Impression materials

impression material in conservative dentistry and endodontics

1. IMPRESSION MATERIALS DR ANJALI SAVITA MDS I DEPT OF CONSERVATIVE AND ENDODONTICS

2. Introduction Definition History Ideal Requirements Classification Basic concept CONTENTS Impression materials Hydrocolloids Elastomeric materials Recent advances Impression Techniques Conclusion References

3. Introduction Impression materials are used to produce the accurate replicas of intraoral tissues. There are a wide variety of impression materials available each with their own properties, advantages and disadvantages.

4. Definition Any substance or combination of substances used for making an impression or negative reproduction.” - GPT

5. “ An impression is an “imprint” or negative likeness of the teeth and/or edentulous areas, made in plastic material which becomes hardened or set while in contact with the tissue.” - Hartwell 1992

6. History 1782 : William Rae used wax with Plaster of Paris. 1940s: American dentists used Plaster OF Paris for impression & the technique was presented to the profession at large by Chaplin Harris in 1953 . 1925 : Alphous Poller of Vienna was granted a British Patent for a totally different type of impression material which was later described by Skinner as Colloidal Sols of Emulsoid type . The possibility of using colloidal substance for dental impression became apparent when Poller’s Negacoll was modified & introduced into the dental profession as Dentacol in 1928. Agar hydrocolloid was introduced to the dental impression.

7. 1930 : JD Hart of Oklahoma began to use Agar for fabrication of cast restoration. 1930 : AW Ward and EB Kelly introduced ZnO Eugenol. 1890s : A chemist from Scotland noticed that Brown Seaweed yielded peculiar mucous extraction. He named it ‘ Algin ’. 1936-40: S William Wilding used Algin as a dental impression material 1950s: Development of Rubber base impression materials (Polysulphides and Condensation Silicones)

8. 1960s : Polyether impression material developed in Germany. 1970s : Addition silicone was introduced as a dental impression material. 1988 : Latest addition and light cure elastomers. 1990-2000 : New auto devices and delivery systems

9. Ideal Requirements Non toxic Accurate Easy to handle Easy to manipulate Consistency Setting time Elasticity Dimensional stability Compatible with die and die materials Thixotropic Economical Disinfection Flavour

10. Classification According to Philips science of dental materials impression materials are classified on the basis of setting and elasticity Mode of setting Rigid Elastic Set by chemical reaction(irreversible) Impression plaster ZOE Alginate Polysulfide Polyether Silicone Set by temperature changes(reversible) Impression compound waxes Agar hydrocolloid

11. GENERAL CLASSIFICATION

12. IMPRESSION TRAYS

13. Basic concept Colloids Often classed as fourth state of matter as colloidal state. Can be considered as a compromise between the very small molecules of a solution & very large particles of a suspension. Two phases Dispersed phase or dispersed(suspended) particle Dispersion phase or dispersion(suspension) medium

14. Types Of Colloids Colloidal sols may be Liquid or solid in air- Aerosol Gas, liquid or solid in liquid lysosol Gas, liquid or solid in solid

15. Hydrocolloid If the dispersion medium is water, the material is known as hydrocolloid. Lysosols Consist of gelatin particles. Particles larger than those in solution. Particle size ranges from 1-200 nm. There is no clear line of demarcation among the solutions, colloids & suspensions.

16. Gels Colloids with a liquid as a dispersion medium can exist in two different forms known as Sol & Gel. Sol- has a appearance & many characteristics of a viscous liquid. Gel- is a jelly like elastic semisolid & produced from a sol by the process of gelation.

17. Gelation It is a process of conversion of sol to gel, to form fibrils, micelles of the dispersed phase which become interlocked to give characteristic jelly like consistency. Within the gel, the fibrils branch & intermesh to give a brush heap structure

18. Gelation Temperature The temperature at which gelation occurs is known as gelation temperature. Agar - secondary bonds (weak) hold the fibrils together- break at slightly elevated temperatures and become reestablished as it cools to room temperature - reversible Alginate - the fibrils are formed by chemical action - irreversible

19. Dimensional effect Dimensional stability Being hydrocolloid The effects of syneresis, evaporation & imbibition on the dimensional changes are of considerable importance in dentistry, since any change in dimension that occurs after the impressions are removed from the mouth will lead to inaccurate casts & models.

20. AGAR (REVERSIBLE HYDROCOLLOID) Reversible hydrocolloids undergo transition from gel to sol on heating. On cooling they return back to the original state. The hydrocolloid supplied as the gel is heated above its liquefaction temperature, cooled to a temperature compatible with the oral tissues & placed in the mouth. Gelation occurs as the tray continues to cool, after which the impression is removed & poured.

21. It is a sulphuric ester of a linear polymer of galactose.. Although it is an excellent impression material & yields accurate impressions, it has been largely replaced by alginates & rubber impressions because The minimum equipment required. Possibility of obtaining metal dies from rubber impression.

22. COMPOSITION COMPONENT FUNCTION % AGAR Brush heap structure 13- 17 BORATES Strength 0.2- 0.5 K SULPHATE Gypsum hardener 1- 2 WAX Filler 0.5- 1 THIXOTROPIC MATERIALS Thickener 0.3- 0.5 WATER Reaction medium 84 ALKYL BENZOATE Preservatives 0.1 COLOR & FLAVOURS Taste & appearance trace

23. MODE OF SUPPLY Gel in collapsible tubes (for impressions) A number of cylinders in a glass jar (syringe material) In bulk containers (for duplication)

24. USES

25. Armamentarium Water cooled rim lock trays Tray and syringe material Conditioning Unit Procedure Tray material Syringe material loaded tray in tempering bath

26. Dental arch flooded with water Water cooling tubes connected to sealed tray Completed impression

27. PROPERTIES According to ADA specification no.11

28. Advantages

29. Disadvantages

30. ALGINATE (Irreversible Hydrocolloid) Developed as a substitute for the agar impression material when its supply became scarce during World War II. Based on a natural substance extracted from certain brown seaweed. This substance is called as anhydro-ß-d-mannuronic acid or alginic acid/ Algin (sodium or potassium or triethanolamine acid).

31. Currently, alginate is more popular than agar because: Easy to manipulate Comfortable for the patient. Relatively inexpensive Does not require elaborate equipment

32. Composition Component Function % Potassium alginate Soluble alginate 15 Calcium sulphate Reactor 16 Potassium titanium fluoride Accelerator 3 Zinc oxide Filler particles 4 Diatomaceous earth Filler particles 60 Sodium phosphate Retarders 2

33. Setting reaction Two main reactions occurs during setting: → ₂ + 3 (Retarder) (Reactor) Sodium Alginate + Ca + → Ca Alginate + (Powder) (Gel)  

34. Classification of alginate ( Robert G. Craig ) Types Mixing time Working time Setting time Fast set 45 sec 1.5 min 1-2 min Normal set 60 sec 2 min 2- 5 min

35. MANIPULATION

36. Morris et al ( J Prosthet Dent 1983,49: 328-330) Demonstrated that smoothing the surface of the mixed alginate with a wet finger, prior to making the impression, consistently resulted in fewer bubbles on the surface of casts

37. PROPERTIES According to ADA specification No 18:

38. USES

39. ADVANTAGES

40. DISADVANTAGES :

41. RECENT ADVANCES IN ALGINATES The two component system may be in the form of two pastes- One contains the alginate sol and the other contains the calcium reactor Siliconised alginates Chromatic alginates eg. Integra & KromaFaze (Dux dental) ,Take one alginate(Kerr) Dustless alginates( glycerin is added on the alginate powder to agglomerate the particles) eg. Identic dust free alginate (Dux dental), Jeltrate Dustless(Dentsply Caulk) , Integra dustfree alginate(Kerr) Alginot

42. Laminate technique ( Alginate – Agar Method ) Proposed by Schwartz in 1951

43. Common failures Grainy material

44. Rough or chalky stone model Tearing

45. Distortion Irregular voids

46. DISINFECTION

47. Elastomeric Impression Materials Elastomer : a polymer that has a glass transition temperature below its service temperature (usually room temperature); these materials are characterized by low stiffness and extremely large elastic strains. Elastomeric impression material : a group of flexible chemical polymers that are either chemically or physically cross-linked; generally, they can be easily stretched and rapidly recover their original dimensions when applied stresses are released.

48. Soft and rubber-like & known as elastomers or synthetic rubbers. As per ADA Sp. No.19- non-aqueous elastomeric dental impression materials. Liquid polymers when mixed with a suitable catalyst are converted into solid rubber at room temperature.

49. Type Max permanent deformation Max flow in compression Max dimensional changes in 24hours Type I 2.5 0.5 -0.5 Type II 2.5 0.5 -1 Type III 5.5 2 -0.5

50. Generalized Properties

51. Dimensional changes occur due to :

52. MODE OF SUPPLY All elastomers supplied as Two Paste Systems (Base And Catalyst) Putty Consistency – Supplied In Jar

53. Uses

54. Polysulfide Synonyms : Rubber base, Mercaptan, Thiokol rubber First elastomeric impression to be introduced Mode of supply Available as 2 systems : Base and accelerator 3 viscosities L ight M edium H eavy bodies

55. Composition Base paste Component % Liquid Polysulphide Polymer 80- 85 Inert fillers( Titanium dioxide, Zinc sulfate , copper carbonate or silica) 16- 18 Plasticizers Reactor paste Component % Lead dioxide 60- 68 Dibutyl phthalate 30- 35 Sulphur 3 Other substances like Magnesium Stearate(retarder) & deodorants 2

56. Tray adhesive Butyl rubber or styrene/acrylonitrile dissolved in a volatile solvent such as chloroform or a ketone is used with polysulfide. Chemistry and Setting Reaction On mixing base and accelerator pastes the liquid polymer sets to form a solid, but flexible and elastic rubber like material.

57. Material sets via condensation polymerization reaction . Water is the reaction by-product. Lead dioxide is toxic and has bad smell, so it has been replaced in recent products by Peroxide compounds . Commercial products Permlastic (Kerr) Coe-flex (Lead dioxide system) Omni-flex (Copper hydroxide system) MERCAPTAN + LEAD OXIDE → POLUSULPHIDE + WATER

58. Properties

59. Advantages Disadvantages

60. Silicone These materials were developed to overcome some of the disadvantages of polysulfide materials Objectionable odor Staining of linen by lead dioxide Amount of effort required to mix the base with the accelerator Long setting times Moderately high shrinkage on setting Fairly high permanent deformation Pouring should be within one hour

61. Condensation silicone Earlier of two silicone material Also known as Conventional silicone Products available: Coltex (Coltene) Cuttersil(Heraeus Kulzer) Silene(Bosworth) Speedex(Coltene Whaledent) Xantopren(Heraeus Kulzer)

62. MODE OF SUPPLY Two-paste system Base-paste and a low viscosity liquid catalyst Two Putty system COMPOSITION Base Accelerator Poly dimethyl siloxane (Hydroxy-terminated) Orthoethyl silicate - (cross linking agent) Colloidal silica or micro sized metal oxide(filler) Stannous octoate - catalyst Colour pigments

63. Setting reaction and chemistry

64. Properties

65. Advantages Clean & pleasant Good working time Easily seen margins Disadvantages High polymerization shrinkage Volatile alcohol by product Low tear strength Hydrophobic Pour immediately

66. ADDITION SILICONE Also called as Polyvinyl siloxanes(PVS) . Has better properties than condensation silicones Products available: Impressiv (Cosmedent) Imprint 3 Penta (Putty impression material with automix) Aquasil/Reprosil/Hydrosil(Dentsply Caulk) Exaflex/ Examix/Exafast/Hydroflex(GC America) Express, Imprint/Imprint II(3M ESPE) Flexitime(Heraeus Kulzer)

67. Composition BASE ACCELERATOR Poly(methyl hydrogen siloxane) Divinyl poly siloxane Other siloxane prepolymers Other siloxane prepolymers Fillers Platinum salt : Catalyst (chloroplatinic acid) Palladium (Hydrogen absorber) Retarders Fillers

68. TRAY ADHESIVE Poly dimethyl siloxane & Ethyl silicate Available in 4 consistencies Light body Medium body Heavy body Putty

69. Setting reaction and chemistry PT SALT

70. Properties

71. Advantages Excellent dimensional accuracy and dimensional stability Pleasant to use Short setting time Auto mix available Disadvantages Hydrophobic Expensive Hydrogen gas evaluation in some materials Hydrophilic formulations imbibe moisture Sulphur contamination by latex gloves

72. Danuta Nowakowska , et al conducted a study on Polymerization time compatibility index of polyvinyl siloxane impression materials with conventional and experimental gingival margin displacement agents They concluded that all of the evaluated displacement agents at laboratory and intraoral temperatures induced changes in the polymerization time of PVS. Therefore, chemical displacement agents should not come into direct contact with PVS impression materials.

73. Polyether Introduced in Germany in late 1960s Good mechanical properties and dimensional stability, but short working time, very stiff material and expensive. Commercial names: Impregnum (ESPE, Germany) Permadyne (ESPE, Germany) Supplies in 2 collapsible tubes Available as 3 viscosities: Light Medium heavy bodied

74. Base Accelerator Polyether polymer Aromatic sulfonate ester (cross-linking agent) Colloidal silica(filler) Colloidal silica (filler) Glycol ether or phthalate(plasticizer) Phthalate or glycol ether (plasticizer) Composition

75. Setting reaction and Chemistry

76. Properties

77. Advantages Dimensional stability Accuracy Short setting time Auto mix available Disadvantages Set material very stiff Imbibition Shorter working time Allergic hypersensitivity

78. CLINICAL PROPERTIES Working & Setting time

79. FACTORS AFFECTING WORKING AND SETTING TIME TEMPERATURE VISCOSITY HUMIDITY WORKING & SETTING TIME

80. Auto mixing and electronic mixing technique improve the quality of impression as compare to hand mixing. Auto mixing technique waste one third of material less than hand mixing so it was considered in a low budget and more cost effective (Daou, E. 2010) . Mixing

81. Accurate impression was made in custom tray more precisely than stock trays. Size of undercuts and volume of impression material are the major significance. Use of custom tray and adhesive to retained polyvinyl siloxanes maintained precision and consistency. (Daou, e. 2010) . Custom tray

82. Disinfection Accuracy of both polyether and VPS should be altered after long term immersion in disinfection solution. So this material be only spray disinfected to avoid imbibition and dimensional change. Immersion disinfection is useful if the recommended time of disinfection is used and impression material accuracy will be unaffected. Reliability of addition silicon and polyether material remains acceptable. (Daou, E. 2010).

83. Elasticity Eliminating or blocking out any undercuts in the tooth preparation before making the impression will maximize the elastic recovery of an impression material. This can be accomplished with any of the modified or resin modified glass ionomer products. (Donovan, T.E & Chee 2004.) COMPARISON PROPERTIES OF ELASTOMERIC IMPRESSION MATERIALS

84. Elastic recovery increases in the following order .

85. Dimensional changes Polymerization shrinkage Loss of by – product Thermal contraction from oral temperature to room temperature Imbibition Incomplete recovery of deformation Pour within 30 mins – polysulfide & condensation silicon

86. Lowest to highest of the impression materials is as follows

87. Permanent deformation Greater in the permanent distortion of the impression material if greater the depth of the undercut, for all impression materials. Thus, the minimum thickness of the material in the tray should be three to four times more than the largest undercut (Hamalian, T. A. Et al. 2011). Lowest to highest of the impression materials is as follows

88. Stiffness Lowest to highest of the impression materials is as follows

89. Accuracy Donovan, T.E., & Chee, W.W.L. 2004). Lowest to highest of the impression materials is as follows

90. Tear strength Chai et al . 2007 Hamalian, T. A. et al. 2011 Lowest to highest of the impression materials is as follows

91. Flow A light-body material, tends to flow off the preparation and possesses excellent flow characteristics (Hamalian, T. A. et al., 2011). When the heavier body tray materials are placed over the top of them most of the newer PVS products and polyether are thixotropic and stay where they are syringed but flow readily. (Donovan, T.E., & Chee, W.W.L. 2004)

92. Hydrophillic behavior Lowest to highest of the impression materials is as follows ( Daou, E. 2010).

93. Probability of allergic reactions is low. Polysulfide has the lowest cell death count. Polyether has the highest cell death count ,toxicity and contact dermatitis among the class. The most likely problem is lodgment of impression material in gingival sulcus resulting in severe inflammation, Biocompatibility

94. Clinical consideration Subgingival regions are very thin – material can tear Residual segment of impression material difficult to detect --Radio opacity of polysulfide can help Severe gingival inflammation. Examine the gingival sulcus immediately after impression removal and also the impression for any evidence of tearing

95. Shelf life Storage Cool, dry environment Tubes always tightly sealed Container closed

96. Recent advances Visible light cured polyether urethane dimethacrylate In early 1988, a visible light cured impression was introduced(Genesis L.D. caulk). Two viscosities :-Light and heavy bodied Composition Polyether urethane dimethacrylate Photo initiators (camphoroquinone) Photo accelerators (Diethyl amino ethyl methacrylate) Silicone dioxide (Filler)

97. Properties

98. Manipulation

99. Advantages Controlled working time Excellent properties Ease of cold disinfection without loss of quality. The impression material is also compatible with gypsum and silver or copper metallizing baths Disadvantages Need special transparent trays Difficult to cure in remote areas

100. Automatic dispensing and mixing devices This latest technique consists of a double barrel caulking gun with mixing tip. The tip contains spirals on the inside. Forcing of the base & accelerator results in its mixing. e.g. Volume mixer (Kerr), Pentamix (3M ESPE) Advantages More uniform mix Less air bubbles Reduced working time

101. Senn (GC America) Hybrid polyether/polysiloxane material that has both hydrophilicity and dimensional accuracy, before, during and after set.

102. Bite registration silicon Used for making intraoral or extraoral occlusal bite registrations for fixed or removable restoration and implants. Fast intraoral set time of 20 secs – 1 min Supplied as cartridges to be used with a caulking gun Commercial name: Exabyte – GC Jet bite – Coltene Whaledent

103. FIT CHECKER SILICONES Specialized addition silicone Used for checking errors in the internal surface of crowns and FPD Available as two paste system Areas of premature contacts are revealed as bare areas, which are marked and removed Commercial name Fit Checker - GC

104. IMPRESSION TECHNIQUES CLASSIFICATION

105. CLASSIFICATION

106. Three most common methods for making impressions for fixed restorations are

107. Simultaneous dual-viscosity technique low-consistency material is injected with a syringe into critical areas & the high-consistency material is mixed & placed in an impression tray. After injecting the low viscosity material, the tray containing the higher viscosity material is placed in the mouth. Since both the materials are mixed together, they join, bond & set together. After the materials have set, the tray & the impression are removed.

108. Advantages Over comes the polymerization shrinkage of the light body material Margins duplicated in light body Disadvantages Use of custom tray An assistant required for mixing the material - tray/syringe simultaneously

109. Single viscosity or monophase technique Impressions often made with a medium viscosity impression material. Addition silicone & polyether are well suited for this technique because both have a capacity for shear thinning. When the medium viscosity material is forced through an impression syringe, viscosity is reduced, whereas the viscosity of the same material residing in the tray is unaffected. This behavior of the materials is referred to as PSEUDOPLASTIC.

110. Advantages Reduced wastage of the material Less time consumption Avoids the time involved in fabrication of custom tray Disadvantages Relatively high viscosity and reduced flow of the monophase materials, makes their injection onto the preparation more difficult to control -increased incidence of surface voids - Stephen M. Dunne et al 1998

111. PUTTY WASH TECHNIQUE Two steps impression procedure whereby a preliminary impression is taken in high or putty consistency material before the tooth preparation is made. Space is provided for a low consistency material by a variety of techniques, & after tooth preparation, a low consistency material is syringed in to the area & the preliminary impression reinserted. The low & high consistency materials bond, & after the low consistency material sets, the impression is removed. This procedure is sometimes called a WASH TECHNIQUE. The Putty consistency materials & this technique were developed for condensation silicones to minimize the effects of dimensional change during polymerization. This technique was extended to addition silicones,after their introduction even though their polymerization shrinkage is significantly lower.

112. Simultaneously technique (One stage) Light body material syringed on to the preparation while the putty material loaded in a stock tray is simultaneously inserted into the mouth.

113. Advantages Reduced chair side time Disadvantages Absolute lack of control in the bulk of wash material By mixing putty, syringe material simultaneously, setting distortion of putty included over all distortion of impression - Chee and Donovan 1992 Possibility of margins duplicated in putty medium Tendency of bubbles to be formed and occluded in the set impression

114. Putty wash relief channel technique Pre-operative putty impression is made intra orally In the area where the tooth is to be prepared, impression material is removed or channels prepared using putty cutter instrument The impression is then relined with low viscosity material

115. Putty wash 2mm spacer technique 2 mm thick wax spacer is prepared on a diagnostic cast, occlusal stops are provided on non-functional cusps. A putty impression is made with a stock tray resulting in a putty custom tray with 2mm space for the wash material. Putty custom tray is then washed with light body material

116. Advantages Wash stage carried out after the putty has set and contracted Controlled wash bulk compensates for this contraction with minimal dimensional change Disadvantages Extra chair side time Extra material

117. Related Studies Gilmore, Schnell and Phillips [4] in a study on the accuracy of rubber impression materials concluded that the most accurate results were attained only when the impression was poured immediately.

118. Sawyer et al studied the accuracy of casts produced from three classes of elastomeric impression materials. They concluded that polyether was the only material, where a second accurate cast in the same impression or a delayed pour after a week, produced essentially the same accuracy, compared to that of the cast poured immediately. The delayed excessive shrinkage of silicones did affect the second and delayed pours. Eames et al in a study evaluated the accuracy and dimensional stability of elastomeric impression materials. They concluded that the new addition silicones exhibited the least change dimensionally. They recommended that in situations, which preclude the immediate pouring of impressions only the stable materials should be selected.

119. Lacy et al investigated the time dependent accuracy of elastomeric impression materials and concluded that polyvinyl siloxanes were the most stable of elastomers. However, with putty wash system, they may reveal some loss of accuracy of dies produced by retrieval from multiple pours after 2-4 days. Marcinak and Draughn evaluated the dimensional change in addition silicones by delaying the pouring of impressions from 2 h to one week. They concluded that these materials remained remarkably accurate even after one week, with the greatest change at any time being 0.3%.

120. Williams et al investigated the time dependent dimensional stability of eleven commercially available elastomeric impression materials and found that the addition silicone materials exhibited excellent dimensional stability for all storage times. Delayed pouring of artificial stone in the impressions made with these materials should result in very little change in die accuracy. Tjan et al conducted a clinically oriented evaluation of the commonly used impression materials, by repouring the impressions at intervals of 6 hours and 24 h. Also a one week delayed pour was made for addition silicones and polyether. They concluded that the advantage of elastomeric impression material is that they may be poured serially (repeatedly) and will still maintain the accuracy. The impressions made of addition silicone and polyether was accurate after one week and possibly longer.

121. Tjan et al evaluated the accuracy of monophase polyvinyl silicones and found that repeat pour at later time periods, did not affect the dimensional accuracy and stability of impression made with these materials. Anusavice et al in a review of nonaqueous elastomeric impression materials reported that, additional silicones are the most dimensionally stable of all the existing materials. This unusual stability means that the impression does not have to be poured in stone immediately. In fact, these impressions are often sent to the laboratory to be poured. They also reported that the combination of excellent dimensional stability and superior elasticity of addition silicones mean that multiple casts made from the same impression, have the same degree of accuracy.

122. Purk, Willes et al studied the effects of different storage conditions on polyether and polyvinylsiloxane. Their study compared the effects of different time and temperature storage conditions, including temperature extremes of 66°C and 10°C, on the accuracy of addition silicone and polyether impressions. The greatest distortion generally occurred as a result of the 66°C temperature extreme. The authors therefore recommend that impressions be poured in stone according to manufacturers’ specifications before being shipped to a dental laboratory to prevent impressions being exposed to excessive temperatures.

123. CONCLUSION Clinicians have an excellent array of impression materials & techniques for fabrication of tooth restorations. Based on the quality of impressions sent to the commercial laboratories, it seems that many impressions fall short of the quality made possible by current impression materials. Thus it is important to review the contemporary principles of impression materials & to take impressions consistent with those principles. It is thus important to familiarize with the various specialty impression techniques available & use them when indicated.

124. REFERENCES Philips science of dental materials 12th edition Craig’s restorative dental materials 13th edition Mc Cabe and walls’ applied dental materials 9th edition William J O'Brien Dental materials selection 3rd edition Evaluation of defects in surface detail for monophase , 2phase, and 3-phase impression techniques (J Prosthet Dent 2015;113:108-113) The dimensional stability of a vinyl polyether silicone impression material over a prolonged storage period (J Prosthet Dent 2013;109:172-178)

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