BY FATEEMA PRIYAM FEROZ

2. IRREVERSIBLE HYDROCOLLOIDS
FATEEMA PRIYAM
1 ST YR P.G
DEPT OF PROSTHODONTICS

3. CONTENTS
• CLASSIFICATION
• IDEAL REQUIREMENTS OF AN IMPRESSION MATERIAL
• ALGINATE
HISTORY
COMPOSITION
SETTING REACTION
PROPERTIES
DIMENSIONAL CHANGES
PERMANENT DEFORMATION
DISINFECTION
COMPATIBILITY WITH GYPSUM

4. • ALGINATES
SELECTION OF THE TRAY
DISPENSING AND STORAGE
MANIPULATION
MIXING
MAKING IMPRESSION
COMMON CAUSES OF REMAKING
MANAGING A GAGGING PATIENT
• MODIFIED ALGINATES
• BIOHAZARDS DUE TO ALGINATES
• RECENT ADVANCES
• DISCUSSION
• SUMMARY
• REFERENCES

5. CLASSIFICATION OF IMPRESSION MATERIALS
BASED ON SETTING MECHANISM
Reversible:
Impression compound,dental waxes ,agar hydrocolloids
Irreversible
Alginate,Zinc oxide eugenol and elastomers

6. BASED ON FLEXIBILITY
Inelastic / rigid:
Plaster of Paris,impression compound,zinc oxide eugenol
Elastic:
Elastomers,Alginate,Agar hydrocolloid
BASED ON THE AMOUNT OF PRESSURE
Mucostatic impression materials:
Zinc oxide eugenol impression paste,Impression plaster
Mucocompressive impression material
impression compound,impression waxes,Alginate

7. BASED ON THE TYPE OF TRAY
Perforated metal tray:
Alginate hydrocolloid
Water cooled metal tray:
Agar hydrocolloid
Custom tray:
Zinc oxide eugenol,Impression plaster,Elastomeric impression
material

8. IDEAL REQUIREMENT OF IMPRESSION MATERIALS
They should be fluid enough to adapt to the oral tissues.
They should be viscous enough to be contained in the impression tray.
They should have a pleasant door,taste and color.
Satisfactory consistency,texture and should wet the oral tissues.
They should set within a suitable amount of time once seated in the mouth.
The set material should not distort or tear during removal from the mouth.

9. It must be dimensionally stable atleast till the cast is poured.
It should be cost effective.
It should be stable for a long period of time long enough to permit pouring
of the cast.
It should be readily disinfected without any loss of accuracy
***No impression material fulfils all the ideal requirements.

10. THE SIX IMPORTANT STEPS INVOLVED IN CREATING A DUPLICATE
CAST OF THE ORAL TISSUES
PREPARATION OF THE TRAY
PREPARATION AND LOADING OF THE IMPRESSION MATERIAL
ONTO THE TRAY
MAKING AN IMPRESSION
REMOVAL OF THE IMPRESSION FROM THE ORAL CAVITY
DISINFECTION OF IMPRESSION
PREPARATION OF THE CAST,MODEL /DIES

11. ALGINATES

12. HISTORY
The making of impressions to construct dentures have always been
difficult. Most failures were due to the fact that compound wax would
usually distort and plaster impressions had to be removed in fragments
and put together with sticky wax. This would result in inaccurate
reproduction of the tissues and undercuts around the teeth.
Only a material that was sufficiently elastic so that it could be removed
from the mouth without distortion could solve this problem . As a result,
flexible impression materials which remain elastic after setting were
developed.

13. The concept evolved from the use of jelly mould for making impressions of
still life objects such as statues. In 1925,Alphonse Poller ,an
Austrian invented and patented a material called Nogacoll. In 1931, after the
inventors death, the formula was acquired by a company that sold it under
the name of Kelco. Within a few years a dozen competing brands were in the
market,mainly reversible hydrocolloids, with the main ingredient being agar,
which is the vegetable colloid derived from seaweed.This jelly like substance
softened when heated and set when cold.

14. The technique of using this was complicated because of the need for
special heaters, syringes and water cooled trays. When the types of agar
used for the manufacture were no longer available in America during the
Second World War the need for brown algae increased.

15. STRUCTURAL FORMULA OF ALGINIC ACID
Derived from brown seaweed (algae)
A linear polymer with numerous carboxyl acid groups and
named anhydro-β-d mannuronic acid-also called as alginic
acid.
Alginic acid and most of the inorganic salts are insoluble in
water ,but the salts obtained with sodium,potassium and
ammonium are soluble in water.

16. Easy to manipulate
Comfortable for the patient
Patient acceptability is high
Inexpensive
Hydrophilic,hence can displace blood and saliva
Easy to pour and retrieve cast
Compatible with gypsum
Does not require elaborate equipment
Elastic in nature
ADVANTAGES OF ALGINATE

17. Might tear on removal from mouth
Must be poured immediately because -dimensionally
unstable due to syneresis and imbibition
Can pour the cast only once
Cannot be electroplated
Limited detailed reproduction
DISADVANTAGES

18. COMPOSITION
SODIUM / POTASSIUM ALGINATE-18%
Main reactive ingredients
Forms sol with water and becomes cross linked to form gel after reacting with
calcium ions.
CALCIUM SULFATE DEHYDRATE-14%
Reacts with potassium alginate to form an insoluble calcium alginate gel,source of
calcium ions which form cross linking of the alginate chains which provides calcium
ion reactor.
POTASSIUM SULFATE,ZINC FLOURIDE,SILICATE AND BORATES-10%
Counteracts the inhibiting effect of hydrocolloid on the setting of gypsum,thus
ensuring that the surface of the stone cast poured in the alginate impression will be
of good quality.
DIATOMACEOUS EARTH/SILICATE-50-60%
Acts as a filler to increase the strength and stiffness of the gel,produces a firm gel
surface that is not tacky

19. SODIUM PHOSPHATE-2%
Reacts preferentially with calcium to provide ample working time before gelation
GLYCOLS
To make the powder dust free
PIGMENTS-traces
to provide colour
PEPPERMINT CHLORHEXIDINE-traces
To produce a pleasant taste
QUATERNARY AMMONIUM SALTS-1-2%
Disinfection of micro-organisms
SODIUM SILICA FLUORIDE-4%
Controls pH (gives a color change when setting is complete)

20. SETTING REACTION

21. When mixed with water, chemical reaction occurs
that cross-links the polymer chains. Simultaneously a
physical change is also taking place, forming a three-
dimensional network structure. This is an irreversible
process, therefore this can be used only once.
(chemical reaction-irreversible)
SOL GEL

22. Sol-gel reaction can be explained as
Soluble alginate+Calcium sulphate
Formation of insoluble calcium alginate gel.
(This forms rapidly thus reducing the working time)
To prevent this Trisodium phosphate is added to prolong the working time
(thus calcium reacts with this rather than reacting with the soluble alginate)
When the supply of trisodium phosphate is exhausted ,the calcium ions begin to
react with the potassium alginate to produce calcium alginate
The setting time can be observed from the time of mixing until the material is no
longer tacky or sticky when it is touched with a clean,dry,gloved finger

23. Later, when the phosphate ions are consumed , the calcium
ions react with the soluble potassium alginate to form an
insoluble calcium alginate gel. The reaction results in tying
altogether a chain of molecules of the salt into a network
structure typical of gels. The calcium ions that are released
from the calcium sulphate, act as a cross-linking agent.

24. The temperature of water controls the rate of the setting
reaction. Warm water increases the setting rate and cooler
water slows the setting reaction. Alginate is supplied by most
manufacturers in the regular set and fast set variety . Regular
set gels in 3 to 4.5 minutes where is fast set materials gels in
1.5 to 3 minutes.

25. PROPERTIES
Working time-defined as the period from the beginning of mix till the
impression material no longer is able to adapt and reproduce finer
details of the surface.
The impression must be thoroughly mixed, loaded into the tray and
seated in place during this period of time.

26. CONTROLLING THE SETTING TIME
Fast setting-1. 5 to 3 minutes
Slow setting-3 to 4.5 minutes
The setting time can be altered by altering the temperature of water.
Materials exhibit different degrees of sensitivity to temperature. In hot
weather special precautions should be taken to provide cool water for
mixing so that premature gelation does not occur.
It may be necessary to pre-cool the mixing bowl and spatula.

27. FACTORS AFFECTING THE SETTING TIME
Changing the water powder ratio
The setting time can be modified to some extent by controlling the
temperature of the mixing water
Decreasing the water temperature increases the setting time
Using water at an elevated temperature reduces the working time
and setting time

28. Alginate material adjacent to the oral tissues sets more rapidly, while
that adjacent to the cooler tray sets more slowly. Hence one must
ensure that the impression tray is not moved during setting else
distortion occurs .

29. Setting time is detected by the loss of surface tackiness.
Colour changing alginates provide a visual indication of working and
setting time. The mechanism of colour change is the pH related
change in the colour of the dye.
How to check setting of the material???

30. CAUSES OF DIMENSIONAL CHANGES IN ALGINATE
Alginate loses or gains water which is trapped within the gel by
syneresis, imbibition and evaporation. Since the impression is
removed from the mouth and exposed to the air at room temperature,
some shrinkage will take place due to syneresis and evaporation.
If immersed in water, swelling will take place due to imbibition.
Thermal changes also contribute to dimensional changes. With
alginates, impressions shrink slightly because of the thermal
difference between the mouth temperature (37℃)and the room
temperature(23℃)

31. METHODS TO AVOID DIMENSIONAL CHANGE
• For best results the impression should be exposed to air for as
short as possible
• The cast can be poured immediately
• The impression should be stored in hundred percent relative
humidity in a plastic bag /wrapped in a damp cotton.

32. STRENGTH
• Maximum gel strength is required to prevent fracture and to ensure
elastic recovery of the impression upon its removal from the mouth.
• Insufficient spatulation results in failure of the ingredients to mix
properly.
• Overmixing can break up the calcium alginate gel network as it forms
and weakens its strength.

33. Spatulation time
Spatulation done insufficiently-results in failure of the ingredients to
dissolve sufficiently and decreases the strength
Overspatulation-breaks off the calcium alginate gel network by
incorporating air bubbles and reduces its strength

34. Permanent Deformation
It mainly depends on
Degree of undercut
Thickness of material between the tissue and the tray
Time duration for which it remains compressed
Recovery time after the release of the load

35. Precautions to reduce permanent deformation of impression
Ensure that there are no deep undercuts, greater it is greater the amount of
compression leading to permanent deformation
Sufficient bulk of material between the tissue and the tray approximately 5 mm
Remove the impression in a snapshot manner
The degree of cross-linking continues to increase after the material has
apparently set. Waiting a minute or two before removing the impression
enhances the elastic nature of the material.
Long recovery time results in lower permanent deformation

36. Flexibility
ADA specification limits a range of 5 to 20% at the stress of
1kg/ cm². Typical values for commercial alginates, are between
12 to 18%, whereas hard setting alginates are 5 to 8 %. Thicker
mix this results in lower flexibility.

37. Disinfection
Since the hydrocolloid material must be poured within a short time the
disinfection procedure should be relatively rapid to prevent
dimensional changes.
Studies have shown that test viruses have been inactivated in alginate
impression by 10 minute soak in 0. 5% sodium hypochlorite or a
10 minute wait after spraying the impression with this solution,or
a 10 minute immersion in gluteraldehyde.

38. Clinical significance
Alginate impression must be removed from the mouth after breaking the
peripheral seal.
When gelation is complete ,the impression is removed with a sudden
pull.
Avoid torquing or twisting the impression in an effort to remove it quickly
Permanent distortions due to viscoelastic effects and tearing are
reduced slightly by using a large bulk of material. It is better to have
approximately 3 to 5 mm of material between the tissue and the tray.

39. Compatibility with gypsum
The impression must be rinsed well in water to remove saliva and blood
as it interferes with the setting of the gypsum model.
After disinfection all the free water should be removed before pouring in
stone, as residual water will dilute the model material and result in a soft,
chalky surface of the model which will be easily damaged.
SODIUM
SULPHATE???

40. • A rough stone will result if excess rinsing water has collected on the
surface of the impression at the time the stone mixture is poured.
• Excessive dehydration can also cause syneresis and dehydration of the
impression.The surface of the impression should be shiny but with no
visible water film or droplets at the time the impression is poured with
model or die material.
• The stone cast should be kept in contact with the impression for a minimum
of 30 minutes ,preferably for 60 mins,before the impression is separated
from the cast.

41. Objectives for taking alginate impressions
All teeth in the upper and lower arch
The entire alveolar process
The retromolar area of the lower arch
The area of the hamular notch in the upper arch
A detailed ,undistorted and bubble free reproduction of the oral tissues.

42. Selection of the tray
Completely cover the tuberosity
Be 4 mm wider than the most apical portion of the alveolar process
at the molar region
Cover the anterior teeth with the incisors contacting the flat portion
of the tray about 4 mm from the rest palatal part of the tray
FOR MAXILLARY TRAY

43. CRITERIA FOR MANDIBULAR TRAY
Cover all teeth and the retromolar pad
Be 4 millimetre wider than the buccal and lingual portions of the anterior
teeth

44. Modification of the tray
To be sure the alginate flows into the labial vestibule when the impression is
added,rope wax may be added to the anterior surface. The rope wax may
be added to other borders to make sure that any extensions of the alginate
are well supported.

45. Dispensing and storage
Alginate is made available in either a sealed pre weighed packet/
or in bulk form
For correct proportioning of the powder and water ,the manufacturer supplies
a suitable measuring spoon.
Individual pouches are preferred because there is less chance for
contamination during storage.

46. Shelf life is affected by storage temperature and moisture.
The powder should be mixed thoroughly before use to eliminate the segregation
that may occur during storage and to incorporate the surface layer,which is often
contaminated with moisture picked up from the atmosphere.
Material should be stored in a dry place with the lid tightly closed in bulk
packing.

47. MANIPULATION
EQUIPMENT REQUIRED
ALGINATE
PLASTIC MEASURING CYLINDER FOR WATER(with special markings
provided to measure the correct amount of water)
SUPPLIED SCOOP FOR POWDER
RUBBER MIXING BOWL
STIFF WIDE BLADED STEEL SPATULA
PERFORATED TRAY IS SELECTED.

48. PROPORTIONING
Measure cool (18℃/24℉) water for required number of scoops.
Amount of alginate powder depends on the size of the arch.
Normally 18-20 grams of powder is sufficient for an impression of one arch.
When dispensing the powder,the scoop is used to remove the appropriate
amount of powder by filling it and levelling it with the blade of the spatula.

49. Fluffing is required as materials supplied in large quantities have a tendency
to undergo separation as the dense ingredient falls to the bottom of the
container.
This must be overcome by inverting the container before use so it prevents
impaction of the powder and ensures that the reproducible volume of
material is used in each mix.
Correct amount of water is emptied into the mixing bowl first ,then the
alginate is carefully dispensed onto the surface of the water.

50. Mixing the alginate
Stir powder and water vigorously to wet powder completely,care should be
taken to avoid whipping air into the mix-to avoid this problem a vacuum
mixer can be used.
Vigorous figure of eight motion is best,with the mix being swiped against
the sides of the rubber mixing bowl with intermittent rotations of the spatula
to press out air bubbles.
Wipe the mix against the side of the bowl for 60seconds to homogenise and
remove air bubbles.

51. The entire spatulation should take approximately 1 minute,fast setting
should be accomplished in no more than 45 seconds.
Care should be taken not to overmix ,because this limits the working time
and breaks up the gel that is forming,thus reducing the strength of the final
alginate.
Inadequate mixing procedures produces a grainy material with low strength.
Mix should be creamy ,thick,smooth consistency that does not drip off the
spatula when it is raised from the bowl.

53. Making the impression
1. Push the left corner of the mouth away with the side of the tray
2.Insert the tray with the rotary motion
3.Place the left heel of the tray in contact followed by the anterior and then the
right heel
4.Have the patient lift the tongue and with the free hand pull the lip down gently.
5.Seat the tray in the direction of the long axis of the anterior teeth, and alginate
should flow into the vestibule
6.Apply the seating force moderately slowly to allow the alginate to flow properly
For lower arch

54. • At final seating the incisal edges and cuspal tips should be atleast 1 to 2 mm
from the metal surface of the train
• The tray is held in position until the alginate has set, which is about one minute
after it has lost its tackiness testing by touching two persons with the finger.
• The set impression is removed with the rapid ,firm pull.

55. For upper arch impressions
Start seating the tray by positioning it's posterior border and then
continue seating parallel to the axis of the central incisors so that most
of the excess alginate flows both in labial or buccal direction but not in
a palatal direction.
Break the peripheral seal by running a finger around the edge and
remove the impression with the rapid firm full,and use a
downwards sideways flipping motion to remove the impression.

56. A thick,pasty consistency can sometimes cause some patients to
gag.Although gagging has a physical component,it is atleast as much
psychologically as well as physically induced.
Therefore how you approach patients has a bearing on whether they
gag or not.
To prevent gagging,avoid anxiety producing actions or words,be gentle
and practice patient distraction.Very occasionally you may need to use
topical anaesthetic,a lozenge etc.
Educate the patient regarding the upcoming procedure.
Just say "I am going to take a duplicate of your teeth rather than saying
I am going to take a bowl full of material and put in your mouth till it
hardens".This will increase their tendency to gag,
PREVENTION OF PATIENT GAGGING

57. • Pleasant conversations distracts the patients.
• Tipping the patients head back slightly for mandibular impressions and forward
for upper impressions helps loosen the muscles.
• Some patients will gag despite your best intentions.Having these patients lift
their leg off the chair helps distract them.Remind them to breathe deeply through
their nose and tell them not to swallow their saliva.
• In worst cases nitrous oxide helps relax the patient and can be administered to
allow an impression to be taken.

58. COMMON CAUSES OF REMAKING HYDROCOLLOID IMPRESSIONS
GRAINY MATERIAL
Improper mixing
Prolonged mixing
Excessive gelation
Water/powder ratio too low
TEARING
Inadequate bulk
Moisture contamination
Premature removal from mouth
Prolong mixing

59. EXTERNAL BUBBLES
Undue gelation preventing flow
Air incorporated during mixing
IRREGULARLY SHAPED VOIDS
Moisture or debris on the tissue
ROUGH OR CHALKY STONE MODEL
Inadequate cleaning of the impression
Excess water left in the impression
Premature removal of the impression
Model left in impression for too long
Improper manipulation of stone
DISTORTION
Impression not poured immediately
Movement of tray during gelation
Premature removal from mouth
improper removal from mouth

60. MODIFIED ALGINATES
ALGINATES IN THE FORM OF SOL
• Traditional alginate material is used as a 2 component system of
powder and water in which no reaction occurs till the powder is
added to the water to initiate the reaction.
• However,the alginate can be purchased in the form of a sol
,containing water but no source of calcium ions.
• A reactor of plaster of Paris can then be added to the sol.

61. SILICONIZED ALGINATES
Considered as hybrids of alginate and silicone elastomers.
Alginates modified by the incorporation of silicone polymers.
Supplied as 2 paste which are mixed together.
One alginate sol and the other calcium reactor.
Impression materials of this type may be supplied both in tray viscosity
and in syringe viscosity.
They are resistant to tearing when compared to modified alginates.

62. DUST FREE ALGINATES
• Alginate powder contains silica dust,a potential biohazard when inhaled.
• Modern alginate powders are coated with glycerin so that the particles
agglomerate ,which keeps them from generating dust when the can is shaken
just before being opened.

63. CHROMATIC ALGINATES
The main purpose of adding indicator is to show the different stages
during manipulation and helps the operator during impression
making.Chemical reaction takes place and it is shown by change in color
in each stage.
Pink colour-during spatulation
Orange colour-during loading
White colour-when the material sets

64. LAMINATE TECHNIQUE
The hydrocolloid in the tray is replaced with a mix of chilled alginate that
bonds to the syringe agar.The agar gels by means of contact with the cool
alginate ,rather than water circulating through the tray and alginate gels
by a chemical reaction.
ADVANTAGES
1.Good surface details recorded by agar.
2.Preparation time is less.
3.Cost effective.

65. DISADVANTAGES
1.The higher viscosity alginate may displace the agar during setting.
2.Bond between agar and alginate is not always strong.

66. BIOHAZARDS DUE TO ALGINATE
SILICOSIS
It is important that care is taken to avoid inhaling the dust especially when
opening the container after shaking it to fluff up the powder.
Now dustless alginates have been emulated to reduce this risk.
It can also result in pulmonary fibrosis which can be progressive and may
lead to death.
INGESTIONS- may result in intestinal obstructions.

67. RECENT ADVANCES IN ALGINATES
PROBLEMS WITH ALGINATE
Alginate is one of the most commonly used impression material but there
are few disadvantages of this material
It has poor dimensional stability ,must be poured within 10 to 12 minutes
impression making or distortion becomes a major issue and can be poured
only once.
Tear strength of hydrocolloids is low ,it may capture sub gingival contours
and anatomy but may tear upon removal.

68. They have a tendency to stick to the teeth,which occurs when alginate radicals
in the impression material form chemical bonds with hydroxyapatite crystals of
the enamel.On removal of the impression the alginate tears.
It consists of silica dust in the form of diatomaceous earth which are highly
toxic.
Poor adhesion with tray.

69. ADVANCES
EXTENDED POUR ALGINATE
If the alginate is poured within 15 minutes ,it can be used as a final impression
material but if not poured it can cause dimensional changes.
CAVEX color change(extended pour alginate) is designed for use with
alginate which enables to delay pouring up impression under specified storage
conditions.
A recent investigation reported that storage of alginate upto 100 hrs did not
result in significant dimensional changes.
Extend-A Pour from Van-R reportedly preserves the alginate impression for
upto 4 weeks.

70. TRAY ADHESIVES FOR ALGINATE
Conventional alginates do not exhibit retention to the impression trays and
hence perforated trays are generally employed to achieve retention.
Recently,a tray adhesive in the form of liquid and spray containing
polyamide,ester gum and rosin in isopropyl alcohol or a combination of
isopropyl alcohol with ethyl acetate has been introduced.
Application of such adhesives prior to the loading of alginates was found to
improve the bond strength of the alginate to the metal and plastic trays.
Along with that Fix solvent is a spray to remove any remaining adhesive
from the impression tray after making impressions.

71. DUST FREE ALGINATES
Sepiolite,a natural mineral fibre containing magnesium silicate, about
20% was added to alginate as a substitute. When added it traps the
alginate particles thus reducing dust generation.

72. INFECTION FREE ALGINATES
To avoid dimensional inaccuracies associated with disinfection
process,manufacturers have incorporated disinfectant materials into the
alginate such as quaternary ammonium compounds,chlorhexidine etc without
altering its properties.Further studies showed that Epimax showed the highest
disinfection after 10 minutes.

73. MIXING DEVICE
• A mixer for alginate has a rotatable bowl and one or more nozzles
positioned above the opening of the rotatable bowl for injecting water into
the bowl.
• The dual-chamber package includes a first chamber containing a pre-
measured volume of water and a second chamber attached to and isolated
from the first chamber and containing a pre-measured quantity of alginate
powder where in the quality of powder and volume of water are in a pre-
determined ratio for making a dental impression paste when mixed together.

75. DISCUSSION

76. CONCLUSION

77. TEXTBOOK REFERENCES
1.Anusavice KJ.Philips Science of Dental Materials.12th Edition,2013
2.John F.McCabe.Applied Dental Materials.9th Edition
3.Gladwin M.Clinical Aspects of Dental Materials.3rd Edition
4.Powers JM.Craigs restorative dental materials.12th Edition
5.Noort RV.Introduction to Dental materials.3rd Edition,2007

78. JOURNAL REFERENCES
1.Demajo K. Effectiveness of disinfectants on antimicrobial and physical
properties of dental impression materials.Int J Prosthodont 2016:29:63-67 .
2.Kaur G,Jain P,Uppal M. Alginate Impression material-From then….Till
now.Heal Talk,2013;5(2).
3.Amalan A,Kishore G.Evaluation of properties of irreversible hydrocolloids
mixed with disinfectant liquids.J Dent Res.2013 ;10(1):65-73.
4.Hamid B,Ehsan G,Navid K. The effect of three different disinfection materials
on alginate impression by spray method.ISRN Dent.2012;6:1-5.
5.Shushing G,Sanjeev M,Sanjay B.A study on imbibition and syneresis in four
commercially available irreversible hydrocolloid impression material.Int J
Prosthodont.2012:2(1):1-4.

79. THANKYOU