II-Duplication of the master cast

Duplication

* Duplication is the procedure of accurately

reproducing a working cast.

*Steps of Duplication

Production of the agar mold

Making the investment ( refractory cast)

Hardening the investment cast.

Duplication of the master cast

Duplication of master cast

* Prepared cast are duplicated to produce

an exact copy of the master cast in an

investment material “Refractory cast”.

* Refractory cast contains ceramic Material

that permits it to withstand burn out

temperature of about 1450 degree.

Refractory cast

Duplicating flask

Duplicating flask is a consists of:

1.Bottom..

2.Feeding top(cover).

Duplicating flask

opened closed

Duplicating colloids Agar-Agar

-Re-used many times.

-Cleaned and melted after each use.

-Prepared and stored in automatic duplicating

machine.

-The suitable working temperature is 63 °c

Production of the agar mold

* Mount master cast

* Seat body of flask

* Prepare agar or silicone

* Filling the flask with agar

* after hardening remove the master cast

from the agar mold

Making the Investment Cast

* Make the investment mix

* Pouring

* Obtaining the investment cast.

Types of investment materials

1-Gypsum-bonded investment.

-It can be burn out to 704 °c without breakdown.

-It is used for low fusing alloys as Gold

2-Phosphate-bonded investment

-It can be burn out to 1037°c without

breakdown.

-It is used for high fusing alloys Cobalt

chromium

Hardening the investment cast

A- heating the refractory cast (pre-heat)

The cast is removed from the colloid mold

& placed in drying oven at 180-200°F for

½-1 hour.

(for hardening to avoid

surface scratches)

Hardening the investment cast

B- treating the refractory cast:

Immerse in hardener liquid

while The cast is still warm ,it is dipped in

Bees Wax at 280-300°F for 15 seconds or

Sprayed

This make the cast smooth and dense

Wax framework

The wax pattern

a-Design transfer to working cast

b-Wax pattern construction

a-Design transfer

* The master cast with the design drawn on it

should be available during making the wax

pattern.

* pencil outline on cast

Filling of beaded areas

Laying sheet of wax

Sheet cut to shape

Second half adapted

Sections sealed together

Position meshwork in place

Meshwork is trimmed

Finish line

Finish line

Ledge in ref. Cast

Adaptation of wax in ledge

Retentive arm in ledge

Recoprical arm in place

Filling occlusalrest with wax

Finished occlusal rest

Clasp unit attached to framework

Gingivally approaching clasp

Occlusal rest connected to minor connector

Distal proximal plate

Finished wax framework

Wax pattern