impression materials

1

IMPRESSION MATERIALS

Dr.Madhu Billa2nd year PG

SIBAR Institute Of Dental Sciences

KEY TERMINOLOGY

• Earliest dental materials were waxes used in the 18th and 19th 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:

• 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

• 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.

CLASSIFICATION

7

ACCORDING TO VISCOSITY OR TISSUE DISPLACEMENTMucostatic Impression Materials

Impression plaster Agar Alginate.Light body elastomers.

MucocompressiveImpression compoundPutty elastomers.

8

ACCORDING TO THE USE OF THE MATERIAL:

Dentulous mouth:AlginateAgar.Non aqueous elastomers.

Edentulous mouth:Impression compoundImpression plaster.Zinc oxide eugenol.Wax.

9

Impr

essio

n M

ater

ials

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

10

Zinc-oxide Eugenol Impression Paste

• Supplied in two separate pastes dispensed in tubes

Components PercentageTube no 1 (base) Zinc-oxide 87 Fixed vegetable or mineral oil 13Tube 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(CaCl2) and color 5

11

• 1st 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

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

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

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

15

Advantages:1. Low viscosity – no compression of soft tissues.2. Dimensional stability (shrinkage less than 0.1 %)3. Good surface detail reproduction4. Low priceDisadvantages:1. Cannot be used in deep undercuts2. Eugenol allergy in some patients

16

PROPERTIESCONSISTENCY AND FLOWAccording 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 flowDIMENSIONAL 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.

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.

18

Impression compound• Also called “modelling plastic”• Thermoplastic material• Supplied in the form of cakes(red) and sticks

(green, gray or red)

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

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

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

22

FUSION TEMPERATURE• When impression compound is heated in a hot water bath

the material starts to soften at approximately 39°CCoefficient 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 immediatelyDETAIL REPRODUCTION• Surface detail reproduction is comparatively less because of

its high viscosity and low flow

23

Types of Impression compound

Type-I(Lower fusing)

Type- II(Higher fusing)

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

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

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

27

Indication: impression of edentulous ridgesAdvantages:

Cheap and long shelf life, easy to prepare Very good surface detail reproductionExcellent 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

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(700C-1000C)• When sol is cooled, it becomes gel at a point known

as the gelation temperature( btw 370C and 500 C)• Thus called reversible hydrocolloid

AQUEOUS HYDROCOLLOIDS

29

Composition

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

31

Liquefy the hydrocolloid gel in the tube in boiling water at 1000C 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)

ADVANTAGES1. Hydrophilic Impression material 2. Good elastic properties, Good recovery from

distortion 3. Can be re-used as a duplicating material4. Long working time 5. High accuracy and fine detail recordingDISADVANTAGES6. Only one model can be used

7. Extensive and expensive equipment required

8. Impossible to sterilize for reuse

9. Low dimensional stability & tear resistance

Uses of Agar

1. Widely used at present for cast duplication

2. For full mouth impression without deep undercuts

3. As tissue conditioner

4. 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

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

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

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

38

Advantages

• Ease of manipulation• No need of expensive

equipments• Relatively low cost• Comfort to patients

• High viscosity• Ability to displace

tissues

Disadvantages

39

40

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.

05/03/2023 41

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.

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.05/03/2023 43

44

Elastomers

Polysulfide Silicones Polyethers

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)

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

47

Composition The BasePolysulfide 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 AcceleratorLead dioxide Reactor

Sulfur Promoter, accelerates the reaction

Oleic acid or Stearic acid Retarder, controls setting reaction

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

49

• Good flexibility• High tear strength• Hydrophobic• Messy, stains clothes and has an offensive

odor• Uses—impression for crown and bridge edentulous impressions

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.

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

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

53

• Working time: 3 min• Setting time: 6-8 min• Impression must be poured as soon as

possible within first 30 min

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

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

57

Composition The Base

Polymethylhydrosiloxane Low molecular weight polymer

Fillers

The Accelerator

Divinyl polymethyl siloxaneOther siloxane pre-polymers

Platinum salt Catalyst

Reatrder Controls working and setting times

58

• Working time: 2-4.5 min• Setting time: 3-7 min• Cast can be poured upto 1 week after making

the impression

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

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

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

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 / cm2)

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

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)

PROPERTIES1. Pleasant odor and taste

2. Mixing time is 30 secs, setting time of 8 mins

3. Dimensional stability is very good.

Curing shrinkage is low (0.24%)

The permanent deformation is also low (1-2%).

4. 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

66

Properties of Elastomeric impression materials

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

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

Modifications in addition silicone

1. Addition silicone with Palladium - Hydrogen absorber. Adv: Impressions can be poured immediately.

2. Fast Setting Addition Silicone: Aquasil Ultra Fast Set

3. Hydrophilized Addition Silicone Adv: Reduced contact angle with water Improved

wettability. Have intrinsic surfactants

Modifications in polyether

1. Soft Polyether: Penta soft, Impregum soft.

Supplied as heavy and light body.

Soft Technology makes it less rigid for easier removal from the

mouth.

2. 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.

73

Comparison of physical properties of light-curing andself-curing dental impression materials

- Heish et al., JPD 1994

• This 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.

• it 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

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

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 stressThixotropic 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

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

Polysulfide

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

FLEXIBILITY

Polysulfide

Polyether

Condensation silicone

PVS

Clinical considerations :

Impression of multiple periodontally compromised teeth

Difficult to remove from undercuts (Exceeds the tear strength of material) - Tearing

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)

Hypersensitivity potential polyether Contact dermatitis

Point of consideration :Residual segment of impression material severe gingival

inflammation. Polysulfide – lowest cell death countPolyether –highest cell toxicity scores

.

BIOCOMPATIBILITY

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 stability6 major sources of dimensional change1. Polymerisation shrinkage2. Loss of condensation reaction by-product3. Thermal contraction from oral temp to room temp4. Absorption of water or disinfectant over a period

of time5. Incomplete recovery of deformation because of

plastic deformation6. Incomplete recovery of deformation because of

viscoelastic behaviour

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.

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

ThankYou…..