Elastic Impression Materials :
Hydrocolloids
What are colloids ?
 Dissolving solid (solute) into Liquids
(solvent) could result in 1 of 3 states
1. Solution
2. Suspen...
Hydrocolloids
 Hydrocolloids are usually exist either in
Sol (Viscous liquid) or Gel (Jelly-like) form.
 The sol can cha...
Hydrocolloid impression
materials
 2 types of hydrocolloid can be used for making
impressions:
1. Agar (reversible hydroc...
1. Agar Hydrocolloid
impression material
 The material is elastic and usually used in special
type of stock trays to make...
Dental applications of agar
hydrocolloid
1. Making 2ry impression for inlay, only crown
and bridge work
2. Making agar-alg...
Presentation forms
Composition
1. Agar…. 12-15%
2. Water…. 85%
3. Borax…. (strengthening agent)
4. K2So4 …. (to overcome the retarding effect...
Setting reaction
 The material changes from Sol to Gel via physical
reaction (Reversible hydrocolloid )
Heating at 70-100...
Mode of material’s setting
Tray Tissue
Water cooling system tray
Mode of agar setting
Agar impression material
Oral tissue...
Boiling room
(100oC)
Syringe and
tray materials
left for 10-15
min.
Storage room
(60-65oC)
Syringe and
tray materials
stor...
Properties
1. Biological properties
 Proper tempering of the agar tray material
is recommended to avoid burning of the
or...
Properties
2. Interfacial properties
 The material is is hydrophilic, easily flow over wet
tissues registering fine detai...
Properties
3. Mechanical properties
 Agar has low tear strength as a result of the
higher water content , however jerk (R...
Properties
4. Chemical properties
 Agar material sets via physical
reaction  can be reused
 A degree of shrinkage is ex...
Properties
1. Imbibition:
Agar material can absorb (Gain) water if
present in wet conditions  expansion
2. Synersis:
Agar...
Properties
5. Practicability
 Making agar impression is complex and
sensitive procedure
 A special equipments (condition...
 Lengthy setting time could reach 8 min
 Jerk removal of the impression and
immediate pouring are both recommended
 Sto...
2. Alginate Hydrocolloid
impression material
Alginate impression material is elastic and
usually used in stock trays to ma...
Presentation forms
A. Powder to be mixed with water
- Regular & Fast set
- Dust free
- Chromatic
B. 2 paste system (Silico...
Powder composition
1. Sodium or potassium alginate  (The principal ingredient)
2. Calcium sulfate  (Reactor)
3. Na-phosp...
Setting reaction
 Chemical reaction named gelation
Calcium sulfate  Sodium phosphate
 Calcium phosphate  + Sodium sulf...
Mode of material’s setting
Tissue Tray
Stock tray
Mode of
alginate setting
Alginate
impression material
Oral tissues
Making the material ready
Properties
1. Biological properties
 Alginate is biologically safe (Has no bad
effect on the patient health)
 Inhalation...
Properties
2. Interfacial properties
 Alginate impression material is hydrophilic
 The material is able to register the ...
 Setting of polymeric die material is affected
by the water content of the alginate
 Gypsum model material should be mix...
Properties
3. Mechanical properties
 Alginate has higher tear strength than that of
agar as a result of its filler conten...
Properties
4. Chemical properties
 Aliginate material sets via chemical reaction
(gelation) single use only
 Several fa...
Properties
5. Practicability
 Making alginate impression is simple and less
sensitive procedure
 The powder container sh...
 Regular perforated or rim-lock stock trays
are recommended for making alginate
impression.
 Both the regular set and th...
Agar-Alginate Impression
(Laminate impression)
 Purpose: to overcome the complexity and high cost of making agar
impressi...
A. Dimensional stability:
Due to the ability of hydrocolloids to gain or loss
water (imbibitions, synersis and dehydration...
Thank you
hydrocolloids impression dental material
hydrocolloids impression dental material
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hydrocolloids impression dental material

  1. 1. Elastic Impression Materials : Hydrocolloids
  2. 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. 3. Hydrocolloids  Hydrocolloids are usually exist either in Sol (Viscous liquid) or Gel (Jelly-like) form.  The sol can change into gel through: 1. Physical (Reversible) reaction Sol gel 2. Chemical (Irreversible) reaction Sol gel
  4. 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.
  5. 5. 1. Agar Hydrocolloid impression material  The material is elastic and usually used in special type of stock trays to make 2ry impressions for fixed restoration (inlay, onlay, crown and bridge).
  6. 6. Dental applications of agar hydrocolloid 1. Making 2ry impression for inlay, only crown and bridge work 2. Making agar-alginate impression (Laminate impression technique) 3. Laboratory duplication of stone casts 4. Help in making acrylic dentures using the fluid resin technique
  7. 7. Presentation forms
  8. 8. Composition 1. Agar…. 12-15% 2. Water…. 85% 3. Borax…. (strengthening agent) 4. K2So4 …. (to overcome the retarding effect of borax on gypsum cast material) 5. Thymol…. (Antifungal) 6. Coloring agent Usually the consistency of the tray material is higher than that of the syringe material as a result of higher agar content
  9. 9. Setting reaction  The material changes from Sol to Gel via physical reaction (Reversible hydrocolloid ) Heating at 70-100oC Sol Gel Cooling at 37-45oC  Factors affecting the gelation time: 1. Sol Temperature 2. Cooling temperature 3. Agar content 4. Thickness of the material 5. Surface area
  10. 10. Mode of material’s setting Tray Tissue Water cooling system tray Mode of agar setting Agar impression material Oral tissues Circulating water 13-18oC
  11. 11. Boiling room (100oC) Syringe and tray materials left for 10-15 min. Storage room (60-65oC) Syringe and tray materials stored up to 24 hrs. Tempering room (45oC) Tray material is only tempered for 2 min. Material’s Conditioning
  12. 12. Properties 1. Biological properties  Proper tempering of 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
  13. 13. Properties 2. Interfacial properties  The material is is hydrophilic, easily flow over wet tissues registering fine details.  No separating medium is required at the time of impression pouring  Setting of polymeric die material is 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.
  14. 14. Properties 3. Mechanical properties  Agar has low tear strength as a result of the higher water content , however jerk (Rapid) removal of the set impression will help in overcoming this drawback  Agar material shows a lower degree of permanent deformation than that of alginate due to the absence of filler particles within the composition
  15. 15. Properties 4. Chemical properties  Agar material sets via physical reaction  can be reused  A degree of shrinkage is expected on material’s gelation (due to cooling)  3 other reasons are responsible for impressions’ dimensional changes
  16. 16. 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
  17. 17. 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 (18oC) to help the gelation
  18. 18.  Lengthy setting time could reach 8 min  Jerk removal of the impression and immediate pouring are both recommended  Storage of impressions is risky and needs certain precautions Properties
  19. 19. 2. Alginate Hydrocolloid impression material Alginate impression material is elastic and usually used in stock trays to make primary impressions.  Other applications: 1. Final impression for complete denture 2. Agar-Alginate impression technique 3. As wash material over 1ry compound impression
  20. 20. Presentation forms A. Powder to be mixed with water - Regular & Fast set - Dust free - Chromatic B. 2 paste system (Siliconized alginate)
  21. 21. 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
  22. 22. Setting reaction  Chemical reaction named gelation Calcium sulfate  Sodium phosphate  Calcium phosphate  + Sodium sulfate   (1) Calcium sulfate  Sodium alginate  Insoluble calcium alginate  (2)  The speed of the reaction is affected by; 1. L/P ratio 2. Temperature 3. Mixing rate 4. powder particle size 5. Additives
  23. 23. Mode of material’s setting Tissue Tray Stock tray Mode of alginate setting Alginate impression material Oral tissues
  24. 24. Making the material ready
  25. 25. 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.
  26. 26. 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 medium is required at the time of impression pouring
  27. 27.  Setting of polymeric die material is affected by the water content of the alginate  Gypsum model material should be mixed with hardening solution, otherwise a cast with chalky easily abraded surface will result. Properties
  28. 28. Properties 3. Mechanical properties  Alginate has higher tear strength than that of agar as a result of its filler content  Jerk removal of the set impression is recommended to minimize the rate of both impression tearing and permanent deformation
  29. 29. Properties 4. Chemical properties  Aliginate material sets via chemical reaction (gelation) single use only  Several factors such as temperature, liquid/powder ratio, particle size, mixing rate and the amount of retarder could affect the rate of the reaction and the setting time.  Imbibition, synersis, and dehydration are also noticed with the material
  30. 30. 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 time to avoid moisture contamination and deterioration of material’s powder
  31. 31.  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 removal of the impression and immediate pouring are both required  Storage of impressions is risky and needs certain precautions Properties
  32. 32. 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 and record the adjacent teeth using alginate  The agar sets by the effect of alginate mixing water and both materials cohere depending on their colloidal nature Alginate overall impression Agar impression material Stock tray Oral tissues Prepared tooth
  33. 33. 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
  34. 34. Thank you

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