working cast &die shams new1

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