hydrocolloids impression dental material

hydrocolloids impression dental material

1. Elastic Impression Materials :
Hydrocolloids

2. What are colloids ?
Dissolving solid (solute) into Liquids
(solvent) could result in 1 of 3 states
1.Solution
2.Suspension
3.Colloid
If the solvent of such colloid is the
water, the material is named
hydrocolloid

3. Hydrocolloids
Hydrocolloids are usually existeither in
Sol (Viscous liquid) orGel (Jelly-like) form.
The sol can change into gelthrough:
1. Physical (Reversible)reaction
Sol gel
2. Chemical (Irreversible) reaction
Sol gel

4. Hydrocolloid impression
materials
2 types of hydrocolloid can be used for making
impressions:
1.Agar (reversible hydrocolloid)
2.Alginate (irreversible hydrocolloid)
To make an impression using hydrocolloid
materials,
The material should be introduced into patient’s
mouth in their sol state (To give sufficient flow and
register the details) and left inside to reach the gel
state (Setting)before removal.

6. 1. Agar Hydrocolloid
impression material
The material is elastic and usually used inspecial
type of stock trays to make 2ry impressions for
fixed restoration (inlay, onlay, crown and bridge).

7. Dental applications of agar
hydrocolloid
1. Making 2ry impression for inlay, only crown
and bridge work
2. Makingagar-alginate impression
(Laminate impression technique)
3. Laboratory duplication of stone casts
4. Help inmaking acrylic dentures using the
fluid resin technique

8. Presentation forms

9. Composition
1. Agar…. 12-15%
2. Water…. 85%
3. Borax…. (strengthening agent)
4. K
2So
4 …. (to overcome the retarding effect of
borax on gypsum cast material)
5. Thymol…. (Antifungal)
6. Coloring agent
Usually the consistencyof the tray materialis
higher thanthat of the syringe material as a
result ofhigher agar content

10. Setting reaction
The material changes from Sol to Gel via physical
reaction (Reversible hydrocolloid )
Heating at 70-100
o
C
Sol Gel
Cooling at 37-45
o
C
Factors affecting the gelation time:
1. Sol Temperature2. Cooling temperature
3. Agar content 4. Thickness of the material
5. Surface area

11. Mode of material’s setting
Tray Tissue
Water cooling system tray
Mode of agar setting
Agar impression material
Oral tissues
Circulating water
13-18
o
C

12. Boiling room
(100
o
C)
Syringe and
tray materials
left for 10-15
min.
Storage room
(60-65
o
C)
Syringe and
tray materials
stored up to 24
hrs.
Tempering room
(45
o
C)
Tray material is
only tempered for
2 min.
Material’s Conditioning

13. Properties
1. Biological properties
Proper temperingof the agar tray material
is recommended to avoid burning of the
oral soft tissue
Reusing of the agar impression material is
not advisable because of the possibility of
cross-infection

14. Properties
2. Interfacial properties
The material is is hydrophilic, easily flow over wet
tissuesregistering fine details.
No separating medium is requiredat the time of
impression pouring
Setting of polymeric die materialis affected by the
water content of the agar
Gypsum model material should be mixed with
hardening solution; otherwise a cast with chalky
easily abraded surface will result.

15. Properties
3.Mechanicalproperties
Agarhaslowtearstrengthasaresultofthe
higherwatercontent,howeverjerk(Rapid)
removalofthesetimpressionwillhelpin
overcomingthisdrawback
Agarmaterialshowsalowerdegreeof
permanentdeformationthanthatof
alginateduetotheabsenceoffiller
particleswithinthecomposition

16. Properties
4. Chemical properties
Agar material sets via physical
reaction can be reused
A degree of shrinkageis expected on
material’s gelation (due to cooling)
3 other reasonsare responsible for
impressions’ dimensional changes

17. Properties
1. Imbibition:
Agar material can absorb (Gain) water if
present in wet conditions expansion
2. Synersis:
Agar material can exudates (Loss) water if
present in humid conditionsshrinkage
3. Dehydration:
Agar material can evaporate (Loss) water if
present in dry conditionsShrinkage

18. Properties
5. Practicability
Making agar impression is complex and
sensitive procedure
A special equipments(conditioner & water-
cooling system trays) are required
Needs circulating cold water (18
o
C)to help
the gelation

19. Lengthy setting timecould reach 8 min
Jerk removal of the impression and
immediate pouringare both recommended
Storage of impressions is risky and needs
certain precautions
Properties

21. 2. Alginate Hydrocolloid
impression material
Alginate impression material is elasticand
usually used instock traysto make primary
impressions.
Other applications:
1. Final impression for complete denture
2. Agar-Alginate impression technique
3. As wash material over 1ry compound impression

22. Presentation forms
A.Powder to be mixed with water
-Regular & Fast set
-Dust free
-Chromatic
B. 2 paste system(Siliconized alginate)

23. Powder composition
1. Sodium or potassium alginate(The principal ingredient)
2. Calcium sulfate(Reactor)
3. Na-phosphate(Retarder)
4. Diatomaceous earth (Filler)
5. Potassium sulfate(Provides proper setting of gypsum
poured against the alginate impression)
6. Color indicatorin chromatic alginates
7. Glycolin dust-free alginate coating the powder particles

24. Setting reaction
 Chemical reaction named gelation
CalciumsulfateSodiumphosphate
Calciumphosphate+Sodiumsulfate(1)
CalciumsulfateSodiumalginate
Insolublecalciumalginate(2)
 The speed of the reaction is affected by;
1. L/P ratio 2. Temperature
3. Mixing rate 4. powder particle size
5. Additives

25. Mode of material’s setting
Tissue Tray
Stock tray
Mode of
alginate setting
Alginate
impressionmaterial
Oral tissues

26. Making the material ready

27. Properties
1. Biological properties
Alginate is biologically safe (Has no bad
effect on the patient health)
Inhalation of dust at the time of
manipulation could precipitate bronchial
asthma in allergic patients. Accordingly,
dust-free alginate is advisable.

28. Properties
2. Interfacial properties
Alginate impression material is hydrophilic
The material is able to register the complete
denture foundation. But, not used to make
final crown and bridge impressions
No separating mediumis required at the
time of impression pouring

29. Setting of polymeric die materialis affected
by the water contentof the alginate
Gypsum modelmaterial should be mixed
with hardening solution, otherwise a cast
with chalky easily abraded surfacewill result.
Properties

30. Properties
3. Mechanical properties
Alginate has higher tear strengththan that of
agar as a result of its filler content
Jerk removalof the set impression is
recommended to minimize the rate of both
impression tearingand permanent
deformation

31. Properties
4. Chemical properties
Aliginatematerialsetsviachemicalreaction
(gelation)singleuseonly
Severalfactorssuchastemperature,liquid/powder
ratio,particlesize,mixingrateandtheamountof
retardercouldaffecttherateofthereactionand
thesettingtime.
Imbibition,synersis,anddehydrationarealso
noticedwiththematerial

32. Properties
5. Practicability
Making alginate impression is simple and less
sensitive procedure
The powder container should be shacked very well
before dispensing the powder ratio to help in
redistributing the ingredients.
The container should be hermetically sealed all the
timeto avoid moisture contamination and
deterioration of material’s powder

33. Regular perforated or rim-lock stock trays
are recommended for making alginate
impression.
Both the regular set and the fast set
alginates are available
Jerk removalof the impression and
immediate pouring are both required
Storage of impressions is risky and needs
certain precautions
Properties

34. Agar-Alginate Impression
(Laminate impression)
Purpose:to overcome the complexity and high cost of making agar
impressions.
How: register the fine details of the prepared teeth using syringe type agar
hydrocolloid andrecord the adjacent teeth using alginate
The agar sets by the effect of alginate mixing waterand both materials
cohere depending on their colloidal natureAlginate overall
impression
Agar impression
material
Stock tray
Oral tissues
Prepared tooth

35. A.Dimensional stability:
Due to the ability of hydrocolloids to gain or loss
water (imbibitions, synersis and dehydration). A
considerable degree of Dim. Changes is expected
unless;
1.Immediate pouring of the impression in stone
2.Storage of impressions in 2% potassium sulfate or
100% humidity
100% humidity could be achieved by wrapping the
impression with wet paper towel and both are stored
in sealed plastic bag.
Care and handling of
hydrocolloid impressions

36. Thank you