Casts, dies and cast forming

CASTS, DIES AND
CAST FORMING
Presented by:
Apurva Thampi
MDS 1st year

A Good Impression…
 Requires time and effort
 Ensures an accurate and detailed cast
Rudd an Morrow, dental laboratory
procedures - complete dentures (volume I),
2nd edition

Definations
 Cast : it is a life-size likeness of some
desired form
 Die : the positive reproduction of the form
of a prepared tooth in any suitable
substance
Glossary of prosthodontic terms

Pre – requisites of casts
 Void free
 Distortion free
 Reproduce both prepared and unprepared
surfaces
 Occlusal surface of all teeth must allow
articulation
 All relevant soft and hard tissue must be
involved
 The side walls should be vertical or slightly
tapered outward
2nd edition

 Peripheral roll : 3-4mm
 Edge of the cast : 3-4mm
 Base of the cast : 15-16mm at the thinnest
point
 Tongue space should be flat nad smooth
2nd edition

Types of casts
Diagnostic casts
Working casts
Refractory casts
2nd edition

 Diagnostic casts : A life size
production of a part or parts of
the oral cavity and/or facial
structures for the purpose of
study and treatment planning
 Working casts: A cast formed of
a prosthesis for the purpose of
mounting on an articulator
 Refractory casts: A cast made
of a material that will withstand
high temperatures without
disintegrating (investment cast)
Glossary of Prosthodontic terms

CAST
FORMING
PRELIMINARY
IMPRESSION
FINAL
IMPRESSION
INVERSION
METHOD
INVERSIO
N
METHOD
WAX
BOXING
METHOD
DENTAL
PLASTER
&
PUMICE
METHOD
CAULKING
COMPOUN
D &
PADDLE
BOXING
METHOD

Preliminary impression
materials
 Alginate
 Impression compound
2nd edition

Alginate impressions
 Used to make diagnostic cast and
removable partial dentures
 Impressions to be poured soon after
taking the impression
2nd edition

 Procedure
 Examine the
impression
 Run cold tap water
and clean it gently
 Trim excess alginate
 Weigh the stone and
mix it with the
recommended W/P
ratio
 Vibrate the tray gently
and add the stone in
increments
 Create undercuts in
the first pour
2nd edition

 After initial set, soak in slurry water from 3-5
mins
 Mix stone and place on glass slab, shape
to approx. size and thickness
 Invert the stone cast onto this
 Remove excess, and shape until surface is
flat
2nd edition

PROBLEM CAUSE SOLUTION
Voids in impression Voids in impression material
during making of impression.
Obtain another impression.
Impression separated from
tray
Too much time between
impression and pouring.
Pour as soon as possible.
Cast surface chalky and
soft
Impression not separated
from cast within 1hr
after pouring.
Incorrect water powder
ratio, making mix too thin.
Separate within 1 hr.
Weigh stone and mix
with required amount of
water.
Voids on surface of cast Mechanical spatulator
not used.
Stone poured into
impression too quickly
Mix it in mechanical
Spatulator.
Pour slowly into only one
distal corner.
2nd edition

Cast too thin or thick Cast trimmed
improperly.
First pour of stone not
checked for thickness.
Trim with care to
prevent over
trimming.
If first pour stone is too
thick trim it before
pouring base.
Critical areas of cast
trimmed away
Trimmed improperly. Check cast frequently
when trimming.
Cast broken easily Improper water powder
ratio.
Cast trimmed too thin.
Use recommended
water
powder ratio.
Do not over trim

Modelling plastic impressions
 Thermoplastic material
 Rigid, hydrocolloid – less subject to
distortion
2nd edition

 Procedure
 Examine the impression
 Place it in a holder and
make a mix of stone
 Gently tap while pouring
mix
 After initial set, pour base
(inversion method)
 After 45min – 1hr, dip in
warm slurry water
 Lift the modelling plastic
off the cast
 Examine the cast and trim
2nd edition

PROBLEM CAUSES SOLUTION
Cast broken during
separation from
impression.
Modeling plastic not
softened adequately
before removal.
Immerse poured impression
in warm water to soften
before separation
Modeling plastic stuck
to cast at time of
separation.
Modeling plastic
overheated when
placed in water that is
too warm.
Do not over soften modeling
plastic, place in warm water
only long enough to soften
and remove.
Cast too thin or thick. Cast poured or
trimmed too thin.
Thick base as a result
of first pour being too
thick.
Pour cast to proper
thickness do not trim
too thin.
Check thickness of
first pour before
pouring base , trim on
cast trimmer if
needed.
2nd edition

Cast forming in final impression
 Wax boxing method
 Dental plaster and pumice boxing
method
 Caulking compound and paddle boxing
method
2nd edition

Wax boxing method
Effective for zinc oxide paste impression
Beading Grip wax, Orthodontic tray wax, and
utility wax are used for beading an impression
2nd edition

 Procedure
 Place the impression such that ridge portion
is parallel to the bench top
 Fill the tongue space with wax and seal it 3-
4mm below the border
 Adapt 4mm wide beading wax 3-4mm
below the border
2nd edition

 Warm boxing wax until flexible
 Seal the ends to the underlying layer of wax
 Check the boxing for adequate width,
height, border and sealing
 Check for leaks
 Pour the impression
2nd edition

Problem Cause SOLUTION
1. Borders of cast too
narrow or wide
Beading wax too narrow or
wide
Make beading wax
approximately 3- 4mm wide.
2. Border of cast not high
enough to preserve
thickness of impression
flange
Beading wax placed too
high
Adapt beading wax 3 –
4mm below border of
impression.
3. Border of cast too high Beading wax placed too low
Place beading wax 3 –
4mm below border of
impression.
4. Base of cast too thin
Boxing strip not extended
too high
Extend boxing strip 13mm
above highest area of
impression.
5. Base of cast too thick
Boxing strip extended too
high
Keep boxing strip
approximately 13mm above
impression.

Dental plaster and pumice
boxing
 Excellent for rubber based silicones
2nd edition

 Procedure
 Mix a 1:1 mix of dental
plaster and pumice
 Place a patty of it on a
glass slab
 Settle the impression into
the patty till 3-4mm below
border
 Remove excess material
 Border is 4mm wide
 Adapt boxing wax (
height – 13mm above the
highest point on the
impression Rudd an Morrow, dental laboratory
2nd edition

 Paint plaster surface with separating
medium
 Check for leaks
 Pour the impression with stone
 After setting place in warm water
 Adjust the dimension on a cast trimmer
2nd edition

1. Border of cast too high
or low
Plaster of paris and
pumice not trimmed to
proper level
Trim it until 3 – 4mm below
border of impression
narrow or wide
Plaster of paris and
pumice border of wrong
width
Make border 4mm wide
3. Cast unable to be
separated
Separating medium not
applied
Apply separating medium
4. Base of cast too high
on one side and low on
another
Impression not oriented
properly before boxing
Place the impression parallel to
bench top
5. Base of cast too thick
or too thin
Height of boxing strip
wrong
Place boxing strip 13mm above
highest point on impression
2nd edition

Caulking compound and
paddle boxing method
 The impression is boxed on a paddle and
wax and caulking compound is used for
beading
 The beading should be 4-5mm wide
 Fold a metal boxing strip around the
impression
 Secure with rubber band
2nd edition

 Procedure
 Strips of caulking compound rope to bead
impressions (3-4mm below border)
 The beading should be 4-5mm wide
 Fold a metal boxing strip around the
impression (13mm above highest point on
impression)
 Secure with rubber band
 Seal the caulking compound to the boxing
strip
 Pour the impression with stone
2nd edition

1. Borders of cast too high /
low
Beading placed at wrong
level
Place it 3 – 4mm below
narrow / wide
Beading too narrow / wide.
Cast over trimmed
Beading approximately
4mm wide
Exercise care when
trimming
3. Base of cast too thick /
thin
Boxing wax at wrong height
Place it 13mm above
2nd edition

Pre-requisits of a Die
 Void free
 Distortion free
 Trimmed to ensure access for carving wax
pattern margins
 Reproduce tooth exactly
 Remaining unprepared tooth structure
should be 0.5 – 1mm visible
Rosenteil, contemporary fixed
prosthodontics, 3rd edition

Material sciences
Dimensional
accuracy Resistance to
abrasion
Both these criteria are achieved by GYPSUM
2nd edition

Gypsum (CaSO4.2H2O)
 Available in 5 forms : type I – V
 When subjected to a temperature of
110C – 120C, water of crystallisation is
driven out and produces CaSO4.1/2H2O
CALCINATION
procedures – Fixed Partial dentures (volume
II), 2nd edition

 Differences between various types of
gypsum are attributed to Calcination
• Beta form(Plaster)
• Irregularly shaped and extremely
porous crystals
Calcination in
open kettle
• Alpha form (type I stone – Hydrocal)
• Dense non-porous crystals, regularly
shaped and cuboidal
Under steam
pressure in
autoclave
• Alpha form(Type II stone – Densite)
• Crystals are dense and larger than
in type I
Boiling in 3-%
solution of
calcium
chloride
II), 2nd edition

Physical properties of Dental
stone
Setting expansion
Setting time
Compressive strength
II), 2nd edition

Setting expansion of dental
stone
 Linear expansion occurs during conversion
from hemihydrate to dihydrate due to the
outward thrust of needle-like crystals
 Expansion ranges from 0.06% - 0.5%
 Can be controlled by:
 Smaller w/p ratio
 Longer mixing time
 Hygroscopic expansion
 Accelerators and retarders
II), 2nd edition

Setting time of dental stone
 Manufacturers
 Accelerator: 2%
K2SO4 - decreases
 Retarders : 2%
Borax - increases
 Powdered
CaSO4.2H20 mixed
with hemihydrate -
increases
 Operators
 Increase amount
of water -
increases
 Longer and faster
mixing time -
decreases
 Exposure to high
humidity -
decreases
II), 2nd edition

Compressive strength of
dental stone
 Inversely proportional to the water powder
ratio
 Presence of accelerators and retarders
decrease compressive strength
 Increasing spatulation time increases strength
 Compressive strength of:
 Dental plaster : 1800 p.s.i
 Type I stone (hydrocal) : 4500 p.s.i
 Type II stone (Densite) : 5500 p.s.i
II), 2nd edition

Strength
Wet strength Dry strength
Gypsum product has excess
Water than that required for
the hydration of the hemihydrate
Excess water present in the
Gypsum Product is driven off
• Dry strength is usually twice that of the wet strength
• Accelerators and retarders decrease compressive strength
• Increasing spatulation time increases compressive strength
II), 2nd edition

Alternative die and cast
material
 Resins
 Electroplated die
 Flexible die materials
Rosensteil, Contemporary fixed
prosthodontics,#rd edition

Resins (Epoxy resin)
 Advantages
 Overcomes low
strength and
abrasion of stone
 Cures at room
temperature without
expensive
equipment
 Dimensionally stable
 Abrasion resistant
 Disadvantages
 More expensive than
gypsum
 Undergoes shrinkage
 Some impression
materials are not
compatible with
resin
prosthodontics,3rd edition

Electroplated dies
 Deposition of a coat of pure copper or silver
on the impression
 Insert cathode wire in the border of the
impression in the metallised area
 Fill the preparations with electrolytic material
 Completely submerge the impression into the
plating solution
 Plate for initially 5mA per tooth for 1 hr. re-
submerge and plate for12hrs at 10mA
 Wash and dry, and use dental stone for the
construction of working casts
Rudd and Morrow, dental laboratory
procedures –volume II, 2nd edition

 Advantages
 Overcome poor
abrasion
resistance of
gypsum
 When done
properly, it can be
as accurate as a
stone die
 Disadvantages
 Distortion commonly
occurs
 Time consuming
 Time required to for
a film is enough for
the development of
dimensional
changes
 All impression
materials are not
suitable due to low
surface energies

Flexible die material
 It is similar to heavy bodies silicone or poly
ether impression
 Selection of compatible impression and
die material is very important to achieve
good surface details
 It is more rapid setting
 Easy to remove

Die systems
 Working cast with removable die
 Straight dowel pin
 Curved dowel pin
 Pindex system
 Di-lok tray
 Working cast with separate die
 DVA model system
 Zeiser model system
Shillingburg, Fundamentals of
fixedproshodontics, 3rd edition

Working cast with removable
die
 Dies that can be removed from the
working cast
 Convenient to use
 It should satisfy the following requirements
 Must return to their exact positions
 Must remain stable even if inverted
 Should be easy to mount on an articulator

Straight dowel pin
 The brass dowel
pin is one of the
most accurate
dowel types
 It resists horizontal
displacement and
vertical deviation

 Procedure
 Dowel is positioned over each
prepared tooth
 Place it between the arms of
a bobby pin
 Push a straight pin between
the arms of the bobby pin
and into the impression
 Pin should be placed parallel
to the long axis of the
prepared tooth
 Pour die stone into the
impression covering the
knurled end of the dowel
 Paperclips can be used to
add retention to the base Shillingburg, Fundamentals of

 Once the stone has set,
remove the straight pins from
the impression
 Place a small ball of soft wax
on the tip of each dowel
 Cut a V-shaped bucco-
lingual orientation groove or
a round dimple on each die
to aid in reseating the die
completely
 Lubricate around each
dowel with separating
medium for easy separation
from working cast
 Pour the base leaving peaks
and curls to facilitate
retention for the mounting Shillingburg, Fundamentals of

 Once the stone is dry, use a saw with a thin
blade to cut through the layer of die stone
on the mesial and distal sides of he
prepared tooth
 The cuts should taper towards each other
from occlusal to gingival
 Trim the die with no.25 blade and mark the
finish line with a red pencil

Curved pin dowel
 Procedure
 To install pins before
pouring the impression, use
finger pressure to insert a
curved dowel, tip first into
an opening in the
positioning bar
 The dowel extends 1-2mm
into the impression of the
prepared tooth, and the
tail points facially

 Insert a straight pin into one of the three holes
in the facial aspect of the bar onto the
impression
 It should not touch the impression and should
be approx. parallel to the long axis of the
tooth.
 Vibrate a mix of die stone into the impression
until it covers the heads of the dowels and 1-
2mm of the thicker hexagonal bodies.
 After the stone has hardened, extract the
straight pins and side the position bar off each
dowel

 Cut a 2mm deep hole on
either side of the dowel with
an acrylic bur
 Paint the stone and the
exposed parts of the dowel
with petrolatum.
 Box the impression with wax
allowing the tails to extend
slightly.
 Fill the boxed impression with
yellow stone

 Remove boxing wax and make vertical saw
cuts on either side of each die
 Separate each segment from the working
cast by tapping on the exposed end with a
knife handle

To place the dowels after the cast
has been made:
 Pour the impression with die
stone to form a horse shoe
shaped working cast
 Trim the bottom to a height of
10mm from the necks of the
teeth
 Drill a 5mm deep hole on the
bottom of the cast directly under
the centre of each prepared
tooth.( with a 2mm bur)
 Clean the hole with a drill if
necessary
 Cement the dowels into the
holes one at a time placing a
drop of cyanoacrylate cement
into each (tails of the dowel
point facially) Shillingburg, Fundamentals of

 Brush a thin layer of petrolatum on the flat
surface of the cast
 Box the cast, pour the base, and separate
the dies

Pindex system

 Procedure
 Pour the impression, adding approximately
20mm of stone.
 Wet the cast prior to trimming
 Use a model trimmer to flatten the heels of
the cast
 It should sit perfectly flat on a tabletop, and
its thickness must be a minimum of 15mm.

 Trim the periphery of the cast
 Remove any excess stone in
the palate/tongue area with
an arbor band on a lathe.
 The lingual border of the cast
should taper slightly toward
the base to facilitate removal
of the dies from the cast later.
 The faciolingual width -20mm.
 Use a pencil mark the desired
location of the pins on the
occlusal surfaces of the teeth
or preparations.
2nd edition

 Place the prepared cast on the
worktable and align the first
pencil mark with the illuminated
dot from the light beam director.
 Using both hands, exert firm
downwards pressure on the cast
with thumbs.
 Raise the handle bar with slow,
even pressure and the drill
assembly moves upwards cutting
the pinholes.
 When proper depth is achieved,
red light goes off.
 Same procedure is repeated with
each mark.
 For better results, cast is made
slightly damp to prevent dust
formation. Shillingburg, Fundamentals of

 Compressed air and brush is used to
remove debris from holes.
 The pin holes are refined with hand reamer.
 Cyanoacrylate cement is placed on the
pins prior to cementing the pin tips.
 Shorter pins are placed before the long pins
in lingual or palatal holes and long pins in
the facial holes.

 White sleeves are placed
on the long pins and gray
sleeves on the short pins.
 The bottom of the cast is
lightly coated with the
petrolatum.
 Gray sleeves are blocked
with small amount of
molten wax to prevent the
sleeve from filling with
stone when secondary
base is added.
 Strip of utility wax along
the ends of the long pins
to facilitate removal of the
dies later.

 A palatal or tongue filler is made of
boxing wax.
 The filler is seated to the cast.
 Boxing wax is applied around the cast.
 Base is poured with the die stone.

 When stone becomes hard, the cast is
seated in the base former.
 Saw cuts are pre-marked with the pencil.
 then dies are sectioned from the
underside.
 It may also be sectioned from the
occlusal aspect.

 After the die are sectioned, trim them in a
conventional manner.
 Mark the finish line with red pencil.
 Apply die hardener and die spacer.
 Then place the completed cast on the
articulator and then cast is ready for
fabrication of the wax pattern.

Di-lok tray system
 A snap apart plastic tray with internal
orienting grooves and notches is used to
reassemble working cast and dies.

 Procedure
 The cast should be poured in a
U shape, with no stone in the
center building it up to 2.5cm.
(1.0 inch)
 A lingual side of the cast base
is trimmed with an arbor band.
 Horizontal grooves are cut in
the base to for retention.
 When stone has set for 1 hr,
separate it from impression.
 Cast is trimmed in horseshoe
configuration to fit in Di-lok tray
and the buccal border is
tapered towards base with
arbor band.

 Soak the base of cast with water for 5 min.
 Pour the base in tray, until ¾ of its is filled
 Seat the cast on tray; in such a way that
cervical line of the prepared teeth should be
approximately 4mm above the level of base.
 Wipe off the excess stone.
 Allow the stone to set until it is hard and dry .
 To complete the dies, the cast must be
removed from the tray.

 Disassemble the tray by lifting
the back up, and then slide
the buccal segment forward.
 Then with a saw frame and a
thin saw blade, cut between
the prepared tooth and the
adjacent tooth.
 The saw cut should start in
the interdental papilla area
and extend downward on a
very slight taper.
 The occlusal saw cut should
extend three-quarters of the
way through the stone base.
 use finger pressure to break
the die and attached teeth
from the cast. Shillingburg, Fundamentals of

 Remove excess stone gingival to the finish
line with a pear-shaped acrylic bur.
 Then cast and dies are reassembled in the
tray.
 cast and tray mounted on the articulator.
 When the stone has set, the articulated
cast in the Di-lok tray is ready for the
fabrication of the wax pattern.

Working casts with separate
die
 ADVANTAGES
 Simple
 Slightly more
accurate.
 Minimum trimming.
 DISADVANTAGES
 Difficult to transfer
complex or fragile
wax patterns from
cast to die.
 Seating the pattern
on the cast may be
problematic.
 Technique can be
used with
elastomeric
impression materials.
Rosensteil, Contemporary prosthodontics,
#rd edition

 Procedure
 The area of preparation is poured with the
stones in small increments.
 When set, it is separated. A second pour is
then made of the entire arch.
 The first pour which is more accurate is
trimmed into a die with a handle.
 A properly trimmed die handle is slightly
larger in diameter than the preparation
#rd edition

 Improperly trimmed die with a handle that
meets the preparation at an angle
 Handle should be 1 inch long
 The die is trimmed with an acrylic bur
 The die is smoothened below the finish line
with the discoid end of a tanner carver
 The prepared finish line on the die should
be outlined with a red pencil.
 Die relief agent is painted on the
preparation-20 to 40mm
#rd edition

DVA system
Trimmed figure on alignment fixture
Marking dowel pin locations on
a clear plate
#rd edition

Drilling holes for dowel pins as marked
Inserting dowels in the base plate
Impression Is poured, stone is placed
Around the dowel pins and the alignment
Fixture is placed over the poured impression
#rd edition
Drilling holes for dowel pins as markedDrilling holes for dowel pins as markedDrilling holes for dowel pins as marked

Cast is removed
Cast is trimmed
2nd edition

Cast is sectioned using a thin
blade saw
Trimmed working cast using
the DVA model system
#rd edition

Zeiser model system
The Zeiser model system
The impression is leveled, blocked out’
With silicone putty and positioned over
The base plate
#rd edition

The pin locations are determined
Pinholes drilled in place
#rd edition

Pins are inserted into the base
Impression is poured
Base inverted into the stone
#rd edition

Cast is separated from the impression when set
#rd edition

Precision saw aids in sectioning
The sectioned cast
#rd edition

Summary
Accurate working casts and dies are essential
to successful restorations. There are various
techniques and materials that provide an
extremely precise reproduction of the prepared
tooth. The die of the prepared tooth can be
made removable by the use of dowels or other
more convenient system. Alternatively, a solid
working cast and separate die can be used.
Whatever system is chosen, it must articulate
precisely with an accurately made opposing
cast

Bibliography
 Rudd and Morrow, dental laboratory
procedures – Volume I, 2nd edition
 Rudd and Morrow, Dental laboratory
procedures – volume II, 2nd edition
 Rosenteil, Contemporary fixed Prosthodontics,
3rd edition
 Shillingburg, fundamentals of fixed
prosthodontics, 3rd edition
 Philips
 Glossary of prosthodontic terms

Casts, dies and cast forming

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