Impression materials

various impression materials used in dentistry

1. IMPRESSION MATERIALS 1 Dr.Madhu Billa 2 nd year PG SIBAR Institute Of Dental Sciences

2. KEY TERMINOLOGY

3. Earliest dental materials were waxes used in the 18 th and 19 th centuries. Beeswax is reported as the material first used in making oral impressions. Philip Pfaff-1756 First described taking impression with softened wax Charles Stent-1857 Introduced the first impression compound Sears-1937 First used agar hydrocolloids for recording crown impressions. Irreversible hydrocolloid are introduced in the early 1940s HISTORY:

4. SL Pearson-1955 Developed synthetic rubber base impression materials Polysulfide- Late 1950’S Condensation Silicone- Early 1960’s Addition Silicone- 1970’s Polyether- Late 1970’s

5. 1. Capable of plastic to rigid body transformation 2. Acceptable for a patient - non-toxic, non-irritant, tasteless, reasonable setting time 3. Good handling properties – easy to prepare/mix, adequate working and setting times 4. Accuracy and detail reproduction 5. Dimensionally stable 6. Resistant to mechanical stress 7. Resistant to disinfectant solutions IDEAL REQUIREMENTS:

6. BASED ON SETTING AND ELASTICITY : MODE OF SETTING RIGID ELASTIC Set by chemical reaction(irreversible) Impression plaster, zinc oxide eugenol. Alginate, polysulfide, polyether, silicone, Set by temperature change(reversible) Compound, waxes Agar hydrocolloid. 6 CLASSIFICATION

7. 7 ACCORDING TO VISCOSITY OR TISSUE DISPLACEMENT Mucostatic Impression Materials Impression plaster Agar Alginate. Light body elastomers . Mucocompressive Impression compound Putty elastomers .

8. 8 ACCORDING TO THE USE OF THE MATERIAL: Dentulous mouth : Alginate Agar. Non aqueous elastomers . Edentulous mouth : Impression compound Impression plaster. Zinc oxide eugenol . Wax.

9. Impression Materials Non-elastic Elastic Aqueous Hydrocolloids Non-aqueous Elastomers Polysulfide Silicones Polyether Condensation Addition Agar (reversible) Alginate (irreversible) Plaster Compound ZnO - Eugenol Waxes O’Brien, Dental Materials & their Selection 1997 9

10. Zinc-oxide Eugenol Impression Paste Supplied in two separate pastes dispensed in tubes 10 Components Percentage Tube no 1 (base) Zinc-oxide 87 Fixed vegetable or mineral oil 13 Tube no 2 (accelerator) Oil of cloves or eugenol 12 Gum or polymerised rosin 50 Filler(silica type) 20 Lanolin 3 Resinous balsam 10 Accelerator solution(CaCl 2 ) and color 5

11. 1 st reaction-hydrolysis of zinc oxide to its hydroxide form When the 2 pastes are mixed,the phenol –OH of the eugenol acts as a weak acid and undergoes an acid-base reaction with zinc hydroxide Forms a salt- zinc eugenolate 11

12. Applications of ZOE Final impression of edentulous ridges As a wash impression with other impression As an interocclusal registration material As a temporary liner material for dentures As a surgical dressing 12

13. Manipulation Mixed on oil impervious paper or glass mixing slab Proper proportion of two pastes obtained by squeezing 2 strips of paste of the same length,one from each tube ,onto the mixing slab Flexible stainless steel spatula used for mixing 2 strips of contrasting colors combined with the first stroke of the spatula ,mixing is continued for approx 1 min, until a uniform color achieved 13

14. Types of ZOE Classified as Hard paste(type I) soft paste(type II) Final set for type I paste-10 min type II paste-15min Setting reaction can be accelerated by adding small amount of Zinc acetate or a drop of water in the paste before mixing or by extending mixing time Retading setting time – by using cool spatula and mixing slab 14

15. Advantages: Low viscosity – no compression of soft tissues. Dimensional stability (shrinkage less than 0.1 %) Good surface detail reproduction Low price Disadvantages: 1. Cannot be used in deep undercuts 2. Eugenol allergy in some patients 15

16. PROPERTIES CONSISTENCY AND FLOW According to ADA specification No. 16, the spread is: Type I — 30 to 50 mm Type II — 20 to 45 mm RIGIDITY AND STRENGTH The compressive strength of hardened ZOE is approximately 7 MPa two hours after mixing . DETAIL REPRODUCTION It registers surface details quite accurately due to the good flow DIMENSIONAL STABILITY A negligible shrinkage (less than 0.1 %) may occur during hardening. BIOLOGICAL CONSIDERATIONS Some patients experience a burning sensation in the mouth due to eugenol . 16

17. NONEUGENOL IMPRESSION AND SURGICAL PASTES The chief disadvantage of zinc oxide eugenol paste is the burning sensation caused by eugenol . Hence noneugenol pastes were developed. Noneugenol pastes consist of a base and reactor paste. The base paste contains ZnO , gum & lorothidol (fungicide ). The reactor pastes contains coconut fatty acids , rosin (thickening), chlorothymol (bacteriostatic), etc. Antibiotics like tetracycline may be incorporated at the time of mixing. Eg . COE-PAK, WARDS WONDRPAK Light cured periodontal dressing materials and single component pastes that set by heat and moisture in the mouth are also available. 17

18. Impression compound Also called “ modelling plastic” Thermoplastic material Supplied in the form of cakes(red) and sticks (green, gray or red) 18

19. Composition Mixture of –waxes(principal ingredient) thermoplastic resins filler(increase viscosity and rigidity) coloring agent Shellac, stearic acid and gutta-percha added to improve plasticity and workability 19

20. Applications For making a preliminary impression in an edentulous mouth For individual tooth impression Peripheral tracing or border moulding To check undercuts in inlay preparation To make a special tray 20

21. PROPERTIES it is used warm and then cooled to oral temperature, at which it is fairly rigid. The setting mechanism is therefore a reversible physical process rather than a chemical reaction . The thermal conductivity of dental impression compounds is very low and therefore require heat soaking to attain a uniform mix 21

22. FUSION TEMPERATURE When impression compound is heated in a hot water bath the material starts to soften at approximately 39°C Coefficient of Thermal Expansion (CTE) The CTE of compound is comparatively high due to the presence of resins and waxes . The linear contraction from mouth temperature to room temperature is 0.3%. DIMENSIONAL STABILITY Since the release of strains is unavoidable, the safest way to prevent distortion is to pour the cast immediately DETAIL REPRODUCTION Surface detail reproduction is comparatively less because of its high viscosity and low flow 22

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24. Advantages: 1. Can be reused, easy to use 2. Non-irritant and non-toxic Disadvantages 1. Poor dimensional stability 2. Easy to distort when withdrawn from the mouth 24

25. Impression Plaster Basically a gypsum product (Type-1) used as mucostatic impression material for making final impressions for edentulous patients Applicable to patients with displaceable soft tissues that should be recorded in a passive state 25

26. Composition CaSO4 . 0.5H2O β- hemihydrate Potassium sulfate – reduce expansion & accelerates setting Borax – a retarder to prolong setting time Diatomaceous earth, quartz, lime - to make the plaster more brittle 26

27. Indication: impression of edentulous ridges Advantages: Cheap and long shelf life, easy to prepare Very good surface detail reproduction Excellent dimensional stability Disadvantages: 1. Very rigid – often need to be fractured when removed from the mouth 2. Fractures if undercuts are present 3. may dry soft tissues, unpleasant to patients 27

28. Agar Reversible hydrocollloid Physical change of agar from sol to gel induced by lowering temperature Gel liquefies to sol when heated to a temperature known as liquefaction temperature(70 C-100 C) When sol is cooled, it becomes gel at a point known as the gelation temperature( btw 37 C and 50 C) Thus called reversible hydrocolloid 28 AQUEOUS HYDROCOLLOIDS

29. Composition 29 Component Function Composition Agar Brush – heap structure 13 – 17% Borates Strength 0.2 – 0.5% Sulfates Gypsum hardener 1.0 – 2.0% Wax Filler 0.5 – 1.0% Thixotropic materials Thickness 0.3 – 0.5% Water Reaction 80% Alkyl Benzoate Prevent growth of mold in impression material during storage. 0.1%

30. Making the Agar impression Process requires a 3 compartment conditioning unit for the agar tray material Allows liquefaction,storage and tempering 30

31. Liquefy the hydrocolloid gel in the tube in boiling water at 100 C for minimum 10 min tube is then placed in a storage bath at 65°C to retain the sol condition until needed impression tray filled with hydrocolloid sol from the tube taken from storage bath , gauze pad placed over the top of the tray material Tray placed in water filled tempering compartment(at abt 45°C) 31

32. ADVANTAGES Hydrophilic Impression material Good elastic properties, Good recovery from distortion Can be re-used as a duplicating material Long working time High accuracy and fine detail recording DISADVANTAGES Only one model can be used Extensive and expensive equipment required Impossible to sterilize for reuse Low dimensional stability & tear resistance

33. Uses of Agar Widely used at present for cast duplication For full mouth impression without deep undercuts As tissue conditioner Was used for crown & bridge before the advent of elastomers

34. Alginate Irreversible hydrocolloid Most widely used impression material Developed as a substitute for agar 34

35. Potassium or sodium alginate dissolves in water and reacts with calcium ions Calcium sulphate dihydrate A reactor ,reacts with potassium alginate to form a dihydrate insoluble alginate gel Zinc oxide Filler particles, affects properties and setting time Potassium titanium fluoride Accelerator ,counteracts the inhibiting effect of the hydrocolloid on the setting of stone,ensures good quality surface of the cast Diatomaceous earth Filler particles, controls the consistency of the mix and the flexibility of the set alginate Trisodium phosphate Retarder,controls the settting time to produce either regular or fast set alginates Coloring agents Flavoring agents Composition 35

36. Gelation process Typical sol-gel reaction Soluble alginate reacts with calcium ions from calcium sulphate and forms insoluble calcium alginate Production of calcium alginate- rapid,doesn’t allow sufficient working time Retarder trisodium phosphate added to extend working time 36

37. The measured powder is sifted into pre-measured water A vigorous figure – 8 motion, with the mix being stropped against the sides of rubber mixing bowl Mixing time between 45 secs – 1 min 37

38. Advantages Ease of manipulation No need of expensive equipments Relatively low cost Comfort to patients High viscosity Ability to displace tissues Disadvantages 38

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41. Dustless alginate Organic glycol Identic dustfree alginate(Dux dental). Jeltrate Dustless( Dentsply Caulk). Integra dustfree alginate.( Kerr) Alginot Multiple automix options Dimensional stability over 24 hours. Multiple pours. Final detailed impressions. 10/2/2016 41

42. CAVEX Color change(chromatic alg.) The alginate impression material with color indications avoiding confusion about setting time. Color changes are visualizing the major decision points in impression making end of mixing time And end of setting time ( tray can be removed from mouth) it indicates two color changes violet to pink indicates the end of mixing time. Pink to white indicates end of setting time. Other advantages of this material are improved dimensional stability ( upto 5 days) Good tear and deformation resistance Dust free Smooth surface, optimum gypsum compatibility.

43. SILICONISED ALGINATES Incorporation of silicone polymers. Hybrids of alginates and silicone elastomers, Properties closely related to alginate Fine detail production and tear resistance ,Poor dimensional stability ANTISEPTIC ALGINATE IMPRESSION MATERIAL Introduced by Tameyuki Yamamoto, Maso Abinu . An antiseptic containing alginate impression material contains 0.01 to 7 parts by weight of an antiseptic such as glutaraldehyde and chlohexidine gluconate per 100 parts by weight of a cured product of an alginate impression material. 10/2/2016 43

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45. Elastomers Formulated in several consistencies in increasing content of filler Extra light body Light body Medium or regular body Heavy body Putty(extra heavy) 45

46. Polysulfides First synthetic elastomeric impression material introduced in 1950 2 paste system Available in low, medium and high consistencies Made up of a base and accelerator/reactor Brands- COE-FLEX,PERMALASTIC,NEOPLEX etc 46

47. Composition The Base Polysulfide polymer(- SH,mercaptan gp ) Principal ingredient Titanium oxide and Zinc Fillers Sulphate ,copper carbonate or silica Strengthener Dibutyl phthalate Plasticizer (confers viscosity to base) The Accelerator Lead dioxide Reactor Sulfur Promoter, accelerates the reaction Oleic acid or Stearic acid Retarder, controls setting reaction 47

48. Working time: 5-7 min( longest among elastomers ) Setting time: 8-12 min Pouring the cast: impression must be poured within 30 min to 1 hr Each paste supplied in a dispensing tube with approx sized bore diameters at the tip Equal lengths of paste extruded from each tube to provide the correct ratio of polymer to cross-linking agent Reaction starts at the beginning of mixing and reaches its maximum rate soon after spatulation is complete 48

49. Good flexibility High tear strength Hydrophobic Messy, stains clothes and has an offensive odor Uses—impression for crown and bridge edentulous impressions 49

50. Advantages Disadvantages - High tear strength - Dimensionally unstable - Long working time - Unacceptable odor - Established precision - Untidy and stains clothing - Economic - Long setting time - Extensive shelf life - Least elastic recovery - Less hydrophobic - Subsequent pours are less accurate. 50

51. Condensation silicone Supplied as two-paste system or base-paste and a low viscosity liquid catalyst or a two-putty system Putty used as tray material in conjunction with a low-viscosity silicone Referred to as the Putty-wash technique Brands- Speedex 51

52. Composition The Base paste hydroxyl-terminated polydimethyl siloxane High molecular weight polymer Silica or calcium carbonate Fillers The Liquid Accelerator Tin octoate Metal organic ester Orthoalkyl silicate Oil-based diluents Thickening agents Increase viscosity 52

53. Working time: 3 min Setting time: 6-8 min Impression must be poured as soon as possible within first 30 min 53

54. Curing involves a reaction of tri- and tetra-functional alkyl silicates in the presence of stannous octoate as a catalyst Condensation polymerisation of hydroxy –terminated polydimethyl siloxane occurs with tetraethyl orthosilicate in the presence of stannous octoate (catalyst) This reaction results in the release of ethanol molecules By-product: Ethyl alcohol 54

55. Properties: Pleasant odor and color . Excellent reproduction of surface details and highly elastic. Lesser dimensional stability - high curing shrinkage (0.4 - 0.6%) - permanent deformation due to shrinkage caused by the evaporation of ethyl alcohol is also high (1-3%). Hydrophobic - needs a dry field.. Biologically inert . Ethyl alcohol bye product on subsequent evapouration causing contraction. Compatible with all gypsum products.

56. Addition silicone Commonly referred to as Polyvinyl siloxanes (PVS) Supplied as low, medium, high and very high consistencies Brand name- Aquasil 56

57. Composition The Base Polymethylhydrosiloxane Low molecular weight polymer Fillers The Accelerator Divinyl polymethyl siloxane Other siloxane pre-polymers Platinum salt Catalyst Reatrder Controls working and setting times 57

58. Working time: 2-4.5 min Setting time: 3-7 min Cast can be poured upto 1 week after making the impression 58

59. Reaction activated by a platinum salt catalyst ( chloroplatinic acid) without the release of by-products In presence of impurites or moisture, secondary reaction takes place between the residual hydrides and moisture leading to evolution of hydrogen gas 59

60. Advantages Most elastic of currently available materials Virtually negligible distortion upon removal from undercuts Exceptional accuracy in reproducing anatomic details Dimensional stability allows pouring long after impression making Excellent occlusal record registration material 60

61. Disadvantages Inherent hydrophobic nature Non-ionic surfactant wetting agent added to silicone paste rendering the surface of the impression more hydrophillic and called hydrophilized addition silicone Sulfur contamination from natural latex gloves inhibits the setting of addition silicone Touching the tooth with latex gloves before seating the impression can inhibit the setting of critical surface next to tooth 61

62. PROPERTIES Pleasant odor and color Excellent reproduction of surface details Mixing time of 45 secs ,setting time of 5-9 mins . Best dimensional stability - low curing shrinkage (0.17 %) - lowest permanent deformation (0.05 – 0.3 %) Stone pouring delayed by 1-2 hours Hydrogen gas bye product result in pinpoint holes in cast when poured immediately Extremely hydrophobic, some manufacturers add a surfactant (detergent) to make it more hydrophilic Good shelf life of 1-2 yrs Good tear strength (3000gm / cm 2 )

63. Polyether Supplied as two-paste system in low, medium and high consistencies 2 types: 1. based on ring-opening polymerization of aziridine group 2. based on an acid-catalyzed condensation polymerization of polyether prepolymer with alkoxysilane terminal groups Brands- IMPREGUM 63

64. 64 Composition: Base Paste Poly ether polymer Colloidal silica (filler) Glycol ether or phthalate (plasticizer) Accelerator paste Aromatic sulfonate ester (cross-linking agent) Colloidal silica (filler) Phthalate or glycol ether (plasticizer)

65. PROPERTIES Pleasant odor and taste Mixing time is 30 secs , setting time of 8 mins Dimensional stability is very good. Curing shrinkage is low (0.24%) The permanent deformation is also low (1-2%). Very stiff (flexibility of 3%), needs extra space, around 4 mm is given. 5. Hydrophilic (moisture control not critical) 6. Shelf life extends upto 2 years

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67. Properties of Elastomeric impression materials

68. RECOMMENDED DISINFECTANTS MATERIAL DISINFECTANTS Polysulfide Glutaraldehyde , Cl compounds, Iodophors & Phenolics for 2min Silicones Glutaraldehyde , Cl compounds, Iodophors Polyether Cl compounds or Iodophors-2min Alginate Cl compounds or Iodophors-2min ZOE Glutaraldehyde or Iodophors Impression compound Cl compounds or Iodophors

69. Modifications in polysulphides Lead dioxide replaced by: Organic reactor like Cumene hydroperoxide or t-Butyl hydroperoxide : Inorganic hydroxides such as Hydrated Copper Oxides : Hydrated copper oxide produces a green mix. RECENT ADVANCES

70. Modifications in addition silicone Addition silicone with Palladium - Hydrogen absorber . Adv: Impressions can be poured immediately. Fast Setting Addition Silicone : Aquasil Ultra Fast Set Hydrophilized Addition Silicone Adv: Reduced contact angle with water  Improved wettability . Have intrinsic surfactants

71. Modifications in polyether Soft Polyether: Penta soft, Impregum soft. Supplied as heavy and light body. Soft Technology makes it less rigid for easier removal from the mouth. Fast Setting Polyether: Impregum quick set Penta soft Quick Set 3. Visible light cure material

72. Visible light cured polyether impression material Consists of visible light cured polyether urethane dimethacrylate resin to which photoinitiator and photoaccelerator are added Filler- Si dioxide which has a refractive index close to that of resin in order to provide translucency for maximum depth of cure. Long working time, short setting time. Tear strength – 6000 to 7500 gm/cm2. Other properties similar to addition silicone. 72

73. Comparison of physical properties of light-curing andself -curing dental impression materials - Heish et al., JPD 1994  T his study evaluated the physical properties and accuracy of light-curing impression material and to compare it with those of self-curing impression materials currently used. Physical properties such as strain in compression, dimensional stability, and tear strength were measured. i t was found that the strain in compression of the polyether urethane dimethacrylate was higher than that of the condensation silicones, but lower than that of the addition silicones The dimensional stability showed that all of the impression materials, except the polyether urethane dimethacrylate , had a negative dimensional change 24 hours after mixing. The polyether urethane dimethacrylate had extraordinary tear resistance compared to the other impression materials 73

74. Rheological properties Viscosity and flow behaviour depends upon - ease of mixing -air entrapment during mixing -tendency of trapped air to escape before the impression is made All elastomers exhibit shear-thinning before setting 74 PROPERTIES OF ELASTOMERIC IMPRESSION MATERIALS

75. 2 categories of shear thinning phenomena— Pseudoplasticity Thixotropy Pseudoplastic material- displays decreasing viscosity with increasing shear stress and recovers its viscosity immediately upon a decrease in shear stress Thixotropic material- doesn’t flow until sufficient surface energy in the form of an impact force or vibration force is applied to overcome the yield stress of material 75

76. TEAR STRENGTH Important property - in inter proximal and sub gingival areas. Influenced by Consistency - increased viscosity increases tear strength Manner of removal - rapid rate of force during removal increases tear strength (Snap removal) Polyether Silicone Hydrocolloids Poly sulfide

77. Elastic Recovery Elastic recovery - “rebound” back to its original shape, when the set impression is removed from the mouth Elastic recovery can be maximized by blocking the undercuts. Polysulfide Polyether Condensation silicone PVS

78. FLEXIBILITY Polysulfide Poly ether Condensation silicone PVS Clinical considerations : Impression of multiple periodontally compromised teeth Difficult to remove from undercuts (Exceeds the tear strength of material) - Tearing

79. HYDROPHILICITY PVS and Condensation silicones –hydrophobic Contains hydrophobic aliphatic hydrocarbon groups surrounding the siloxane bond Polyether - hydrophilic Contain functional groups that attract and interact with water molecules through hydrogen bonding Use of extrinsic /topical surfactant Dilute solution of soap. To lower the surface tension (decreases contact angle)

80. Hypersensitivity potential  polyether Contact dermatitis Point of consideration : Residual segment of impression material  severe gingival inflammation. Polysulfide – lowest cell death count Polyether –highest cell toxicity scores . BIOCOMPATIBILITY

81. Direct inhibition Direct contact with latex gloves Impression are made with rubber dam in place Indirect inhibition Indirect contact of tooth and periodontal tissues during tooth preparation and gingival displacement procedures. Contaminated surface will be slippery and sticky to touch Clinical consideration : Use of non latex gloves – Vinyl gloves , Polyethene gloves Avoid touching the tooth preparation and gingival areas Avoid handling retraction cord with gloved hands. CONTAMINATION Unpolymerized material remain adherent to prepare teeth surface

82. Dimensional stability 6 major sources of dimensional change Polymerisation shrinkage Loss of condensation reaction by-product Thermal contraction from oral temp to room temp Absorption of water or disinfectant over a period of time Incomplete recovery of deformation because of plastic deformation Incomplete recovery of deformation because of viscoelastic behaviour 82

83. CONCLUSION It is important that the dentist fully appreciates the various features of these materials, what it is that makes them so useful for dental applications, and what their limitations are. Only then will the dentist be able to select the most appropriate material for a particular application.

84. References Kenneth J. Anusavice : Philips’ Science of Dental Materials Eleventh Edition William J. O’Brien: Dental Materials Properties and Selection E. C. Combe : Notes on Dental Materials Fifth Edition John F. McCabe: Applied Dental Materials Seventh Edition V. K. Subbarao : Notes on Dental Materials Fourth Edition Clair D. Reitz, DDS and Nereyda P. Clark, DMD The setting of vinyl polysiloxane and condensation silicone putties when mixed with gloved hands. JADA Vol. 116:371-5, 1988 Winston W.L. Chee , T.E. Donovan, R.L. Kahn. Indirect inhibition of polymerization of a polyvinyl siloxane impression material: a case report, Quint . Int. Vol. 22:133-5, 1991 D. H. Pratten , M. Novetsky . Detail reproduction of soft tissues: A comparison of impression materials. JPD Vol. 65:188-191, 1991 John F. Lontz : State-of-the-Art Materials Used for Maxillofacial Prosthetic Reconstruction DCNA- Vol. 34, No. 2, April 1990 Terry E. Donovan, Winston W. L. Chee: A review of contemporary impression materials and techniques DCNA- Vol. 48, No. 2, April 2004

85. 85 ThankYou …..