Die materials in fpd /certified fixed orthodontic courses by Indian dental academy

DIE MATERIALS IN FIXED
PARTIAL PROSTHESIS

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INDIAN DENTAL ACADEMY
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INTRODUCTION
Accurate duplication of prepared
teeth and maintaining their relationship to one
another are important in constructing fixed partial
prosthesis . For this it is necessary to obtain an
accurate reproduction of prepared tooth, adjacent
opposing tooth and surrounding soft tissues.
Since direct
fabrication in the mouth is
inconvenient, difficult, time consuming and
virtually impossible all wax patterns for
extracoronal restorations are made by indirect
technique in the laboratory.

An accurate working cast with removable dies is
essential to make a well fitting restoration .
Detailed reproduction of die materials for
fixed prostheses affects the accuracy of working
casts and is related to the compatibility between
the die and impression materials.
A working cast is the replica of the
prepared teeth, ridge areas and other parts of
the dental arch.

Die may be defined as :
It is the positive reproduction of the form of the
prepared tooth in any suitable substance. (GPT 7)

A reproduction of a prepared tooth made from a
gypsum product, epoxy resin, a metal or a
refractory material. Anusavice ( 11th edition )

A die is a model of a single tooth, again prepared
from an impression. (E.C.Combe)
The die is a positive reproduction of the prepared
tooth and consists of a suitable hard substance of
sufficient accuracy usually an improved stone,
resin or metal. (Rosenstiel et.al)
The die is a model of the individual prepared
tooth on which the margins of the wax patterns
are finished. (Schillingburg)


A cast and die system captures the necessary
information so that it can be transferred to the
laboratory. There are two basic working casts and
die systems : A working cast with a separate die
and a working cast with a removable die.


MATERIALS USED FOR MAKING DIES IN
FIXED PARTIAL PROSTHESIS
1. Gypsum products-

Type IV Dental Stone
Type V Dental stone

2 Die stone -

Investment combination

3. Electroformed dies-

Silver plated
Copper plated


4. Epoxy resins
5. Polyurethane

Alternative die materials
6.Silicophosphate cement
7.Amalgam
8.Metal sprayed dies
9.Ceramic die materials
10.Flexible die materials

DESIRABLE

QUALITIES

OF

DIE

MATERIALS
They should accurately reproduce all fine
details in the impression.
They should be dimensionally stable. Setting
expansion, contraction and dimensional variation
in response to setting or change in temperature
should be minimal.
The die should have a smooth surface that is
sufficiently strong to withstand the subsequent

manipulative procedures without abrasion of the
surface that is it should have the ability to resist
abrasion.
They should be compatible with impression
materials and there should be no interaction
between the surface of the impression and cast or
die.
Toughness to resist breakage during fabrication
or burnishing of fine edges.

Colour of the die should be in contrast to the
colour of wax. This helps to facilitate the
manipulative procedures that will be carried out.
It should be reasonably easy to use without
excessive manipulative procedures.
It should be relatively inexpensive.


THE REQUIREMENTS FOR DIE AND
WORKING CASTS
It must reproduce the prepared tooth exactly.
All surfaces must be accurately duplicated, and
no bubbles or voids should be present.
A die must be made of a material that is dense,
hard and capable of being used in production of
wax patterns and in fitting and finishing of casting
without undue risk of damage to its surface.

Die must be given a form that allow easy
handling during waxing and other procedures.
The die must have root like extension that
serves as a handle.
The

remaining

unprepared

tooth

structure

immediately cervical to finish line should be easily
distinguished on the die, ideally with 0.5 to 1mm
visible.
Adequate access to the margin is necessary.

GYPSUM PRODUCTS
It is a mineral mined in various parts of the world
chemically
applications

the
is

gypsum
pure

produced

calcium

sulfate

for

dental

dihydrate

[CaSo4.2H2O].
Gypsum products are used in dentistry for the
preparation

of

study

maxillofacial structures

models

for

oral

and

and as important auxillary

materials for dental laboratory operations that are
involved in the production of dental prosthesis.

International standard ISO 6873:1998 “ Dental
gypsum products“This standard identifies five
types of materials.

TYPES OF GYPSUM PRODUCTS :
1. Impression plaster [Type I]: Used to make replicas
of the soft tissues when making prosthesis.
2. Mounting plaster [Type II]: used to mount casts on
an articulator and make casts of oral structures
when strength is not an important consideration.
Both Type I and Type II are white plaster [plaster
of paris ].

3.Dental stones [Type III]: These are products used to
make yellow coloured casts used as models of the
hard and soft tissues of the mouth.
4.Dental stone high strength [Type IV] and
5.Dental stone, high strength, high expansion [Type V]
These special stones are much harder and denser
then regular stones. In general these are used when
extreme accuracy in the models is demanded, such
as in the dies used to make crowns, bridges and
frame works for prostheses.

PRODUCTION OF STONE :
Plaster and stone products are produced by
calcining calcium sulphate dihydrate or gypsum.
Gypsum is ground and subjected to
temperatures of 1100 to 1200c to drive off part of
the water of crystallization and is converted to
calcium sulphate hemihydrate[ CaS04 .1/2 H2O]. :

The temperature is further raised and following
products are formed

1100-1300c

1300-2000c

CaSO4.2H2O → CaSO4.1/2 H2O →
Calcium sulphate
Dihydrate

Calcium sulphate
hemihydrate


2000-10000C

CaSO4
→ CaSO4
Hexagonal
orthorhombic
Anhydrite
Anhydrite

The principal constituent of gypsum – based
products such as dental plasters and stones is
calcium sulphate hemihydrate.
Depending on the method of calcinations,
different forms of the hemihydrate can be obtained
They are - α hemihydrate
- α -modified hemihydrate
- β -hemihydrate
The differences between alpha & beta
hemihydrates are a result of differences in crystal
size, surface area www.indiandentalacademy.com perfection.
& degree of lattice

The α-hemihydrate is called artificial stone, die
stone or improved stone and it requires much less
water when it is mixed than does the βhemihydrate.
The β-hemihydrate particles absorb more water
because the crystals are more irregular in shape
and are porous in character.


The beta form, which is known as dental plaster,
consists of largely irregularly shaped orthorhombic
crystal particles with capillary pores.
The alpha form consists of smaller, regularly
shaped crystalline particles in the form of rods or
prisms.
The alpha modified hemihydrate is made by
boiling gypsum in a 30% aqueous solution of calcium
chloride & magnesium chloride. This process yields
the smoothest, most dense powder particles of the
three types, and the powder is used primarily for dies.

The amount of mixing water required depends on
Particle size
Total surface area
Particle size distribution
Adhesion between the particles
Grinding the particles after the preparation of the
hemihydrate can eliminate needle like crystals and
provide

better

packing

characteristics.

lowering the amount of mixing water required.

Thus

Adhesion between the particles of hemihydrate is
also a factor in determining the amount of water
required to produce a product that can be poured.
Small amounts of surface active materials, such
as gum arabic plus calcium carbonate, added to
the

hemihydrate

can

reduce

the

water

requirements of both plaster and dental stone.

SETTING REACTIONS:The setting reaction of gypsum occurs by
dissolution of calcium sulfate hemihydrate, formation of
a saturated solution of calcium sulfate, aggregation of
less soluble calcium sulfate dihydrate and precipitation
of dihydrate crystals.
The crystallization

of calcium sulfate dihydrate

occurs while most of the remaining hemihydrate
particles dissolve.
Hemihydrate is four times more soluble in water
than is the dihydrate near room temperature (20°c).

Setting reactions can be understood as follows:
1. When the hemihydrate is mixed with water, a
suspension is formed that is fluid and workable.
2. The hemihydrate dissolves until it forms a saturated
solution.
3. This saturated hemihydrate solution, supersaturated
in dihydrate precipitates out dihydrate.

4. As the dihydrate precipitates, the solution is no
longer saturated with the hemihydrate, so it continues
to dissolve.
Dissolution of the hemihydrate and precipitation
of the dihydrate proceeds as either new crystals form
or further growth occurs

on the crystals already

present. The reaction is continuous and it continuous
until no further dihydrate precipitates out of solution.
The anhydrite is not formed in aqueous media.

As the amount of gypsum increases during the
setting period, the mass thickens because of the
formation of needle-like crystals.
When a lower W/P ratio is used the crystals
grow and through intergrowth they form a strong solid
mass. At a W/P ratio near the theoretical limit of 0.18,
some of the hemihydrate crystals do not fully dissolve,
but they hydrate and still tend to harden the structure.

PROPERTIES:
Water /Powder ratio:
The ratio of the water to the hemihydrate powder
is usually expressed as the W/P ratio. It is an
important factor in determining

the physical and

chemical properties of the final gypsum product,
As the W/P ratio increases, the setting time
increases, the strength of the gypsum product
decreases, and the www.indiandentalacademy.com decreases.
setting expansion

This is the reason why plaster of Paris which
has the highest water powder ratio has the least
compressive strength and Type V dental stone which
has the least water: powder ratio has the maximum
strength.
When a lower water: powder ratio is used the
crystals become broader and through intergrowth they
form a strong solid mass.

According to A.D.A specification No, 25 the W/P ratio
for:
Type I

0.40- 0.75

Type II

0.45- 0.50

Type III

0.28- 0.30

Type IV

0.22- 0.24

Type V

0.18 -0.22


Mixing time:
Mixing time is defined as the time from the
addition of the powder to the water until the mixing
is completed. Mechanical mixing of stones and
plasters is usually completed in 20 to 30 sec.
Hand spatulation requires at least a minute to
obtain a smooth mix.

Working Time:
Working time is the time available to use a workable mix,
one that maintains a uniform consistency to perform
one or more tasks.
Generally, a 3 min working time is adequate.
Setting Time:
The powder mixed with water, and the time that elapses
from the beginning of mixing until the material hardens is
known as the setting time.
According to A.D.A specification No.25 the setting time
for the various die materials is
Type IV dental stone 12 min±4 minutes.
Type V dental stone 12 min±4 minutes

Control of setting time :
Three basic methods are used to control the setting
time
-The solubility of the hemihydrate can be increased or
decreased. If the solubility of the hemihydrate is
increased super saturation of the calcium sulfate
increases, and the rate of crystallization deposition is
also increased .
-The number of the nuclei of crystallization can be
increased or decreased .The greater the number of
nuclei of crystallization the faster the gypsum crystals
form and the sooner the hardening of the mass occurs
because of crystalline intermeshing .

-The setting time can be accelerated or retarded
by increasing or decreasing the rate of crystal
growth.

Operator can vary the setting time within reason
by changing the W/P ratio and mixing time .


Factors effecting the setting time.
Effect of spatulation : Within practical limits, the
longer and the more rapidly the plaster is mixed, the
shorter is the setting time.
When the powder is placed in water the chemical
reaction starts and some calcium sulphate dihydrate is
formed.
During spatulation the newly formed calcium
sulfate dihydrate breaks down to smaller crystals and
starts new centers of nucleation, around which the
calcium sulfate dihydrate can be precipitated.

Because an increased amount of spatulation
causes more

nuclei centers to be formed, the

conversion of calcium sulfate hemihydrate to
dihydrate requires somewhat less time.
Thus the setting time is decreased. The longer &
more rapidly the plaster is mixed, the shorter is the
setting time.

Effect of Humidity:
During the calcination process

most of the

gypsum particles are changed to the hemihydrate,
although a small portion may remain as the dihydrate,
and possibly some particles may further dehydrate
completely to form anhydrous soluble calcium sulfate.
Soluble calcium sulfate to a greater degree and
plaster to a lesser degree are hygroscopic materials by
nature and can easily absorb water vapor from a humid
atmosphere to form calcium sulfate dihydrate, which

changes the original proportion of calcium sulfate.

The presence of small amounts of calcium
sulfate dihydrate on the surface of the hemihydrate
powder provides additional nuclei of crystallization.
Thus if the calcination is not complete and gypsum
particles remain, or if the manufacturer adds
gypsum, the setting time is shortened because of
the increase in potential nuclei of crystallization.
For best results all gypsum products should
be kept in a closed container and well protected
from the atmospheric humidity.

Fineness:
The finer the particle size of the hemihydrate, the
faster the mix hardens, particularly if the product has
been ground during manufacture.
Fineness results in
-Increased rate of dissolution of the
hemihydrate.
-Gypsum nuclei are more numerous and
thus a more rapid rate of crystallization occurs.

According to ADA specification no. 25 the
fineness of the various dental stone is as follows:
Type IV dental stone :
98% passes through 150mm
Type V dental stone :

Water: powder ratio:
The more water used for mixing, the fewer nuclei there
are per unit volume .Thus the setting time is prolonged
but the set material is weak.
Temperature:
The effect of temperature on the setting time is
likely to be erratic and may vary from one plaster [stone]
to another, little change occurs between 0ºc and 50ºc .
If the temperature of the plaster- water mixture
exceeds a 50ºc gradual retardation occurs .
As the temperature approaches 100ºc no reaction
takes place.

Retarders & accelerators :
Setting time can be controlled by the addition of certain
chemical modifiers to the mixture of plaster or dental
stone.
If the chemical added decreases the setting time it
is known as an accelerator,
if it increases the setting time it is known as
retarder .
Retarders generally act by forming an adsorbed layer on
the hemihydrate to reduce its solubility and on the
gypsum crystals present to inhibit growth.
Many inorganic salts in smaller concentration may act as
accelerators, but when the concentration is increased
they can become retarders .

Sodium chloride [NaCl] is an accelerator upto
about 2% but at higher concentration acts as a
retarder.
The setting time can be accelerated by adding
gypsum[<20%], potassium sulfate, or sodium
chloride[<28%].
Organic materials such as glue, gelatin and
some gums act as retarders.
Another type of retarder consists of salts
that form a layer of a calcium salt that is less
soluble than is the sulfate .These may include
borax, potassium citrate, and sodium chloride.

Setting expansion:
Crystallization process is pictured as an outgrowth
of crystals from nuclei of crystallization. On the
basis of entanglement of the dihydrate crystals,
crystals growing from the nuclei can intermesh with
and obstruct the growth of the adjacent crystals.
If this process is repeated by thousands of the
crystals during growth, an outward stress or thrust
develops that produces an expansion of the entire
mass. Thus a setting expansion will take place.

This expansion of the die material is a desirable
quality as it is one of the means of compensation of
the thermal shrinkage of casting alloy.
As far as the dentist is concerned only the
setting expansion that occurs after the initial set is of
interest. Any expansion or contraction that occurs
before this time can be overcome by friction between
the mold surface against which the fluid mixture is
poured.
At the time of initial set the crystalline framework is
sufficiently rigid that it can overcome for most part,
such frictional retention.

Any initial contraction that occurs
during the induction period does not affect
the accuracy, because the mix is fluid at this
stage and the contraction occurs at the free
surface.


According to ADA specification no.25 the setting
expansion of
Min Max
TYPE IV stone - 0.00 0.10
TYPE V stone 0.10 0.30
Control of setting expansion:
Setting expansion must be controlled to obtain the
desired accuracy in dental applications.
-A lower W/P ratio and a longer mixing time
increases the setting expansion. Each of these factors
increases the nucleiwww.indiandentalacademy.com
density.

At higher Water powder ratio, fewer nuclei of
crystallization per unit volume are present than with
the thicker mixes because it can be assumed that the
space between the nuclei is greater in such a case, it
follows that there is less growth interaction of the
dihydrate crystals and less outward thrust.
The most effective method of controlling setting
expansion is through the addition of chemicals. The
setting expansion can be reduced by adding either
potassium sulphate, sodium chloride or borax.

Strength
The strength of the gypsum products is generally
expressed in terms of compressive strength. The
strength of plaster or stone increases rapidly as
the material hardens after the initial setting time.
But the free- water content of the set product
affects its strength.
For this reason two strength properties of
gypsum are reported:
wet strength.
dry strength

The wet strength is the strength obtained when the
water in excess of that required for hydration of the
hemihydrate is left in the test specimen.
When the excess water in the specimen has
been driven off by drying, the strength obtained is the
dry strength. The dry strength may be two or more
times as high as wet strength.
According to the ADA specification no 25 is at 1 hour:
Type IV - 5000 psi
Type V - 7000 psi

FACTORS AFFECTING STRENGTH:
Water powder ratio:
Greater the water powder ratio the less is the dry
strength of the set material because the greater the
porosity, the fewer crystals are available per unit
volume for a given weight hemihydrate .
Spatulation time:
With an increase in mixing time the strength is
increased to a limit that is approximately equivalent to
that of hand mixing for 1min.If the mixture is over
mixed the gypsum crystals formed are broken up and
less crystalline interlocking results in the final product.

Chemical modifier :
Addition of an accelerator or retarder lowers both
the wet and the dry strengths of the gypsum
product.


TYPE IV DENTAL STONE
These are high strength dental stone.
The principal requisites for a die material stone are
strength
hardness
resistance to abrasion
minimum setting expansion
To obtain these properties one should use an
α-hemihydrates of the “densite”-type .The cuboidal
shaped particles and the reduced surface area produce
such properties .
Surface detail reproduction is acceptable with type
IV and type V gypsum products.

The materials are capable of reproducing a 20μm-wide
line as prescribed by A.D.A specification No.19.
A hard surface is necessary for a die stone because the
cavity preparation is filled with wax that is carved flush
with the margins of the die.
A sharp instrument is used for this purpose therefore the
stone must be resistant to abrasion.
Since the surface dries more rapidly the surface
hardness

increases

more

rapidly


compressive strength.

than

does

the

Even though the surface of the type IV stone is
harder, care should be observed

when the

pattern is being carved.
It has been recommended to wait for 12-24 hrs to
avoid the stone fracturing during removal from
the type IV dental stone high strength.


W: P ratio

-

0.22 -0.24

Setting time

-

12 ±4

Setting expansion

-

0.10

Compressive strength

-

5000 psi

Hardness

-

92 RHN


TYPE

V

DENTAL

STONE,

HIGH

STRENGTH,

HIGH

EXPANSION:

The Type V dental stone gypsum product exhibits an
even higher compressive strength than does the type IV
dental stone.
In addition setting expansion has been increased
from a maximum of 0.10% to 0.30%. This is because
certain newer alloys such as base metal alloys have a
greater casting shrinkage than noble metal alloys.
Thus higher expansion is required in the stone
used for the die to aid in compensating for the alloy

solidification shrinkage.

Type V stone is indicated when inadequate
expansion may have been achieved during the
fabrication of cast crowns.
It should be avoided in the production of
dies for inlays since the higher expansion may
lead to unacceptably tight fits.

W: P ratio

-

0.18 -0.22

Setting time

-

12 ±4

Setting expansion

-

0.30

Compressive strength

-

7000 psi


Advantages of Type IV & Type V stones :
 They are relatively inexpensive
 Easy to use
 Compatible with all impression material
Disadvantages of Type IV gypsum die
 Susceptibility to abrasion during carving of wax
pattern.


Gypsum dies are sometimes
modified to:
To make them more abrasion-resistant
To change the dimensions of the dies.
To increase the refractoriness of the dies.
To produce a combination of these effects.

Several means are used to increase the abrasion
resistance
•Including silver plating,
•Coating the surface with cyanoacrylate
• Adding a die hardener to the gypsum
However each of these methods may increase the
die dimensions slightly thus reducing accuracy.


Special gypsum products ;
Since 1991, a plethora of new dental stones
have been introduced One type is extremely
fast- setting and ready to use in 5min,but it as
little working time another product changes color
to help denote when it is ready for use .
Most recently another trend is the addition
of a small amount of plastic or resin ,which
reduces brittleness and improves resistance to
abrasion during the carving of wax patterns.

Usually in the production of gypsum products when
one feature is improved another feature is sacrificed.
A faster set may be accepted in return for less
working time.
An improved resistance to carving may be
gained in return for greater difficulty in manipulation
and decrease in detail reproduction

Methods of altering die dimensions
To reduce the setting expansion of the type IV die stone
to less than 0.1% additional accelerator such as
potassium sulphate and retarders (Borax) can be added
to the gauging water this will reduce the diameter of the
die.
To produce relief space for cement, a die spacer with a
stone die is used.
Die spacer : An agent applied to a die to provide space
for the luting agent in the finished casting.

Types of die spacers :
Resins (Commonly used)
Paint or liquids
Model paint
Coloured nail polish
Thermoplastic resins dissolved in volatile
solvents.


Spacers are applied in several coats to within 0.5mm
of the preparation finish line to provide relief for the
cement luting agent and to ensure complete seating
of an otherwise precisely fitting casting or coping.


DIE STONE INVESTMENT COMBINATION :
A technique has been developed which the die material
and the investing medium have
a comparable
composition .
A commercial gypsum- bonded material called
divestment is mixed with a colloidal silica liquid. The
die is made from this mix, and the wax pattern is than
constructed on it then the entire assembly [die and
pattern] is invested in a mixture of divestment and water
thereby eliminating the possibility of distortion of the
pattern on removal from the die or during the setting of
the investment.

When it is heated to 677°c the setting expansion of
the material is 0.9% and the thermal expansion is
0.6% because divestment is a gypsum- bonded
material it is not recommended for high-fusing alloys
that are used for metal-ceramic restorations but it is
a highly accurate technique for use with
conventional gold alloys especially for extra coronal
preparations.
Divestment phosphate recommended for high
fusing alloys.

ELECTROFORMED DIES :
Besides resins, electroplating can be used to overcome
the poor resistance of gypsum. The metal dies that are
produced when an impression material is electroplated
have moderately high strength, adequate hardness and
excellent abrasion resistance.
Detail reproduction of a line

4µ-m or less is readily

attainable on an electroplated die when an nonaqueous
elastomeric impression material is used.

The first step in the procedure is to treat the
surface of the impression material so that it
conducts electricity. This process is referred to as
metalizing This technique has been used for
many years and involves the deposition of a coat of
pure silver or copper on the impression.
The areas to be coated are first coated with
finely powdered silver or graphite to make them
conduct electricity, and the impression is than
placed in an electroplating bath.
A layer of pure metal is deposited on the
impression and is supported with type IV stone or
resin.

Silver formed dies : (Silver plating)
Copper plated compound dies began in the early 1930’s
and the silver plated dies became more popular in later
years.
Polysulphide and silicone impression materials can be
silver plated.
In this process
A thin layer of metal such as silver powder is
deposited on the surface of the impression material.
Various metallizing agents are available, including
bronzing powder and aqueous suspensions of silver
powder and powdered graphite.

These agents can be deposited on the surface of
the impression with the camel hair brush.
The electroplating bath is a solution of silver
cyanide. Chemical deposition of silver from a silver
nitrate solution can be used if greater surface detail
reproduction is required .
The greater the concentration of silver in the bath,
the faster the silver is deposited. The acid content
increases the throwing power , a term that refers to
the penetration of current into a concave structure,
such as an impression for a full crown.

An electrical contact is made with the metallized
surface of the impression, which is the cathode in
the electroplating bath.
A plate of silver is used as the anode.
A direct current is applied for approximately 10hr.
Electroformed dies made from polysulphide
rubber impressions are clinically acceptable when
a silver cyanide bath is used, but they are
generally slightly less accurate than a properly
constructed stone www.indiandentalacademy.com
die .

Polysulphide

rubber

impressions

are

cleaned

thoroughly and dried .
They are then metallized

with a fine silver powder

although other metallizing agents can be used, the
silver powder results in a superior surface on the
electroformed die.
A anode of pure silver, at least twice the size of the
area to be plated, is employed and the electroplating
is carried out as before for approximately 10hrs, using

5- 10mA/cm2 of cathode surface.

An impression that contains the electroformed die
surface is then filled with dental stone.
When the stone hardens. It is mechanically locked into
the rough interior of the electroformed metal shell.
The impression material is then removed to provide a
die with greater surface hardness and resistance to
abrasion.
The model and die are prepared in the normal manner
and margins of the die are trimmed with a finishing disk.

Composition of solution for silver forming bath
Ingredients
Quantity
Silver cyanide
36gms
Potassium cyanide
60gm
Potassium carbonate
45gms
Water(distilled)
1000ml
Advantages
Moderately high strength
Adequate hardness
Excellent abrasionwww.indiandentalacademy.com
resistance

DISADVANTAGES :
The electroplating bath is a solution of silver cyanide.
This solution is poisonous, and extreme care should be
taken that the hands workbench area and clothing not
become contaminated.
The addition of acid to the solution produces hydrogen
cyanide, an extremely poisonous gas and for this reason
copper-forming solution should be kept far away.
The plating bath should have a cover that can be in
placed at all times to control evaporation and dissipation
of fumes.
Because of this risk, www.indiandentalacademy.comnot often used.
silver plating is

COPPER PLATING OR COPPER FORMED DIES :
Metal dies can be made by copper plating compound
or silicon such a die is tough and has good strength
characteristics and metal inlays restorations can be
finished and polished on these dies .
The following process is involved :
-The surface of the impression is coated with fine
particles of copper or graphite to make them conduct
electricity.

When the impression is in compound, a colloidal
dispersion of graphite is painted on the surface to
be plated and allowed to dry before it is placed
into the plating bath .
When the impression is a silicone rubber ,finely
divided copper powder is brushed on the surface
to be plated before placing the impression into the
bath.
-The coated impression is made the cathode of a
plating bath, with an anode of copper.

- The electrolyte is an acid solution of copper sulphate
together with organic constituents [ex: alcohol or
phenol ]which help in increasing the hardness of the
deposited metal.
Sulphuric acid increases the conductivity of the solution
and the phenol sulphonic acid assists the penetration of
copper ions to the deeper parts of an impression and
improves the throwing power of the solution .
-A current is passed, causing slow dissolution of the
anode and movement of copper ions from anode to
cathode, so plating the impression.

About 15mA is a suitable current to start plating a
single tooth impression . Once a thin layer of
copper has covered the entire surface of the
impression, the current can be increased to as
much as two or three times the initial current. If too
high a current setting is used, the copper deposit
will be granular and friable in nature, and the die
will be unsatisfactory.

High current densities also produce a heavier deposit on
the areas of the impression nearest to the anode, and
sometimes rapid plating results in a failure to adequately
cover the deeper areas of an impression.
Plating is allowed to proceed for 12 to 15 hours;
overnight usually is a convenient period of time.
In copper forming, the distance between the anode
and impression to be plated is important in relation to
plating the deeper areas of an impression.
The greater the anode to impression distance the more
even is the quantity of copper deposited over the
impression the morewww.indiandentalacademy.comdeep areas plated.
readily are the

Dental stone is than cast into the plated impression
when the stone has set the metal covered die can
be removed from the impression
This technique is often not considered suitable for
the elastomeric materials because they are not
dimensionally stable in an acid solution.

Composition for solution for copper forming bath

Ingredients

Quantity

Copper sulfate

200 gms

Sulphuric acid ( conc )

30 ml

Phenosulphonic acid

2 ml

Water ( distilled )

1000 ml

Problems in Electroplating
Variable degrees of distortion commonly occur and
hence the technique must be performed slowly.
Otherwise distortion in the metal will subsequently
stress the impression.
The time required to produce a cohesive film of
metal(typically 8 hrs) is ample for the development
of dimensional changes in the impression.
Not all the impression materials are suitable for
plating because of their low surface energies,
silicone impression materials are difficult to
electroplate evenly.

Polyether

impressions

because

of

their

hydrophilic nature imbibe water & become
distorted. Therefore they cannot be plated
accurately.
Poly sulfide polymers can be silver plated but it
is difficult to copper plate them
Drawback of silver plating is the use of a
cyanide

solution,

which

requires

special

precautions because of its extreme toxicity.

Epoxy resins
Resins are used as die materials to overcome
the low strength and abrasion resistance of die
stones. Most available resin die material is epoxy
resin but polyurethane is also used.


Epoxy materials until recently where supplied
in the form of a paste to which a liquid activator was
added to initiate hardening. Since the activators are
toxic they should not come into contact with the skin
while mixing and manipulating of the unset material
Shrinkage of 0.1% has occurred during
hardening, which may take up to 24 hours.The
hardened resin is more resistant to abrasion and
stronger than a high strength stone die.

The viscous paste is not so readily introduced
into the details of a large impression as high
strength dental stone .Recently fast setting epoxy
materials have been supplied in automixing
systems .
The epoxy resin is in one cartridge and the
catalyst is in the other. Forcing the two pastes
through the static mixing tip thoroughly mixes the
epoxy material, which can be directly injected into
a rubber impression.

The fast setting epoxy hardens rapidly so that dies
can be waxed up in half an hour after injecting into
the impression .Epoxy resins cannot be used with
water containing agar and alginate impression
materials because the water retards the
polymerization of the resin and thus are limited to
use with rubber impression materials .
Working time
– 15 min
Setting time
_ 1-12 hrs
(depending on product)
Shrinkage
_ 0.03%-0.3%
Compressive strength _ 9500-14200psi
Hardness www.indiandentalacademy.com
_
83Rhn

Advantages:
-It can be cured at room temperature without
expansive or complicated equipment.
-It is dimensionally stable .
-Its abrasion resistance is many times greater
than gypsum products.
-high strength.
-Suitable for fabrication of precision dies .
-Detail reproduction is better than die stone
Hence prostheses fabricated on resin dies
will fit more tightely than those made on
gypsum.
-Good results are achieved with silicone and
polyether

Disadvantages:
-It undergoes shrinkage during polymerization.
The amount of shrinkage is approximately equal to

the expansion with gypsum.
-It is more expansive than gypsum.
-Not compatible with impression materials such as

polysulfide and hydrocolloid.

Polyurethane
These resins compared to epoxy resins were
inexpansive and easily manipulated.
Unfilled polyurethane resins demonstrated
considerable shrinkage during polymerization, but
these materials then appeared to swell slightly.
Long and narrow tooth preparations must be
reproduced with high transverse-strength working
cast materials to avoid fracturing;thus filled
polyurethane resins could be indicated for these
conditions .

Silicophosphate cement:
This is similar to the filling and cementing material.
Advantage :
Harder than die material.
Disadvantage:
-Shrinkage on setting.
-Loss of water on standing.

Amalgam:
Advantage:
-Produces a hard die
-Reproduces fine details and sharp margins.
Disadvantages:
-Can only be packed into a rigid impression .
-Long time to reach a maximum hardness.
-High thermal conductivity hence can cool a
wax pattern rapidly which can lead to distortion of the
pattern. This can be overcome by warming the die , a
separating agent is needed as with stone dies.

Metal sprayed dies:
A bismuth-tin alloy, which melts at 138 0c, can be
sprayed directly on to an impression to form a
metal shell, which can then be filled with dental
stone.
Advantage
-A metal coated die can be obtained rapidly
from elastomeric impression materials.
Disadvantage
-The alloy is rather soft, care is needed to
prevent abrasion of the die.

Ceramic die materials:
Two ceramic die materials are available
-A material for the production of dies on which
porcelain restorations are to be fabricated, without
the use of a platinum foil matrix. To form the dies
heating to over 10000c is necessary.
-A ceramic material, supplied as a powder and
liquid, and mixed to a putty like consistency. After 1
hour the material is removed from the impression
and fired at 6000c for 8 minutes to produce a hard
strong die.

Flexible die material :
-Similar to silicone or polyether impression
material.
-Used to make provisional restorations or indirect
composite resin inlays .
eg; polyvinyl medium viscosity impression
material
Advantages:
-More rapid setting
-ease of removal of provisional or inlay
Disadvantages:
-expensive

Compatibility with impression
materials :
Dental stone

Electroplated Cu
Electroplated silver

-Impression compound
-Zinc oxide eugenol
-Agar-agar
-Alginate
-Impression plaster when
used with separator
-Rubber base material
- Rubber base material

-Polysulphide
-Polyether
-Addition silicone

Polymer

-Rubber base material

Epoxy Resin

-Polyether
-Addition silicone
-Polysulphides(Separator)


Comparisons of the various die materials :
According to
Craig: The epoxy resin dies reproduce detail the
best followed by metal die and high strength dental
stone .
Chaffe et al in 1997 reported that epoxy resins
reproduce a single die with a degree of accuracy
similar to gypsum material used.
Derriem et al in 1995 reported that the detail
reproduction of stone was inferior epoxy and
polyurethane resins stone cannot reproduce details
smaller than 20 nm as the gypsum crystal size
ranged formal 15 to 25 nm.

Bailey et al in 1984 found no difference in the
accuracy of stone, epoxy resins and electroplated
silver dies .
Nomura et al in 1980 concluded that the detail
reproduction of epoxy resin dies was comparable to
stone .
Moser et al in 1975 found that the epoxy resins
reproduced detailswww.indiandentalacademy.com
better than stone.

Dimensional stability:
Chaffee et al in 1997 concluded that the improved
dental stone dies were significantly larger in
occluso-gingival dimension than epoxy resins.
Derriem et al in 1995 were able to show that the
dies exhibited slight shrinkage as compared to
stone , which exhibited slight expansion. This
required the epoxy dies to be coated with several
layers of spacers .
Nomura et al in 1980 and Mose et al in 1975
demonstrated thatwww.indiandentalacademy.comwere under sized
the epoxy dies

Abrasion resistance and strength
Chaffee et al in 1997, Derriem et al 1995 ,Nomura
et al in 1980 and Moser et al in 1975 concluded
that metal formed dies have superior abrasion
resistance ,epoxy dies have good resistance and
the high strength dental stones have the least
resistance to abrasion

Philip Duke et. al in 2000 conducted a study of
the physical properties of type IV gypsum, resin
containing and epoxy die materials. The results
were all gypsum products expanded where as the
epoxy resin material contracted during setting. The
epoxy resin exhibited much better detail
reproduction, abrasion resistance, transverse
strength than gypsum materials. In general the
epoxy resin exhibited the best properties of the
materials studied

Jacinthe M et al in 2000 conducted a study
on the dimensional accuracy of an epoxy resin
die material using two setting methods and
concluded that retarding the setting reaction of
an epoxy resin die material improved its
accuracy. Epoxy resin die materials had a net
shrinkage but the gypsum based materials had
a net expansion .

Summary
Detailed reproduction of die materials for fixed
partial prosthesis affects the accuracy of working
casts and is related to the compatibility between the
die and impression materials.
Hence an accurate working cast and die are
essential in making successful cast restoration .
Different types of materials and techniques are
available that will give an extremely precise
reproduction of prepared teeth .
Dental stone is compatible with majority of
impression materials.

This material is inexpensive easy to use and
generally compatible with all impression material.
Resistance to abrasion of the material can be
effectively increased by using gypsum hardner, such
as aqueous colloidal silica or soluble resin .
Epoxy resin and electroplated dies are good
alternatives

Conclusions:
A good impression and an accurate die are
the first step towards the fabrication of an accurate
restoration whether its inlay, onlay or crown.
Proper selection of the die material and its
manipulation are paramount to achieve accuracy
in the die.
In conclusion, a wise choice of material,
combined with proper handling and meticulous
approach to the details of each step of fabrication
will bring us that much closer to perfection .

References:
Fundamentals of fixed Prosthodontics:Shillingberg.
Contemporary fixed Prosthodontics

:

Stephen F.Rosenstiel
Philip’s science of dental materials

:Anusavice

Dental material -properties and manipulation :
Craig ,powers

Notes on dental materials- E C Combe
Restorative dental materials- Robert G Craig
Philip Duke et al ;Physical properties of type IV
gypsum, resin containing and epoxy die materials
JPD April 2000 vol 83, no. 4 p-466-73.
Jacinthe M et al in 2000 dimensional accuracy of
an epoxy resin die material using two setting
methods. JPD March 2000 vol 83 no3 p 301-305

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Die materials in fpd /certified fixed orthodontic courses by Indian dental academy

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