Definitive Casts and Dies

Dr. Hesham Ibrahim Othman

Professor and Head of Crowns and Bridges

Department, Al-Azhar University

Definitive Casts and Dies

Solid cast

with individual dies

with removable dies

Virtual

Solid Definitive Cast (master or working

cast); It is the positive replica of the

prepared tooth or teeth, ridge area ,and

other parts of the dental arch

Die ;

The die is the positive reproduction of the

prepared tooth/teeth and consists of a

suitable hard substance of sufficient

accuracy (usually an improved stone,

resin, or metal plating

Working cast

Non-working cast

Die

Prerequisites

- It must be an exact reproduction of both

prepared and unprepared tooth surfaces.

- All the prepared and unprepared teeth

should voids free.

- All surfaces of any teeth involved in

anterior guidance and the occlusal surfaces

of all unprepared teeth must allow for precise

articulation of the opposing casts.

- All relevant soft tissues should be

reproduced in the definitive cast, including

all edentulous spaces and residual ridge

contours that will be involved in the fixed

prosthesis.

Requirements of the die(s)

1- It must produce the prepared tooth/teeth

exactly

2- All surfaces must be accurately

duplicated and no bubbles or voids

3- The remaining unprepared tooth

structure immediately cervical to finish

line (0.5 : 1.0 mm) should be discernible

on the die to help technician establish the

correct contour

4- Adequate access to the margin is

imperative

Requirements of die materials 1- Should have high mechanical strength to

withstand handling

2- Should have high stability and dimensional accuracy

3- Should be compatible with the impression

materials

4- Should have good color contrast with other

materials being used

5- Should be compatible with the separating

medium that will be used

6- Easy wettable by wax

Die Material 1- Gypsum: ( universal die materials) Type IV (High strength dental stone)

Type V (High strength, high expansion dental stone)

Advantages;

1- Straight forward technique

2- The most cheapest material

Disadvantage;

• Gypsum is relatively poor resistance to abrasion.

To overcome this problem use ;

1- Surface hardener as (colloidal silica)

2- Cyanoacrylate

3- Other additives, like concretes or resin materials with low viscosity and low expansion

2- Resin Die

Example

Epoxy resin & Polyurethane

Advantage

Higher strength and abrasion resistance

than stone die

Disadvantages

1- Slight polymerization shrinkage

2- More expensive than stone

3- Not compatible with polysulfide and

hydrocolloids

3- Electroplated Die

Silver plated die

Copper plated die

The technique involve deposition of a coat of pure

silver or copper on the impression, and supported

by type IV stone or resin.

polysulfide can be plated with silver

Impression compound can be plated with copper

polyether and hydrocolloids can’t plated due to

imbibition

Silicones can’t plated due to low surface energy

Sliver Plating

Copper Plating

Metalizing Agent

Bronze, Graphite, or Silver

powder

Metalizing agent

Sensitizing solution (stannous

chloride, hydrochloric acid,

distilled water) then silver

nitrate + reducing agent

(Pyrogallic acid, citric acid,

distilled water)

Cathode away from anode by

4 inches

Cathode away from anode by

8 inches

Current

10 milliampere

Current

20 milliampere

Tank Solution

Silver Cyanide

Tank Solution

Copper Sulphate + H2So4

4- Refractory Die (Ceramic Die)

A ceramic material composed of powder and liquid

mixed together and poured into the impression ,

after one hour separated and fired at 1000°C for

8 minutes to produce strong die used for all

ceramic restorations

Solid cast with individual dies

(multiple poor technique) -The first pour, which is the most accurate,

is trimmed into a die with a handle of

sufficient length (similar to a tooth root)

- The second pour is mounted on an

articulator

- The wax pattern is started on the first pour

(the die) and is then transferred to the

articulated cast for refinement of axial

contours and occlusal anatomy

- When completed, this pattern is returned

to the die so that the margins can be

readapted immediately

before the pattern is invested

Advantages; -minimal lab. Procedures

Disadvantages; 1- It may be difficult to transfer complex or

fragile wax patterns from cast to die

2- Seating the pattern on the definitive cast

may be problematic because the second

pour of some impression materials is

slightly larger than the first

3- The technique can be used only with

elastomeric impression materials

Solid cast with removable dies Techniques For Removable Die

Dowel Pin Technique

Pindex System

Die-lock Tray technique

Preparation of the

impression for pouring

Trim the excess impression 5.0 mm above the finish

line and at the area of palate or tongue

Dowel Pin Technique

Dowel Pin Technique 1- Dowel pin is positioned over each prepared tooth in the

impression

Accurate position of the pin is important, other wise it will weaken the die or prevent

the easy removal or

insertion of the die

2- insert the dowel free hand

parallel to the path of removal

and insertion in the centre

of the prepared tooth

3- A dowel is placed between the arms of a bobby pin, the bobby pin is positioned buccolingually across the impression and stabilized by two pins

4- Die stone is then poured into the impression, filling the impression of the teeth and cover the knurled end of the pin

5- Paper clips are set into the stone before it set, to provide retention for the base which will be placed later

6- these clips should be placed in all parts of the model that are not to be removable from the complete cast

7- When the stone has set, the straight pins and the bobby pin are removed from the impression

8- A ball of soft wax is placed on the tip of each dowel

9- A V-shape buccolingual orientation grooves or a round dimple is cut on each die to aid in the complete and accurate reseating of the die during use

10- the stone around each dowel should lubricated with a thin coat of petrolatum to permit easier separation of the die from the working cast

11- Pour another stone with

different color to make the

base of the cast

12- After complete setting of

the stone remove the cast

from the impression and

trim of the excess by

model trimmer

13- Use sharp knife to

uncover the spheres of

wax and remove them

14- When the stone become

hard and dry, use a saw

frame and blade to cut

through the first layer of

the stone, mesially and

distally to each die.

15- The cut should parallel to

each other or slight

occlusal diverge to the

path of

removal

16- Loosen the die gently

using an instrument handle

INCORRECT

17- Trim away any excess stone

gingival to the finish line

18- Ditching the die 0.5 : 1.0 mm

below the level of the finish

line for proper carving the

cervical wax pattern

19- Correction of defects

above the finish line

20- The finish line should be

colored with red pencil

21- Reseat the die on the

working cast, place wax ball

around the tips of the

dowel

22- Sock the cast in water and

mount it on the articulator,

using mounting plaster, and

after hardening of plaster

remove wax covering the

tip of the dowel

Pindex System

Pindex system consists of:

Special drill press

Brass dowel

plastic sleeves

Pour the impression in stone

Defects at critical areas (line or point angles,

and margins) should not be neglected

Separate the stone cast when set and trim

it to horse show shape

Trimmer

The base must be absolutely flat

1- Mark the location of each

dowel on the occlusal

surface (two dowels are

needed to stabilize each

segment)

2- Position the cast on the drill

stage, a light indicates the

location of the drill

- Clean the pin holes by air stream

-Try the pins and cement them in place with Cyanoacrylate

- Short locating dowels should be used on the lingual

surface

- Coat the dowels with petrolatum

to ensure clean separation

- Position the plastic sleeves

- Place the assembly into a special

rubber mold

- Put a piece of wax over a head

of each sleeve

- Make the second pour of stone

with different color into the

mold

- Marking the sawing cuts with

pencil

- Sawing the dies

- Reassemble to the base

- Finish the die (as discussed

before)

- Mount to the articulator

Di-Lock Technique

1- Pour the entire full arch impression with die

stone , respected to U-shaped arch, up to one

inch

2- After setting of the stone separate the U-shape

cast, trim the buccal and lingual to be fit

loosely into the Di-Lock tray

3- One or two horizontal grooves are placed on

the inner and outer aspect of the cast to

provide undercuts for holding the cast into the

other stone in the tray

It consists of 3 parts;

1- Base

2- Curved arm

3- Lock

4- Soak the base of the cast in

water for 5 min.

5- Mix a stone with different color

and fill ¾ of the tray

6- Seat the first cast to the tray.

The cervical margin of the teeth

should be above the periphery

of the tray by 4.0 mm, then

remove the excess cement

7- Disassemble the tray after

complete setting of the second

stone by lifting the back up, and

slide the buccal facing forward,

then slide the cast forward to

remove it from the base

8- By the use of frame and blade saw, cut

between the prepared dies by the

same way like dowel pin technique

9- Cutting extend ¾ of the way through

the stone cast

10- Use finger pressure to break the dies

11- finishing the die by the same way like

dowel pin technique

12- Reassemble the dies

and the other parts of

the cast in the tray

13- Die-Lock tray is ready

for the fabrication of the

wax pattern after

mounting on the

articulator

Virtual Definite casts and

Die Systems

Optical Capture

Closed System

Scanner, design unit, and

milling machine

(CAD/CAM)

Open System

Scanner

Design unit, and

production center

at remote area

Scanner

Contact Probe touch

the cast

Non-contact

Ultrasound

waves

Light

Virtual Cast;