die mat and die sys

DIE MATERIALS AND DIE SYSTEMS

Indirect fabrication of wax pattern and casting by lost-wax technique is still

continuing as the most common technique for construction of cast restorations.

For this, it is necessary to obtain an accurate reproduction of the prepared tooth,

the surrounding tissues and the adjacent and opposing teeth. For an accurate

reproduction of the teeth and associated structres, a thorough knowledge of the

materials and technique for making impression and preparing cast and dies are

essential.

DEFINITIONS:

Cast:- A dimensionally accurate reproduction of a portion of the oral cavity and

extra oral facial structures produced in a durable hard material and used as a base

for construction of orthodontic and prosthetic appliances.

Die:- The positive reproduction of the form of a prepared tooth in any suitable

hard substance, usually in metal or specially prepared artificial stone.

Model:- A facsimile used for display purposes; a miniature representation of

something; an example for imitation or emulation.

PREREQUISITES:

Cast:-

It should be free of defects.

It must reproduce both prepared and unprepared surfaces.

Unprepared tooth immediately adjacent to the preparation must be free

of voids.

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Die Materials and Die Systems…………

Teeth involved in anterior guidance and occlusal surface of unprepared

teeth must allow for precise articulation.

All relevant soft tissues should be reproduced in the working cast. i.e.

edentulous spaces and residual ridge contours.

Die:-

It must reproduce the prepared tooth accurately without any bubbles or

voids.

The remaining unprepared tooth structure immediately cervical to the

finish line should be easily discernible on the die, ideally with 0.5 – 1

mm visible.

Adequate access to the margin is imperative.

MATERIAL SCIENCE

The materials available for making dies are numerous and range from stone

to metal, resin and cement. The successful production of dies is to a considerable

extent dependent upon choosing a die material that is suitable for a particular

impression material.

REQUISITES:

1. Dimensional Stability:-

They should not expand and contract or distort after pouring into the

impression under normal storage and use.

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2. Accuracy:-

All the surfaces of the impression must be accurately duplicated. No voids

or bubbles should be present. It must have a good flow to reveal the minute details

of tooth and supporting tissues.

3. Surface Hardness and Abrasion Resistance:-

Should be made of a material that produce smooth hard surface. It should

be strong enough to withstand subsequent manipulation procedures without

abrasion of the surface or fracture of the die.

4. Compatibility:-

Should not react with impression materials and should be compatible with

the lubricating agents used to separate wax.

5. Colour:-

It should be available in a colour that contrasts with the wax used, so that

the preparation margin can be seen.

6. It should be easily wettable by wax.

7. It should be easily sectionable and easy to trim with the routinely available

equipments.

8. Production of die in a short time.

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CLASSIFICATION OF DIE MATERIALS:

1. Dental stone IV and V.

2. Electroplated silver and copper.

3. Epoxy resins.

4. Divestments.

5. Silver amalgam.

6. Flexible die materials

Selection of one of these materials is determined by the particular

impression material in use and the purpose for which the die is to be used.

1. DIE STONE (TYPE IV & V)

The hemihydrate is manufactured by heating the dihydrate under controlled

conditions to drive off some of the water of crystallization. The improved physical

properties of die stone is due to the fact that less water is needed to obtain a

sufficiently fluid mix. W /P ratio is 18.6 gm /100 ml.

Mechanical mixing under vacuum is preferred to hand mixing. Newly

poured cast should be left undisturbed for at least 30 minutes. The surface

reproduction is acceptable with Type IV gypsum. The material is capable of

reproducing a 20µm wide line as prescribed by ADA Specification No. 19.

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If soaking is required, it should be done in water saturated with plaster

slurry and only enough to achieve the desired degree of wetting.

Advantages:

1. Dimensional stability.

2. Dimensional accuracy – expansion 0.1 % or less.

3. Surface reproduction is adequate.

4. Relatively inexpensive.

5. Compatibility with impression material – generally compatible with

most impression materials and adapt easily to them.

6. Easy to use and ready for use in approximately 1 hour.

7. Colour contrast.

Disadvantages:

The greatest disadvantage of gypsum is its relatively poor resistance to

abrasion.

Gypsum dies are some times modified to,

i) make them abrasion resistant

ii) change the die dimension.

iii) increase the refractoriness.

iv) combination of these effects.

i. Improving abrasion resistance:

a) ‘Gypsum hardeners’ (colloidal silica) have relatively little effect on the

hardness of the stone, but they do improve abrasion resistance as much as

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100 %. Their use is accompanied by a slight expansion, which is not

clinically significant.

b) Low viscosity resins such as cyanoacrylate.

Care is needed in selecting and applying resin so resin film has no

significant thickness.

ii. Changing die dimension :

a) To reduce the dimension, additional accelerators and retarders can be

added.

b) Apply die spacers – polymers dissolved in volatile solvents are applied in

several coats to within 0.5 mm of the preparation finish line to provide

relief for the luting cement.

Die lubricants (oil, liquid soap, commercial preparations) has to be

applied to prevent the wax from adhering to die spacer during construction of wax

pattern.

iii. Increase refractoriness:

Die material and investment medium have a comparable composition. A

commercial gypsum bonded material, called Divestment (Whipmix Corp. USA) is

mixed with a colloidal silica liquid. The die is made from this mix and the wax

pattern is constructed on it. The entire assembly (die pattern) is invested in a

mixture of Divestment and water, thereby eliminating the possibility of distortion

of the pattern on removal from the die or during the setting of the investment. The

setting expansion is 0.9 % and thermal expansion is 0.6 % when it is heated to

677˚C. Divestment is not suitable for casting base metals and metal-ceramic

alloys.

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Divestment phosphate is a phosphate-bonded investment that is used in the

same manner as Divestment and is suitable for use with high-fusing alloys.

Disadvantages:

Application of die spacer is difficult.

Sending divestment cast for interocclusal records may be

problematic.

The die will be destroyed, hence, second cast & die material must be

made to permit finishing and polishing.

Dental stone, high strength, high expansion (Type V):

This is a recent gypsum product, having even higher compressive strength

than type IV. The improved strength is attained by making it possible to lower the

water: powder ratio. Setting expansion is increased to 0.3 %. Higher expansion is

required in the stone used for the die to aid in compensating for higher casting

shrinkage of base metal alloys.

2. RESIN BASED DIE MATERIALS

Resins are used as a die material to overcome the low strength and abrasion

resistance of die stone. Resins used are acrylic, polyester, epoxy resins and

polyurethane. These materials are limited in their compatibility with non-aqueous

elastomers. Abrasion resistance is many times greater than gypsum. It is more

expensive than gypsum and has longer setting time. Autopolymerizing acrylic

resin cannot be used to produce accurate die since their casting shrinkage is high

(0.6 %). The same is true for polyester resins.

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Epoxy resins are reliable with respect to the 0.1% – 0.2% shrinkage on

polymerization. They exhibit more shrinkage in axial direction. Polymerization

shrinkage is less of a problem with polyurethane resins.

In the last few years, gypsum die stones have been compounded with resin

to provide the advantage of each material. These modified die stones maintain the

low expansion of stone and toughness and abrasion resistance of resin. E.g.

ResinRock ( Whipmix Corporation). They have high strength and and low

expansion, and are particularly suitable for casts for implant restorations.

3. ELECTROFORMED DIES

Electroplating can be defined as the process of covering the surface of an

object with a thin coating of metal by means of electrolytes.

Review of literature:

The German scientist Jacobi laid the groundwork in 1837 for industrial and

dental electroforming. Electroplating activity in fixed prosthodontics and

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restorative dentistry started in the early 1930s with the introduction of modelling

compound copper plated dies. Hydrocolloid was the first elastic impression

material to be used as a substrate for obtaining electroformed copper dies in the

1950’s. However it proved to be unstable and hence its usage declined. The initial

enthusiasm for copper as an electroplating metal soon faded and silver became the

metal of choice with the introduction of mercaptan rubber. But soon after the

dimethyl siloxane impression material appeared both copper and silver were

reported as acceptable die materials.

Procedure:

The basic system consists of an electrolytic solution of CuSO4, or AgCN

and a source of direct current. The anode is either pure Cu or pure Ag. The surface

to be electroplated is the cathode. Generally, Cu plating is used for compound

impression and Ag plating for poly sulphide impression. Silicone impression

materials by virtue of their low surface energy are difficult to electroplate.

1. Clean and dry the impression and coat the surface to be electroplated with

metallising powder like Ag powder or graphite.

2. Direct the cathode wire in the border of the impression in the metallised areas but

not too close to preparations.

3. Fill the preparations and teeth with electrolytic solution with eyedropper to

prevent air bubbles and voids and completely immerse the impression in the

solution. The Ag anode immersed in the solution should be at least equal in size to

the area of the surface to be plated.

4. Proceed with the plating initially at approximately 5 mA per tooth for 1 hour and

examine the impression after 1 hour to check for deposition of metal and to make

certain there are no voids. Resubmerge the impression in the plating solution,

plate for12 hour at 10mA per tooth.

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5. After completion of electroplating, wash the impression and use dental stone as a

backing material.

Advantages:

i. More surface hardness.

ii. Superior surface detail, which exceeds most of the die materials.

Disadvantages:

i. Incompatibility with some impression materials – condensation

silicone impression materials are difficult to electroplate evenly due to

their low surface energy. Polyether and hydrocolloid imbibe water and

become distorted. Therefore cannot be electroplated accurately.

ii. Time consuming and expensive

iii. Extreme toxicity of AgCN solution – when it contacts acid, it produces

fumes of extremely toxic hydrogen cyanide.

iv. Variable degrees of distortion (limited control of die accuracy).

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Electroplating unit for silver and copper plating of impressions This electroplating unit allows

you to electroplate impressions in as little as 3 to 6 hours. The system ensures an even and

homogenous deposition of silver or copper and offers high stability whilst providing ideal

coverage on both large and small surface areas.

4. AMALGAM

Amalgam dies are used with copper band modelling plastic impression.

The impression has to be wrapped in wax or tape and embedded in a rigid matrix

such as plaster to resist the pressure necessary to condense the amalgam

effectively.

Disadvantage:

Time consuming – 12 hours to set.

5. FLEXIBLE DIE MATERIALS:

Flexible die materials are similar to heavy-bodied silicone or polyether

impression materials and have been used to make interim restorations or indirect

composite resin inlays or onlays chairside. The advantages of the flexible material

over a stone die include more rapid setting and the ease of removal of the interim

restoration or inlay. When choosing materials for flexible dies, the dentist must be

sure to select a compatible combination of impression and die materials that

provide good surface details. One study revealed that the best detail reproduction

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was obtained when Impregum F die material (3M ESPE) was combined with

Extrude Light impression material.

OTHER DIE MATERIALS:

Few other die materials were discussed in the review of literature but not

popular nowadays.

1) Bismuth-Tin alloy:

Described by Stallwood (1964) and Friend & Barrell (1965). The alloy

which melts at 138˚C is sprayed directly on to the impression, forming an an

accurate metal shell which is subsequently backed up with self-cure acrylic or

stone. Suitable for polysulfides and silicones. Difficult to spray in narrow

confined areas. The fine spray is injurious to health.

2) Ceramic Die:

Diamond die, Ceramco die

Supplied in powder and liquid. When mixed it has a putty like consistency.

The initial set is reached after 45 minutes, when care is needed while removing

from impression as the material is weak at this stage. To obtain maximum

hardness it heated in a oven at 600˚C for 8 minutes and **** in light mineral oil.

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The material is suitable for use with flexible impression materials such as

polysulfide or silicones. Dies with well-defined margins can be made quickly with

experience.

3) Cement Dies:

Model Kryptex

It is supplied as a powder and liquid. The mixing and working properties

are similar to those of dental cements. It can be used successfully with any

impression material.

Sharp well-defined margins are reproduced. Flow properties are good when

assisted by vibration. Dies can be produced in an hour. If the material is allowed

to dry out, it becomes brittle. Die when not in use can be placed in to liquid

paraffin or light mineral oil.

METHODS FOR MAKING SEPARABLE DIES:

In fabrication of wax pattern, working cast provides articulation; it

normally should represent the entire arch and is used to establish interproximal

contacts, buccal and lingual contacts and occlusion with opposing tooth.

The die is a model of the individual prepared tooth on which the margins of

the wax pattern are finished. With the help of die, proper proximal contacts can be

established. There are two working cast and die systems. – a working cast with a

separate die and a working cast with a removable die.

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Working cast with a separate die:

The working cast with a separate die is the simplest means of fabricating a

working cast and die. On ethanol advantage is that the gingival tissue and other

landmarks are intact in the cast. One of the disadvantage encountered is that the

wax pattern must be transferred from one to other which can cause distortion of

pattern or can destroy some of the internal adaptation. Technique utilizes double

pouring. Double pouring possible only with elastomeric impression materials.

Procedure:

Impression is poured in Type IV stone in the area of preparation(s) only.

When set, it is separated and a second pour is made of the entire arch.

The first pour is trimmed into a die with a handle of sufficient length

(similar to a tooth root). The complete arch cast is mounted on an articulator. The

wax pattern is started on the initial pour (the die) and is then transferred to the

articulated cast for refinement of axial contour and occlusal anatomy. When

completed, this pattern is returned to the die so the margins can be readapted

immediately before investing.

Die Preparation:

The handle of the die should be slightly larger in diameter than the

preparation and octagonal in cross-section. Its side ought to be parallel or slightly

tapered toward the base. Handle should be parallel to the long axis of the tooth

preparation. The handle should be approximately 1 inch long.

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A pear shaped acrylic bur to trim the die apical to the finish line of the

preparation. Begin final trimming of the die with a sharp no.25 blade. The area

apical to the finish line should be smoothed and made free of ridges with the

discoid end of a Tanner carver.

The contour of the die apical to the finish line should approximate that of

the root to facilitate good axial contours in the finished restoration.

Sharply undercutting or ditching the die below the finish line is not

advised. Because the instrument used for finishing the margin of the wax pattern

will rest against this portion of die, acute angulations can be exaggerated by

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undercuts. This will result in a thick gingival area on the restoration and an axial

contour that is not conducive the good gingival health.

After the die has been trimmed, the finish line should be highlighted with a

sharp colorbrite red pencil. Do not use excessive pressure when marking the finish

line as it may be rounded over. A black graphite pencil should not be used for this

purpose. When used with usual blue or green wax, a finish line outlined in black

does not become more visible, but instead makes every wax pattern margin

appear unsealed or open. In addition, remnants of clay binder used in graphite

pencil could contaminate the margin of the casting.

Relief should be applied to the

preparation area of the die to produce

space for cement. Enamels and laquer

have been used for this purpose. A relief

of 20 – 40 µm is desired. The tooth

preparation on the die is painted to

within 0.5 mm of the finish lines.

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A die hardening agent cyanoacrylate or acrylic resin laquer can be applied

to the finish line area of the die to prevent abrasion by waxing instruments during

fabrication of wax pattern. Coating material must have a low viscosity and it must

be applied lightly. Thickness for cyanoacrylate – 1 to 25 µm , acrylic – 4 to 10

µm.

Working cast with removable die:

1. Straight Dowel Pin:

This means of orienting dies have been in use for a number of years and

most of the dowel systems are modifications of it. A dowel pin is positioned over

each prepared tooth in the impression. The accurate placement of dowels can be a

problem. If the dowel pins are positioned inaccurately, they may impinge on the

margins, weaken the die, or prevent the die from being easily removed from the

cast. There are devices made specifically for precise positioning of dowels before

the pouring of impression.

1 – Utilized putty on a movable table to hold the impression in an exact,

repeatable position while pins are suspended above the impression from magnets

on a larger immovable table.

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2 – Wire clasps that can be stack in to the periphery of impression can be

purchased or they can be fashioned from orthodontic wire.

3 – Other items like paper clips, bobby pins etc.

Procedure:

1. The position of the dowel pin is located and marked in the impression.

2. Dowel pins are positioned over the impression with bobby pin /wire and

stabilize the bobby pin to the impression with straight pin and sticky wax.

3. Pour die stone in the impression, filling the impression of the teeth and

covering the knurled end of the dowel pin. Pin should parallel the log-axis

of the preparation and it must not touch impression.

4. Paper clips can be added to non-removable parts of the unset first pour to

provide retention for the second pour of stone.

5. When the stone has set, remove the straight pins and bobby pins from the

impression. Place a small ball of soft utility wax on the tip of each dowel.

Cut a v-shaped buccolingual orientation groove or a round dimple on each

die to aid in reseating the die completely and accurately during use.

Lubricate the stone around each dowel with a thin coat of petrolatum.

Remove excess lubricant.

6. Seal the open lingual space with wax or paper towel. Box the impression

and pour the stone.

7. When stone sets, remove the cast from impression and trim the excess with

a model trimmer.

8. Wax at the ends of the dowel pins are located and removed. Allow the

stone to harden for 24 hours.

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9. When the stone is hard and dry use a saw to cut through the layer of die

stone. There should be a cut on the mesial and distal side of each die and

the cut should taper towards each other from occlusal to gingival. Gently

tap on the end of the dowel with an instrument handle to loosen the die.

10. Die trimming should be done as discussed previously.

11. Reseat the dies to make certain that they will seat completely and will be

stable.

12. Place utility wax back into the wells around the tips of the dowel to protect

from plaster contamination. Soak the cast in water and mount it on the

articulator using mounting stone. When the stone has se, remove the wax

covering the tips of the dowels. Make certain that no chips of stone or wax

are left in the wells.

Types of dowel pins:

1. Flat-sided single dowel.

2. Single curved dowel

3. Double straight dowel with a common head

4. Two separate parallel dowels

5. Parallel dowel with plastic sleeve. e.g.Cross pin.

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Flat-sided single dowel Single curved dowel Double straight dowel Two parallel dowels

2. Curved Dowels: (Outside curve, Wimbledon midwest OK)

Curved dowels can be incorporated into a working cast by fixing the

dowels to the impression before it is poured, or by cementing the dowels into

holes drilled in a previously poured cast. The dowel held on a holding unit should

be fixed on the impression. The head of the dowel extends 1 – 2 mm into the

impression of the prepared tooth. The tail of the dowel normally points facially.

Rest of the procedures are similar to straight pins.

A –Curved dowel

B –Positioning bar

C –Straight pins

D –First pour of die stone

After the stone has hardened, make vertical saw cuts on either side of each

die. Separate each segment from working cast by pressing or tapping on the

protruded tail of the curved dowel with a knife or handle.Placing pin in prepared

cast is similar to Pindex system.

3. Pindex System:

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(Coltene / Whaledent International Newyork NY)

In the Pindex system the impression is poured without positioning and

attaching dowel pins. A reverse drill press accurately drills parallel holes from the

underside of a trimmed cast.

Pour the impression in the usual manner adding enough base

(approximately 20 mm from the edge of the tray) to facilitate trimming.

Thoroughly wet the cast before trimming to prevent the accumulation of sludge on

the prepared teeth. Use a model trimmer to flatten the head portion. Then trim the

bottom of the cast, resting the heels on the table of the trimmer to thickness of 15

mm height from the finish line. Use model trimmer to trim excess cement from

the periphery. Remove excess stone from the palatal / tongue area with the help of

a palatal trimmer or with an arbor band on a lather. The lingual border of cast

should taper slightly towards the base to facilitate removal of dies from the cast

later.

Mark the desired locations of pins on the occlusal surface. There should be

two pins for each die. Two for each pontic area and two pins in each terminal

segment containing unprepared teeth.

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Place the prepared cast on the worktable and align the first pencil mark

with the illuminated dot from the light beam director. Using both thumb and index

finger stabilize the cast on the table and press the table downward slowly. This

enables the drill assembly to move upward and cutting the pinholes. Release the

hand and the table will come upward. Repeat the procedure for other holes. Use

compressed air and brush to remove debris from the pinholes.

Prior to cementation, try-in the pins to insure complete seating. The collar

of pin should be flush with the base of the cast to avoid creating an undercut.

Cyanoacrylate cement can be used to lute the pins in their holes. The cast must be

thoroughly dry before cementation. Place the sleeves on the pins.

Apply a thin coat of petrolatum to the bottom of the cast. Wipe of excess

with a cotton roll. Run a strip of utility wax along the ends of long pins to

facilitate removal of dies.

Pouring of base can be done by boxing the cast or by using specially

designed base formers. Care should be taken to avoid void formation around the

pins. Add a small amount of stone to the bottom of the cast in the area of pin and

carefully vibrate between pins. Invert the cast and seat it slowly in the base former

until the wax on the ends of the pins contacts the bottom of the mould. Allow the

stone to set.

Pinned casts can be removed from the base in one piece, which permits

sectioning of the cast into dies from the underside and thus reduce the damage to

the finish lines. After dies are sectioned, trim them in the conventional manner.

Advantages:

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1. Final impression is poured immediately and without the disadvantages of

pins suspended to the impression.

2. The removable sections are planned with the finished master cast rather

than the impression.

3. Dies can be sectioned from the under side of the cast, reducing chances

of damaging the stone at the finish line

4. Double pinning with parallel pins for each die improves accuracy and

stability.

Steps during the fabrication of PINDEX System

Stone model with a thickness Location of drill position withbetween 10-15 mm. light beam indicator

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Cementing of pins with any Notching of the hole lingually tocyanoacrylate cement. prevent rotation

Precision sleeves are placed over Pouring of the base using the the pins. PINDEX® rubber base mold.

Self-articulating PINDEX® Pins with Removal of the model in one piece

sleeves in place. due to completely parallel pins.

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Safe alignment of the die with Completed PINDEX® model with

Tri-Plus® Pins. gingival mask in place

During the placing of pins anti rotation grooves should be placed. Now

Dowel Pin Indexers are also available. Indexers work with most dowel pins to

provide anti-rotational stability and color coded location for removable dies.

4. Di-Lok System:

This is a snap-apart plastic tray with internal orienting grooves and notches

and can be used to reassemble the working cast and die. Like all removable die

systems, great care must be taken to keep it clean so that the parts will fit together

with the greatest possible accuracy. Before using the tray, examine the mounting

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of diagnostic casts on the articulator to determine whether there is space for the

bulky tray.

Pour the entire full arch impression with die stone approximately inch

height. Trim the palatal / lingual and buccal sides to make sure the U-shaped cast

to fit into DI-LOK tray. Score the base of the cast with a separating disc in a

straight handpiece. Place one or two horizontal grooves on the inner and outer

aspects of the cast to provide undercuts for holding the cast in stone in the tray.

Soak the base of the cast in water for about 5 minutes. Mix stone and

vibrate into the tray until the tray is filled to ¾. Seat the cast into the tray jiggling

it slightly as it settles to eliminate bubbles. The cervical lines of the teeth should

be about 4 mm above the edge of the tray when the cast has been seated. Wipe of

the excess stone and allow it to set.

Disassemble the tray by lifting

the back up and slide the buccal

segment forward. The cast is jarred

loose from the tray base by tapping

on the front of the base.

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After separating the cast from the tray saw cuts are made on each side of

the prepared tooth to separate it from the cast. The die is trimmed apical to finish

line with an acrylic bur.

Check the tray for any stone flush and remove it with compressed air and

stiff brush. When the tray is completely clean, reassemble the dies and other parts

of the cast in the tray and lock the tray in the reverse order.

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To attach the Di-Lok tray to the articulator, put the mounting stone on the

articulator ring and on the bottom of the tray, which has undercut rails on it.

Preparation of refractory die:

e.g. Accutrack. JF Jelenko NY

This is a modification of Di-LOK system. Separable dies are prepared in

Di-LOK tray as described earlier. In order to duplicate the material in refractory

material, low viscosity polyvinyl siloxane is used.

Step-by-step procedures:

1. Assemble the dies and other parts in the tray.

2. A strip of putty is wrapped around the part of the cast that contain die of

the prepared tooth.

3. Duplicating paste is carefully poured into the area encircled by the strip of

putty.

4. The mold is allowed to set for 30 minutes.

5. The strip of putty is removed from the mold.

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6. The tray is carefully removed from the mould and disassembled and is

removed from the cast without disturbing the mould.

7. The master die(s) is removed from the mould.

8. Refractory materials is poured through openings in the underside of the die

tray.

9. The refractory die duplicated the master die in relation to other teeth as

well as in configuration.

Alternative Die Systems:

The DVA model system and the Zeiser model system use a precision drill

and special baseplates that are aligned and drilled to provide die removal. These

systems offer the advantage for the expansion of stone which is relieved by the

saw cuts.

DVA Model System:

Trimmed impression on alignement fixture Marking dowel pin locations on clear plate

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Drilling pins for dowel pins as marked Inserting pins in the dowel plate

Impression is poured and stone is placed The alignment fixture is replaced over

around the dowel pins poured impression

The cast is trimmed Cast is sectioned

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Definitive casts trimmed with the DVA Model System

Zeiser Model System:

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Trim all unncessary parts of the Impression is leveled and blocked

impression out with silicone putty

The pin locations are determined and the pinholes are drilled into the base

Pins are inserted into the base The impression is poured

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The base is inverted into the stone

The cast is separated from the impression when set and then separated from the base.

Dry trimming of the dental arch iun the vestibular area and palatal area.

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Sectioning of the cast with a precision saw The sectioned cast

SELECTION OF SYSTEM:

Several methods for preparing separable dies are discussed here. The

selection of any of these systems depends upon the technical skill and experience,

as the principal disadvantages of a removable die system is the risk of introducing

error in the pattern if the die does not reseat accurately in the working cast.

Single dowel are simple to use, but they do not provide anti-rotation

resistance as double dowels. Pindex systems with double pins provide excellent

stability and reduce the chance of damaging the finish lines. But they require

costly equipments.

FUTURE TRENDS:

The current available die systems are working with satisfactory result.

However, the preparation of a die is a tedious procedure. Research should be

directed to simplify the procedures involved in fabrication of these systems. With

the introduction of stronger and durable direct restorative material, the necessity

for indirect fabrication can be reduced. With the advent of CAD-CAM system the

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whole impression procedures and die preparations is eliminated. Successful

restorations with minimal visits and laboratory procedures can be fabricated in

metal and ceramic. However, this system has to be developed more to compete

with conventional technique.

The future of die systems is not promising. The invention of durable and

esthetic direct restorative material may effectively reduce the number of indirect

restorations.

CONCLUSION:

Accurate working cast and dies are essential in making successful cast

restorations. Different materials and technique are available that give extremely

precise reproduction of the prepared tooth. The choice of working cast and dies

depend upon the advantages and disadvantages of each method and operator’s

preference. If done carefully all the available systems are capable of achieving

clinically acceptable results.

REFERENCES:

1. ROSENSTEIL S.F, LAND M.F, FUJIMOTO J.:

Contemporary Fixed Prosthodontics.

( 4th Edition, 1995 Mosby Publications )

2. JOHNSTON J.F, PHILLIPS R.W, DYKEMA R.W.:

84 Dr. Vinni T.K


Modern Practice in Crown and Bridge Prosthodontics.

( 3rd Edition, W.B.Saunders Co. Philadelphia )

3. KOTH D.L, MALONE F.P.:

Tylman’s Theory and Practice of Fixed Prosthodontics.

( 8th Edition, Ishiyaku EuroAmerica Inc. St. Loius )

4. SHILLINBERG S.T, HOBO S, WHITSETT L.D.:

Fundamentals of Fixed Prosthodontics.

( 2nd Edition, Quintessence Publications Co. Inc. Chicago )

5. ANUSAVICE K.J:

Philip’s Science of Dental Materials.

( 10th Edition, W.B. Saunders Co.)

85 Dr. Vinni T.K