MATERIAL USED IN PROSTHOOTNTICS

1. 1
HYDROCOLLOIDS
IMPRESSSION MATERIALS
Presented by-
Dr. SANJANA AGRAWAL
M.D.S 1ST
Year
RUNGTA COLLEGE OF DENTAL SCIENCES & RESEARCH
Department of Prosthodontics and Crown & Bridge

2. 2
SPECIFIC LEARNING OBJECTIVES
Sr.
No.
Core area Domain Category
1 - Introduction
- Classification
- Properties of Hydrocolloid Impression
materials
- Hydrocolloid Impression materials
- Recent Advances in Irreversible Hydrocolloid
- Techniques in Hydrocolloid Impression
materials
Cognitive Must Know
2 - Conclusion
- Take home message
Affective Must Know

3. 3
CONTENT
• Introduction
• Classification
• Properties of Hydrocolloid Impression materials
• Hydrocolloid Impression materials
Reversible Hydrocolloid - Agar
Irreversible Hydrocolloid – Alginate
• Recent Advances in Irreversible Hydrocolloid
• Techniques in Hydrocolloid Impression materials
• Conclusion
• Take Home Message
• References

4. 4
INTRODUCTION
• IMPRESSION-A negative likeness or copy in reverse of the surface of an
object; an imprint of the teeth and adjacent structures for use in dentistry.
• IMPRESSION MATERIAL- Any substance or combination of
substances used for making an impression or negative reproduction.
• The negative reproduction of the tissues given by the impression material
is filled up with dental stone or other model materials to get a positive cast.
Phillips’ Science of Dental Materials, Twelfth edition

5. IMPRESSION MATERIAL
Elastic Non-Elastic
Hydrocolloid Rubber
ZOE Imp. Compound
Agar Alginate
Polysulfide Polyether Silicone
Condensation Addition
CLASSIFICATION
William J O’Brien Dental Materials and their selection, Third edition

6. HYDROCOLLOID IMPRESSION
MATERIALS

7. A substance that is microscopically dispersed
uniformly throughout another substance
HYDROCOLLOIDS
Phillips’ Science of Dental Materials, Twelfth edition

8. True solutions
• If the size of the dispersed particles are small
(<10-7
cm).
Suspension or emulsion
• If the size of the dispersed particles are larger
(>10-4
cm).
• The colloidal state is an intermediate state
between true solution and suspension.
Phillips’ Science of Dental Materials, Twelfth edition

9. FLOWABLE STATE SOLID STATE
SOL-GEL TRANSFORMATION
V Shama Bhat Science of Dental Materials, Second edition

10. SOL-GEL TRANSFORMATION
SOL STATE GEL STATE
Micelles
A suspension that behaves like
an elastic solid
V Shama Bhat Science of Dental Materials, Second edition

11. PROPERTIES OF HYDROCOLLOID
IMPRESSION MATERIALS

12. Tear and Compressive Strengths
• Agar has a tear strength of 715 gm/cm2
and compressive strength of 8000 gm/
cm2
.
• Alginate tear strength varies from 350-
700gm/cm2
and compressive strength
ranges from 5000-8000gm/cm2
V Shama Bhat Science of Dental Materials, Second edition

13. Syneresis and Imbibition (Dimensional Stability)
• Since hydrocolloids use water as the dispersion medium,
they are prone for dimensional change due to either loss or
gain of water.
• If left in a dry atmosphere, water is lost by evaporation,
and if it is immersed in water, it absorbs water by a process
known as ‘imbibition’.
• The gel may also loose water by exuding of fluid in a
process known as ‘syneresis’.
• To avoid this hydrocolloid impressions should be poured
immediately. Phillips’ Science of Dental Materials, Twelfth edition

14. Gelation, Liquefaction and Hysterisis
• Most materials melt as well as resolidify at the same temperature.
However, in agar this does not coincide.
• Gelation (solidification) occurs at 37° C approximately, whereas
liquefaction (melting) occurs at a higher temperature, i.e. 60 to 70° C
higher than the gelation temperature.
• This temperature lag between liquefaction and gelation is known as
hysterisis.
V Shama Bhat Science of Dental Materials, Second edition

15. Flexibility
• The flexibility of the gel is between 4-15%
• A few set materials, however, have a flexibility of
20%.
• On an average a flexibility of 11% is desirable.

16. Elasticity and Elastic Recovery
• Hydrocolloids are highly elastic in nature and elastic recovery occurs to the
extent of 98.8% for agar, alginate 97.3% elastic recovery occurs.
• Thus permanent deformation is more for Alginate (about 1.2%)
• Permanent deformation is less if the set impression is removed from the mouth
quickly.
Phillips’ Science of Dental Materials, Twelfth edition

17. Shelf Life and Storage
• Alginate material deteriorates rapidly at elevated
temperatures and humid environment.
• The material should be stored in a cool, dry environment.
• The lid of bulk pack a gecan, must be replaced after every
use, so as to minimize moisture contamination.
• Stock only for one year.
Phillips’ Science of Dental Materials, Twelfth edition

18. REVERSIBLE HYDROCOLLOIDS
AGAR

19. • Agar hydrocolloid was the first successful elastic impression
material to be used in dentistry.
• It is an organic hydrophillic colloid extracted from certain types
of seaweed.
Agar Hydrocolloids (Cool)
GEL STATE
Agar Hydrocolloids (Heat)
SOL STATE
William J O’Brien Dental Materials and their selection, Third edition

20. COMPOSITION OF AGAR

21. Ingredient Weight % Function
Agar 12-17 Dispersed phase of sol and continuous fibril
of gel.
K2SO4 1.7 Plaster hardener
Borax 0.2 Improves gel strength and viscosity of sol.
Alkyl Benzoate 0.1 Preservative
Diatomaceous 0.3-0.5
Fillers
Water 85.5 Continuous phase in sol and 2nd
continuous
phase in gel.
Color & Flavors Trace Improve appearance and taste.

22. 1. Widely used at present for cast duplication
2. For full mouth impressions without deep undercuts
William J O’Brien Dental Materials and their selection, Third edition
USES

23. • Gelin collapsible tubes
• A number of cylinders in a glass jar
• In bulk containers
SUPPLIED
Phillips’ Science of Dental Materials, Twelfth edition

24. MANIPULATION OF AGAR

25. Agar hydrocolloid requires special equipment's:
• Hydrocolloid conditioner
• Water cooled rim lock trays
Phillips’ Science of Dental Materials, Twelfth edition

27. • The filled syringes and tubes are placed in the water bath at about 100°C
for 10-15 minutes.
Liquefaction
(gel-sol)
Storage
• After the agar gel has been converted to sol, the tubes and syringes are placed in
storage bath which is maintained at 63-65°C. It can be stored at this temperature for
several hours.
Conditioning
• The stored agar sol is squeezed on to a perforated water cooled tray, a gauge
pad or glass is placed over the top of the tray and the tray is placed in
conditioning bath at 43°C or 45°C for 10-15 minutes.

28. ADVANTAGES DISADVANATGES
It has good elastic properties and
reproduces undercut areas correctly.
During insertion it may be painful to
patient
It has good recovery from distortion. Tears relatively easily.
As its non-hydrophobic, it gives good
model surface.
Only one model can be poured.
It can be reused when used as a
duplicating material.
Extensive and expensive equipment is
required.
Accurate dies can be prepared It cannot be electroplated.
Phillips’ Science of Dental Materials, Twelfth edition

29. CAST DUPLICATION

30. IRREVERSIBLE HYDROCOLLOIDS
ALGINATE

31.  The word Alginate comes from ‘Algin’ which is a
peculiar mucous extract yielded by certain brown
seaweed (Algae).
TYPES
• Type I- fast setting.
• Type II- normal setting.

32. COMPOSITION OF ALGINATE

33. Ingredient Weight % Function
Soluble salts of alginates 15% Forms sol with water
Reacts with Ca to forma gel of alginate.
Ca sulphate dihydrate
solution 16 Reactor
Trisodium phosphate 2 Retarder
Diatomaceous earth 60 Filler
Zinc Oxide 4 Filler
Potassium titanium
fluoride 3 Gypsum hardener
Colour & Flavours Trace Pleasant taste to make it more acceptable.

34. 1. For making preliminary impressions for complete
dentures.
2. For impressions to make study models and
working casts.
3. For duplicating models.
USES
William J O’Brien Dental Materials and their selection, Third edition

35. A powder that is packed
• In bulk containers
• In pre-weighed packets for single impression.
• A plastic scoop and a plastic cylinder.
SUPPLIED
William J O’Brien Dental Materials and their selection, Third edition

36. SETTING REACTION
V Shama Bhat Science of Dental Materials, Second edition
• Calcium sulphate prefers to react with the retarder first.
• Only after the supply of the retarder is over does calcium sulphate react with
sodium alginate.

37. MANIPULATION OF ALGINATE

39. Mixing Time
1. For fast set alginate 45 seconds.
2. For normal set alginate 60 seconds
Working Time
• Fast set alginate: 1 minutes.
• Normal set alginate: 2 minutes.
Setting Time
• Type I (fast set): 1-2.0mins.
• Type II(normal): 2-4.5mins
John J Manappallil Basic Dental Materials, Fourth edition

40. Test for Set
• The material loses its tackiness when set.
• It should rebound fully when prodded with a blunt instrument.
• Colour indicators
John J Manappallil Basic Dental Materials, Fourth edition

41. ADVANTAGES DISADVANATGES
It is easy to mix and manipulate. Cannot be electroplated.
Minimum requirement of equipment. It cannot be corrected.
Flexibility of the set impression Distortion may occur without it being
obvious if the material is not held steady
while it is setting.
Comfortable to the patient.
Poor dimensional stability—it cannot be
stored for long time.
It is hygienic, as fresh material must
be used for each impression.
Poor tear strength.

42. FAILURES IN HYDROCOLLOIDS

43. FAILURES CAUSES
Agar Alginate
Grainy material surface In adequate boiling
Too low storage temperature
Too long storage time
In homogeneous mixing
Prolonged mixing
Too low W/P
Tearing Inadequate thickness
Premature removal
Delay in seating tray material
Prolonged mixing
Inadequate thickness
Moisture contaminations
Premature removal
External bubbles Gelation of syringe material Pre-gelation before seating/ Air trapped while
mixing
Irregular voids Too cold material Water and debris on the tissues
Distortion Movement of tray during gelation
Removal before completion of gelation
Improper removal from mouth
Delay in pouring the cast
Rough and chalky stone
model surface
Inadequate cleaning, Excess water or surface hardener left
Incomplete gelation, Improper mixing or high W/P

44. • Impressions must be poured as soon as possible.
• If it becomes necessary to store the impression, the following
methods may be used:
• Wrap the impression lightly in a wet paper towel and cover
with a rubber bowl Or Keep the impression in a plastic bag.
STORAGE OF HYDROCOLLOIDS
Phillips’ Science of Dental Materials, Twelfth edition

45. • Immersion in sodium hypochlorite
(1:2000), iodophors, or 2%
glutaraldehyde's.
• The manufacturer's recommendations
for proper disinfection should be
followed.
DISINFECTION OF HYDROCOLLOIDS
Phillips’ Science of Dental Materials, Twelfth edition

46. RECENT ADVANCES IN IRREVERSIBLE
HYDROCOLLOIDS

47. Dustless Alginates
• These fillers are low-density siliceous fibres with dimensions of
3-20 μm.
• These fibers will raise in the form of dust during usage and
inhalation of those fibers may cause respiratory problems.
• Sepiolite (natural mineral fiber-containing magnesium silicate -
20%) was added that helps in holding alginate particles together
to prevent the leaping of dust particles.
Alaghari S, Velagala S, Alla RK, Ramaraju AV. Advances in alginate impression materials: a review. Int J Dent Mater 2019;1(2): 55-59

48. Alginate in the form of Two-paste System
• Alginates were developed in two-paste systems to prevent the
contamination of powder.
• It consists of base paste and catalyst paste.
• The base paste contains soluble alginate, water, and fillers,
whereas catalyst paste contains calcium salts, viscous liquids
like liquid paraffin and magnesium hydroxide as a pH
stabilizer.
Alaghari S, Velagala S, Alla RK, Ramaraju AV. Advances in alginate impression materials: a review. Int J Dent Mater 2019;1(2): 55-59

49. Chromatic Alginates
• Various color indicators were added to the alginate
impression materials to identify the different stages of
manipulation.
• These color indicators change the color of the alginate
mix as setting reaction taking place.
• This change in the color of the alginate mix facilitates
identification of the ideal consistency to load it into the
tray and make accurate impressions.
Alaghari S, Velagala S, Alla RK, Ramaraju AV. Advances in alginate impression materials: a review. Int J Dent Mater 2019;1(2): 55-59

50. Self-disinfected Alginates
• Disinfection of impression is an essential and necessary procedure in
dental practice to prevent cross- infection and safety of patients,
dentists, and dental personnel.
• The disinfectant materials incorporated include quaternary
ammonium compounds, chlorhexidine, bisquanidine compounds,
didecydimethy ammonium chloride.
• Nanoparticles were also proved to be effective self-disinfecting
agents for alginate impression materials with no adverse effect on
physical and mechanical properties.
Alaghari S, Velagala S, Alla RK, Ramaraju AV. Advances in alginate impression materials: a review. Int J Dent Mater 2019;1(2): 55-59

51. Extended pour Alginates
• Development of two new alginate materials such as
CAVEX Color Change (Darby Dental Supply, USA)
Extend a Pour (Dux Dental Products).
• Cavex color change material can be preserved for
about 100hrs and extend a pour can be preserved up
to 4 weeks.
Alaghari S, Velagala S, Alla RK, Ramaraju AV. Advances in alginate impression materials: a review. Int J Dent Mater 2019;1(2): 55-59

52. Alginate with Polyacrylamide Incorporation
• On mixing with water, conventional alginates may tend to form a
grainy mass with lumps of unmixed material as the water does not wet
the powder easily.
• A thickening and stabilizing agent such as 0.01- 0.25wt%
polyacrylamide were incorporated into the conventional resulted in
improving the mixing characteristics, and the formation of smooth
alginate sol with water.
Alaghari S, Velagala S, Alla RK, Ramaraju AV. Advances in alginate impression materials: a review. Int J Dent Mater 2019;1(2): 55-59

53. TECHNIQUES IN HYDROCOLLOIDS

54. • The oral tissues are flooded with warm water.
• The syringe material is then injected in to the surface to be recorded.
• Before the syringe material undergoes gelation process, tray material is
seated.
• The hydraulic pressure of the viscous tray material forces the fluid syringe
material down in to the areas to be recorded.
• The motion displaces the syringe material as well as blood and debris
throughout the sulcus.
WET FIELD TECHNIQUE
Naveed N, Kishorekumar. Use of Agar as a Dental Impression Material. Indian Journal of Forensic Medicine &
Toxicology, 2020 October-December;. 14( 4)

55. • The general procedure is to heat the agar to be placed into re-usable syringes
for about six minutes in boiling water.
• The agar is stored for at least 10 minutes at 65°C before being syringed around
the preparations.
• A mix of alginate containing 10% more water than normally recommended is
placed in a tray and it is immediately seated over the agar syringe material.
• The cool mix of alginate helps gel the agar and when the alginate has set, the
combined impression is removed.
LAMINATE TECHNIQUE
Naveed N, Kishorekumar. Use of Agar as a Dental Impression Material. Indian Journal of Forensic Medicine &
Toxicology, 2020 October-December;. 14( 4)

56. ADVANTAGES & DISADVANTAGES
• Cost of equipment's is lower
because only the syringe material
needs to be heated.
• Less preparation time required.
• Eliminates water cooled
impression trays.
• Records all surface details very
clearly because of agar
• Cost-effective technique to
produce adequate details.
• Poor dimensional stability due
to syneresis and imbibition.
• The bond between the agar and
alginate is not always strong.
• High viscosity alginate displaces
the agar during seating.

57. • An alginate or putty impression is used to record the complete arch.
• The region involving flabby tissues or relief areas which need to be
recorded undisturbed (mucostatic) is cut off from this first impression,
creating a window-like opening in the initial impression.
• A low viscosity light body or impression plaster is syringed onto these
areas and when set a plaster scaffold is created over this to support the low
viscosity material while pouring the cast.
WINDOW TECHNIQUE
S. Mahalaxmi Materials used in Dentistry, First edition

58. • Despite the advancement in science and technology,
hydrocolloids have remained relevant in dentistry,
particularly as an impression material.
• The recent modifications in the composition of alginate
impression material led to the enhancement of handling
and clinical performance.
CONCLUSION

59. • Hydrocolloids impression material is widely used for making the
primary impression of edentulous and partially edentulous patients.
• Hydrocolloids have a high hydrophilic nature that allows this material
to capture accurate impressions even in the presence of some saliva or
blood.
TAKE HOME MESSAGE

60. REFERENCES
• Phillips’ Science of Dental Materials, Twelfth edition
• S. Mahalaxmi Materials used in Dentistry, First edition
• Craig’s Restorative Dental Materials, Fourteenth edition
• William J O’Brien Dental Materials and their selection, Third edition
• John J Manappallil Basic Dental Materials, Fourth edition
• V Shama Bhat Science of Dental Materials, Second edition

61. • Alaghari S, Velagala S, Alla RK, Ramaraju AV. Advances in alginate
impression materials: a review. Int J Dent Mater 2019;1(2): 55-59
• Onwubu S, Stellamaris Okonkwo C. Hydrocolloids in Dentistry: A Review
Colloids - Types, Preparation and Applications. IntechOpen; 2021
• Naveed N, Kishorekumar. Use of Agar as a Dental Impression
Material. Indian Journal of Forensic Medicine & Toxicology, 2020
October-December;. 14( 4)
• Nandini VV, Venkatesh KV, Nair KC. Alginate impressions: A practical
perspective. J Conserv Dent. 2008 Jan;11(1):37-41.

63. Q n A
• Highest tear strength: Polysulphide (2500-7000 g/cm2
)
• Sodium Phosphate as Retarder: Calcium phosphate will be more
formed than calcium alginate because it has a lower solubility, so
sodium phosphate is called a retarder because it provides working time
for alginate mixtures

64. 3. Molecular structure of Alginate