Impression Techniques and Materials for Fixed Partial Dentures

IMPRESSIONS IN FIXED
PARTIAL DENTURE
INDIAN DENTAL ACADEMY
Leader in continuing dental education
www.indiandentalacademy.com

Table of contents:
• Introduction
• Definitions
• History
• Review of literature
• Impression materials
• Tray selection and custom tray fabrication
• Impression techniques
• Summary
• Conclusion

Introduction

• An impression is an imprint or negative likeness
Well-fitting indirect restorations can only be made if
there are accurate models of the oral tissues available,
made from high quality impressions.
A good quality impression is only obtained when we
have a thorough knowledge of materials, their properties,
and techniques for their best manipulation.

Definitions:
GPT - 8

GPT - 8
• IMPRESSION:
• a negative likeness or copy in reverse of the surface of
an object;
• an imprint of the teeth and adjacent structures for use in
dentistry

GPT - 8
• IMPRESSION MATERIAL :
any substance or combination of substances used for
making an impression or negative reproduction
• IMPRESSION TECHNIQUE :
a method and manner used in making a negative
likeness

GPT - 8
IMPRESSION TRAY
• 1: a receptacle into which suitable impression material is
placed to make a negative likeness
• 2: a device that is used to carry, confine, and control
impression material while making an impression

GPT - 8
• SECTIONAL IMPRESSION :
a negative likeness that is made in sections.
• TUBE IMPRESSION :
1: a cylinder used as a tray to confine and direct impression
material to make an impression of a single tooth.
2: the impression resulting from this procedure.

• Elastomer – lightly crosslinked impressin mateial with
elastic properties
• Gelation – transformation from sol to gel
• Hydrocolloid – colloid that contains water as the
dispersion phase.
• Imbibition – absorption of water
• Synersis – fluid exuded when gel structures reconfigure
to achieve equilibrium through stress relaxation.
Phillips`s Science of dental materialswww.indiandentalacademy.com

• Thixotropic – the time-dependent pseudoplastic flow of
polymers that is characterized by the gradual decrease
of viscosity under a constant applied shear rate.
Phillips`s Science of dental materialswww.indiandentalacademy.com

History

• Philip Pfaff-1756
– First described taking impression with softened wax
• Christophe Francois Delabarre-1820
– Introduced the metal impression tray
• Chapin Haris-1853
– First used Plaster of Paris for making impressions.
• Charles Stent-1857
– Introduced the first impression compound

• Sears-1937
– First used agar hydrocolloids for recording crown
impressions.
• United States-1945
– Introduced alginate during World War II.
• SL Pearson-1955
– Developed synthetic rubber base impression materials

• Polysulfide- Late 1950’S
– First developed as an industrial sealant.
• Condensation Silicone- Early 1960’s
• Addition Silicone-1970’s
• Polyether- Late 1970’s
• Polyether Urethane Dimethacrylate - Late 1980’s

Review of literature

• Hudson (1958) described the clinical use of rubber
impression materials
• a combination of light and heavier bodied materials may be
used in a disposable stock tray or a custom made acrylic resin
tray for making impressions for fixed partial dentures.
• The special syringe is used to inject the light bodied material
into the prepared cavities or about the crown preparation.

Multiple abutment impressions using vacuum adapted temporary splints.
LaForgia A. J Prosthet Dent. 1965;Jan;15(1):44-50.
A LaForgia (1965)
described an impression technique using vacuum
adapted temporary splints

• Irreversible hydrocolloid for fixd partial denture impressions. G. R. Zuckerman. J
prosthet Dent. 1974;32;657.
Zuckerman. (1974) described a dechnique of making
impression.

Culbreath JC. (1975)
described A technique for making impressions for cast
restorations. It can be used for a single preparation or for
multiple preparations in a single arch. The most unique
feature of the technique is that the tray is formed over the
prepared teeth, either directly or indirectly.
An impression technique for cast restorations.
Culbreath JC. J Prosthet Dent. 1975 Apr;33(4):417-21.www.indiandentalacademy.com

Bonding properties and dimensional stability of hydrocolloid impression systems in
fixed prosthodontics.
Dahl BL, Dymbe B, Valderhaug J. J Prosthet Dent. 1985 Jun;53(6):796-800.
Dahl BL, Dymbe B, Valderhaug J.(1985)
Four hydrocolloid impression systems for fixed
prosthodontics and one conventional alginate were tested
for bonding properties between the syringe and the tray
materials of the systems. Their dimensional stability was
tested also after the impressions were kept in a humidor for
1, 3, and 24 hours before casts were poured.

Findings showed that there was a true bond between the
syringe and the tray materials for all combinations. The
precision tests gave a mean percent difference between
the master model and the cast of less than 0.15 for all
material combinations at both the 1- and 3-hours
observations.

Incidence of impression material found in the gingival sulcus after
impression procedure for fixed partial dentures.
Marshak BL, Cardash HS, Ben-Ur Z. J Prosthet Dent. 1987 Mar;57(3):306-8.
Marshak BL, Cardash HS, Ben-Ur Z. (1987)
After impression-making procedures, remnants of Xantopren
impression material were found in the gingival crevices in
eight of 125 patients. In three of the eight patients, remnants
were only discovered subsequent to a systematic exploration
with a fine curette.

Although eight of 125 is not a statistically significant number,
it would be nonetheless prudent to consider a routine
curettage of abutment sulci after impression-making.
This procedure is even more strongly recommended when a
defect be detected in the crevicular region of the impression.
Impressions should remain in the mouth until full setting and
maximum tear strength is reached. Strict adherence to the
manufacturers' instructions is necessary.

Accuracy of impression materials for complete-arch fixed partial dentures.
Lin CC, Ziebert GJ, Donegan SJ, Dhuru VB. J Prosthet Dent. 1988 Mar;59(3):288-91.
Lin CC, Ziebert GJ, Donegan SJ, Dhuru VB. (1988)
The accuracy of 12 impression materials of six different types
were studied by using complete-arch FPD impressions.
A one-piece casting was constructed by connecting the four
individual castings made for the four abutment teeth. The master
prosthesis was seated on the stone casts produced from the
impressions.
The marginal adaptation on the four abutments was then
evaluated with a travelling microscope. The individual marginal
adaptation of the four castings on the abutments was also
examined after sectioning the four joints.

They concluded that
1. The polyethers produced the most accurate complete-
arch replicas. The second most accurate were the vinyl
polysiloxanes, followed by the polysulfides and the
irreversible-reversible hydrocolloids. The least accurate
were the reversible hydrocolloids and the irreversible
hydrocolloids.
2. The polyether impression materials exhibited the most
consistent accuracy for a master cast to fabricate a
complete-arch FPD.

The effect of tray selection on the accuracy of elastomeric impression materials.
Gordon GE, Johnson GH, Drennon DG. J Prosthet Dent. 1990 Jan;63(1):12-5 .
Gordon GE, Johnson GH, Drennon DG. (1990)
study evaluated the accuracy of reproduction of stone casts
made from impressions using different tray and impression
materials. The tray materials used were an acrylic resin, a
thermoplastic, and a plastic.

• The impression materials used were an additional
silicone, a polyether, and a polysulfide. Impressions
were made of a stainless steel master die that simulated
crown preparations for a fixed partial denture and an
acrylic resin model with cross-arch and anteroposterior
landmarks in stainless steel that typify clinical intra-arch
distances. Impressions were poured at 1 hour with a
type IV dental stone.

Results indicated that custom-made trays of acrylic resin
and the thermoplastic material performed similarly
regarding die accuracy and produced clinically acceptable
casts. The stock plastic tray consistently produced casts
with greater dimensional change than the two custom
trays.

A comparison of impression materials for complete-arch fixed partial dentures.
Dounis GS, Ziebert GJ, Dounis KS. J Prosthet Dent. 1991Feb;65(2):165-9.
Dounis GS, Ziebert GJ, Dounis KS (1991)
This study compared the marginal fit of complete-arch fixed
prostheses under simulated clinical conditions. Prostheses
were made on casts constructed from three commonly used
impression materials; polyether, polyvinyl siloxane (medium-
viscosity and putty-wash), and reversible hydrocolloid.

they concluded that,
the polyether and both addition silicone impression
materials were significantly more accurate than the
reversible hydrocolloid in both situations. All of the single
castings were clinically acceptable, but the luted
restorations made from reversible hydrocolloids were not.

Accuracy of one-step versus two-step putty wash addition silicone impression
technique. Hung SH, Purk JH, Tira DE, Eick JD. J Prosthet Dent. 1992 May;67(5):583-9.
Hung SH, Purk JH, Tira DE, Eick JD (1992)
study compared the accuracy of one-step putty wash with
two-step putty wash impression techniques. Five addition
silicone impression materials-Mirror 3 (MR), Mirror 3 Extrude
(ME), Express (E), Permagum (P), and Absolute(A)--were
tested.
Accuracy of the materials was assessed by measuring six
dimensions on stone dies poured from impressions of the
master model.

They concluded that
• Accuracy of addition silicone impression material is
affected more by material than technique.
• Accuracy of the putty wash one-step impression
technique was not different from the putty wash two-step
impression technique except at one of the six
dimensions where one-step was more accurate than
two-step. Mirror 3 putty wash two-step impression
presented less distortion than Mirror 3 Extrude putty
wash one-step or two-step impression.

Irreversible hydrocolloids for crown and bridge impressions: effect of different
treatments on compatibility of irreversible hydrocolloid impression material with type
IV gypsums.Eriksson A, Ockert-Eriksson G, Lockowandt P, Linden LA. Dent
Mater. 1996 Mar;12(2):74-82.
• Eriksson A, Ockert-Eriksson G, Lockowandt P,
Linden LA. (1996)
The aims of their research were:
1) to determine if the compatibility between irreversible
hydrocolloids (alginates) and type IV gypsums (die
stones) is affected by different treatments of the
impressions before pouring, and

• The results showed that dentists and dental technicians
need to know how each specific irreversible hydrocolloid
should be treated and also with which type IV gypsum it
is compatible.
• This research also indicated that an irreversible
hydrocolloid impression should not come into contact
with any liquid within the first 15 min.

• Lepe X, Johnson GH (1997)
• study evaluated the materials after simulating overnight
disinfection.
• They concluded that,
• Accuracy of both impression materials was adversely
affected with 18 hours of immersion disinfection.
• Long-term (18 hours) immersion disinfection will affect
the fit of fixed partial prostheses.
Accuracy of polyether and addition silicone after long-term immersion
disinfection. Lepe X, Johnson GH. J Prosthet Dent. 1997 Sep;78(3):245-9.www.indiandentalacademy.com

Accuracy of irreversible hydrocolloids (alginates) for fixed prosthodontics. A
comparison between irreversible hydrocolloid, reversible hydrocolloid, and addition
silicone for use in the syringe-tray technique. Eriksson A, Ockert-Eriksson G,
Lockowandt P. Eur J Oral Sci. 1998 Apr;106(2 Pt 1):651-60.
Eriksson A, et al (1998) The aim was to study their ability to
reproduce six differently shaped abutments of a full arch
stainless steel master model correctly, by measuring:
1) the accuracy of irreversible hydrocolloid impressions with
different storage periods of 15 min, 2 h, 24 h and 95 h,
reversible hydrocolloid stored 15 min and 2 h, and Type III
addition silicones stored 24 h when the syringe-tray technique
was used; and
2) whether mixing technique or tray design had any influence
of the accuracy of irreversible hydrocolloid impressions

They concluded that,
• Storage time, mixing technique and tray design were of
significant importance for the irreversible hydrocolloids.
• Concerning the accuracy at the gingival margin, a shorter
storage time resulted in improved accuracy, and
• mechanical mixing without a vacuum and a tray designed
similar to a perforated stock tray gave most accurate
impressions.

Impression materials and techniques for crown and bridgework: a survey of
undergraduate teaching in the UK. Randall RC, Wilson MA, Setcos JC, Wilson NH.
Eur J Prosthodont Restor Dent. 1998 Jun;6(2):75-8.
Randall RC et al (1998) The aim of this study was to
document the teaching of impression materials and
techniques for crown and bridgework in the undergraduate
curriculum in UK dental schools
Addition-cured silicones were found to predominate;

71% of schools taught and used clinically a one-stage, full
arch impression technique involving stock trays,
and 57% of schools a full-arch custom tray technique.
Routine disinfection of impressions was taught and
practised in 43% of schools

Crown and bridge impressions--a comparison between the UK and a number
of other countries. Winstanley RB.
Eur J Prosthodont Restor Dent. 1999 Jun-Sep;7(2):61-4.
Winstanley RB. 1999
The quality of impressions for crown and bridge work in seven
countries were compared with the results found in the United
Kingdom in a previous study.
The results showed that metal impression trays were used
more frequently, and flexible plastic trays less frequently, in the
countries visited than in the United Kingdom.

Accuracy of three polyvinyl siloxane putty-wash impression techniques.
Nissan J, Laufer BZ, Brosh T, Assif D. J Prosthet Dent. 2000 Feb;83(2):161-5.
Nissan J et al 2000. This study assessed the accuracy of 3 putty-
wash impression techniques using the same impression material
(polyvinyl siloxane) in a laboratory model.
The 3 putty-wash impression techniques used were
(1)1-step (putty and wash impression materials used
simultaneously);
(2) 2-step with 2-mm relief (putty first as a preliminary impression to
create 2-mm wash space with prefabricated copings. In the
second step, the wash stage was carried out); and
(3) 2-step technique with a polyethylene spacer (plastic spacer used
with the putty impression first and then the wash stage).

• CONCLUSION.
• The polyvinyl siloxane 2-step, 2-mm, relief putty-wash
impression technique was the most accurate for
fabricating stone dies.

• Influence on dimensional accuracy of volume of wash material introduced
into pre-spaced putty/wash impressions.
Omar R, Abdullah MA, Sherfudhin H.
Eur J Prosthodont Restor Dent. 2003 Dec;11(4):149-55.
Omar R et al (2003), This study compared the accuracy of stone
models obtained from two-stage, pre-spaced putty/wash impressions
under conditions in which known volumes of wash material were
introduced during the second stage of the impression:
Group I, a quantity of wash material corresponding to the space provided;
Group II, double the quantity of wash material as the space provided;
Group III, double the quantity of wash material, but with V-shaped vents in
the putty for escape of excess material.

• Percentage deviations of the vertical dimensions of stone
dies with respect to the master model were significantly
different between Groups I and II (the latter being shorter)
• For horizontal dimensions, differences were less consistent,
although the deviations for Groups I and II and Groups II
and III, with respect to the master model, were significantly
different from each other for two of the three dimensions
measured (Group II inter-abutment distances were
generally larger)
• It was concluded that putty recoil, resulting from
compression by excess wash material, plays a significant
role in the undersizing of working dies, although the level of
clinical relevance is less clear.

Alginate impressions for fixed prosthodontics. A 20 year follow up study.
Eriksson A, Ockert-Eriksson G, Eriksson O, Linden LA.
Swed Dent J. 2004;28(2):53-9.
The aim of this study was to estimate whether the survival
ratios after 20 years of fixed prosthodontics made of alginate
impressions was higher, equivalent or lower, compared to the
survival ratios, shown in studies, where different impression
materials were used.
Eriksson A, Ockert-Eriksson G, Eriksson O, Linden LA. (2004)

Concluded that, fixed prosthodontics made according to the
syringe-tray alginate impression method may have the
same success rates after 20 years compared to that of
fixed prosthodontics presented in previous longitudinal
clinical studies where other impression materials

• A clinical evaluation of fixed partial denture impressions.
Samet N, Shohat M, Livny A, Weiss EI.J Prosthet Dent. 2005 Aug;94(2):112-7.
Samet N, et al 2005 This study evaluated the quality of
impressions sent to commercial laboratories for the
fabrication of fixed partial dentures (FPD) by describing the
frequency of clinically detectable errors and by analyzing
correlations between the various factors involved.

• The impression technique and material used, tray type, and
number of prepared units were recorded for each impression.
• Data relating to errors and faults, including defects in material
polymerization, retention to tray, tissue contact by tray, crucial
areas beyond tray borders, heavy-bodied material exposure
through the wash material (for double-step impressions),
inadequate union of materials, retraction cords embedded in
impressions, and air bubbles, voids, or tears along the margin
were also documented.
• And concluded that impressions made with polyethers had
the most detectable errors, followed by condensation-type
silicones.

[Full arch impression techniques utilizing addition type poly vinyl siloxane for fabrication of
tooth born fixed partial dentures] Nissan J, Rosner O, Barnea E, Assif D.
Refuat Hapeh Vehashinayim. 2006 Jan;23(1):42-6, 71
• Nissan J et al 2006 This article presented several
impression techniques using PVS and recommends the
one that provides the most accurate impression, utilizing
the superior qualities of the PVS.
• The one step impression technique where no control of
wash bulk and thickness exists, is considered to be the
least accurate impression method with measured
discrepancies as large as 7 times the original inter
preparation distance and 40 times the original cross arch
dimensions.

• Furthermore, the direct contact between the less refined
putty material and the tooth preparation, as well as the
high prevalence of air bubble entrapment, seriously
compromises restoration longevity.
• The two stage impression technique has proved to
produce the most accurate and reliable impressions due
to complete control of the wash bulk and thickness
entailed.

• The ideal wash bulk thickness should range between 1 to
2.5 mm all around the abutment tooth in order to
minimize distortion of its subsequent die.
• The easiest and most clinically applicable method to
achieve the desired space around the preparations is by
loading the Putty material with the temporary crowns in
place, followed by their removal at the second stage and
occupation of the created space by the wash.

IMPRESSIONS IN FIXED
PARTIAL DENTURE

Impression materials

Impression
Materials
Aqueous
Hydrocolloids
Non-aqueous
Elastomers
Polysulfide
Silicones
Polyether
Condensation
Addition
Agar (reversible)
Alginate (irreversible)

Hydrocolloids

Reversible Hydrocolloid
(Agar)

History
• In 1925,Alphous Poller of Vienna was granted a British
patent for a totally different type of impression material.
• Later Poller's 'Negacoll’ was modified and introduced to
the dental profession as 'Dentacol’ in 1928.
• In 1937 by Sears introduced Agar was first into dentistry for
recording crown impressions
• and was the first elastic impression material available.

• Example
– Slate Hydrocolloid (Van R)
– Cohere
– Superbody
– Super syringe

Component Function Composition
Agar Brush – heap structure 13 – 17%
Borax Strength 0.2 – 0.5%
Potassium Sulfate Gypsum hardener 1.0 – 2.0%
Water Reaction 80%
Alkyl Benzoate Prevent growth of mold in
impression material during
storage.
0.1%
Color and Flavors Taste & appearance Trace
Composition
• Fillers; diatomaceous earth, clay, silica, wax, rubber, and similar inert
powders.
• Thymol and glycerin act as plasticizer and bactericide.www.indiandentalacademy.com

agar hydrocolloid (hot) agar hydrocolloid (cold)
(sol) (gel)
cool to 43 C
heat to 100 C

Available as
– syringe and tray material

• 3 chamber conditioning unit
(1) liquefy at 100°C for
10 minutes
• converts gel to sol
(2) store at 65°C
– place in tray
(3) temper at 46°C for 3 minutes
– seat tray
– cool with water at 20°C for 3
minutes
• converts sol to gelwww.indiandentalacademy.com

Advantages
• Accurate reproduction of surface detail
• Hydrophilic
– displace moisture, blood, fluids
• Inexpensive
– after initial equipment
• No custom tray or adhesives
• Pleasant
• No mixing required
Phillip’s Science of Dental Materials 1996

Disadvantages
• Initial expense
– special equipment
• Material prepared in advance
• Thermal shock to the patient.
• Tears easily
• Dimensionally unstable
– immediate pour
– single cast
• Difficult to disinfect

Irreversible Hydrocolloid
(Alginate)

Irreversible Hydrocolloid
(Alginate)
At the end of the last century, a chemist from Scotland
noticed that certain brown seaweed (algae) yielded a
peculiar mucous extraction. He named it algin.
This was later identified as a linear polymer with numerous
carboxyl acid groups and named anhydro-β-d-mannuronic
acid (also called alginic acid).

• When the agar impression material became scarce
because of World war II (Japan was a prime source of
agar), research was accelerated to find a suitable
substitute. This result was present alginate impression
material.
• The general use of irreversible hydrocolloid far exceeds
that of other impression materials available.
• Because
– Easy to manipulate
– Comfortable for the patient
– Relatively inexpensive (no elaborate equipment)

• Examples
– Jeltrate (Dentsply/Caulk)
– Coe Alginate (GC America)
– Integra
– Superjel
– Tropicalgin
– Xantalgin

I. According to setting time.
• Fast set 1.25 – 2min
• Regular set 3 – 4.5 min
II. According to concentration of filler
• Soft set
• Hard set
Classification of alginateClassification of alginate

Component Function Weight
percentage
Na / Potassium
alginate
Soluble alginate 15
Calcium sulfate
dihydrate
Reactor 16
Potassium titanium
Fluoride
Accelerator 3
Zinc oxide Filler particles 4
Diatomaceous earth Filler particles 60
Sodium phosphate Retarder 2
Composition

2 Na3PO4 + 3 CaSO4 Ca3(PO4)2 + 3 Na2SO4
Na alginate + CaSO4 Ca alginate + Na2SO4
(powder) (gel)
H2O
Reaction

Alginate in the form of sol
- containing the water but no source of calcium
ions - a reactor of Plaster of Paris
Modified alginatesModified alginates
Two component system (paste form)
- alginate sol
- calcium reactor

– Alginates modified by the incorporation of
silicone polymers (paste form)
- fine detail reproduction
- tear resistance
- good dimension stability

• Dustless alginate glycerin incorporated to
agglomerate the particles.
• Making the powder more dense so that no dust is
formed when the lid is opened after tumbling.

NEWER ALGINATES
• Millenium algin
• manufactured by LASCOD
• MILLENIUM ALGIN is considered an alginate of new generation
• Maximum preciseness (15 µ)
• The formulation was optimized to reduce natural contraction with
water loss. The impression can be stored for many hours in a Long
Life Bag before casting the model without undergoing any
change for over 100 hours

• No hand mixing. Eliminates mess and cleanup.
Saves time and material.
• Delivery options. Cartridge or Volume™ automix
dispensing.
• Impressions remain stable. You can pour
immediately or when it’s convenient. Impressions
retain dimensional stability for months.
NEWER ALGINATES

Additives
• flavorings

Tray adhesive
sticky wax or methyl cellulose can be applied to the tray
(adhesive sprays are also available).

Manipulation
• Fluff or aerate the powder by inverting the can several
times. This ensures uniform distribution of the filler
before mixing.
• Measured amounts of powder and water are taken as
specified by the manufacturer.

Mixing is done in a clean flexible plastic bowl with a clean
wide bladed, reasonably stiff metal spatula.
• It is better to use separate bowls for plaster and alginate as
plaster contamination can accelerate setting.
Mixing technique

• The mixing is started with a stirring motion to wet the
powder with water.
• Once the powder has been moistened, rapid spatulation
by swiping or stropping against the side of the bowl is
done.
• A vigorous figure-eight motion can also be used .

Mechanical mixing devices

MIGMA™ Alginate Mixing Machine

Properties of alginates

• Reproduction of Tissue Detail
• ADA Sp. requires the material to reproduce a line that is
0.075 mm in width.
• Detail reproduction is lower when compared to agar
hydro-colloid.

Dimensional Stability
• Set alginates have poor dimensional stability due to
evaporation, syneresis and imbibition. Therefore, cast
should be poured immediately.
• If storage is unavoidable, keeping in a humid
atmosphere of 100% relative humidity (humidor) results
in the least dimensional change.
Strength
Water: powder ratio
Overmixing and Insufficient spatulation

Elasticity and Elastic Recovery
• Alginate hydrocolloids are highly elastic but less when
compared to agar and about 97.3% elastic recovery
occurs.
• Thus permanent deformation is more for Alginate (about
1.2%).
• Tear strength - varies from 350-700 gm/cm2
• Increased when the impression is removed with a snap

• Compatibility with gypsum:
– Immersion of impression in a solution containing an accelerator for
the setting of the gypsum product, before pouring the impression
with the gypsum
– Incorporation of a plaster hardener or accelerator
• Accelerator increases the hardness of cast by
– Accelerating the set of gypsum to overcome the retarding action of
gel.
– may react with the gel to produce a surface layer that reduces or
prevents syneresis and eliminates the retarding action of the gel.
Hardening solutions: potassium sulfate, zinc sulfate,
manganese sulfate and potash alum
2% potassium sulfate is most effective.www.indiandentalacademy.com

• Pouring of stone mixture to fill the impression should
start from one end of the arch. After the impression has
been filled with stone, it may be placed in either a
humidor or a 2% potassium sulfate solution while the
stone hardens in an atmosphere of approximately 100%
relative humidity.
• Cast should be kept in contact with the impression,
preferably for 60 min or minimum 30 min.
• If the cast is allowed to remain in contact with the
hydrocolloid impression overnight, a chalky stone
surface may be produced.

• Over Mixing Results In
• Reduction in final strength as the gel fibrils are broken.
• Reduction in working time.
• Under Mixing Results In
• Inadequate wetting, lack of homogeneity and reduced
strength.
• The mix being grainy and poor recording of detail.

Preserving alginate impression

Diatomaceous earth
• DE, diatomite, diahydro, kieselguhr,
kieselgur and Celite
• is a naturally occurring, soft, chalk-like sedimentary rock
that is easily crumbled into a fine white to off-white
powder.
• This powder has an abrasive feel, similar to pumice
powder and is very light, due to its high porosity.
• The typical chemical composition is
– 86% silicon, 5% sodium, 3% magnesium and 2% iron.

• Diatomaceous earth consists of fossilized remains of
diatoms, a type of hard-shelled algae.
• It is used as a filtration aid, as a mild abrasive, as a
mechanical insecticide, as an absorbent for liquids, as
cat litter, as an activator in blood clotting studies, and as
a component of dynamite.
• As it is also heat-resistant, it can be used as a thermal
insulator.

Disinfection
• The current protocol for disinfecting hydrocolloid
impressions recommended by the
• Centers for Disease Control and Prevention is to use
household bleach (1-10 dilution), or synthetic phenols as
disinfectants.
• After the impression is thoroughly rinsed, the disinfectant
is sprayed liberally on the exposed surface.

Advantages
• Inexpensive
• Easy to use
• Hydrophilic
– displace moisture, blood, fluids
• Stock trays

Disadvantages
• Tears easily
• Dimensionally unstable
– immediate pour
– single cast
• Lower detail reproduction
– unacceptable for working cast of fixed prosthodontics
• High permanent deformation
• Difficult to disinfect

Non aqueous elastomeric
impression materials

• Synthetic rubbers
• mimic natural rubber (scarce during World War II)
• Initially called rubber impression materials
• Currently referred as elastomers or elastomeric
impression materials.
• ADA Specipication no. 19 identifies as “nonaqueous
elastomeric dental impression materials”
Phillip’s Science of Dental Materialswww.indiandentalacademy.com

Aqueous
Hydrocolloids
Non-aqueous
Elastomers
Polysulfide
Silicones
Polyether
Condensation
Addition
Agar (reversible)
Alginate (irreversible)Classification

Non-Aqueous Elastomers
• Viscosity classes
– low, medium, high, putty
– Monophase
Phillip’s Science of Dental Materials
Single phase or monophase – single component material
with sufficient shearing potential that it can be used as the
syringe material and the tray material.

Polysulfide

Polysulfide
• The first elastomer used for dental impressions
• Sometime referred to
– By the type of material, such as rubber base
impression material
– By the processing terminology, such as vulcanizing
impression material
– By chemistry, such as mercaptan impression material
or
– By the name of one of the first manufacturers, such
as the Thiokol Corporation.

• Examples
– Permlastic (Kerr)
– Omni-Flex (GC America) – copper hydroxide system.
– Coe-flex (GC-Amer)
– Neo-plex (Miles)
Supplied as :
Paste in collapsible tubes as base and accelerator.
Base is white and accelerator is brown or grey.

Composition
Base paste
Polysulphide
polymer
Lithopone and
titanium dioxide
filler strength
Di butyl phthalate plastisizer viscosity
Sulphur0.5% Enhance
the
reaction
Reactor paste
Lead dioxide Gives Dark
brown color
filler
plasticizer
Oleic acid or
stearic acid
Retarders Control rate
of setting

• Available in 3 viscosities,
• light body and medium body heavy body.
• Tray adhesive:
• Butyl rubber or styrene/ acrylonitrile dissolved in
a volatile solvent such as chloroform or a ketone

Reaction
lead dioxide reacts with the polysulfide polymer causing:
• Chain lengthening by oxidation of terminal – SH groups.
• Cross linking by oxidation of the pendant – SH groups.

Modifications
• Reactor – lead dioxide replaced by organic hydroperoxide
e.g. t-butyl hydroperoxide.
– But this has poor dimensional stability because of volatility.
• Inorganic peroxides such as copper.

Manipulation
• With the proper lengths of the two pastes squeezed onto
a mixing pad or glass slab,
• the catalyst paste is first collected on a stainless steel
spatula and then distributed over the base, and the
mixture is spread out over the mixing pad
• The mass is then scraped up with the spatula blade and
again smoothed out.

• If sufficient force is applied and spatulation is performed
rapidly, the material will seem thinner and easier to
handle.
• This phenomenon is known as pseudoplasticity.
• Most accurate impressions are made using custom
acrylic trays because of uniform thickness of the
material.

• Mean working time
– 6.0 min at 23 degree
• Mean setting time
– 16 min at 23 degree

Accelerators of curing
• An increase in temperature
• A drop of water
Retarders of curing
• A decrease in temperature (chilled, dry glass slab)

• Elasticity improves with time, so longer the impression
can remain in the mouth before removal, greater the
accuracy.
• Polysulfide ranks as one of the least stiff of the
elastomeric impression materials.

• Unset material has high level of viscosity. This thick
consistency of the uncured material helps displace an
unwanted fluid present while seating the impression.
• Also, the excess material extruded from the tray does
not flow easily because of the high viscosity, reducing
the potential discomfort to the patient during seating of a
tray.

Advantages Disadvantages
Long working time Requires a custom tray
Proven accuracy Must be poured in stone immediately
High tear resistance Potential for significant distortion
Less hydrophobic Odor offends patients
inexpensive to use Messy and stains clothes
Long shelf life Second pour is less accurate
Polysulfide

Silicones

silicones
Condensation
Addition

Condensation reaction – a polymerization reaction in which
the polymer chains all grow simultaneously and a reaction
byproduct is formed.
CONDENSATION SILICONE
Also known as conventional silicone

Available in 3 viscosities
– Light body
– Medium body
– Putty body
• Paste – two pastes in collapsible tubes
• Putty – jars

Condensation Silicone
• Examples
– Speedex (Coltene/Whaledent)
– Primasil (TISS Dental)
– Accoe (GC-Amer)
– Xantopren (Unitek)
– Elasticon (Kerr)
– Cuttersil (Miles)

Composition
Phillip’s 1996
Composition Components Function
Base paste
Hydroxyl terminated
polydimethyl siloxane
prepolymer
undergoes cross linking
to form rubber
Silica Filler
Reactor
Orthoethyl Silicate Cross linking agent
Stannous octate Catalyst

The polymerization occurs as a result of cross linkage
between the orthoethyl silicate and the terminal hydroxy
group of the dimethyl siloxane, to form a three
dimensional network.
The reaction is exothermic ( 1deg C. rise)

Properties
• Setting time is 8-9 minutes
• Mixing time is 45 sec

• Tear strength 3000gm/cm lower than polysulfide
• Hydrophobic – area should be dried. Avoid air bubbles
while pouring the cast
• It is stiffer and harder than polysulfide. The hardness
increases with time.

• The spacing in the tray is increased to 3mm to
compensate for the stiffness.
• Can plated with silver/ copper. Silver plating is preferred.
• Shelf life is slightly less than polysulfides due to the
unstable nature of the orthoethyl silicates.

Advantages
• Better elastic properties
• Clean, pleasant
• Stock tray
• putty-reline
• Good working and setting time
Phillip’s Science of Dental Materialswww.indiandentalacademy.com

Disadvantages
• Permanent deformation – high – 1-3%
• Poor dimensional stability
– high shrinkage
• polymerization
• evaporation of ethanol
– pour immediately
• within 30 minutes
• Hydrophobic
– poor wettability Phillip’s Science of Dental Materialswww.indiandentalacademy.com

Addition Silicones

• Frequently called polyvinylsiloxane or viny polysiloxane
impression materials.
Addition silicones

Supplied in
• 4 viscosities
– Light body
– Medium body
– Heavy body
– Putty

Addition Silicones
• Examples
– Extrude (Kerr)
– Express (3M/ESPE)
– Aquasil (Dentsply Caulk)
– Genie (Sultan Chemists)
– Virtual (Ivoclar Vivadent)

Composition
Components Function
Base paste
Hydroxyl terminated
polymethyl siloxane
prepolymer
Undergoes
cross linking
to form rubber
Colloidal silica Filler
Reactor
Polyvinyl silicone
prepolymer
Colloidal silica Filler
Chloroplatinic
acid
Catalyst

Reaction

• Improper balance between the vinyl siloxane and silane
siloxane contribute to the liberation of hydrogen gas
• To overcome this manufacturer adds palladium
(scavenger) or wait for an hour before pouring the
impression.

• Setting time – 5-9 min
• Mixing time – 45 sec
• Best dimensional stability among elastomers.
• Curing shrinkage 0.17%
• Permanent deformation 0.05-0.3%
• Tear strength -3000gm/cm
• Extremely hydrophobic surfactant detergent

• Electroplated with silver or copper.
• Low flexibility
• Harder than polysulfide – extra spacing 3 mm should be
provided in the impression tray.
• Care should be taken while removing the cast from the
impression to avoid any breakage.
• Shelf life ranges from 1-2 years

Advantages
• Excellent reproduction of surface details
• Highly accurate
• High dimensional stability
– pour up to one week
• Stock or custom trays
• Multiple casts
• Easy to mix
• Pleasant odor

Disadvantages
• Expensive
• Sulfur inhibits set
– latex gloves
– ferric and Al sulfate
retraction solution
• Short working time
• Lower tear strength
• Possible hydrogen gas release
– bubbles on die
– palladium added to absorb
– Moisture control – impression making

Modifications in PVS
• Adding palladium scavenger to tie up any
hydrogen gas
• Less hydrophobic
• Smaller holding device, cartridges making
easier to use.

Polyether
• First material introduced for dental impressions.
• Introduced in Germany in late 1960s.

Available as
• base and accelerator in collapsible tubes.
• The accelerator tube is usually smaller.
• Earlier supplied in single viscosity.
• A third tube containing a thinner was provided.
• Available in 3 viscosities
– Light body
– Medium body
– Heavy body

Polyether
• Examples
– Impregum F (3M/ESPE)
– Permadyne (3M/ESPE)
– Pentamix (3M/ESPE)
– P2 (Heraeus Kulzer)
– Polygel (Dentsply Caulk)

Composition
Base Paste
Imine terminated
prepolymer
Becomes cross linked
to form rubber
Silica Filler – to control viscosity
Glycol ether or Pthalate Plasticizer
Reactor
paste
Alkyl aromatic
sulfonate ester
Initiates cross linking
Silica Filler
Pthalate Plasticizer

• Polyether based polymer that is cured by the reaction
between aziridie rings
• The main chain is a copolymer of ethylene oxide and
tetrahydrofuran.
• Cross linking and thus setting, is brought about by an
aromatic sulfonate ester.
• Is an exothermic reaction – 4-5deg C.

• Elasticity – stiffest of impression materials
– New formulation of medium or regular body are less stiff
– When used in thinner sections decreases the stiffness.
• Impressions must be kept in cool, dry environment.
Properties

• Sulfonic ester may cause skin reaction. To avoid this,
mix thoroughly before making an impression and direct
skin contact should be avoided.
• Setting time is around 8.3 min.
• mixing time - 30 sec.
• Heat increases the setting time.

• Is extremely stiff – flexibility 3%
• Its hardness is higher than polysulfides and increases
with time. Removing it from undercuts is difficult, so extra
spacing 4mm should be given.
• Tear strength is good 3000gm/cm
• Hydrophilic – so moisture in the impression field is not so
critical. It has the best compatibility with stone.
• Can be electroplated with silver or copper.
• Shelf life > 2 years.

Advantages
• Highly accurate
• Good dimensional stability
• Least hydrophobic
• Good surface detail
• Pour within one week
– kept dry
• Multiple casts
• Good wettability
• Good shelf life

Disadvantages
• Expensive
• Short working time
• Rigid
– difficult to remove from undercuts
• Bitter taste
• Low tear strength
• Absorbs water
– changes dimension
– Leaches components

Modifications
• Reducing the stiffness and producing polyether in low
and heavy viscosities have been the major changes.

Comparison of Properties
• Working time
– longest to shortest
• agar > polysulfide > silicones > alginate = polyether
• Setting time
– shortest to longest
• alginate < polyether < agar < silicones < polysulfide
O’Brien Dental Materials & their Selection

• Stiffness
– most to least
• polyether > addition silicone > condensation silicone >
polysulfide = hydrocolloids
• Tear strength
– greatest to least
• polysulfide > addition silicone > polyether > condensation
silicone >> hydrocolloids

• Cost
– lowest to highest
• alginate < agar = polysulfide <condensation silicone <
addition silicone < polyether
• Dimensional stability
– best to worst
• addition silicone > polyether > polysulfide > condensation
silicone > hydrocolloid
Phillip’s 1996

• Wettability
– best to worst
• hydrocolloids > polyether > hydrophilic addition silicone >
polysulfide > hydrophobic addition silicone = condensation
silicone
• Castability
– best to worst
• hydrocolloids > hydrophilic addition silicone > polyether >
polysulfide > hydrophobic addition silicone = condensation
silicone

Removal of impression
• One method for determining the time of removal is
– to inject some of the syringe material into an interproximal space
that is not within the area of operation.
– Can prodded with a blunt instrument from time to time, and when
it is firm and returns completely to its original contour

POLY ETHER URETHANE
DIMETHACRYLATE

Composition
- polyether urethane
dimethacrylate resin.
- diketone initiator
- amine accelerator
- 40 – 60% silica filler
(SILICON DIOXIDE)

• Clear tray(TRANSPARENT), photo initiated by 400 –
500 nm blue light
• Advantage - unlimited working time (CONTROLLED
BY OPERATOR),
• TEAR STRENGTH-6000-7500 gm/cm
• short setting time
• Disadvantage - surface polymerization

Fabrication of custom tray

Armamentarium

Tray stops

0.025 mm

2-3 mm

Thermoplastic tray

Vacuum formed

Visible light polymerized

• The advantages of this combination system compared with
agar or alginate used individually is
• The minimization of equipment required to record an agar
impression (no water cooled tray is needed) and
• The fact that agar is more compatible with gypsum model
materials than alginate.
• It is also relatively cheap in comparison to many synthetic
elastomers.

• Lin et al. demonstrated that the accuracy of this
combination system is better than either the reversible or
irreversible materials used separately and
• is comparable to that of polysulphide impression
materials.

Vinyl polysiloxane addition silicone
Extrude xp (kerr) - putty impression material
Extrude (kerr) - extra heavy body impression
material
Extrude (kerr) – medium body impression
material
Extrude (kerr) - wash light body impression
material

Condensation silicone
1. Xantopren(kulzer) Comfort - Regular body
Silicone Impression Material
2. Speedex (coltene)- light body silicone
impression material
3. Speedex (coltene) - putty silicone impression
material
4. Xantopren m mucosa (kulzer)- medium body
impression material

Polyether impression material
• Impregum penta (3M/ESPE)— light viscosity
Polyether impression material
• Impregum Penta (3M/ESPE)— - Medium
viscosity Polyether Impression Material
• Impregum Penta (3M/ESPE)— —Heavy body
polyether impression material
• P2 Standard -- Regular set Monophase
polyether impression material

Polysulfide impression
material
permalastic (kerr) – heavy body
permalastic (kerr)– light body
permalastic (kerr)– regular body

Addition Silicones
• Surfactants added
– reduce contact angle

SO3
-
+ R+
CH3 – CH – CH2 – CO2 – CH – (CH2)n – O – CH – (CH2)n – CO2 –CH2 – CH –CH3
N
H2C CH2
R R
m
N
H2C CH2
N
H2C CH2
R – N – CH2 – CH2 – +
N
H2C CH2
N
H2C CH2
R – +
+
Polyether Reaction
catalyst
base
ring opening

• These materials were developed to
overcome some of the disadvantages of
polysulfide materials, such as their
objectionable odor, the staining of linen
and uniforms by the lead dioxide, the
amount of effort required to mix the base
with the accelerator, the rather long setting
times, the moderately high shrinkage on
setting and the fairly high permanent
deformation.

Thank you
For more details please visit

Impression Techniques and Materials for Fixed Partial Dentures

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