hydrocolloids impression dental material
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Transcript of hydrocolloids impression dental material
Elastic Impression Materials :Elastic Impression Materials :
HydrocolloidHydrocolloidss
What are colloids ?What are colloids ?
Dissolving solid (solute) into Liquids (solvent) could result in 1 of 3 states
1. Solution2. Suspension
3. Colloid
If the solvent of such colloid is the water, the material is named
hydrocolloid
HydrocolloidsHydrocolloids
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
Hydrocolloid impression Hydrocolloid impression materialsmaterials
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.
1. Agar Hydrocolloid1. Agar Hydrocolloid impression materialimpression 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).
Dental applications of agar Dental applications of agar hydrocolloidhydrocolloid
1. 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
Presentation formsPresentation forms
CompositionComposition
1. 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
Setting reactionSetting reaction The material changes from Sol to Gel via physical
reaction (Reversible hydrocolloid )
Heating at 70-100oCSol 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
Mode of material’s settingMode of material’s setting
Tray Tissue
Water cooling system tray
Mode of agar setting
Agar impression material
Oral tissues
Circulating water 13-18oC
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 ConditioningMaterial’s Conditioning
PropertiesProperties
1. Biological propertiesProper 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
PropertiesProperties2. 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.
PropertiesProperties3. 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
PropertiesProperties4. 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
PropertiesProperties1. 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
PropertiesProperties
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
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
PropertiesProperties
2. Alginate Hydrocolloid 2. Alginate Hydrocolloid impression materialimpression 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
Presentation formsPresentation forms
A. Powder to be mixed with water- Regular & Fast set - Dust free- Chromatic
B. 2 paste system (Siliconized alginate)
Powder compositionPowder composition1. 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
Setting reactionSetting 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
Mode of material’s settingMode of material’s setting
Tissue TrayStock tray
Mode of alginate setting
Alginate impression material
Oral tissues
Making the material readyMaking the material ready
PropertiesProperties
1. Biological propertiesAlginate 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.
PropertiesProperties2. 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
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.
PropertiesProperties
PropertiesProperties3. 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
PropertiesProperties4. 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
PropertiesProperties5. 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
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
PropertiesProperties
Agar-Alginate ImpressionAgar-Alginate Impression(Laminate 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 overallimpression
Agar impressionmaterial
Stock tray
Oral tissues
Prepared tooth
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 stone2. 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 Care and handling of hydrocolloid impressionsimpressions
Thank you