complete review of impression materials used in prosthodontics

1. IMPRESSION MATERIALS
PRESENTED BY : DR.ANIKET SHINDE
1ST YEAR PG STUDENT
DEPARTMENT OF PROSTHODONTICS

2. CONTENTS
 INTRODUCTION
 HISTORY
 CLASSIFICATION
 IMPRESSION MATERIALS
- Nonelastic
- Elastic
 LATEST ADVANCES

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 9
 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
 An impression is the perpetual preservation of what already exists and not
the meticulous replacement of what is missing – M. Devan 1995

5. EVOLUTION OF IMPRESSION MATERIALS
 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.

6.  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)
 1960s : Polyether impression material developed in Germany

7.  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

8. IDEAL REQUIREMENTS
 They should have low enough viscosity to adapt to the oral tissue, yet be
viscous enough to be contained in the impression tray.
 Should have adequate wettability.
 The material must have pleasant taste and odour.
 It should show adequate elastic recovery with no permanent deformation.
 It should have adequate strength to prevent tear or breakage

9.  The impression should be dimensionally stable after setting.
 The material must be bio-compatible.
 It should compatible with cast material.
 The material could be easily disinfected without loss of accuracy
 Material must have adequate shelf life for storage.
 Materials must be cost effective.

10. CLASSIFICATION
CLASSIFICATION BASED ON THEIR MECHANICAL PROPERTIES

11. Based on tissue compressibility
 Mucocompressive
 Mucostatic

12. Based on their chemical composition
Non elastic
• Impression plaster
• Impression
compound
• Impression waxes
Synthetic
• Polysulphide
• Polyether
• Silicones -
Condensation
Addition
Hydrocolloids
• Irreversible
• Reversible

13. According to use materials in dentistry
 Materials used for making impression of dentulous mouth:
1. Alginate
2. Agar
3. Non aqueous elastomers
 Materials used for edentulous mouth:
1. impression compound
2. Impression plaster
3. Zinc oxide eugenol
4. Waxes

14. NON ELASTIC IMPRESSION MATERIALS
 1. Impression Plaster
- used as mucostatic impression material for making final impressions for
edentulous patients
- Doesn’t compress and displace tissues during seating of tray due to its
fluidity
- Applicable to patients with displaceable soft tissues that should be recorded
in a passive state

15.  Composition
 ß-calcium sulphate hemihydrate
 Reacts with water to form calcium sulphate dihydrate
 W/P ratio– 0.5-0.6
 Expansion and setting times controlled by incorporating compounds designed to mediate
handling properties
 Potassium sulphate added as an anti-setting expansion agent
 Borax(retarder)- added to the powder to balance the setting acceleration caused by Pot.
Sulphate and to bring the setting time under control

16.  Alzarin red-to make clear distinction between the impression and model
 Custom tray constructed using 1-1.5mm spacer with acrylic resin or shellac
 Impression plaster can be used as wash material
 Techinque- “Puddling” the impression into place
 With remaining plaster in tray, the tray is seated in single movement
 Then tray is gently moved from side-to side and antero-posteriorly to take advantage of
fluidity of material
 Hemihydrate particles absorb moisture from the surface of the oral tissues allowing intimate
contact between impression material and the tissues

17.  Plaster impression material –very brittle and fractures easily
 When undercut is involved, fracture the impression to facilitate removal from mouth
 Beading of the impression done
 Coated with separating medium and cast in fresh plaster
 Disinfection- achieved with a 10 min soak in sod hypochlorite solution
 Not used regularly due to mechanical limitations
 Used frequently as occlusal registration material

18. ZINC-OXIDE EUGENOL IMPRESSION PASTE
 Composition-2 separate pastes dispensed in tubes
 One tube contains zinc oxide and vegetable or mineral oil • Other tube contains eugenol and
rosin

19.  Composition

20.  Setting reaction of ZOE
 Ionic in nature
 Requires ionic medium in which it can proceed at any desired rate
 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
 Two further coordinate bonds are formed by donation of pairs of electrons from methoxy
oxygen to zinc

21.  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

22.  Types of ZOE
 Classified as base paste(type I) catlyst paste(type II)
 Final set for type I paste-10 min type II paste-15min Actual time shorter when setting occurs
in mouth
 Shorten the setting time – by adding small amount of Zinc acetate or additional accelerator or
a drop of water in the paste before mixing or by extending mixing time
 Prolonging the setting time- cool spatula and mixing slab

23.  Disinfection
 2 % alkaline glutaraldehyde solution
 Immersed in solution for required time, rinsed and poured immediately

24.  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

25. IMPRESSION COMPOUND
 Also called “modelling plastic”
 Thermoplastic material
 Supplied in the form of cakes(red) and sticks (green, gray or red)
 Composition
 Types of Impression compound
 Type-I (Lower fusing)
 Type- II (Higher fusing)
Material Role
Mixture of
waxes
Principle ingredient
Thermoplasti
c resin fillers
Increase viscosity
and rigidity
Shellac,
stearic acid
and gutta
percha
Improve plasticity
and workability
Coloring
agents

26.  Type I (Lower fusing material)
 Cakes as a impression material for completely edentulous patients, the material is softened
by heat, inserted into the tray and placed against the tissues before it cools to a rigid mass
 Sticks- as a border molding material for the custom tray ,the material is used before making
the final impression

27.  Type II( Higher fusing material)
 Used as an adaptation material which requires more viscous properties
 Used for making primary impression of the soft tissues and then used a tray to support a thin
layer of a second impression material such as ZnOE paste, hydrocolloids or nonaqueous
elastomers

28. ELASTIC IMPRESSION MATERIALS
 1. Hydrocolloids
Reversible hydrocolloids: In which the bond holds the fibrils of colloid together
breaks at elevated temperature and becomes re-established when it is cooled.
Example : agar
Irreversible hydrocolloids : fibrils of the sol is formed by chemical reaction and
the process is irreversible
Example : alginate

29.  Basic concepts about colloids :
- often classed as fourth state of matter as colloidal state.
- can be considered as a compromise between the very small molecules
in solution & very large particles in suspension.
- Two phases :
Dispersed phase or dispersed particles
Dispersion phase or dispersion medium
- All colloidal dispersions are termed as sols.

30.  Types of colloids :
Solid or liquid in air (aerosols)
Gas liquid or solid in liquid (lyosol)
Gas liquid or solid in solid

31.  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 semisolid & produced from a sol by the process of gelation.
 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
 Gelation temperature : The temperature at which gelation occurs is known as
gelation temperature

32.  Dimensional effects :
 The Gel may lose water by evaporation from its surface or by exuding fluid
onto the surface by a process known as SYNERESIS. The gel shrinks as a result
of evaporation & syneresis.
 If a gel is placed in water, it absorbs water by a process known as IMBIBITION.
The gel swells during imbibition, thereby altering the original dimensions.
 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

33. AGAR – REVERSIBLE HYDROCOLLOID
 It is a sulphuric ester of a linear polymer of galactose.
 Gelation Temperature of agar is approx- 37˚-50˚c.
 The temperature at which the gel changes to sol i.e. liquefaction temperature is 70˚-
100˚c.
 Although it is an excellent impression material & yields accurate impressions, it has
been largely replaced by alginates & rubber impressions because of the minimum
equipment requirement and Possibility of obtaining metal dies from rubber
impression.
 Supplied as gel
 Available in tray and syringe consistencies
 Tubes used to fill water cooled trays and cartridges used with syringes

34.  Composition :

35.  Fillers such as diatomaceous earth, wax, clay, silica, rubber and similar inert
powders– used to control strength , viscosity and rigidity
 Thymol and glycerine added as bactericidal agent and plasticiser

36.  Making the agar impression :
- Process requires a 3 compartment conditioning unit for the agar tray material
- Allows liquefaction,storage and tempering
- Syringe material used only in liquefaction and storage compartments

38.  Liquefy the hydrocolloid gel in the tube in boiling water at 1000C for
minimum 10 min
 tube 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)

39.  Just before tempering completed,syringe material taken directly from storage compartment
and applied to the prepared teeth
 Note--- tempering time-3-10 min • if >10 min, partial gelation occurs
 syringe material doesn’t require tempering because maintained in fluid state to enhance
adaptation to tissues
 Syringe material first applied to the base of the preparation, then remainder of the prepared
tooth is covered
 Tip of the syringe is held close to the tooth and it remains embedded below the surface of
the syringe material to prevent entrapment of air bubbles

40.  Water soaked outer layer of hydrocollloid loaded tray and the gauze covering the tray
impression material are removed to ensure firm bonding to the syringe hydrocolloid
 Tray immediately brought into position,seated with light pressure and held with a very light
force
 Gelation accelerated by circulating cool (1821°C)through tray for 3-5 min
 During gelation process, tray must be held in mouth until gelation has proceeded to a point
at which gel strength is sufficient to resist deformation or fracture
 Tray removed with a snap

41.  Compatibility with gypsum : Contains borax- retarder for setting of gypsum products •
Deficiency of gypsum setting can be overcome by--Immersing agar impression in a solution
containing a gypsum accelerator(2% pot sulfate solution) prior to pouring of the impression •
By incorporating gypsum surface hardener in the material such as sulfate
 Disinfection : House hold bleach or iodophors
 Accuracy : most accurate
 Uses : Full mouth impressions without deep undercuts • Quadrant impressions without deep
undercuts • Single impressions • Can be used for crown and bridge impressions because of
their accuracy • Cast duplication • Tissue conditioner

42. 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 (sodium or
potassium or triethanolamine acid) (insoluble in water)
 Currently, alginate is more popular than agar because : • easy to manipulate •
comfortable for the patient. • relatively inexpensive • does not require
elaborate equipment

43.  Composition :

44.  Setting reaction : Two main reactions occurs during setting –
2Na3PO4 + 3 Ca SO4 Ca3(PO4)2 + 3 Na2SO4
(Sodium phosphate) (Calcium sulphate)
(Retarder) (Reactor)
Sodium Alginate + CaSO4 + H2O Ca Alginate + Na2SO4
(Powder) (Reactor) (Gel)

45.  Types of alginates :
 I. According to concentration of sodium phosphate
• Fast set • Regular set
 Types Mixing time Working time Setting time
I- Fast set 45 sec 1.25 mins 1-2 mins
II- Normal set 60 sec 2 mins 2-4.5 mins

46.  Making of alginate impression :
 Measured powder added slowly to premeasured water already poured into clean rubber
bowl
 Powder incorporated into water by carefully mixing with a metallic spatula flexible enough to
adapt well to the wall of the mixing bowl
 Avoid incorporating excessive air into the mix
 Vigorous figure of 8 stropping motion
 Mixing time- 45sec to 1 min
 Result should be a smooth creamy mixture that doesn’t drip off the spatula when raised from
bowl

48.  Mechanical mixing devices Include rotating mixing bowl , mechanical mixer with time-control
unit, a vaccum mixer for water/powder mixing
 Advantages- convenience, speed and reduction of human error

49.  Controlling the setting time :
Ideal W/P ratio- 20 ml water/8gms of powder 40 ml water/16gms of powder
Powder should be weighed not measured
Approx 2.5:1
Slight modification in W/P ratio affects 2 important properties--- tear strength elasticity
setting time best regulated by amount of retarder added during manufacturing
Can also be influenced by altering the temperature of water
Cool water in hot weather
Precool mixing bowl and spatula
Tap water-contains certain levels of metallic ions(Ca,Mg)
Tap water with a high hardness may accelerate setting time

50.  PROPERTIES :According to ADA specification No 18:
1.Flexibility : 14% at a stress of 1000gm/cm2
2.Elastic recovery : 97.3%
3.Tissue detail reproduction : 0.075mm
4.Compressive strength : 5000-8000/cm2
5. Tear strength : 350-700gm/cm2
6.Poor dimensional stability

51. ADVANCES IN ALGINATE
 Dust free alginate : no diatomaceous earth
 Two paste system: prevents contamination of the powder
 Chromatic alginate : determines the setting time
 Self disinfected alginate
 Extended pour : cavex – 100 hrs
extend a pour 4 weeks
storage solution is available
 Aliginate with polyacrylamide : to create smooth mix
 Alginate with improved wettability

52.  Laminate technique:The hydrocolloid in the tray is replaced with a mix of chilled alginate that
bonds to the syringe agar.
 Alginate gels by a chemical reaction whereas agar gels by means of contact with the cool
alginate rather than with the water circulating in the tray.
 Since the agar, not the alginate is in contact with the prepared tooth, maximum detail is
produced.

53. ELASTOMERIC IMPRESSION MATERIALS
 Soft and rubber-like & known as elastomers or synthetic rubbers
 Types :
 According to chemistry –
Polysulphides
Condensation polymerizing silicone
Addition polymerizing silicone
Polyether
Visible light curable polyether urethane dimethacrylate ( a new class added recently)

54.  According to Viscosity(ISO 4823)
Type 0—Putty consistency (very heavy)
Type 1—Heavy-bodied consistency (tray consistency)
Type 2—Medium-bodied consistency (regular bodied)
Type 3—Light-bodied (syringe consistency)
Extra low and putty available only for condensation and addition silicones • Polysulfide provided
only in light body and heavy body • No heavy body for condensation silicone

55.  Polysulphides:
 First synthetic elastomeric impression material introduced in 1950
 It is also known as Mercaptan or Thiokol. Interestingly, they were first developed as an
industrial sealant for gaps between sectional concrete structures.
 Supplied as : 2 paste system
 Available in low, medium and high consistencies
 Made up of a base and accelerator/reactor
 Brands- COE-FLEX,PERMALASTIC,NEOPLEX

56.  Composition :

57.  CHEMISTRY AND SETTING REACTIONS
 When the base and accelerator pastes are mixed, it undergoes a chemical reaction, whereby
the liquid polymer sets to form a solid, but highly elastic and flexible rubber like material.
 The lead dioxide reacts with the polysulfide polymer causing
 Chain lengthening by oxidation of terminal—SH groups
 Cross-linking by oxidation of the pendant—SH groups
 The reaction is exothermic with a 3–4 °C rise in temperature. It is accelerated by heat and
moisture.

58.  1. Unpleasant odor and color. It stains linen and is messy to work with
 2. These materials are extremely viscous and sticky. Mixing is difficult. However, they exhibit
pseudoplasticity, i.e. if sufficient speed and force is used for spatulation, the material will seem
easier to handle.
 3.The mixing time is 45 seconds.
 4. It has a long setting time of 12.5 minutes (at 37 °C).
 5. Excellent reproduction of surface detail.

59.  6. Dimensional stability The curing shrinkage is high (0.45%) and continues even after setting.
It has the highest permanent deformation (3–5%) among the elastomers. Elastic recovery
improves with time and so pouring of the model should be delayed by half an hour
 7. It has high tear strength
 It is hydrophobic so the mouth should be dried thoroughly before making an impression.
Care should also be taken while pouring the stone to avoid air pockets.

60.  Making of polysulphide impression:
 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
 Resilient network started to form
 During final set, a material of adequate elasticity and strength is formed that can be
removed past undercuts

61.  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
 - Subsequent pours are less
accurate.

62. SILICONES
 1. Condensation Silicone
 2. Addition Silicone

63. CONDENSATION SILICONE
 Followed in 1955
 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

64.  Composition :

66.  Working time: 3 min
 Setting time: 6-8 min
 Impression must be poured as soon as possible within first 30 min
 Curing involves a reaction of tri- and tetrafunctional alkyl silicates in the presence of stannous
octoate as a catalyst
 Sets by cross-linking between terminal groups of the silicone polymers and the alkyl silicate
to form a 3-D network
 Condensation polymerisation of alpha-omega hydroxy – terminated poly(dimethyl siloxane)
with tetraethyl orthosilicate in the presence of stannous octoate(catalyst) This reaction results
in the release of ethanol molecules

67. ADDITION SILICONE
 Commonly referred to as Polyvinyl siloxanes(PVS)
 Tubes The base and catalyst pastes come in equal sized tubes (unlike condensation silicones).
The different viscosities usually come in different colors like orange, blue, green, etc.
 Cartridge form with static mixing tips For use with a dispensing gun.
 Putty jars Two equal sized plastic jars—containing the base and catalyst.
 A larger electric driven autodispenser and mixing device is also available (Pentamix— ESPE).
This machine stores larger quantities. At the press of the button, it dispenses and mixes the
material.
 Brand name- Aquasil

68.  Composition :

69.  Working time: 2-4.5 min
 Setting time: 3-7 min
 Cast can be poured upto 1 week after making the impression
 Reaction activated by a platinum salt catalyst (chloroplatinic acid) without the release of
byproducts
 In presence of impurities or moisture, secondary reaction takes place between the residual
hydrides and moisture leading to evolution of hydrogen gas
 This can cause minute gaseous voids in the gypsum casts and reduce the effectiveness of
cross-linking polymer structure
 Automatic mixing systems simplified their manipulation, reduced voids in impressions,
reduced the amount of material wasted and reduced the sensitivity of their mixing technique

70.  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

71.  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

72. POLYETHER
 Introduced in Germany in late 1960s
 Good mechanical properties and dimensional stability, but short
 working time, very stiff material and expensive
 Supplied as two-paste system in low, medium and high consistencies
 2 types: 1. based on ring-opening polymerization of aziridine rings which are at the end of branched
polyether molecules . based on an acid-catalyzed condensation polymerization of polyether prepolymer
with alkoxysilane terminal groups
 Brands- IMPREGUM

74.  1st type :Main chain probably a copolymer of ethylene oxide and tetrahydrofuran
 Cross-linking and setting promoted by an initiator and an aromatic sulfonate ester
 R alkyl group • Produces cross-linking by cationic polymerisation via the imine end groups
 Supplied as 2 pastes: base and accelerator

75.  Composition :

76.  Working time: 2.5 min
 Setting time: 4.5 min
 Poured upto 1 week of storage

77.  Type 2nd : Based on an acid-catalyzed condensation polymerization of polyether prepolymer with
alkoxysilane terminal groups
 Mechanism similar to condensation silicones
 Material often called hybrid
 Behave very much like the 1st type due to ether linkages
 High degree of wettability
 Inherent hydrophillic nature
 Relative stiffness Excellent material for good duplication of fine details and rigid support for pick-up
copings

78.  Advantages Disadvantages
 Dimensional stability - Set material very stiff
 Accuracy - Imbibition
 Shorter setting time - Short working time.
 Automix available - Allergic hypersensitivity in some
cases.

79. MAKING OF IMPRESSION WITH ELASTOMERIC MATERIALS
 Fabrication of gypsum models ,casts and dies involves 6 major steps:
 1. Preparing a tray
 2. Managing tissue
 3. Preparing the material
 4. Making the impression
 5. Removing the impression
 6. Preparing stone casts and dies

80. IMPRESSION TRAYS
 Custom tray recommended to reduce the quantity of material required
 In case of severe undercuts, custom tray avoided
 Prior to impression making, uniform thickness of tray adhesive applied

81. SOFT TISSUE MANAGEMENT
 Displace the gingival tissues, control gingival haemorrhage and control sulcular fluids to ensure access
for the tooth preparation and making impression
 Gingival retraction cord- most commonly used

83. MANIPULATION OF IMPRESSION MATERIALS
 The 5 main mixing techniques are
 1. Hand or manual spatulation
 2. Manual kneading
 3. Rotary table assisted mixing
 4. Static or extrusion mixing
 5. Dynamic mechanical mixing

84.  Hand mixing :
 Dispense the same length of materials onto a mixing pad or glass slab • Catalyst paste first
collected on stainless steel spatula and then spread over base paste • Mixture is then spread
over the mixing pad • Mass is then scraped up with the spatula blade and spread uniformly
back and forth on the mixing pad
 Process continued until the mixed paste is uniform in color with no streaks of the base or
catalyst appearing in the mixture • 2 putty systems(condensation and addition silicone)
dispensed by volume using equal number of scoops of each material • Knead the material
with fingers until a uniform color is obtained

85.  Static mixing :
 Transforms 2 fluid(or paste-like) materials into a homogenous mixture without mechanical
mixing • Device used- gun for compressing materials into a 2cylinder cartridge, which
contains the base and catalyst separately, as well as mixing tip
 Mixing tip is made of helical mixer elements in a cylindrical housing • Mixer elements are
series of alternating right and left –turn 180°helixes positioned so that leading edge of one
element is perpendicular to the trailing edge of the next • Length of each material is the same
as the inner diameter of the cylinderical housing

86.  Dynamic mechanical mixing :
 Device uses motor to drive parallel plungers,forcing the materials into a mixing tip and out
into an impression tray or syringe • Motor driven impeller mixes the materials as they are
extruded through the tip • Materials supplied in collapsible plastic bags housed in cartridge •
Polyether and addition silicone

87. MAKING OF AN IMPRESSION
 3 techniques:
 Multiple-mix technique
 Monophase technique
 Putty wash technique

88.  Multiple mix technique :
 Syringe material(light body)and tray material(heavy body)
 Lighter material injected within or around the tooth preparation
 Filled tray then inserted in the mouth and seated over the syringe material
 Tray material force the syringe material to adapt to the prepared tissues

89.  Monophase technique(single stage) :
 Medium body polyether and addition silicone
 Only one mixture is made and a part of the material is placed in the tray and another portion
in syringe for injection in the prepared tissues
 Success depends on pseudoplastic (shear thinning) property of material

90.  Putty wash technique (two stage):
 Originally developed for condensation silicone to minimize the effect of associated
dimensional changes
 Thick putty material placed in stock tray and a primary impression made
 Space for light-body “wash” material provided
 Mixture of thin consistency wash material placed into putty impression and preparation

92. REMOVAL OF THE IMPRESSION
 Shouldn’t be removed until curing progressed sufficiently to provide adequate elasticity ,so
distortion doesn’t occur •
 Typically impression should be ready for removal within at least 10 min from time of mixing,
allowing 6-8 min for impression to remain in mouth
 Mechanics of removing impression– separation at the impression/tissue interface and
stretching of the impression • 1st step to break the physical adhesion between the tissue and
the impression • Polyether requires extra effort • 2nd step stretches the impression enough to
pass under the height of contour of hard tissue to remove impression

93. RECENT ADVANCES
 Advances in alginate
 Pentamix
 Intraoral scanners

94. ADVANCES IN ALGINATE
 Dust free alginate : no diatomaceous earth
 Two paste system: prevents contamination of the powder
 Chromatic alginate : determines the setting time
 Self disinfected alginate
 Extended pour : cavex – 100 hrs
extend a pour 4 weeks
storage solution is available
 Aliginate with polyacrylamide : to create smooth mix
 Alginate with improved wettability

95.  Pentamix :Automatic Mixing System for Impression Materials
 • Economical: Use only the exact amount of material you need • Reliable:
Remarkably mixed material assures consistent quality • Hygienic: Direct filling
of tray and syringe reduces the risk of cross-contamination • Efficient: Push
button activation makes it fast and easy to handle

96.  The innovative design of the Red Penta™ Mixing Tip reduces dispensing
forces by up to 50 %. This also allows heavybodied pastes to be reliably
conveyed and mixed without the cartridge and foil bag caps being subjected
to excessive pressure.
 The tried and tested PentaMatic™ Auto Open System from 3M ESPE base
paste foil bag cap has been reinforced with additional struts helps to prevent
breakage. The PentaMatic foil bag cap of the catalyst features a redesigned
opening with a widened base helps to prevent the opening from snapping off
even when under load.
 The new Penta™ Cartridges now include an integrated steel cylinder, designed
helps to prevent the expansion or breakage of cartridges.

98.  Intra oral scanners :
 Trios, 3Shape.
 Sirona, Cerec.
 Itero Element 2.
 Planmeca® Emerald Scanner.
 3M Tru def.
 Carestream.
 Advantages: less patient discomfort
time efficient
simplified clinical procedure
no more plaster cast

100. REFERENCES
 Text book of phillip’s dental material sciences 12th edition
 Text book of boucher 13th edition
 Alaghari S, Velagala S, Alla RK, Ramaraju AV. Advances in alginate impression materials: a review.
International Journal of Dental Materials. 2019 Nov 15;1(2):55-9.
 Mangano F, Gandolfi A, Luongo G, Logozzo S. Intraoral scanners in dentistry: a review of the current
literature. BMC oral health. 2017 Dec 1;17(1):149.