working cast &die shams new1
TRANSCRIPT
by Shams Waaz Amgad Ali
Lecturer of Fixed ProsthodonticsMinia University
DEFINITION
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???
REQUIRMENTS
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 productsCompound impression are usable with
stone, amalgam, electro-deposition of metalPolysulfide impression are usable with
stone, resin and electro-deposition of metal
DIE SYSTEMS
DIE SYSTEMS
I-SINGLE DIE
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 dieLong setting timeDimensionally 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 settingease of removal of the provisional or
inlay
Electrolytic deposition of a coat of pure metal
on the impression
Impression compound Silicon rubber baseMetalizing 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 dieImpression
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.BronzeGraphiteSilver
1. The impression compound metalized by painting graphite.
2. The impression rubber base metalized by copper powder.
Current intensity
10 (mA) for band impressionOr 60 mA for tray impression
20) mA*(
Distance between
impression and plate
4 inch 8 inch**
Time of plating 12 hours 12 hours
Electrolyte Silver cyanide +Potassium cyanide + Potassium carbonate
Copper sulfate+ sulfuric acid + phenosulfuric acid***.
Thank you
by Shams Waaz Amgad Ali
Lecturer of Fixed ProsthodonticsMinia University
DIE SYSTEMS
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 baseAvoid 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 sleevesA 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
Box and seal cast
Pour second base with yellow stone
•Saw mesial and distal to each removable die.
Parallel saw cuts or converging towards the baseAvoid damaging margin or proximal contact
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
Sectioning (sawing)the die
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
ZEISER MODEL SYSTEM
Place the impression in base plate
Determine the locations on pin holes
Insert the pins in the base
Pour the impression
Invert the base with pins over the impression
Working cast after sectioning
DIE TRIMMING & DITCHING
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.
Die ditching
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)
Thank you