Medium (regular) High (tray)

89. Non Aqueous Elastomers Consistencies: Addition silicones are available in the same viscosities as polysulphides plus Extra low Monophase extra high (putty) consistencies

90. Non Aqueous Elastomers Consistencies: Polysulphide has the lowest viscosity, while polyether and addition silicone have a Pseudoplastic property. Polysulphides Addition Silicones Condensation Silicones Polyethers Low (syringe or wash) High (tray) Low Low% putty (Catalyst supplied in putty or as a liquid). Low Medium (regular) Medium Medium High (tray) High High Extra low Monophase Extra high (putty)

91. Non Aqueous Elastomers Mixing systems: 3 types of systems are available to mix catalyst and base thoroughly. 1. Static mixing system. 2. Automixing system…… Cartridge & Extruder Gun – automix tips used. 3. Dynamic mechanical mixing system…… Cartridge & Motor-driven Mixer – automix tips used. Two tubes – pastes mixed by hand Two putties – mixed/kneaded by hand

92. Non Aqueous Elastomers Mixing systems Static mixing system: Impression paste are dispensed from collapsible tubes. Equal lengths of catalyst and base paste are dispensed on a paper pad. Initial mixing is accomplished with a circular motion. Final mixing is done with broad strokes of spatula. Final mix should be smooth mixing is readily accomplished in 45 seconds. All 4 types of elastomers are available for mixing in this fashion.

93. Non Aqueous Elastomers Automixing system: Very popular means for mixing catalyst and base. Base and catalyst are in separate cylinders of plastic cartridge. Cartridge is placed in mixing gun containing 2 plungers. Equal quantities of base and catalyst are forced through static mixing tip. The tip contains stationary internal plastic spiral to fold both the components over each other to get a uniform mix at the end of the tip. The first part of the mix should be discarded for a uniform consistency. Mixed material can be extruded directly either into an injection syringe or impression tray. Intra-oral injection tips can be placed at the end of the static mixing tip. Material left at the tip gets wasted (1 – 2ml). 3-4 times less waste as compared to hand mix. Silicones (both addition and condensation) and polyethers are available with this means of mixing.

94. Non Aqueous Elastomers Dynamic mechanical mixing system: Newest system Catalyst and base are supplied in large plastic bags, housed in a cartridge. Cartridge is inserted into the top of the mixing machine. A new plastic mixing tip is placed on the front. On pressing the buttons, parallel plungers push against the plastic bags, thus opening the bag. Material is forced into the dynamic mixing tip. Mixing tip differs from that of automixing (internal spiral is motor driven i.e. it rotates with speed. Mixing is accomplished by rotation and forward motion of material through the spiral. It is a helpful technique for mixing highly viscous materials. Polyether and addition silicone are available for mixing with this system. Advantages are ease of use, speed and thoroughness of mixing.

95. Non Aqueous Elastomers…(Mixing systems)

96. Non Aqueous Elastomers Dynamic mechanical mixing system: Advantages Disadvantages Ease of use Cost of the system Speedy and thorough mixing Slightly more material is retained at the tip than the automixing but still less wastage as compared to hand mixing.

97. Non Aqueous Elastomers Impression techniques 3 common methods for taking impressions of fixed restorations are Dual viscosity technique Monophase technique Puttywash technique I n nearly all these methods impression material is injected directly on and into the prepared teeth and the tray containing the bulk of the material is placed thereafter.

98. Non Aqueous Elastomers Impression techniques Dual Viscosity Technique (Simultaneous or multiple mix technique) Low consistency material is injected with a syringe into and around the critical area and a high consistency material is placed in the tray. Both materials bond, join and set together. When partially set material is used in this technique, the resulting dies are narrower and shorter.

99. Non Aqueous Elastomers Impression techniques: Single viscosity technique ( Monophase ): Often taken with medium viscosity material. When forced through impression syringe, the viscosity decreases ( pseudoplasticity ) but when used with tray, the viscosity is unaffected. Addition Silicones and Polyethers are well suited for this technique

100. Non Aqueous Elastomers Impression techniques: Putty Wash Technique / Reline technique: It is a 2 step impression procedure. Preliminary impression is taken in high or putty consistency material before cavity preparation. Cavity is prepared. Low consistency material is syringed into the prepared cavity. Preliminary impression is then reinserted. The low and high consistency materials bind. When low viscosity material sets, the impression is removed. This technique is developed for condensation silicone to minimize dimensional changes.

101. Comparative analysis of properties of elastic impression materials Working time: Setting Time: Longest Shortest Agar > Polysulphide > Silicones >Alginate = Polyether. Shortest Longest Alginate < Polyether < Agar < Silicones < Polysulphides

102. Comparative analysis of properties Stiffness: Tear Strength: Most Least Polyether > Addition Silicone > Condensation Silicone > Polysulphide = Hydrocolloid. Greater Least Polysulphide > Addition Silicone > Polyether > Condensation Silicone > > Hydrocolloid.

103. Comparative analysis of properties Dimensional Stability Wettability: Best Worst Addition Silicones > Polyether > Polysulphide > Condensation Silicone > Hydrocolloid. Best Worst Hydrocolloid > Polyether > Addition Silicones > Polysulphide > Condensation Silicones.

104. Comparative analysis of properties Cost: Lowest Highest Alginate < Agar < Polysulphide < Condensation Silicones< Addition Silicone < Polyether

105. Cross Infection Control It is important to disinfect the impression before sending it to the laboratory for making models / prosthesis or appliances. Important for the protection of the laboratory staff, for the transmission of infection from the patient. Properties of impression materials needs to be considered before disinfecting.

106. Cross Infection Control 2% Gluteraldehyde Is a satisfactory disinfectant for all elastomers Materials Methods Disinfectant Comments Alginate Immersion < 10 min (short exposure time) Chlorine compounds Iodophores Short term gluteraldehyde has been shown to be acceptable but the time is unacceptable for disinfection. Agar Do not immerse in alkaline gluteraldehyde . Polysulphide Silicones Immersion Gluteraldehyde Chlorine compounds Iodophores Phenols Disinfectants requiring > 30 min are not recommended.

107. Cross Infection Control Materials Methods Disinfectant Comments Polyether Immerse with caution, less than 10 minutes. Chlorine compounds Iodophores ADA recommends any of the disinfectant classes, however short term exposures are recommended to avoid distortion. ZOE Impression paste Immersion preffered but spraying can be used for bite registration. Gluteraldehyde Iodophores Not compatible with chlorine compounds. Phenolic sprays can be used. Impression compounds Same as above Chlorine compounds Iodophores Phenolic sprays can be used

108. Duplicating materials

109. Duplicating Materials Both types of hydrocolloids are used in dental lab to duplicate dental casts or models. Reversible hydrocolloids are more popular as it can be used many times and can be stored in liquid form for 1 or 2 weeks. Disadvantages are same as agar impression material. These duplicating materials have the same composition as impression materials but the water content is higher and the agar and alginate content is lower. Silicones and polyethers are examples of irreversible non aqueous types for duplicating materials. Their cost and techniques for taking an impression are the main disadvantages.

110. Altered cast / Applegate technique “A corrected functional impression of the distal extension areas of the patients mouth, made after the fit of the framework is confirmed in the mouth and before artificial teeth are arranged.” Purpose: this procedure is designed to ensure the best possible soft tissue support for a distal extension framework. Anatomical master impression of oral structure is made Construct master cast and refractory cast Construct metal framework with temporary self-cured acrylic resin saddles

111. The metal frame is located onto the abutment teeth The saddle area is beaded and boxed The saddle area is cast (2-part stone cast) In the lab, the saddle area is cut away from stone cast Altered cast technique

112. 1 Dentist adjusts and fits the framework in the patient’s mouth and designs outline of proposed impression tray. 2 Adapt a sheet wax spacer to the edentulous area and the retromolar pad, trim wax.  3 Place the framework on the master cast with the rests fully seated. 4 Mix self curing resin and adapt resin over the edentulous area to form a tray . 5 After resin is cured, lift the framework with attached tray from the cast.   6 Making the corrected impression: Impression material is placed in the tray and the entire framework is seated in the mouth.  7 Altering the Master Cas t: a)Draw design for saw cuts across the distal extension, and another saw cut line that is parallel and lingual to the lingual sulcus to join with the first cut. b)Cut along design lines, place multiple dovetail cuts, to create mechanical retention for the corrected addition.  8 Place and secure (sticky wax) the framework with corrected impression on the prepared master cast (all rests completely seated).  9 Bead and box around the borders of the impression 10 Mix stone and pour impression. 11 After stone sets : Remove wax, separate Cast, remove framework and tray from the cast, completely clean debris and trim cast, preserving the land area. 12 Remove acrylic resin tray: a)Flame tray until it softens b)Peel tray from the framework c)Clean framework thoroughly d) Seat the framework back on the cast with all rests seated .  Procedures for the Altered Cast Technique