2.  A dental impression is defined as the negative record of the
tissues of the mouth . It is used to reproduce the form of the
teeth and surrounding tissues.

3.  Have pleasant taste, odor and esthetic color.
 Not contain any toxic or irritating ingredients.
 Be economical.
 Have adequate shelf life for storage and distribution.
 Be easy to use with minimum equipments.
 Exhibit dimensional stability.
 Have adequate strength so that it will not break or tear while
removing from the mouth.
 Posses elastic properties with freedom from permanent
deformation after strain.
 Be able to be electroplated
 Be compatible with die and cast materials

4.  There are several 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,
zinc oxide eugenol.
Alginate,
polysulfide,
polyether, silicone,
Set by temperature
change(reversible)
Compound, waxes Agar hydrocolloid.

5.  Impression compound is
rigid,reversible impression material
sets by physical change.
 It softens on heating and hardens on
cooling.
 ADA specification no 3
 Supplied as sheets,sticks,cakes and
cones.

6.  Making preliminary impression of edentulous mouth.
 For individual tooth impression.
 To make a special tray.
 Border moulding.
 To check undercuts in inlay preparations.
Composition:
INGREDIENTS PARTS
resin 30
Copal resin 30
Carnauba wax 10
Stearic acid 5
Talc 75

7.  Glass transitional temperature =39 degree centigrade.
 Fusin temperature=43.5 degree centigrade.
 They are poor conductors of heat.
 Coefficient of Linear Expansion is high.
 Good dimensional stability.
 Good flow.
 Fine reproduction of detail.

8.  Material can be reused several times.
 Inaccurate portions can be remade without having to remake
the entire impression.
 Accuracy can be improved by flaming surface material.
Disadvantages:
 Distortion due to poor dimensional stability.
 Compress soft tissue while making impression.
 Difficult to remove if there are undercuts.
 Difficult to record details because of high viscosity.

9. Applications:
 Cementing and insulating medium.
 Temporary filling.
 Root canal filling material.
 Bite registration paste.
 Impression material for edentulous
patients.
 Temporary relining material for
dentures.

10. Composition:
Base paste Accelerator paste
Zinc oxide-87% Eugenol-12%
Fixed vegetable oil or
mineral oil-13%
Gum-50%
Filler(silica)-20%
LANOLIN-3%
Resinous balsam-10%
Accelerator solution
(calcium chloride)-5%

11.  Setting reaction is an acid base reaction to form a chelate.
 This reaction is also known as chelation and the product is
called zinc eugenolate.
 Zno + H2O Zn(OH)2
 Zn(OH)2 +2HE ZnE2 +2H2O
(Base) (Acid) ( Salt)
Setting time;
Initial setting
time
Final setting
time
Type 1 3-6 min 10 min
Type 11 3-6 min 15 min

12.  Particle size of zinc oxide powder.
 Longer mixing time, shortens setting time.
 High atmospheric temperature and humidity accelerate
setting.
 Setting can be delayed by cooling mixing slab, spatula or
adding small amount of retarder or oils or waxes.
Properties:
 Good consistency and flow.
 Detail reproduction.
 Rigid and having good strength.
 Good dimensional stability.

13.  Mixing is done on an oil-impervious paper or glass slab.
 Two ropes of paste of same length and width, are squeezed
on mixing slab.
 A flexible stainless steel spatula is used for mixing.
 Two ropes are combined until a uniform colour is obtained.
 Mechanical rotary mixing are also used.
 Mixing time is one minute

14.  It has enough working time to complete border moulding.
 It can be checked in mouth repeatedly without deforming.
 It registers accurate surface details.
 It is dimensionally stable.
 Does not require separating media since it does not stick to
cast material.
 Minor defects can be corrected.
Disadvantages:
 Requires special tray for impression making.
 Sticky in nature and adheres to tissues.
 Burning sensation of eugenol causes tissue irritation.
 Highly inelastic in nature.

15.  NON-EUGENOL PASTE are
developed to overcome the burning
sensation caused by eugenol.
 Bactericides and other medicaments
are also incorporated.
 Used in eugenol irritant patients.

16.  Agar hydrocolloid was the first successful
impression material to be used in dentistry.
 It is an organic hydrocolloid extracted from
certain types of seaweeds.
 Agar is a reversible hydrocolloid.
 Since it is reversible can be reused.

17.  As tissue conditioner.
 For full mouth impression without deep undercuts.
 Used extensively for crown and bridge impression before
elastomers came to the market.
 Widely used at present for cast duplication.
 Supplied as;
 Gel in collapsible tube(for impression)
 A number of cylinders in a glass jar(syringe material).
 In bulk containers(for duplication)

18. INGREDIENTS PERCENTAGE BY WEIGHT
Agar 13-17%
Borates 0.2-0.5%
Potassium sulphate 1-2%
wax, hard 0.5-1%
Thixotropic material 0.3-0.5%
Alkylbenzoates 0.1%
water Around 84%
Coloring and flavoring agents Traces

19.  Agar-basic constituent.
 Potassium sulphate-It counters retarding effects of
borates.
 Wax-filler.
 Thixotropic material-plasticizer.
 Alkylbenzoates-preservative.
 Coloring agents-for patients comfort
 Water-dispersion medium.
Manipulation;
Agar hydrocolloid requires special equipments ;
 Hydrocolloid conditioner.
 Water cooled rim lock tray.

20.  Rim lock trays with water circulating
devices are used (water cooled rim
lock tray).
 Rim lock has a beading on the
inside edge of the tray which help
to retain the material within the
tray.
 It also has an inlet and outlet for
connecting water tubes.
 The tray should allow a space of
3mm occlusally and laterally and
extend distally to cover all teeth.

21. Boiling section or liquefaction section Ten minutes in
boiling water at
100 degree
Storage section 65-68 degree
is ideal
Tempering section 46 degree for
two minutes
with material
loaded in tray

23. Syneresis and imbibition;
 The hydrocolloid gel may loose water by exuding of fluid. and
this process is known as synersis.
 Imbibition is the process of gaining of water when immersed
in water.
 Importance-both the phenomenon can cause dimensional
changes and produce inaccurate casts. To avoid this
impressions should be poured immediately.
Flow;
The material is sufficient fluid to record fine details.

24.  Material is sufficiently fluid to record details.
Flexibility;
 Material is highly flexible.
Hysteresis;
Temperature lag between liquefaction and gelation.
Elasticity and elastic recovery;
 Highly elastic in nature. Elastic recovery occurs to the extent
of 98.8%
Fine reproduction of detail;
Accuracy and dimensional change
 They expand when stored in water or 100% relative humidity
Working and setting time
 Working time- 7 to 15 min
 Setting time – 5 min


25.  Main disinfectants used include iodophor,bleach or
glutaraldehyde.
ADVANTAGES
 Accurate die can be prepared, if material is properly handled
 Has good elastic properties.
 Good recovery from distortion
 Palatable and well tolerated by patient
 Cheap

26.  Not flow well compared to newly available material
 It cannot be electroplated
 Tears relatively easily
 Only one model can be poured

27.  Its an irreversible elastic
hydrocolloid
 It is a mucous extract yielded
from certain brown sea weeds
 Types
 type 1 – fast setting
 type 2- normal setting
 Applications
 Used for impression making;
 when there are undercuts
 in mouth with excessive flow of
saliva
 For impression to make study
models and working casts
 For making preliminary
impression

28. INGREDIENTS FUNCTIONS
Sodium or pottasium alginate-15% React with calcium ion
Calcium sulphate(reactor) - 16% React with potassium alginate
Zinc oxide - 4% Acts as filler
Potasium titanium flouride -3% Gypsum hardener
Diatomacous earth -60% Acts as filler
Sodium phosphate(retarder) -2% React with calcium sulphate
Colouring and flavouring agents Wintergreen, orange etc.

29.  Two main reaction occur
 2Na3Po4 + 3CaSo4 Ca3 (PO4)2
+3Na2So4
 Here firstly the retarder is completely get
reacted to delay the reaction time.
 Sodium alginate + CaSo4+H2O calcium
alginate +Na2So4

30.  Alginate has pleasant taste and smell
 It is highly flexible
 Good elasticity and elastic recovery
 Fine reproduction of tissue detail
 Compressive strength – ranges from 0343-70
mpa
 Tear strength- 350-700gm/cm2
 Dimensionally stable
 Poorly adheres to the tray
 Biological properties- inhalation of silica particles
cause health hazards.

31.  steps in manipulation
 fluff or aerate the powder by
investing can several times.
 for mixing a clean flexible
plastic bowl and clean wide
bladed stiff metal spatula is
being used.
 proper water powder ratio
specified by the manufacturer
should be used(1 measure water
with two level scoops of powder)
 mixing is started with a stirring
motion. vigorous figure 8 motion
can also be used.

32.  Mixing time
 fast setting - 45 sec
 normal setting- 60sec
 Working time –
 fast setting – 1min
 normal setting – 2 min
 Gelation time
 fast setting - 1 to 2min
 normal - 2 to 4.5 min

33.  Easy to mix and manipulate
 Low cost
 Comfortable to patient
 Hygienic
 Good surface detail even in presence of saliva
 Accuracy if properly handled
 Minimum requirement of equipment

34.  Cannot be electroplated
 It cannot be corrected
 Poor dimension stability
 Poor tear strength
 Distortion may occur if not properly handled

35.  Classification
 A) according to chemistry
 1) polysulfide
 2) condensation polymerizing silicones
 3) addition polymerizing silicon
 4) polyether
 B) according to viscosity
 1) light bodied(syringe consistency)
 2) medium(regular)
 3) heavy body(tray consistency)
 4) very heavy(putty consistency)


36. A) Base paste
 liquid polysulfide polymer – 80-85%
 inert fillers - 16-18%
B) reactor paste
 lead dioxide -60-68%
 dibutyl phthalate -30-35%
 sulphur -3%
 retarders like magnesium stearate

37.  Base and accelaration paste are mixed
together which undergoes chemichal reaction
to form polymer
 The reaction is exothermic – 3-4 degree
Celsius rise in temperature
 Mercaptan+lead oxide polysulfide
+water

38.  Unpleasant order and colour
 Material is extremely viscous and sticky and
exhibits pseudoplasticity
 Long setting time of 12.5min
 High tear strength
 Good flexibility
 Excellent reproduction of surface detail

39.  Types;
 1-condensation silicones
 2-addition silicones
 Condensation silicones;
 Also known as conventional silicones.
 Available in three viscosities namely
light,medium bodied and heavy.
Composition;
Base
 1-polydimethyl siloxane.
 2-colloidal silica
 Color pigments.
Accelerator
Stannous octoate

40.  Dimethyl siloxane+orthoethyl silicate silicone in
presence of stannous octoate.
Addition silicone
Composition;
Base paste and catalyst paste;
Setting reaction;
Vinyl siloxane+silane siloxane silicone rubber

41. ◦ Good mechanical and compressive
strength comparing other
elastomers.
◦ Available in three viscosities.
◦ Consist of base paste and catalyst.