hydrocolloids impression materials agar and alginate

1. Elastic Impression Materials
Hydrocolloids
Vinay Pavan Kumar .K
1st year MDS
Dept of Prosthodontics
AECS Maaruti College of Dental Sciences

2. Hydrocolloids
Definition
Classification
Composition
Properties
Manipulation
Advantages and
disadvantages

3. Impression
Negative record of tissues of mouth used to
reproduce the form of teeth and the surrounding
tissues (GPT 8)
Impression material
Any substance or combination of substances
used for making an impression or negative
reproduction (GPT 8)

4. Colloid
“Kola” means “glue”
“oid” means “like”
First described by Thomas Graham (1861)
Colloidal state
State of subdivision such that the molecules or
polymolecular particles dispersed in a medium have
at least one dimension between approximately 1 nm
and 1 μm

5. Solution - a homogeneous mixture consisting of
a single phase
Colloid - a heterogeneous mixture of not readily
differentiated two phases
Suspension - a mixture of two distinct phases

6. Dispersed
phase
Dispersion
phase
Type
Solid Liquid Sol
Solid Gas Solid Aerosol
Liquid Liquid Emulsion
Liquid Gas Aerosol
Gas Liquid Foam
Gas Solid Solid Foam
•Dispersed phase
•Dispersion phase

7. Gelation
There is a phase change from
SOL GEL
• Gel state - the dispersed phase agglomerates
to form a chain of fibrils called “micelles”
• Fibrils form a “brush heap structure”
• The dispersion medium is held in the interstices
between the fibrils by capillary attraction

8. Elastic impression material
Hydrodocolloids
Agar
Alginate
Non-aqueous
elastomers
Polysulfide Polyether
Condensation siliconeAddition silicone

9. What is hydrocolloid?
Colloid that contains water as the dispersion
phase
Hydrocolloid impression material are based on
colloidal suspensions of polysaccharides in
water.
Exists in two forms
• Sol form - fluid with low viscosity
• Gel form - a jelly like elastic semisolid

10. Types of hydrocolloid impression
material
Based on the mode of gelation:
Reversible – Agar
• Secondary bonds hold the fibrils together
• Bonds break at slightly elevated temperatures
and become re-established
Irreversible – Alginate
• Fibrils are formed by chemical action

11. Imbibition
Process of water sorption i.e. the gel swells when
placed in water
Syneresis
Expression of fluid on to the surface of gel structure

12. A. Shrinkage phenomena occur if syneresis forces (F syneresis) are higher
than osmotic forces (F osmotic). B. Osmotic active ingredients within color-
changing irreversible hydrocolloid shift force balance towards F osmotic,
resulting in overall expansion of material.
Schematic drawing illustrating presumed processes within
irreversible hydrocolloid on molecular level.
Erbe C, Ruf S, Wöstmann B, Balkenhol M Dimensional stability of
contemporaryirreversible hydrocolloids: Humidor versus wet tissue storage
J Prosthet Dent 2012;108:114-122

13. Liquifaction Temperature
Temperature at which gel changes to sol (70 -100°C)
Gelation Temperature
Temperature at which sol changes to gel (37-50°C)
Hysteresis – Temperature lag

14. REVERSIBLE HYDROCOLLOID - AGAR
• Agar is an organic hydrophillic colloid
(polysaccharrides) extracted from certain types
of seaweed.
• 1937 – Agar was introduced by Sears.
Component Function Composition
Agar Brush heap structure 13 – 17%
Water Reaction medium >80%
Borax Strength 0.2-0.5%
Sulfate Accelerator 2%-5%
Wax Filler 0.5%-1%
Thymol and glycerine Bactericidal and plasticiser

15. 1,3- linked â-D-galactopyranose and 1,4-linked 3,6-anhydro-á-L-galactopyranose
 Agarose, is a strongly gelling, non-ionic polysaccharide
 Agaropectin, is more complex polysaccharide having
sulfate groups
• Sol: random coils
• Gelation I : Double helices
• Gelation II :aggregation of helices

16. Manipulation

17. Agar hydrocolloid requires special equipment:
Hydrocolloid Conditioning unit
“Conditioning unit” is a thermostatically controlled
unit having 3 compartments:
•Boiling compartment --- water at 1000 C.
•Storing compartment --- water at 650 C
•Tempering or conditioning compartment --- water
at 450 C.
•Water cooled rim lock trays

18. Conditioning unit
Liquefying Store Tempering
1000 C 650 C 460 C

19. Steps in impression preparation
1.Liquefaction - at 1000 C
2.Store in 650 C
3.Load agar in tray
4.Temper at 460C
5.Seat in patient’s mouth
6.Cool with water of 180 C – 210 C for 5mins
7.Remove by snap action
8.Pour the mold material

20. Strength
The tear strength of agar - 0.8 to 0.9 N/mm
ANSI/ADA Specification - 0.75 N/mm
Compatibility with Gypsum
More compatible than alginates
Dimensional stability
•Less stable due to imbibition and syneresis
•Cast to be poured immediately
•Agar is best stored in 100% humidity for maximum
of 1hr

21. Advantages:
•Dimensionally accurate
•Hydrophilic - displace moisture, blood, fluids
•No custom tray or adhesives required
•Pleasant
•No mixing required
•Stone casts easily removed
•Cheap compared to synthetic elastic materials
•Can be reused when used as duplicating
material

22. Disadvantages:
•Initial expense –special equipment
•Material prepared in advance
•Tears easily
•Dimensionally unstable
•Cannot be electroplated
•Difficult to disinfect
•Only one model can be poured

23. Irreversible hydrocolloid – Alginate
• Developed by S. William Wilding in 1941
• As a substitute to agar during World War II
• Alginic acid prepared from marine brown sea
weed
Examples
◦ Jeltrate (Dentsply/Caulk)
◦ Coe Alginate (GC America)

24. (a) β-D-mannuronic acid. (b) α-L-guluronic acid.
(c) Structural formula of sodium alginate molecule
Alginate composition

25. Composition
Component Function
Weight
percentage
Sodium or potassium
triethanolamine
alginate
Dissolves in water and reacts
with calcium ions
15%
Calcium sulphate
dehydrate
Reactor 16%
Zinc oxide Filler particles 4%
Potassium titanium
fluoride
Accelerator 3%
Diatomaceous earth Filler particles 60%
Sodium phosphate Retarder 2%
Coloring and
flavoring agent
Give coloring change when
setting is complete
Traces

26. FORMS OF ALGINATE
• Powder
• Sol – Plaster of Paris acts as reactor
• 2 paste system - alginate sol
calcium reactor

27. Setting reaction:
A reaction of soluble alginate with calcium sulphate
and the formation of an insoluble calcium alginate gel
Na alginate + CaSO4 Ca alginate + Na2SO4
(Powder) (Gel)
Irreversible chemical reaction
Working and setting times are determined by the rate
of release of calcium ions
(CaSO4).2H2O 2Ca2+ + 2SO4
2- + H20

28. Gelation of homopolymeric blocks of α-L-guluronic acid junction with calcium
ions. Binding of divalent cations by alginate: the “Egg-box” model

29. Retarder
•Calcium ions will react preferentially with the
phosphate ions to form an insoluble calcium
phosphate
2Na3PO4 + 3CaSO4 Ca3(PO4)2+3Na2SO4
Water powder ratio
•16g of powder is mixed with 38ml of water- gelation
in 3 to 4 minutes

30. Controlling setting time
•Type-I : Fast setting (1- 2 minutes)
•Type-II : Normal setting (4 - 5 minutes)
Comparison Of Regular And Fast Set Alginate
Regular set Fast Set
Mixing Time 1 min 45 sec
Working Time 3 min 1.25 to 2 min
Setting Time 4 to 5 min 1.5 to 3 min

31. • Manufacturers adjust the concentration of sodium
phosphate to produce regular and fast-set
alginates
• Setting time can be altered by change in
temperature of the water
• Higher the temperature, faster the setting
• 1-minute reduction in setting time occurs for each
100 C temperature increase

32. Manipulation
• Weigh powder- W/P ratio (16 g powder, 38 ml
water)
• Powder added to water
• rubber bowl
• vacuum mixer
• Mixed for 45 sec to 1 min
• Place tray
• Remove after 2 to 3 minutes or after gelation
(loss of tackiness)

33. Alternatives to Hand Mixing
• Two alternatives exist for mixing alginates other than
manual manipulation of the impression material.
• The Alginator and the Vac-U-Mix automatically mix the
alginate through the use of motorized electrical
equipment

34. Stock trays-perforated – 20 holes per Sq Inch,
distance between holes – 2mm
Customization of trays :
Modifications-wax/tracing stick impression
compound/heavy-bodied silicone
IMPRESSION TRAYS

35. TRAY ADHESIVES FOR ALGINATE
Liquid
• Diethylenetriamine polymer
• Xylene
• Erythrosine
Spray
Solvents - used to remove this adhesive

36. Properties
Flexibility
• ANSI/ADA Specification permits a range of 5% to 20% at a
stress of 0.1MPa and most alginates have a value of 14%.
•Strength
• ANSI/ADA Specification :compressive strength of 0.35 MPa
• Compressive strength - 0.5 to 0.9 MPa
• Tear strength range from 0.37 to 0.69 MPa
Sketch of tear strength specimen with load applied in the directions of
the arrows; the specimen tears at the V-notch.

37. Elastic recovery
Recovery >95% when the material is compressed 20% for 5
seconds. Alginate – 98.2%
Variation of compression set with time of an alginate impression material
at strains of 10%, 20%, and 30% applied for 5 and 10 seconds.

38. Shelf Life
• One year
• It deteriorates rapidly at high temperature
Dimensional Stability
• It has poor dimensional stability because of either
syneresis or imbibition
• Impressions should be stored in 100% relative
humidity
Reproduction of tissue details
• low when compared with agar

39. Representative photographs of alginate impressions after each
storage time.
JeltratePlus after (a) 30 minutes, (b) 48 hours, and (c)100 hours;
Alginmax after (d) 30 minutes, (e) 48 hours, and (f) 100 hours; and
Kromopan 100 after (g) 30 minutes, (h) 48 hours, and (i) 100 hours.

40. WORKING TIME
The working time of alginate is determined by the help of the
penetrometer (from the start of mixing to the start of gelation)
Fast set : 1.25 – 2mins
Regular set : 2 – 4.5mins
SETTING TIME
The initial setting time of alginate is determined by placing
a flat Polymeric cylindrical rod in contact
The cylinder is withdrawn and is repeated till no alginate
is sticking to its surface

41. TESTS FOR COMPRESSIVE STRENGTH
• The compressive strength should exceed 0.35Mpa
Tear Strength and Compressive Strength for CA37 (0,95 N/mm – 1,06 MPa) and
Orthotrace (0,83 N/mm – 1,06 MPa) were significantly higher than for Hydrogum
(0,54 N/mm – 0,69 MPa), Aroma Fine(0,51 N/mm – 0,57 MPa) and
Blueprint(0,49 N/mm – 0,61 MPa)
WOORTMAN.R, KLEVERLAAN.C.J, IPPEL.D, FEILZER.A.J Tear strength as indicator for
the stability of Alginates

42. Taste and Odor
• Pleasant taste and odor
Compatibility of agar and alginate with
gypsum
• Agar and alginate cause retardation of gypsum
• Overcome by immersing the impression in a
solution of gypsum accelerator (2% potassium
sulphate)
• Incorporating a plaster hardener

43. Model plaster poured against
alginate
Dental stone poured against
the same alginate

44. Disinfection
 Immersion in 1% Sodium Hypochlorite or 2%
Gluteraldehyde < 10 min immersion or sprayed
with disinfectant
 Current protocol (by centre for disease control and
prevention) :
Use of household bleach (1-10 dilution)
Iodophor
Synthetic phenol

45. Storage
• Storage at 100% relative humidity (RH) reportedly results
in minor dimensional changes
Placed on pane of clear acrylic
resin on top of wet sponge inside
air-tight humidor
Wrapped in wet tissues in contact with
entire specimen surface and placed in
zipper plastic storage bag
If humidor storage is used, IH impressions should be poured
within 4 hours. If bag/tissue storage is used, non-color
change IH impressions should, preferably, be poured within
2 hours
Erbe C, Ruf S, Wöstmann B, Balkenhol M Dimensional stability of
contemporaryirreversible hydrocolloids: Humidor versus wet tissue storage
J Prosthet Dent 2012;108:114-122

46.  There is a greater chance for distortion the longer the impression is
stored
 New alginates have improved long-term storage ranging from 48 to
120 hours when stored in a plastic bag

47. Advantages
 Easy to mix and manipulate
 Minimum requirement of equipment
 Hydrophilic ,gives good surface detail even in
saliva
 Low cost
 Comfortable to the patient
 Hygienic ,as fresh material must be used
 It records fine details in patients with undercuts
 Good surface details are recorded even in
patients with excessive salivation

48. Disadvantages
 Poor tear strength
 Dimensionally unstable
 Lower detail production
 Difficult to disinfect
 High permanent distortion
 Cannot be electroplated
 It cannot be corrected

49. Dustless alginate
• Inhaling fine airborne particles from alginate
impression material can cause silicosis and
pulmonary hypersensitivity
• Dustless alginates were introduced which
give off or no dust particles so avoiding dust
inhalation
• This can be achieved by coating the material
with glycerine or glycol. This causes the
powder to become more denser than in
uncoated state

50. • Introduced by Schunichi, Nobutakwatanate in 1997
• This of comprises sepiolite and a tetraflouroethylene
resin having a true specific gravity of from 2-3
• The material generates less dust, has a mean particle
size of 1-40microns
Low dust alginate :

51. Antiseptic alginate :
• Introduced by Tameyuki Yamamoto, Maso Abinu
patented in 1990.
• 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.
• The antiseptic may be encapsulated in a microcapsule
or clathrated in a cyclodextrin.

52. Chromatic alginate
• The alginate impression material with color indications
avoiding confusion about setting time.
• Color changes are visualizing the major decision points in
impression making
 pH of fluid mass changes during setting
 Acid /base indicator in their formulation.
Ex : KromaFaze (Dux Dental), Integra (Dux Dental)

54. Agar Alginate
Preparation Boil, temper, store Powder, water
Ease of Use Technique sensitive Good
Patient
Reaction
Thermal Shock Pleasant, clean
Ease of removal Very easy Very easy
Disinfection Poor Poor
Handling Properties

55. Agar Alginate
Working Time
(min)
7 – 15 2.5
Setting Time
(min)
5 3.5
Stability 1 hour 100% RH Immediate
pour
Wettability and
castability
Excellent Excellent
Cost Low Very low

56. Laminate (Agar-Alginate) technique:
Inject syringe material around the
prepared tooth
Seat the tray loaded with alginate & allow
it to set
Cool alginate gels the agar

57. Advantages:
Equipment cost is lower
Less preparation time is required
Disadvantages:
Bond between agar and alginate is not
always sound
Alginate materials displaces the agar
during seating

58. Wet field technique:
 Wet the tooth surface with warm water
 Syringe materials applied over the occlusal
and incisal portion
 Seat the tray with material
 Hydraulic pressure forces the fluid material
down the tooth displacing the blood & debris

59. TRIPLE TRAY TECHNIQUE
• In this technique one impression records both
the mandibular, maxillary arches and the
occlusal relationship

60. Effect
Causes
Agar Alginate
Grainy material
Inadequate boiling
Storage temperature too low
Storage time too long
Improper mixing
Prolonged mixing
Excessive gelation
W/P ratio too low
Separation of tray and
syringe material
Water soaked
tray material surface not removed
Premature gelation of either
material
Not applicable
Tearing
Inadequate bulk
Premature removal from mouth
Syringe material partially gelled
when tray was seated
Inadequate bulk
Premature removal from mouth
Moisture contamination
Prolong mixing
Effects of mishandling:

61. Effect
Causes
Agar Alginate
Irregularly shaped
voids
Material too cold Moisture or debris on tissue
Rough or chalky
stone model
Inadequate cleansing of
impression
Premature removal of die
Improper manipulation of
stone
Excess water or hardening
solution left in the impression
Air drying the impression
before pouring
Inadequate cleaning of
impression
Premature removal of
impression
Improper manipulation of stone
Excess water left in impression
Model left in impression too
long

62. Effect
Causes
Agar Alginate
External bubbles
Gelation of syringe material
prevents flow
Undue gelation preventing flow
Air incorporated during mixing
Distortion
Impression not poured
immediately
Movement of tray during gelation
Premature removal of
impression
Improper removal from mouth
Use of ice water during initial
stages of gelation
Impression not poured immediately
Movement of tray during gelation
Premature removal of impression
Improper removal from mouth

63. Duplicating Materials
 Both types of hydrocolloids are used for
duplication of casts and models in dental
laboratory for fabrication of prosthetic
appliances and orthodontics models
 The composition of hydrocolloid type for
duplicating materials are same
 Agar hydrocolloid is more popular in labs
because it can be used many times

64. Errors during impression making
•Mix too thick
•Continuous pressure
•Movement during setting
•Separation of alginate from tray
•Inadequate working time limiting flow
•Teasing the impression while removal
•Too much air blown to dry the impression
•Moist towel or cotton over impression for storage
Rudd RW and Rudd KD. A review of 243 errors possible during the fabrication of a
removable partial denture: Part I. J Prosthet Dent 2001;86:251-61.

65. ALGINATE IMPRESSION TECHNIQUE IN HIGH
PALATE VAULT
Nandini VV, Venkatesh K V, Nair K C Alginate impressions: A practical perspective, J Conserv Dent
2008;11: 37-41.

66. SINGLE STEP APPROACH TO MAKE DIAGNOSTIC
IMPRESSIONS OF BOTH THE ARCHES & FACE BOW TRANSFER
Komuravelli AK, Suresh Sajjan MC ,Single step approach to make diagnostic impressions of both the
arches and face bow transfer: a novel technique. Indian J Dent Res. 2012 Jan-Feb; 23(1):2-6

67. CONCLUSION
Hey……
What are you
doing???
I’m trying to make a
really good first
“IMPRESSION”

68. REFERENCES
•Craig G R, Powers J M, Sakaguchi R L
Restorative Dental Materials,13th edition, USA,
Elsevier publications, 2012, pg 277- 86.
•Ferracane J L, Materials in Dentistry, 2nd edition,
USA, Susan Katz publishers, 2001, pg 173 - 99.
•Anusavice, Sheen, Rawls, Philips Science of
dental materials, 12th edition, Florida, Elsevier
Health Sciences, oct 2012, pg 168 - 77.

69. •Rudd R W and Rudd KD, A review of 243 errors
possible during fabrication of a removable partial
denture: part 1. J Prosthet Dent 2001;86:251- 61.
•Walker.M.P,Burckhard.J,Mitts.D.A,Williams.K.B
Dimensional change over time of extended-storage
alginate impression materials.
AngleOrthod. 2010;80:1110 – 1115.
•O’Brien W J, Dental materials and their selection,
2nd edition, Canada, Quintessence publications,
1997,pg 127 - 32.

70. • Nandini V V, Venkatesh K V, Nair K C
Alginate impressions: A practical perspective,
J Conserv Dent 2008;11: pg 37 - 41.
• Keita Kashima and Masanao Imai. Advanced
Membrane Material from Marine Biological
Polymer and Sensitive Molecular-Size
Recognition for Promising Separation
Technology, Advancing Desalination,2012.

71. Erbe C, Ruf S, Wöstmann B, Balkenhol M, Dimensional
stability of contemporary irreversible hydrocolloids:
Humidor versus wet tissue storage, J Prosthet Dent
2012;108: pg 114 - 122
Hiraguchi H et al, Effects of Disinfection of Combined
Agar/Alginate Impressions on the Dimensional
Accuracy of Stone Casts, Dent Mater Journal 26 (3):
457－ 462, 2007
Komuravelli A K, Suresh Sajjan M C ,Single step
approach to make diagnostic impressions of both the
arches and face bow transfer: a novel technique.
Indian J Dent Res. 2012 Jan-Feb; 23(1):2-6