irreversible dental materials. irreversible dental materials

1. GOOD MORNING !!!
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2. IRREVERSIBLE
IMPRESSION
MATERIALS
Dr.Ashitha Dominic
Dept. of Prosthodontics, Kannur dental college

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× Nontoxic & nonirritant to dentist & patient
× Pleasant taste, odor, consistency & color
× Should be accurate
× Dimensionally stable
× Adequate shelf life
× Economical
× Sufficient working time
× Satisfactory consistency & texture
× Adequate strength
× Compatible
Desirable properties of impression
materials

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Definition :any substance or
combination of substances used for
making an impression or negative
reproduction

5. CLASSIFICATION
- according to mode of setting & elasticity
Rigid
Impression plaster ,
zinc oxide eugenol
Compound , waxes
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Mode of
setting
Set by chemical
reaction
(irreversible)
Set by temp
change
(reversible)
Elastic
Aliginate ,
polyether
Polysulfide,
silicone
Agar hydrocolloid

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Mucostatic
Mucocompressive
- according to their uses in dentistry
Impression materials used for complete denture prosthesis
Impression materials used for dentulous mouths
CLASSIFICATION
- according to tissue displacement

7. ZINC OXIDE EUGENOL
Applications
• cementing & insulating medium
• temporary filling material
• root canal filling material
• bite registration paste
• temporary relining material for dentures
• impressions for edentulous patients
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8. Base paste
Zinc oxide - 87%
Mineral oil – 13%
COMPOSITION
Accelerator
paste
Eugenol – 12%
Polymerized rosin – 50%
Filler (silica type) – 20%
Lanolin – 3%
Resinous balsam – 10%
Calcium chloride – 5%
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9. SETTING REACTION
× It is a acid base reaction to form a chelate.
× This reaction is also known as chelation.
× The product is called zinc eugenolate.
ZnO + H2O Zn(OH)2
Zn(OH)2 + 2HE ZnE2 + 2H2O
SETTING TIME
Type I 3 – 6 min 10 min
Type II 3 – 6 min 15 min
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10. MANIPULATION
× Mixing on oil impervious
paper or glass slab
× Two ropes of paste of same
length width
× Base paste is white &
accelerator paste is red in
color.
× Mixed until a uniform color is
observed.
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11. Factors controlling setting time
× Delayed by cooling
the mixing slab ,
spatula.
× Adding small amount
of retarders or oil or
vaseline.
× Accelerated by longer
mixing time.
× High atmospheric
temp & humidity.
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12. Properties
consistency & flow – good flow
detail reproduction – registers good surface details
dimensional stability – satisfactory
biological considerations – burning sensations
× Advantages
Registers accurate
surface details
Dimensionally stable
× Disadvantages
Requires special tray
for impression making
Sticky in nature
Cause burning
sensation
and irritation
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13. IMPRESSION PLASTER
× USES
Making impressions in complete
denture & maxillofacial
prosthesis
Bite registration
× COMPOSITION
Dental plaster
Potassium sulphate
Borax
Coloring & flavouring agents
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14. MANIPULATION
• Water/powder ratio 0.50 to 0.75
• Water is taken first to prevent adherence of dry
powder to the sides of the bowl.
• It is allowed to settle for 30 sec
• Mix is stirred vigorously. Spatulation is done in 45 to
60 sec
• Vibrating the mix can prevent air entrapment.
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15. PROPERTIES
× SETTING EXPANSION
× STRENGTH
× HARDNESS & ABRASION RESISTANCE
× REPRODUCTION DETAIL
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16. Irreversible hydrocolloid
Types : Fast setting
Normal setting
For making preliminary impression
To make study models and cast
ALGINATE
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17. COMPOSTION
Sodium/potassium alginate – react with calcium ion
Calcium sulphate – reacts with potassium alginate
Zinc oxide – filler
Potassium titanium fluoride – gypsum hardner
Diatomacous earth – filler
Sodium phosphate – reacts with calcium sulphate
Colouring & flavouring agents 17

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MANIPULATION
Water is taken first.
Powder is sprinkled into the water
mixing is started with stirring motion
once the powder is moistened , rapid spatulation by
swiping or stropping against the side of the bowl is done.
Vigorous figure eight motion can be also used

19. MIXING TIME
fast alginate – 45 sec
normal alginate – 60 sec
over mixing results in reduction in working time &
reduction in final strength.
WORKING TIME
Fast set alginate – 11/4 min
normal set alginate – 2 min
GELATION TIME
Fast set – 1.5-2 min
normal set – 2 min
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PROPERTIES
Taste & odour – pleasant taste & smell
Flexibility – lower w/p ratio results in lower
flexibility
Elasticity – highly elastic
Reproduction – lower when compared to agar
Strength – compressive strength : 0.5 – 0.9
Mpa
- tear strength : 0.4 – 0.7 KN/m
Synersis & Imbibition – placed in water
alignates absorbs water & swell. Continued
immersion results in
total disintegration
Dimensional stability - set alginate has poor
dimensional stability due to evaporation synersis
imbibition.
Therefore cast has to be poured immediately.

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Advantages
Easy to mix & manipulate
Flexibility
Low cost
Disadvantages
Irreversible
Poor dimensional stability
Poor tear strength

22. POLYSULFIDES
First elastomeric impression material - 1850
Also known as mercaptan
COMPOSITION
Base paste
liquid polysulfide polymer - 80 to 85%
inert fillers - 16-18%
(titanium dioxide, zinc sulfate, silica)
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23. Reactor paste
lead dioxide - 60-68%
dibutyl phthalate - 30-35%
sulfur - 3%
others like magnesium stearate - 2%
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24. Advantages Disadvantages
No special equipment needed custom tray needed
Superior strength hydrophobic
Pouring can be delayed to 1 hr sensitive to heat
high shrinkage
high permanent deformation
Disinfection - 2 % glutaraldehyde
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25. PROPERTIES
• Unpleasant odor& color. It stains linen & messy to work
• Extremely viscous & sticky
• Long setting time of 12.5 min
• Excellent production of surface details
• Dimensional stability – curing shrinkage is high
- highest permanent deformation
• High tear strength (4000gm/cm)
• Good flexibility & low hardness
• Hydrophobic
• Can be electroplated
• Shelf life is good - 2 yrs
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26. SILICONE RUBBER
IMPRESSION MATERIAL
2 Types based on polymerisation reaction
• Condensation silicone
• Addition silicone
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27. Condensation silicone
Composition
Base Accelerator
Polymethyl siloxane orthoethyl silicate
Colloidal silica stannous octoate
Color pigments
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28. PROPERTIES
Pleasant color & odor
Setting time is 6 to 9 min
Excellent reproduction of surface details
Dimensional stability – less because of curing
shrinkage
Tear strength – 3000gm/cm
Stiffer & harder than polysulfide
Hydrophobic
Shelf life is slightly less than polysulfides 28

29. ADDITION SILICONE
× Also known as polyvinyl siloxane
× Available in 4 viscosities
light bodied
medium bodied
heavy bodied
putty
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30. COMPOSITION
Base Accelerator
polymethyl hydrogen siloxane divinyl polysiloxane
other siloxane platinum salts
fillers palladium
retarders
fillers
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31. PROPERTIES
× Pleasant odor & colour
× Cause allergic reaction
× Excellent reproduction surface details
× Setting time ranges from 5 – 9 min
× Best dimensional stability – low curing
shrinkage
× Good tear strength 3000gm/cm
× Extremely hydrophobic
× Low flexibility
× Shelf life ranges from 1 – 2 yrs
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32. POLYETHER
Material with good mechanical properties & dimensional stability
Composition
Base Accelerator
polyether polymer aromatic sulfonate ester
colloidal silica colloidal silica
glycolether phathalate
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33. PROPERTIES
× Pleasant odor & taste
× Setting time is around 6 – 8 min
× Dimensional stability is very good since the
curing shrinkage is very low
× Extermely stiff , harder than polysulfides
× Tear strength is good – 3000gm/cm
× Hydrophilic
× Shelf life is excellent – more than 2 yrs
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REFERENCES
× Anusavice , Philip’s science of dental materials , 11th edition ,
saunders publications. Impression materials.
× Zardiackas.L.D, dental materials , dental clinics of north
america,july 2007
× A review of contemporary impression materials and
techniques,terry e donovan, the dental clinics of north america

35. THANK YOU !!!
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