Working cast &die shams new1

by
Shams Waaz Amgad Ali
Lecturer of Fixed Prosthodontics
Minia University

It is the positive reproduction of the
prepared teeth, ridge areas and other
parts of the dental arch.

- It is the positive reproduction of the prepared
tooth on which the wax pattern is made and are
finished.
- It consists of a suitable hard substance of
sufficient accuracy.

The cast can not contain more
information than the impression
from which it was made.
IS IT TRUE???

 Reproduction of both prepared teeth and
edentulous area ( for pontic fabrication)
 Reproduction of occlusal surfaces of un prepared
teeth to allow proper articulation with opposing
teeth
 Reproduction of the adjacent and contra lateral
teeth to allow proper alignment and contouring

 Reproduction of the gingival tissue accurately
 Free from bubbles specially at the finish line of
the prepared tooth
 Free from distortion
 The cast must be trimmed to insure access for
carving wax pattern margins

1. It must reproduce the prepared tooth exactly.
2. All surfaces must be accurately duplicated.
3. No bubbles or voids especially along Finish line.
4. The remaining unprepared tooth structure
immediately cervical to the finish line should be
easily discernible on the die, ideally with 0.5 to1
mm visible

Allow 0.5-1mm of
unprepared surfaces
apical to the Finish line
WHY ?????????
To identify the contour of the
tooth & allow margin
adaptation

 High dimensional accuracy and stability on
setting
 High strength and abrasion resistance to
withstand handling without fracture
 Contrast color with wax to facilitate defining
preparation margin
 Good wetting with wax

 Compatible with the separating agent, so that the
wax pattern does not stick.
 Compatible with the impression material used.
 Ease of sectionable & trim.
 Ease of manipulation and time saving

How select
the die
material????
.

The type of impression material
determines the choice of the die or cast
material
.
Hydrocolloid impression are effective only with
gypsum products
Compound impression are usable with
stone, amalgam, electro-deposition of metal
Polysulfide impression are usable with

 Impression for a single full metal crown
preparation.
 Used with either impression compound or
rubber base impression material.
 Copper band are supplied in different sizes and
diameter to fit for anterior, premolars and
molars.

 Inexpensive
 Compatible with most impression materials
 Reproduce fine details in the impression.
 Easy to use
Advantages

1) Poor resistance to abrasion
Disadvantage
Overcome by:
Gypsum hardeners (colloidal silica)
Application of low viscosity resin (Cyanoacrylates).
Resin-strengthed gypsum product e.g Resin Rock
 Gum arabic and calcium hydroxide mixture.

DIVESTMENT DIE
Gypsum bonded investment+ colloidal silica
The wax pattern is constructed on the die &
not removed during setting the investment.
BUT , Used for gold alloys only ??????

To Control setting expansion: Avoid:
1. Decrease water/ powder.
2. Increasing mixing time.
3. Immersion of gypsum products in water during the
setting process. ?????
4. Increasing temperature of mixing water( from 23-
30°).
2)Setting expansion:
Linear expansion occur during setting (0.06-0.9%).
Follow the manufacturer’s instruction for the
current water/powder ratio and manipulation.

 High abrasion resistance & compressive st.
 Compatible with rubber base ??& compound
 Very long setting time
Resin are used as a die material to overcome the low
strength and abrasion resistance of die stone
e.g. Autopolymerizing resin,Epoxy Resin & Polyurethane
Advantages

 Expensive
 High polymerization shrinkage
(under sized die )
 Incompatible with poly-sulfides &
hydrocolloids. WHY?????
Disadvantages

Used only with copper bands with
impression compound
Very hard die
Long setting time
Dimensionally unstable(delayed
expansion)

 It is a special type of ceramic supplied as powder
and liquid (Mainly quartz silica )
 Special for construction of all-ceramic restorations
 It allows porcelain to be built direct on the die?????
 Can withstand very high temperatures without any
distortion
 Expensive

Flexible die materials is similar to heavy bodied
silicone or polyether impression materials
Indications:
•Provisional restorations.
•Indirect composite resin inlays or onlays.
Advantages:
more rapid setting
ease of removal of the provisional or
inlay

Electrolytic deposition of a coat of pure metal
on the impression

 Impression compound
 Silicon rubber base
Metalizing stage
 The impression compound metalized by
painting graphite to conduct electricity.
 The impression rubber base metalized by
copper powder.

 Impression connected to cathode (-ve)

 Impression submerged into tank
solution( electrolyte)
 Copper plate at anode must be 8 inches away
from impression.
 20 mA current
 12 hours plating
 After complete plating ,pouring the impression
with stone or resin.

 The impression material is rubber base.
 Washing and drying impression
 Metalizing the impression (silver powder).

 Impression submerged into tank
solution( electrolyte)
 Bar of silver as anode (+ve),
 placed 4 inches away from impression
 10 mA current
 12 hours plating
 After complete plating ,pouring the impression
with stone

 . The main disadvantage of silver plating is that a
cyanide solution is used & this needs special
precautions because of its extreme toxicity
 This technique cannot be performed with all
impression materials.
 Silicone impression materials have low surface
energy, are difficult to be electroplated.

 Polyether impressions, because of their
hydrophilic nature imbibe water & become
distorted.
 Polysulfide polymers can be silver plated, but it
is much more difficult to copper plate them.

Silver plated die Copper plated die
Impression
material
Rubber base • Impression compound
• Silicon rubber base
Impression is
metalized by
Applying metalizing
powder( which increase
the affinity of impression
toward silver) e.g.
•Bronze
•Graphite
•Silver
1. The impression
compound metalized by
painting graphite.
2. The impression rubber
base metalized by copper
powder.
Current
intensity
10 (mA) for band
impression
Or 60 mA for tray
impression
20(mA)*
Distance
between
impression and
plate
4 inch 8inch**
Time of plating 12 hours 12 hours

WORKING CAST WITH
SEPARATE DIES
(Multiple Pour Technique)
(Solid cast with individual
die)

 The impression is poured twice or triple:
 Full arch cast for proximal contact and
occlusion.
 Sectional cast (Separate die) for wax coping
and margins.

Advantages:
 Ease of fabrication
Keep the relationship between
abutments fixed and immovable
The gingival tissues are intact,
so we can easily obtain
harmonious contour of the wax
pattern.

Disadvantages:
 Difficult to transfer fragile wax
patterns from cast to die
(distortion of internal adaptation )
The second pour of the impression
may be different (slightly larger)
than the first,
(seating of the wax pattern may be
problematic).
Used with elastomeric impression
material only

WORKING CAST WITH
REMOVABLE DIES

Eliminates discrepancies between a
separate die and working cast that may be
caused by impression distortion or
deterioration between pours, or by a cast
and die made from separate impressions
that are not identical.

Impression is poured to get a stone cast,
 Trimming of the base is performed and lubricated ,
 another color stone is poured in wax box then the cast is
inserted into it to a depth of 1.5cm(plaster index ). To prevent
rocking ,two vertical cuts are then done adjacent to the
prepared tooth extending 3mm shorter than the base
Using the finger pressure at either end of the cut will separate
the dies.

 It is a non anatomic cover which fits to a single die, its
advantage is a single die can be used as a removable die. A
coping is constructed and transferred to the patient mouth
and the impression is taken and removed including the
coping. The single die is placed in its position in the
impression with the die on it. After lubrication of the
impression and the die, box it and a stone cast is poured
with the die in it. The single die can then be removed from
the cast to produce a removable die.

Single tapered Pin Single curved Pin
Doubled Pins
Separated cemented Pins Performed tray

 It is positioned over each prepared tooth in
the impression.
 Dowels are parallel to the long axis of the
tooth
 Not impinge on the margins.
 Flat from one side ???? to prevent rotation.

Bobby pins used for positioning the dowel pins.
A dowel is placed between the arms of the bobby
pins.

 Bobby pin is positioned BL across the impression.
 Dowel pin must not touch the impression.

The first pour of stone should completely cover the
dowel head but not on the shaft ???
( to allow dowel stability)

Paper clips are put into the stone before it sets to provide
retention for the base which will be placed later, then
straight and bobby pins are removed

Place wax around the tips of the dowels to protect
them from the plaster contamination

Two vertical cuts adjacent to the abutments and to the
depth of the 2nd
stone pour

Parallel saw cuts or converging towards the base
Avoid damaging margin or proximal contact

What happens if saw cuts
are made diverging
towards the base of the
cast ?????

Curved dowel pin
The tail of the dowel
pins protrudes from
the facial surface of the
cast for convenience of
accessibility while the
cast is mounted

A snap-apart plastic tray with internal orienting
grooves and notches also can be used to reassemble
the working cast and die

Pour the full arch impression with die stone,
restricted to U- shaped arch
(with no stone on the center)

Mix another color of extra hard stone, put it into
Di lock tray then seat the cast (above the cervical
line)

After stone
hardening, remove
excess stone and
disassemble the tray

By using a saw blade, cut between the prepared
tooth and the adjacent one till approximately ¾ the
way of the stone base

Reassemble the dies & other parts of the cast in the
tray

The Pindex system is a reverse drill press is used to
create a master cast with dies that can be removed and
replaced repeatedly with great precision
The impression is poured without positioning and
attaching dowel pins. The machine accurately drills
parallel holes from the underside of trimmed cast.

 Pour the impression with correct w/p ratio of
extra hard stone

Base of cast to gingival crest 15-20 mm .
Flat, smooth and parallel to the occlusal plane

Direct the light
indicator to be
centralized over
the prepared
teeth.

Drill from the other
side (toward the base)
with drill a hole in the
base in the center of
the die

•Repeat drilling for each prepared tooth.
(all holes will be parallel to each others).

Pins (long & short ) their sleeves
A dowel pin is attached to hole using cyano-
acrylate cement

•Long pin toward facial
•Short pin toward lingual (Glue first for better access)

Apply of petroleum( separating media) WHY????
to allow easy separation

Pour second base with yellow stone

•Saw mesial and distal to each removable die.

 It is a model consists of :
1-Underside base plate having an alignment
fixture for impression
2-A top clear plate which having another fixture
opposing to those on the bottom base plate.
Attach the dowel pins to a clear plate so, that when
the clear plate is positioned over the impression ,
the dowels are suspended in their selected locations

Underside base plate having an
alignment fixture for impression

Mark the dowel pin locations in a clear plate

Drilling holes for dowel pins as marked

Inserting dowel pins in base plate (no adhesive )

Pouring the impression &put stone around pins

Replace the alignment fixture over poured impression

Remove the set cast from the base plate by gentle tapping

Working cast with DVA Model system

 Similar to DVA but instead of visual
determination of dowel pin position.
A drilling device supplied with a pointer is used
to locate the pin position in an attaching plate
and drilling a hole in it

Place the impression in base plate

Determine the locations on pin holes

Insert the pins in the base

Invert the base with pins over the impression

Working cast after sectioning

 Remove most of excess stone with #7 lab carbide
bur with protective eyewear
 Fine trimming with scalpel or cleoid-discoid
carver
 Margin should be sharp and distinct for access,
but it should not be undermined
 0.5-1mm uncut tooth beyond finish line should be
maintained to provide proper contours in wax

A sharp scalpel is used to trim to final contour,
working away from the margin.

Axial contour affected by die trimming & ditching

 The original contour of
cervical tooth structure
should be preserved.
 Over trimming results in
an over contoured
restoration

DIE PREPARATIONDIE PREPARATION

 Mark the margin with red pencil, not a graphite,
traces of the graphite (an antiflux) can prevent
complete casting of the margins.
 1. Apply die hardener
Allow to set for 5 minutes
 2. Apply die spacer(cement spacer)
20-40 micron thickness allows space for cement
1 mm short of finish line WHY?????
for optimum marginal adaptation

Die spacer ( relief application)

Working cast &die shams new1

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