LAB PROCEDURES INVOLVED IN THE

FABRICATION OF FPD

Prepared By:

INTRODUCTION

Fabrication of a fixed partial denture involves Fabrication of a fixed partial denture involves

the fabrication of the wax pattern, casting, the fabrication of the wax pattern, casting,

soldering and finishing. Here we shall study in soldering and finishing. Here we shall study in

detail about these proceduresdetail about these procedures.

MODELS,CAST,& DIES

MODELMODEL: : It a positive replica of the teeth and adjacent It a positive replica of the teeth and adjacent

structures used primarily for observation and diagnosis.structures used primarily for observation and diagnosis.

CAST: CAST: A working model, master cast.A working model, master cast.

DIE:DIE: Die is a positive replica of the individual pre-pared tooth Die is a positive replica of the individual pre-pared tooth

on which the inlays,crowns,bridges are made. These are individual on which the inlays,crowns,bridges are made. These are individual

tooth replicas prepared for easier handling during wax pattern tooth replicas prepared for easier handling during wax pattern

fabrication and finishing of inaccessible areas of the castfabrication and finishing of inaccessible areas of the cast

..

TYPES OF CAST AND DIE TYPES OF CAST AND DIE MATERIALSMATERIALS

GYPSUM:

a) Type IV-Dental stone, Highstrength

b) Type V-dental stone ,High Strength, high Expansion

c) Dental stone+lignosulphonates

METALS:

a) Electroformed/Eletroplated.

b) Sprayed metals.

c) Amalgam.

POLYMERS; a) Metal-filled resins or inorganic filled resins.b) Epoxy.

CEMENTS:a) silicophosphate or polyacrylic acid bonded cements.

CERAMIC OR REFRACTORY DIE MATERIALS:CERAMIC OR REFRACTORY DIE MATERIALS:

a)a) For direct baking of porcelain crown or preparation of wax For direct baking of porcelain crown or preparation of wax

pattern for casting.pattern for casting. Type IV& Type V Stone dies, Electroformed dies, Epoxy resins

, Refractory or materials are recommended die materials.

IDEAL PROPERTIES OF DIE MATERIALS

1. It should be dimensionally accurate.2. It should have high abrasion resistance, should possess

good strength,& have smooth surface .3. Toughness – to allow burnishing of foil & resist breakage.4. Ability to reproduce all fine details in the impression.5. Compatibility with all impression materials.6. Colour contrast with wax, porcelain & alloys.7. Easy & quick manipulation & rapid fabrication.8. Non-injurious to health by touch or inhalation.9. Economic.

IDEAL REQUIREMENTS OF A DIE SYSTEM

The die should be easy to remove and replace The die should be easy to remove and replace

in its original position.in its original position.

The die must be stable when placed in the The die must be stable when placed in the

cast.cast.

It should be easy to mount in the articulatorIt should be easy to mount in the articulator

TYPES OF DIESBased on the design, die systems can be classified into:

11 WORKING CAST WITH SEPARATE DIE SYSTEMWORKING CAST WITH SEPARATE DIE SYSTEM

22 WORKING CAST WITH REMOVABLE DIE SYSTEMWORKING CAST WITH REMOVABLE DIE SYSTEM.

There are three commonly used removable die systems,

they are:a)Dowel pin system -Straight -Curvedb)Di-lok tray systemc)Pindex system

33 ACCUTRAC SYSTEMACCUTRAC SYSTEM

WORKING CAST & SEPARATE DIE SYSTEM

Here, two casts are poured from a single impression and one cast is Here, two casts are poured from a single impression and one cast is sectioned and used as a die and the other is not sectioned and is used sectioned and used as a die and the other is not sectioned and is used as the working cast. The wax pattern is prepared on the die and later as the working cast. The wax pattern is prepared on the die and later transferred to the working cast. The die is shaped and finished using transferred to the working cast. The die is shaped and finished using an acrylic trimmer and the portion of the die below the cervical line is an acrylic trimmer and the portion of the die below the cervical line is finished using a scalpel. Sharp undercuts in the base should be finished using a scalpel. Sharp undercuts in the base should be avoided.avoided.ADVANTAGEADVANTAGE• Simplest and easiest methodDISADVANTAGEDISADVANTAGE•The wax pattern may get distorted while transferring it from the die to the cast.•Proximal margins tend to get overcontoured.

WORKING CAST WITH A REMOVABLE DIE SYSTEM

In this system a special type of working cast is prepared and the dies In this system a special type of working cast is prepared and the dies

are carefully sectioned so that the individual dies can be removed are carefully sectioned so that the individual dies can be removed

and replaced in their original position in the cast. Dowel pin and replaced in their original position in the cast. Dowel pin

systems, di-lok tray systems and the pindex systems come under systems, di-lok tray systems and the pindex systems come under

this category.this category.

DOWEL PIN SYSTEMSDOWEL PIN SYSTEMS

• Dowel pins may be straight or curved:

1.STRAIGHT DOWEL PIN SYSTEMS

• They are prepared using two techniques,

namely

• the pre-pour and post-pour techniques.

PRE-POUR TECHNIQUE

Here the die pins are positioned in their

appropriate places within the impression using

bobby pins and sticky wax.

The dowel pin is positioned within the impression using sticky wax

After positioning the pins, the impression is

poured up to the level of the alveolar process

of the remaining teeth. First pour is poured upto the level of the alveolar process

Separating medium is applied over the first

pour and die pin and the remaining portion of

the cast is poured. Separating medium is applied and the base is poured

After the cast is set, the dies are sectioned by After the cast is set, the dies are sectioned by

placing vertical sections on the interproximal regions placing vertical sections on the interproximal regions

of the cast using a die sectioner or a manual saw. of the cast using a die sectioner or a manual saw.

Vertical sections at the inter proximal regions should Vertical sections at the inter proximal regions should

be made without damaging the contour of the be made without damaging the contour of the

adjacent teeth.adjacent teeth.

Since the separating medium was applied before pouring the Since the separating medium was applied before pouring the

second half of the cast, the dies can be easily separated with second half of the cast, the dies can be easily separated with

vertical sections alone.vertical sections alone.

The die is carefully separated from the cast without chipping. After The die is carefully separated from the cast without chipping. After

removing the die, a small hole will be visible in the cast. This indexing removing the die, a small hole will be visible in the cast. This indexing

hole will guide the pin into position while replacing the diehole will guide the pin into position while replacing the die.

POST-POUR TECHNIQUE

Here, the cast is poured upto the level of the Here, the cast is poured upto the level of the

crowns of the teeth in the impression. crowns of the teeth in the impression.

Subsequen tly, small holes are drilled within Subsequen tly, small holes are drilled within

the first pour in the required places and the the first pour in the required places and the

dowel pins are cemented into the holes The dowel pins are cemented into the holes The

remaining part of the cast is poured and the remaining part of the cast is poured and the

dies are sectioned as described in the pre-dies are sectioned as described in the pre-

pour technique.pour technique.ADVANTAGES• Easy to prepare• No special equipment is necessaryDISADVANTAGES• The pins may get displaced while pouring the cast.

2. CURVED DOWEL PIN SYSTEMThis is similar to straight dowel pin technique except that curved pins This is similar to straight dowel pin technique except that curved pins

are used. The curved pins will project from the sides of the base of the are used. The curved pins will project from the sides of the base of the

cast. When the projecting pins are pressed, the die unit attached to cast. When the projecting pins are pressed, the die unit attached to

the respective pin will pop out from its place.the respective pin will pop out from its place.

Curved dowel pin system (pushing the pin from the side pops the die out).

B) DI-LOK TRAY SYSTEMThis technique uses a special tray to pour the cast. This special tray has orientation grooves on the inner aspect. Actually the tray is made of multiple components, which can be assembled or dismantled as required (Fig. 33.7).Impression is poured using a two-pour technique. The first pour is poured up to the level of the impression and the second or base pour is poured after positioning the rim of the di-lok tray over the impression. Before the second pour is set, the base of the di-lok tray is assembled and the cast is allowed to set. Later, the di4ok tray is dismantled and the grooves on the base of the cast formed by the di-lok tray is used as a guide to do die sectioning.

Advantages• Simple and easy to prepare• The cast can be mounted in an articulator

Disadvantages• Requires special equipments.

C) PINDEX SYSTEM

This system is similar to the post-pour dowel pin technique. Here a special drill This system is similar to the post-pour dowel pin technique. Here a special drill

press equipment is used to do die sectioning. The drill press has a platform with a press equipment is used to do die sectioning. The drill press has a platform with a

slot like opening through which the drill pin will project during the procedure. The slot like opening through which the drill pin will project during the procedure. The

entire platform is spring mounted and when pressed down automatically starts entire platform is spring mounted and when pressed down automatically starts

the drill, which will project through the slot. The unit has a red pilot light lamp on the drill, which will project through the slot. The unit has a red pilot light lamp on

top, which will shoot a point exactly on the drill. This red pilot pointer will act as a top, which will shoot a point exactly on the drill. This red pilot pointer will act as a

guide while drilling (Fig. a).guide while drilling (Fig. a).

Fig - guide to drill holes in the base of the cast. The platform of the pindex machine is spring loaded. When the cast is passed against the platform, the motor will get activated and drill a hole in the casta. The cast is placed on the pindex machine and the pilot light is used as a

• Die sectioning procedure is simple wherein the cast Die sectioning procedure is simple wherein the cast of 15 mm base is placed on the drill press and drill of 15 mm base is placed on the drill press and drill holes are prepared in the under surface of the base holes are prepared in the under surface of the base of the cast using the pilot light as a guide. After of the cast using the pilot light as a guide. After making the drill holes to the required depth, sleeved making the drill holes to the required depth, sleeved die pins are placed and cemented using die pins are placed and cemented using cyanoacrylate adhesive. Remember that the holes cyanoacrylate adhesive. Remember that the holes will not be very deep. Hence a portion of the pins will will not be very deep. Hence a portion of the pins will be projecting from the base of the cast.be projecting from the base of the cast.

After cementing the pins, a base is poured over the base of drilled After cementing the pins, a base is poured over the base of drilled

cast. Consecutively the dies are sectioned but not upto the base as cast. Consecutively the dies are sectioned but not upto the base as

described in the dowel pin system.described in the dowel pin system.

ADVANTAGES ADVANTAGES ..

Allows accurate placement of the die pins.Allows accurate placement of the die pins.

DISADVANTAGES .DISADVANTAGES .

Special equipment is required.

THE ACCUTRAC SYSTEM

These dies are exclusively used in the fabrication of These dies are exclusively used in the fabrication of

laminate veneers. Basically this system involves the fabrication of laminate veneers. Basically this system involves the fabrication of

two casts as described in the working castwith separate die system. two casts as described in the working castwith separate die system.

One cast (master cast) is sectioned into dies and used to prepare One cast (master cast) is sectioned into dies and used to prepare

the coping. After preparing the wax pattern, the sectioned dies are the coping. After preparing the wax pattern, the sectioned dies are

reassembled in the master cast.reassembled in the master cast.

The master cast is blocked out with wax (filled with wax to The master cast is blocked out with wax (filled with wax to

seal the crevices). The second cast (refractory cast) is seal the crevices). The second cast (refractory cast) is

duplicated from the blocked out, sectioned, die master cast duplicated from the blocked out, sectioned, die master cast

using addition silicone. The second cast is poured using using addition silicone. The second cast is poured using

specially formulated stone, whose expansion will specially formulated stone, whose expansion will

compensate for the shrinkage of porcelain when fired in the compensate for the shrinkage of porcelain when fired in the

furnace.furnace.