1. ne may not get a chance to make a good first
impression. But remember that the first impressio
is not the last chance to make a good impression
o
GOOD
MORNiNG
5. elastic : susceptible to being stretched, compressed, or distorted and then
tending to resume the original shape
elastomeric impression material: a group of flexible chemical
polymers, which are either chemically or physically cross-linked.
Generally, they can be easily stretched and rapidly recover their original
dimensions when applied stresses are released.
7. 7
â â â â
I 1920 I 1930 I 1 940 I 1950 I 1960 I 1970 I 1980 I1990 I
2000
â â
8. A solid, liquid or gaseous substance made up of
large molecules or masses of smaller molecules
that remain in suspension in a surrounding
continous medium of diffrent matter*
A colloid that contains water as the dispersion
phase is called as
*Anusavice KJ: Philipsâ Science of Dental Materials.
11th Edition
9. ďOrganic hydrophillic colloid extracted from
SEAWEED. It chiefly contains agarose and
agaropectin.
ďIntroduced by Alphous Poller of Viennaâ in
1925.
ďChemically it is a sulfuric ester of galactan
complex.
10. The agar used in dentistry is supplied in the following
forms-
1) Tray material
2) Syringe material
3) Agar for duplication
14. LIQUEFACTION
⢠100°C
⢠Minimum of
10 minutes.
⢠Propylene
glycol
STORAGE
⢠65°C
⢠Several days
TEMPERING
⢠~45°C
⢠3 to 10 min
⢠Never for
syringe
material
15. â˘Just before completion of tempering of tray material
the syringe material is taken from the storage
compartment and applied to the base of preparation
â˘Water soaked outer layer of the tray hydrocolloid is
removed
⢠Tray is seated with light pressure & held with light
force
â˘Gelation is accelerated by circulating cool water
(approximately 18 to 21 C) through the tray for 3 to
5 minutes.
16.
17. Area to be recorded is flooded with warm
water
Syringe agar material â is quickly & liberally
syringed over prepared tooth
Tray agar placed over the syringed agar
18. ⢠Greater than 96.5% (permanent deformation less than 3.5%)
after the material is compressed 20% for 1 second
⢠Tray types have elastic recovery of about 99%
Elastic Recovery
⢠The ANSI/ADA Specification 11 requirement for flexibility allows
a range of 4 to 15%
Flexibility
19. ⢠Compressive strength is 0.8 MPa
⢠Tear strength is 0.8 to 0.9 N/mm.
⢠The ANSI/ADA Specification requirement: 0.75 N/mm
Strength
20. ⢠If the material is held rigidly in the tray, the impression material
shrinks toward the center of its mass
⢠Rapid cooling may cause a concentration of stresses near the
tray where the gelation first takes place
Distortion during Gelation
⢠It must be sufficiently viscous so that it will not flow out of the
tray
⢠It must not be so great that it will not readily penetrate every
detail of the teeth and the soft tissues
Viscosity of the Sol
21. ADVANTAGES
Good elastic properties.
Good recovery from distortion.
Accurate dies can be prepared.
Palatable and well tolerated by the
patient.
Can be used for duplicating models.
As it is not hydrophobic, it gives a
good model surface.
DISADVANTAGES
Extensive and expensive
equipment.
Dimensional instability.
Pain and thermal shock.
Cannot be electroplated.
Tears easily.
Disinfection.
21
23. â˘Developed as a substitute for agar during World War
II
â˘E.C.C. Stanford, a Scottish chemist, discovered
alginates from from brown seaweed (algae) also called
algin in the 1880s
40 yrs later, âS. William Wildingâ received the patent
for alginate as impression material.
It is a linear polymer of anhydro - -D mannuronic acidâ
of high molecular weight.
26. 26
*Lemon JC et al ( J Prosthet Dent: 2003 Sep;90(3):276-81.
Never change the water powder ratio
27.
28. Frey G, Lu H, Powers J (J
Prost: 2005 Dec;14(4):221-5)
Concluded that mechanical
mixer improved elastic
recovery and compressive
strength of the alginate
impression materials and had
no effect on strain in
compression and tear energy.
A mechanical mixer facilitates
the mixing of alginate
impression materials and
improves some mechanical
properties.
Mechanical mixer
29. Select a perforated tray
Mixing and loading
Making the impression
Wait for
3mins
Remove impression rapidly
in a single jerk
Cut off the excess
30. Morris et al ( J Prosthet Dent 1983,49: 328-
330)
⢠Demonstrated that smoothing the surface of the
mixed alginate with a wet finger, prior to making
the impression, consistently resulted in fewer
bubbles on the surface of casts.
31. Mixing time
Setting time
Working time
1. Fast set: 45 sec.
2. Regular set: 60 sec.
1. Fast set: 1.25 to 2 min.
2. Regular set: 3 to 4.5 min.
1. Fast set: 1.5 to 3 min.
2. Regular set: 3 to 4.5 min.
31
32. Elastic
recovery
ďą Greater than 95% when the material is
compressed 20% for 5 seconds.
Flexibility ďą Range of 10 to 20% at a stress of
1000g/cm2
Strength
ďą Compressive strengthâat least
0.35MPA
ďą Tear strength â 0.37 to 0.69 MPa
32
33. Factors affecting strength
Too much or too little
water used for mixing
Insufficient spatulation
Over mixing
Failure of ingredients to
dissolve sufficiently
Breaks up the calcium
alginate gel network
Results in weakened final
gel, making it less elastic
34. Accuracy
1. Increase in concentration of alginate to
make the material more accurate
2. Roughness of the impression surface is
sufficient to cause distortion
3. Sufficiently accurate to be used for making
impressions for removable partial denture
prosthesis
1. Model should be poured as soon as possible
2. Stored in 100% relative humidity in a plastic
bag or wrapped in a damp paper towel
3. Greater chance of distortion the longer the
impression is stored
Dimensional
stability
34
35. Easy to mix and manipulate
Minimum requirement of
equipment
Accuracy (if properly handled)
Low cost
Comfortable to the patient
Hygienic (as fresh material is
used for each impression)
35
36. Not accurate for crown
and bridge impressions
Cannot be electroplated
Distortion occurs easily
Poor dimensional stability
Poor tear strength
36
37. 1. Complete and removable
denture prosthesis
2. Study models and working casts
3. Duplicating models
37
39. 39
ADA specification 20 -
Type I (thermo reversible)
Type II (nonreversible)
Hydrocolloids are popular and
have the same composition as
the impression materials, but
their water content is
higher, consequently agar
or alginate content is
lower
40. 1. In the form of a sol, containing the water. A reactor of
plaster of Paris is supplied separately.
2. Two paste system, one containing the alginate
sol, and second containing the calcium reactor. These
materials are said to contain silicone and have superior
tear resistance.
3. Lee YK et al in this study concluded that addition of
NaF in an alginate impression material may result in
effective release of fluoride without deteriorating the
properties of material itself*
40
41. ď§ These alginates change color during
manipulation to give a clear indication of mixing
time, loading into mouth & setting of the material
ď§ They contain acid/base indicators that are
responsible for change in color at different
critical points due to changes in pH that occur
during setting
ď§ Three phases of chromatic alginates are â
RED PHASE: MIXING TIME
ORANGE PHASE: WORKING TIME
YELLOW PHASE: TIME IN THE MOUTH
41
Chromatic
42. Impression is rinsed
Disinfectant sprayed liberally
Wrapped in disinfectant soaked
paper towel
Placed in a sealed plastic bag for
10 minutes
Wrapped impression is
removed, rinsed and poured
Household bleach
Iodophor
Synthetic phenols
42
43. â˘Shorter storage time of hydrocolloid impressions
before pouring is desirable.
â˘Agar Impressions can be stored up to 1 hour in
100% humidity or in storage media like 2%
potassium sulfate*
â˘If irreversible hydrocolloid impression pouring is to
be delayed up to three hrs, then it should be
wrapped with a wet towel and poured within 3 hrs, as
this did not appear to affect their accuracy
significantly.**
*J Prosthet Dent 2001:86(3); 244-50.
**Saudi Dental Journal 2002,:14(3).
44. C o m m o n f a i l u r e s
a n d
c a u s e s .
45. Agar
Inadequate
boiling
Storage
temperature
too low
Storage time
too long
Alginate
Improper
mixing
Prolonged
mixing
Excessive
gelation
Water
powder ratio
too low
Grainy material
Agar
Water-
soaked tray
surface
material not
removed
Premature
gelation of
either
Alginate
Not
applicable
Separation of tray and syringe
materials
45
46. Tearing
Agar
Inadequate bulk
Premature removal
from mouth
Syringe material
partially gelled when
tray was seated
Alginate
Inadequate bulk
Moisture
contamination
Premature removal
from mouth
Prolonged mixing
46
47. Agar
Inadequate cleansing
Excess water
Improper manipulation of
stone
Air drying the impression
before pouring
Alginate
Inadequate cleansing
Excess water left on the
impression
Premature removal
Model left in impression too
long
Improper manipulation of
stone
47
Rough or chalky
stone model
48. Agar
Impression not poured
immediately
Movement of tray during
gelation
Premature removal from
mouth
Improper removal from
mouth
Use of ice water during
initial stages of gelation
Alginate
Impression not poured
immediately
Movement of tray during
gelation
Premature removal from
mouth
Improper removal from
mouth
Separation of alginate
from the tray 48
Distortion
50. 50
Chemically, there are
3 kinds of elastomers
1)Polysulfides
2)Silicone
a. Addition
b. condensation
3) Polyethers
51. Current ADA specification 19 recognizes 3 types of elastomeric materials
This classification is based on selected elastic properties & dimensional change
Type Max permanent
deformation
Max flow in
compression
Max
dimensional
change in 24
hrs
I 2.5 0.5 -0.5
II 2.5 0.5 -1.0
III 5.5 2.0 -0.5
51
Type Decription
consistency
Consistency test disc
Diameter(mm)
min max
0 Very high(putty) - 35
1 High(heavy bodied) - 35
2 Medium(medium bodied) 31 41
3 Low(light bodied) 36 -
According to ISO 4823 the method of classification according to
consistency is as following-
52. First synthetic elastomeric impression material
Also known as MERCAPTAN or THIOKOL
-Mode of supply
ď§Collapsible tubes
ď§One labeled Base paste and
ď§Other labeled Accelerator paste
-Consistencies
ď§ Light body(syringe or wash)
ď§ Medium body (regular)
ď§ Heavy body
1950
53. Polysulfide polymer - 80 to 85%
Fillers - 16 to 18%
Titanium dioxide, lithopone, zinc sulfate,
copper carbonate or silica
Dibutyl phthalate-plasticizer
Sulfur (0.5%) â accelerator
Lead dioxide; 60 to 68%
Oleic/stearic acid
Retarder
Deodorants
BASE
PASTE
REACTOR
PASTE
54. ďźChain lengthening by oxidation of
terminal âSH groups
ďźCross linking by oxidation of pendant
âSH groups
Polysulfide
polymer
Lead
dioxide
Polysulfide
water
â 3 to 4 C
54
55. Long working time
Good tear strength
Radiopaque
Good reproduction of surface detail
High flexibility
Lower cost
Need to use custom made trays
Bad odor
Tendency to run down patientâs
throat
Stains clothing & messy to work
with
Must be poured within 1 hour
Hydrophobic so impression area
has to be dry
DISADVANTAGES
55
56. Mode of supply
ď§ Collapsible tubes
Base paste and
Accelerator paste / liquid
ď§ Putty is supplied in jars
Consistencies
ď§ Light body (syringe or wash)
ď§ Putty
Also known as conventional silicones
19
55
57. Polydimethyl siloxane
Fillers; 16 to 18%
Calcium carbonate or silica
Tetra-ethyl
Orthosilicate- reactor
Stannous octoate - catalyst
BASE
PASTE
REACTOR
PASTE
59. Clean, pleasant materials
Highly elastic
Putty-wash system
improves accuracy
Inaccuracy due to
shrinkage
Must be poured within 1
hour
Hydrophobic so impression
area has to be dry
59
60. Mode of supply
ď§ Collapsible tubes
Base paste and
Accelerator paste
ď§ Putty is supplied in jars
Consistencies
ď§ Light body (syringe or wash)
ď§ Medium body (regular)
ď§ Heavy body
ď§ Putty
Also known as polyvinyl siloxane or vinyl polysiloxane
1975
60
63. Highly accurate
High dimensional stability
Recovery from deformation on
removal is excellent
May be used with stock or
custom trays
Can be poured after 1 week
Multiple pours are possible
Expensive â twice the cost of
Polysulfides
More rigid than condensation &
difficult to remove around undercuts
Moderate tear strength, making
removal from sub-gingival areas risky
Sulfur in latex gloves and rubber dam
inhibit polymerization
Pouring of the stone should be
delayed by 1-2 hrs, liberation of H2 gas
DISADVANTAGES
63
64. 1960s
Mode of supply
ď§ Collapsible tubes
Base paste
Accelerator paste
ď§ Third tube containing thinner may be
supplied
Consistencies
ď§ Light bodied(syringe or wash)
ď§ Medium bodied (regular)
ď§ Heavy bodied
First elastomer to be developed primarily
to function as an impression material
64
65. ⢠Base paste
Poly ether polymer
Fillers; colloidal silica
Glycoether or phthalate;
plasticizer
⢠Reactor paste
Alkyl â aromatic sulfonate ester;
cross linking agent
Fillers and plasticizers
Octyl phalate and 5% methyl
cellulose-thinning agents
66. The main chain is a copolymer
of ethylene oxide and tetrahydrofuran.
Cross linking is brought about by the
aromatic sulfonate ester via the imine end
Groups. 66
Polyether
Sulfonate
ester
Cross linked
rubber
67. Pleasant mixing and ease of
handling
More accurate than polysulfide
and condensation silicone
Good surface detail reproduction
Easily poured in stone
If kept dry, will be dimensionally
stable for up to 1 week
High cost
High stiffness
Bitter taste
Storage of impressions is
critical
cannot be left in disinfectants
for long
67
71. Heavy and light body
mixed simultaneously
light body loaded in syringe
Tray adhesive applied
Light body injected into
prepared teeth
Heavy body loaded in the
tray
Final impression
72. Only one mix is made- Part of it is placed in the
tray
Another portion is placed in syringe for injection
Medium viscosity of addition and polyether can
be used.
73.
74. All elastomers are compatible with
gypsum products
Excellent dimensional stability of
addition silicone and polyether
makes it possible to construct 2 or
3 casts
Hydrophobic addition silicone â
problem ????
74
75. ⢠Surfactants are added to reduce the contact angle;
dilute solution of soap
⢠Most commonly used â non-ionic surfactants
oligoether or
polyether substructure
Hydrophilic part
Silicone compatible
Hydrophobic part
PVS
Diffusion â controlled transfer of
surfactant molecules from PVS to
aqueous phase
Reduction in surface tension
Greater wettability
75
water
80. 1)Polymerization shrinkage
2)Loss of by â product
3)Thermal contraction from oral temperature to
room temperature
4)Imbibition
5)Incomplete recovery of deformation
86. Probability of allergic reactions is low
Polysulfide has the lowest cell death count
Polyether has the highest cell death count
,toxicity and contact dermatitis among the
class.
The most likely problem is lodgment
of impression material in gingival sulcus
resulting in severe inflammation,
87. Clinical consideration :
o Subgingival regions are very thin â material
can tear
o Residual segment of impression material
difficult
to detect radio opacity of polysulfide can
help
o Severe gingival inflammation.
o Examine the gingival sulcus immediately
after impression removal and also the 87
88. 2 years
stannous
octoate oxidizes
Orthoethyl silicate is not stable in presence
of tin ester
1 to 2 years
Excellent shelf life; more than 2 years
Cool, dry environment
Tubes always tightly
sealed
Container closed
88
89. MATERIAL DISINFECTANTS
Polysulfide
Silicones
(by immersion-not
more than 30
min/spray)
2% Glutaraldehyde
Chlorine compounds
Iodophors
Phenolics
Polyether Chlorine compounds
Iodophors
Use disinfectant with short
immersion time(less than 10 min)
to avoid distortion(Polyether is
hydrophilic)
89
90. ⢠1)Impression making
⢠2)Bite registration
â The material is fast setting.
â There is no resistance to biting forces.
â There is no odor or taste for the patient.
â It gains dimensional stability over time.
â It is convenient to use.
⢠3)Duplication
Polyvinyl siloxane and polyether duplicating materials are superior in
accuracy than agar reversible hydrocolloid duplicating materials. *
*Accuracy and reproducibility of reversible hydrocolloids versus
elastomers duplicating materials Bahannan, S et al. The Saudi
Dental Journal 1995:7( 1)
92. ROUGH OR UNEVEN SURFACE
ON IMPRESSION
1. Incomplete polymerization cause
by premature removal.
2. improper ratio or mixing of
components
3. presence of oil or other organisms
on the teeth
4. Too rapid polymerization from high
humidity or temperature
5. Excessively high accelerator/base
ratio
93. BUBBLES
1. Too rapid polymerization
, preventing flow
2. Air incorporated during
mixing
IRREGULAR
SHAPED
VOIDS
1. Moisture or debris on
surface of teeth
94. ROUGH OR CHALKY STONE CAST
1. Inadequate cleaning of impression
2. Excess water or wetting agent left on surface of the impression
3. Premature removal of cast
4. Improper manipulation of stone
5. Failure to delay pour of addition silicone at least 20min
95. 1. Lack of adhesion of rubber to the tray
caused by not applying enough coats of
adhesive
2. filling tray with material too soon after
applying adhesive or using wrong
adhesives
3. Lack of mechanical retention for those
materials where adhesive is ineffective
4. Development of elastic properties in the
material before tray is seated
5. Excessive bulk of material
DISTORTION
95
96. 6. Insufficient relief for the reline
material
7. Continued pressure against
impression material that has been
developed elastic properties
8. Movement of tray during
polymerization
9. Premature removal from the mouth
10.Delay pouring of the polysulfide or
condensation silicone impression
97. Introduced in early 1988 by Genesis & LD Caulk
1. Polyether urethane dimethacrylate â elastomer resin
2. Chloroquinone â photoinitiator
3. Silicon dioxide â filler 0
Light body â syringe
Heavy body â tubes
97
98. Manipulation
1. Loaded tray is seated in the mouth
2. 8mm or larger diameter optical probe is placed in the
mouth below the tray
3. Blue light is activated for 3 minutes
4. Impressions can be poured immediately or stored up to 2
weeks
1. Long working time and short setting time.
2. Blue light is used for curing with transparent impression
trays.
3. Tear strength â 6000 to 7500 gm/cm2 (Highest among
elastomers)
4. Other properties are similar to addition silicones
Properties
99. 1. Special transparent trays
2. Difficult to cure in remote
area
DisadvantagesAdvantages
1. Controlled working time
2. Excellent properties
3. Ease of cold disinfection
without loss of quality.
4. The impression material is
also compatible with
gypsum and silver or
copper metallizing baths
99
100. It combines the benefits
of polyether and vinyl
polysiloxane impression
materials. The pleasant
tasting hybrid impression
material purportedly has
hydrophilic properties, high
tear strength, excellent
dimensional accuracy and
resistance to deformation.
It is available in two setting
times (fast and regular) and
four viscosities (putty, heavy
body, monophase and light
body)
101. ďź Soft elastomers
ďź Composed of powder that contains poly(ethyl methacryalte)
and liquid that contains an aromatic ester â ethyl alcohol
mixture (up to 30%)
ďź Within few days they become stiffer as a result of loss of
alcohol so need to be replaced every 3 days
1. Tissue conditioners for irritated mucosa
2. Temporary soft liners
3. Functional impression materials
101
102. 1. Hydrophilic; accurate impression in presence of saliva
2. Dimensional stability is fair
3. Low rigidity , Low tear strength
4. Adhere to themselves and are excellent for border molding and
correctable impression technique
5. Do not distort from water absorption, but they distort easily
when exposed to alcohol based disinfectants
6. Properties which make s the material effective are-
Viscous behaviour-allow adaptation to irritated denture bearing
mucosa for several days
Viscoelasticity which cushions the cyclic forces of mastication and
bruxism
103. â˘Tissue conditioners should not be cleaned by
scrubbing with a hard brush in order to prevent
tearing of the material. The use of soft brush
under running water is recommended.
â˘The greatest virtue of tissue conditioners is their
versatility and ease of use.
â˘The biggest flaw is that they are also misused
104. Elastomers since their introduction have
revolutionised the art of impression making hence
allowing the operator to provide acuurate fitting
restorations
Addition silicones and polyethers account for major
portion of the current practice.
Condensation silicones, Polysulfides and
irreversible hydrocolloids â more sensitive with
respect to handling considerations , mix-and-pour
techniques, which may affect accuracy. 104
105. The understanding of basic knowledge of the
impression materials and their behavior during
handling are important for their use in the oral
environment and clinical success.
The selection of the material best suited for a
particular clinical situation and technique rests
with the operator.
106. ⢠Anusavice KJ: Philipsâ Science of Dental
Materials. 11th Edition. Elsevier:S Louis;2003
⢠William J. OâBrien: Dental Materials Properties
and Selection
⢠Craig RG,Restorative Dental Materials.9th
Edition. Mosby:St Louis;1993
⢠Impression materials: A comparative review of
impression materials most commonly used in
restorative dentistry DCNA 2007;51(3):629-642
⢠McCabe JF, Walls AW:Applied Dental
Materials.9th Edition.Blackwell
Publishing:Singapore;2008
⢠Kowdi MS, Patil SG.Prep manual for
undergraduates: Dental materials.
107. ⢠Schleier PE, et al The effect of storage time on the
accuracy and dimensional stability of reversible
hydrocolloid materials. J Prosthet Dent 2001
;86(3):244-50.
⢠Jamani KD The effect of pouring time and storage
condition on the accuracy of irreversible hydrocolloid
impression. Saudi Dental Journal 2002:14(3).
⢠Woody et al Hydocolloids: A comparative study.J Am
Dent Assoc 1977,94:501-504
⢠Lemon JC et al Facial moulage:The effevt of a
retarder on compressive strength and working and
setting times of irreversibe hydrocolliid impression
material. J Prosthet Dent: 2003 ;90(3):276-81.
108. ⢠Lee YK et al in this Effect of fluoride addition on the
properties of dental alginate impression materials study J.
Mater Sci Mater Med : 2004 ;15(3):219-24
⢠Morris et al Effect on surface detail of casts when
irreversible hydrocolloid was wetted before impression
making.J Prosthet Dent 1983,49: 328-330
⢠Bahannan, S et al Accuracy and reproducibility of reversible
hydrocolloids versus elastomers duplicating materials.The
Saudi Dental Journal 1995:7( 1)
⢠Stackhouse, J.A., Jr., Harris, W.T., Mansour, R.M. and
Von Hagen, S. A study of bubbles in a rubber elastomer
manipulated under clinical conditions. J Prosthet Dent
57:591-596, 1987
The first elastic dental impression material was the hydrocolloid, which was introduced to dentistry in 1925.Since then, many elastomeric impression materials have become available, as indicated on the time line
REVERSIBLE HYDROCOLLOIDOrganic hydrophillic colloid extracted from SEAWEED. It chiefly contains agarose and agaropectin.It was first discovered by AlphousPoller of Vienna in 1925 when he was trying to develop a material that could be sterilized and applied without pressure to the exposed surface of the dura matter for perfectly recording the bony margins of the skull.which was termed as âNegacolâ which became âDentacolâ when introduced into dentistry.Chemically it is a sulfuric ester of galactan complex.
Re-usability of agar is the biggest advantageImpression material approx 4 timesDuplicating mat approx 20 times
Basic Constituent is agar 13-17%Borate is added to stengten the gel structure but is a gypsum retarder to counteract the effect of which pot sulfate is addedWater is the principle ingredient by wt.Thymol as bactericidal agent and glycerine as plasticizer can be added
The temp lag between gelation n liguefaction temp makes it possible to use agar as a dental impression material
The 1st step in preperation of agar is to liqufy the gel to sol.
Special metal stock tray with narrow bore metal tube attached to outer surface connected to cold water supply are used.
Hydraulic pressure
Developed as a substitute for agar during World War IIE.C.C. Stanford, a Scottish chemist, discovered alginates from from brown seaweed (algae) also called alginin the 1880s40 yrs later, âS. William Wildingâ received the patent for alginate as impression material.Linear polymer of anhydro -ď˘-Dmannuronic acidâ of high molecular weight.
Potassium alginate which dissolves in water and react wid ca ionsCalcium sulfate dihydrate-reacts widpottasium alginate to form insoluble ca alginate gel.Zinc oxide- acts as filler Potassium Titanium fluoride- acts as an accelerator for setting of the stone to be poured and ensure a hard dense cast surface.Diatomaceous earth â acts as filler and increases the strength and stiffness of the gel.Sodium phosphate â acts as a retarder by reacting preferentially wid ca ions to provide working time b4 gelation.
Lemon JCet al ( J Prosthet Dent: 2003 Sep;90(3):276-81.)reported that within the limitations of this study, predictable longer working and setting times were demonstrated for the irreversible hydrocolloid specimens with 1 to 8 drops of the sodium phosphate solution tested.The specimens with 8 drops of retarder solution exhibited variable setting times and would not be suitable for clinical use. The compressive strength of the modified irreversible hydrocolloid material tested was compromised because of the addition of sodium phosphate solution; however, recovery from deformation remained satisfactory as retarder solution was added
Clean armamrntariun is a mustâŚprevious set gypsum in bowl accelerates settingwoody found airborne particles and assessed the levels of airborne particles of alginate impression materials. They found that 10-15% of the particles were siliceous fibers. Based on this evidence it was recommended that inhalation of dust from Woody et al .J Am Dent Assoc 1977,94:501-504
The compressive strength of alginate doubles during the first 4 min post geation but not laterâŚalginate improve in elasticity over time which minimizes distortionâŚhence a 3 min wait is recommended
AdvantagesMaximum reproduction of detailsEquipment cost is lowerLess preparation time is requiredDisadvantagesWeak bond between alginate and agarHigher viscosity alginate displaces agarDimensional inaccuracy of alginate limits its use to single units?????
For duplication agar is the most used,howevrpvc silicones are good wgichliq at 99-104 degreesPolyether also used
The Journal of Prosthetic DentistryVolume 55, Issue 3, March 1986, Pages 304â308Accuracy of a hydrophilic irreversible hydrocolloid/silicone impression materialD.R. Davis, D.D.S., *, J.S. Preble, D.D.S
 pH indicators selected from Cresol Red, ι-naphtholphthalein, Tropaeolin 000, Thymol Blue, and phenolphthalein in general alginate impression materials, while the pH immediately after the mixing is slightly higher than 8, the pH is lowered according to the progress of the gelation, and the pH becomes lower than 8 when the gelation is completed. Thus, in the conventional alginate impression material compositions which change the color tone, by utilizing this phenomenon, a pH indicator that distinctly forms a color at the pH before the gelation is contained, and by utilizing the pH change after the gelation, the completion of the gelation is visually confirmed
GRAINY PIC
HM TRAY
Elastomers refer to a group of rubbery olymers which are either chemically or physically crosslinked.Polysulfides were the first elastomeric impression materials.2Â For over 30 years, these remained the primary elastomeric material of choice until polyethers burst on the scene with their improved hydrophilicity. Â Polyethers still had challenges due to poor taste, relatively low tear-strength, rigidity upon removal, and difficulty in mixing. This led to the development of the first condensation-reaction silicones and then VPS in the 1970s. These materials had excellent tear strength, great dimensional stable, a good or neutral taste, and were more flexible and not subject to plastic deformation upon removal. They had one glaring deficiency in that they are extremely hydrophobic. Â Over the years, surfactants and scavengers have been added to this class of impression materials to reduce the contact angle, and to make them less hydrophobic, with a great deal of success.
T butylhydroperoxide
Plysulfide polymer has multifuncmercaptan group with 1 mole % of pendant âSH groupWeight percent of filler increases from low to high consistenciesDibutyl is added as placticiserLead dioxide gives the brown colorOtheroxidizn agents can be added as MgO, c
ELECTROPLATED ??
Siloxane is moderately low mol silicone with reactive terminal hydroxygrpFilers impart strength-with increase in consistency content increasesFiller particle size â 2 to 8Âľm 35% - low consistencies 75% - puttylike consistenciesReactor is the orthosilicateStannous octoate acts as catalyst
Condensation reaction Polymerization is accompanied by the release of ethyl alcohol which causes shrinkage The two step putty-wash technique reduces polymerization shrinkageTop : Structural formula of the molecules of dimethylsiloxane. Middle and bottom: Condens reaction between the OH terminal and tetraethyl orthosilicate in the presence of stannous octate. Thereaction results in the release of two ethanol molecules.
Filler particle size â 5 to 10 Âľm Particles are surface treated to make it more compatible with silicone
addition reactionNo reaction by-products develop as long as correct proportions are maintained.
A secondary reaction between moisture and residual hydrides of base polymer may lead to development of hydrogen gasThis results in pin-point voids in gypsum castsplatinum/palladium delay pouring for an hour or more
Polyethers go through a âsnap set,â meaning the material's initial viscosity upon mixing remains relatively unchanged throughout the working time, and rapidly changes during the rest of the setting phase. Polyether materials have excellent flow properties from the start of the mix until the end of the stated working time. This is one of the properties that allows for the capture of fine details even when syringing multiple teet
Available intwo types:1. Paint on adhesives EgColtene, Kerr Universal VPS.2. Spray adhesives Eg Sili spray10 min
The 2-step putty/light-body impressions were made with 2-mm-thick resin-prefabricated copings. The 2-step injection impressions were made with simultaneous use of putty and light-body materials. In this injection technique, after removing the preliminary impression, a hole was made through the polymerized material at each abutment edge, to coincide with holes present in the stock trays. Extra-light-body material was then added to the preliminary impression and further injected through the hole after reinsertion of the preliminary impression on the stainless steel model.The 2-step putty/light-body and 2-step injection techniques were the most dimensionally accurate impression methods in terms of resultant casts. (J Prosthet Dent 2008;99:274-281)
Two stageSingle stage
Poured impression is immersed in clean rubber bowl filled with solution of slurry water and dishwashing soap. Impression must be submerged in this solution for at least 10 minutesProcedure to prevent cast breakage during separation from elastomeric impressions â ââDaniel Galindo, DDSa, Michael E. HaganbThe Journal of Prosthetic DentistryVolume 81, Issue 1, January 1999, Pages 37â38
The surfactants used were nonylphenoxy poly(ethyleneoxy) ethanol homologs of varying ethyleneoxy chain lengthWettability is max with polyether-less hydrophobic addition siliconeHydrophobic are condensation silicone-addition silicone-void-free die stone casts from the addition type silicone materials.
This material also has a better marginal accuracy
This is at 24 hours of low bodied consistencyDimensional stability is best with addition-polyether-polysulfide-condensation
This is at 24 hours of low bodied consistencyAddition silicone exhibit best while polysulfide exhibit least diamensional stability.
Polyulfide has lowest viscosity and is one of the least stiff hence can be used in undercut areas.
PICS
Stackhouse conducted A study of bubbles in a rubber elastomer manipulated under clinical conditions.Andrecommend that bubbles can be minimized by extruding the first part of the syringe contents onto a mixing pad or distant intraoral site before injecting around the critical tooth preparations.
The impression material has excellent physical, mechanical, and clinical qualities with noteworthy long working times, short setting times, dimensional stability, accuracy, high tear strength, good wettability, biocompatibility, and ease of cold disinfection without loss of quality. The impression material is also compatible with gypsum and silver or copper metallizing baths. Accurate casts can be obtained by means of either a double-impression technique or a double-mix techniqueProperties of a new polyether urethane dimethacrylatephotoinitiated elastomeric impression materiaThe Journal of Prosthetic DentistryVolume 63, Issue 1, January 1990, Pages 16â20
it was shown that vinyl siloxanethermonophase impressions and vinyl siloxanether dual-viscosity impressions display acceptable accuracy for clinical use with immersion disinfection, since the results for vinyl siloxanether were comparable to the results for representative polyether and vinyl polysiloxane materials.Â