modelndiematerial

MODEL AND DIE MATERIAL

CONTENTS

Introduction Review of literature Definition Requirements of cast Requirements of die preparation Ideal requirements of die material Materials Methods Bibliography

INTRODUCTIONDirect fabrication of patterns

for extracoronal restorations in the mouth is inconvenient, difficult, time consuming, and virtually impossible. A cast and die system captures the necessary information so that it can be transferred to the laboratory.

Rosensteil (2001) Contemporary Fixed Prosthodontics 3rd edition Mosby

James Stackhouse (1970) conducted a study concerning the accuracy of stone dies affected by the dimensional changes in rubber impressions

They concluded that

1. More uniform dies were produced from silicon

2. One silicone material was more significant than the others

3. Perforated tray technique caused the dies to be undersized in diameter

4. Bench setting caused the stone dies to be shorter in length and thicker in diameter

REVIEW OF LITERATURE

Gerald T Nomura et al(1980) evaluated the accuracy, fit, detail registration and Knoop hardness of 3 commercially available resin die systems

They concluded :

1. Complete crown epoxy resin dies are undersized

2. MOD onlay epoxy resin dies are accurate

3. Detail duplication of epoxy resin dies is comparable to die

stone

4. Hardness values of epoxy resin are less than those of

stone

Myers M., Hembree J.H.(1982) – conducted a study on the relative accuracy of four removable die systems. 4 die systems were studied i.e. the brass dowel pin, the Plastipin, the J-pin, & Logix Model System & they determined the vertical shift & the horizontal shift of the dies.

They concluded that Plastipin exhibited least amount of horizontal shift & the brass dowel pin exhibited greatest shift in both directions.

DEFINITION MODEL : “A MODEL IS A REPLICA OF A

TEETH AND THE ASSOCIATED SUPPORTING BONY TISSUE OF A JAW,WHICH IS PREPARED FROM AN IMPRESSION.”

DIE : “A POSITIVE REPRODUCTION OF PREPARED TEETH AND CONSISTS OF A SUITABLE HARD SUBSTANCE OF A SUFFICIENT ACCURACY.”

REQUIREMENTS OF THE CAST Accurate surface detail

Free of voids.

Precise articulation.

Soft tissue should be reproduced


REQUIREMENTS FOR THE DIE PREPARATION Reproduce the prepared tooth exactly.

No bubbles or void

The remaining unprepared tooth structure immediately cervical to the finish line should be 0.5 to 1mm visible.

Adequate access to the margin is imperative.


IDEAL REQUIREMENTS FOR DIE MATERIAL Accurate

Dimensionally stable

Setting expansion and contraction, variations in

response to change in temperature need to be minimum

It should reproduce the fine details


Strong and durable

Withstand the carving and finishing procedures

The color should contrast that of the wax to ease the

manipulation

Economical

Easy to use


MATERIALS It includes :

Gypsum Type1-Impression Plaster Type2-Model Plaster Type3-Dental Stone Type4-Dental Stone(High strength) Type5 –Dental Stone(High strength and high expansion)

Resin Epoxy Resin Polyurathane

Electroplated Dies Copper plated Silver plated

Flexible Die Materials Amalgam used die material Metal sprayed die


GYPSUM Gypsum(CaSO4.2H2O) is a mineral mined

product used extensively in dentistry to make dental models.In its unrefined state, gypsum is the dihydrate form of

calcium sulfate. Model plaster

Commonly called plaster of Paris, is used primarily for pouring preliminary impressions and the making of diagnostic models.

Dental stone For use as a working model when a more durable

diagnostic cast is required.

Philips (1992) Science of dental materials 11th edition W.B Saunders

-

Die Stone, High Strength (Type IV):

•α- hemihydrate of the “Densite” type.•Cuboidal shaped particles & reduced surface area produce such properties without undue thickening of mix.•W/P ratio – 0.22 – 0.24•Setting time - 12±4min.•2hr Setting Expansion – Maxi. 0.10%•1hr compressive strength – 5000psi.


Die Stone, High Strength, High Expansion (Type V)

Higher compressive strength than Type IV. Setting Expansion – 0.10% - 0.30%. W/P ratio – 0.18 – 0.22 Setting time - 12±4min. 1hr compressive strength – 7000psi.

GYPSUM HARDENER


RESINS

EPOXY RESIN

Used effectively with rubber based impression materials

available in the form of a paste to which an activator is

added to initiate hardening

Care should be taken that the activator not come in

contact with the skin as it is toxic


PROPERTIES Working time -15min Setting time 1 to 12 hours depending on the products Compressive strength after 7days is 16,000psi Abrasion resistance is superior to stone dies Dimensional change due to shrinkage during

polymerization is between 0.03% to 0.3% and continues to occur for up to 3 days

Epoxy resin are very viscous when pored hence porosity can occur


Advantages 1. More resistant to abrasion 2. Dimensionally stable

Disadvantage1. The epoxy resin cannot be readily introduced into

the details of a large impression as dental stone and requires a centrifugal machine for the same

2. It shrinks by about 0.1to 0.2% in about 24 hours3. It is expensive


ELECTROPLATED DIES Electroplated dies are the ones that are produced

when an impression material is electroplated When a die is made in this manner this process is

known as electroforming The impression materials which can be

electroplated are impression compound and elastomeric materials

The types of dies are-- Copper plated dies- Silver plated dies

The popularity of copper plated dies began in the early 1930’s


ADVANTAGES

No dimensional changes occur during electro

deposition of a metal

It reproduces the impression accurately

The die is tough and has good strength characteristics


COPPER PLATED DIES Impression compound is usually copper plated The impression material is the cathode and it is

connected to the anode which is made of electrolytically pure copper and is immersed in the plating solution so that the area of copper immersed is approximately equal to that of the impression to be plated

COMPOSITION OF SOLUTION FOR COPPERPLATING BATHS

Copper Sulphate (crystals) - 200gms H2SO4 (conc) - 30ml Phenol Sulfonic Acid - 2ml Water Distilled - 1000ml


TECHNIQUE The surface of the impression is coated with a conductor of

electricity such as graphite, copper powder, silver before it is attached to the cathode lead wire. This process is known as “metalizing”. This determines the surface character of the finished die

The copper sulphate is the source of copper, the sulphuric acid increases the conductivity and phenol sulfonic acid helps to assist the penetration of the copper crystals into the deeper parts of the impression

Initially 15 ma current is given which can later be increased to 2 to 3 times the initial current

The plating is allowed to proceed for 12 to 15 hours (usually overnight)


SILVERPLATED DIES Silver plating is done over rubber based

impression materials Silver plated dies show more vertical change than

stone dies, the difference being between 0.25% to 0.45% depending on the impression material , while the horizontal changes are not significant

COMPOSITION OF THE SOLUTION Silver cyanide - 36gm Potassium cyanide - 60gm Potassium carbonate - 45gm Water (distilled) -1000ml

Silver plated dies marginal accuracy of cast restorations J Prosth Dent 51;1984: 768-772

Technique

The impression is first made conductive by

brushing the surface with powdered silver

A current of 5ma is suitable to start plating a

single tooth impression and 10 ma for larger

areas

Once a layer of silver is deposited the

current can be doubled or trebled

Time period is usually 12 to 15 hours

Silver plated dies marginal accuracy of cast restorations J Prosth Dent 51;1984: 768-772

FLEXIBLE DIE MATERIALS

They are similar to heavy bodied silicone or

polyether impression materials

Selection of a compatible die and impression

material is very important in case of flexible dies

Advantages over die stone

Rapid setting

Ease to removal

Comparision of surface detail reproduction of flexible die materials J Prosth Dent 1998; 80:485-9

AMALGAM DIES Model amalgam is similar to silver amalgam which

is used for fillings It is used to make hard metal dies which

reproduce fine details and sharp margins from impression compound of prepared teeth

They cannot be made in hydrocolloid impressions as they cannot withstand condensation pressure

After packing the impression with amalgam the die can be removed after a minimum of 12 hours, by gently warming the compound


As amalgam is a good conductor of heat ,

softened wax applied to them cools rapidly

This may produce internal stresses which

may distort the wax pattern after removal

from the die

Sudden cooling of the wax may also result in

contraction of the wax away from the die

A separating agent is needed as with die

stone


METAL SPRAYED DIES

A bismuth – tin alloy which melts at 138oCcan be

sprayed directly on to an impression to form a metal

shell which can than be filled with dental stone

A metal coated die can be obtained rapidly from

elastomeric impression material

Disadvantage the alloy is soft care is needed to

prevent abrasion of the die


CAST & DIE SYSTEMS

1) Working cast with removable die

i. Straight dowel pin

ii. Curved dowel pin

iii. Di-lok tray

iv. Pindex system

2) Working cast with separate die

3) DVA model system

4) Zeiser model system

Shillenberg (1981) Fundamentals of fixed prosthodontics 3rd edition Quintessence

STRAIGHT DOWEL PIN

The brass dowel pin is one of the most accurate dowel types in terms of resisting horizontal displacement and the second lowest in vertical deviation of four types of removable dies.

A dowel pin is positioned over each prepared tooth in the impression.

Place a dowel between

the arms of a bobby.


Push a straight pin between the arms of the bobby pin and into the impression material on both the buccal and the lingual surfaces of each tooth to have a dowel pin placed over it.

Stabilize the dowel in the bobby pin.

Pour die stone into the impression, filling the impressions of the teeth and covering the knurled end of the dowel pin.

The pin should parallel the long axis of the preparation.


When the stone is hard and dry, use a

saw frame with a thin blade

There should be a cut on the

mesial and distal side of each die,

and the cuts should taper toward

each other slightly from

occlusal to gingival.

Take the die form the cast and trim away excess stone gingival to the finish line.

Complete the trimming of the die with a no.25 blade in the laboratory knife and then mark the finish line with the red pencil.

Repeat the procedure for each die on the cast.


CURVED DOWEL PIN To install pin before pouring the impression, use finger

pressure to insert tip of dowel into large opening of position bar.

Hold the bar faciolingually, so that head of the dowel is 1-2mm into the proposed area of impression.

The tail of dowel extends facially; however if the tooth is linguoversion, turn it towards lingual side for easy removal.


Insert a straight pin into one of 3 holes into the facial aspect of bar and into the facial flange of impression and another pin into lingual flange through lingual holes of bar.

The dowel should not touch the impression and its head should be parallel to long axis of prepared tooth or teeth.

This procedure is repeated for all abutments and pontic areas.

One pin is placed near the center of each segment of unprepared teeth, this wall help in removal of segment for better access of gingival wax pattern.

Impression is poured with die stone until it covers heads of dowel. This will fill the impression about 4 mm above gingival finish line.

The straight pins and positioning bar are removed as soon as stone is set.


To assist in orienting each large segments of unprepared teeth, cut a 2mm deep hole on either side of each dowel with a large acrylic bur.

Petrolatum is applied on stone and also an exposed part of dowel for easy separation from the base.


•Impression is boxed, allowing the tails of the dowels to extend slightly through the heat softened wax.

•Fill the boxed impression with dental stone. The dowel should be covered by at least 2mm of stone.

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

•A die is removed by pressing the dowel


•Pour the impression with die stone to form a horseshoe shaped working cast. •Trim the bottom of cast flat to level 10mm from the necks of teeth.This is done because thin cast are easy to saw and short dowels are more stable than larger ones.

•Drill a 5mm deep hole in the bottom of the cast directly under the center of each prepared tooth, pontic area, and segment containing unprepared teeth.•This can be made with 2mm diameter drill in hand piece or drill press.

TO PLACE THE DOWELS AFTER THE CAST HAS BEEN MADE.


•Clean the dowel holes, insert the curved dowel pin properly and then adjusted for proper fit. •Cement the dowels into holes one at time with placing a drop of cyanoacrylate cement into each hole.

•The head of a curved dowel is seated into the holes.

•Seat the heads completely with tail pointing facially. •Then same procedure of pouring base and preparing dies is repeated


PINDEX SYSTEM(Coltene/Whaledent,Mahwah,NJ)

In the pindex system 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 beforehand.

The machine accurately drills parallel holes from the underside of trimmed cast.


PINDEX SYSTEM

Diagram showing the pindex machine


•Pour the impression, adding approximately 20mm of stone.•Wet the cast prior to trimming

•It should sit perfectly flat on a tabletop, and its thickness must be a minimum of 15mm.

•Then trim the bottom of the cast, resting the heels on the table of the trimmer.


•Remove any excess stone in the palate/tongue area with an arbor band on a lathe.•The lingual border of the cast should taper slightly toward the base to facilitate removal of the dies from the cast later.•The faciolingual width -20mm.

•Use a pencil mark the desired location of the pins on the occlusal surfaces of the teeth or preparations.

•Periphery of the cast should be trimmed.


•Place the prepared cast on the worktable and align the first pencil mark with the illuminated dot from the light beam director.•Using both hands, exert firm downwards pressure on the cast with thumbs. •Raise the handle bar with slow, even pressure and the drill assembly moves upwards cutting the pinholes. •When proper depth is achieved, red light goes off. •Same procedure is repeated with each mark. •For better results, cast is made slightly damp to prevent dust formation.


•Compressed air and brush is used to remove debris from holes.

The pin holes are refined with hand reamer.

•Cyanoacrylate cement is placed on the pins prior to cementing the pin tips.

•Shorter pins are placed before the long pins in lingual or palatal holes and long pins in the facial holes.


•White sleeves are placed on the long pins and gray sleeves on the short pins.

•The bottom of the cast is lightly coated with the petrolatum.

•Gray sleeves are blocked with small amount of molten wax to prevent the sleeve from filling with stone when secondary base is added.

•Strip of utility wax along the ends of the long pins to facilitate removal of the dies later.


•A palatal or tongue filler is made of boxing wax.

•The filler is seated to the cast.

•Boxing wax is applied aaround the cast.

•Base is poured with the die stone.


•When stone becomes hard, the cast is seated in the base former.

•Saw cuts are premarked with the pencil.

•Then dies are sectioned from the underside.

•It may also be sectioned from the occlusal aspect.


After the die are sectioned, trim them in a conventional manner.

Mark the finish line with red pencil.

Apply die hardener and die spacer.

Then place the completed cast on the articulator and then cast is ready for fabrication of the wax pattern.


DI-LOK TRAY SYSTEM A snap apart plastic tray with internal orienting

grooves and notches is used to reassemble working cast and dies.


TECHNIQUE The cast should be poured in a U shape, with no stone in

the center building it up to 2.5cm. (1.0 inch) A lingual side of the cast base is trimmed with an arbor

band.

Horizontal grooves are cut in the base to for retention.

When stone has set for 1 hr, separate it from impression. Cast is trimmed in horseshoe configuration to fit in Di-lok

tray and the buccal border is tapered towards base with

arbor band.


Soak the base of cast with water for 5 min. Pour the base in tray, until ¾ of its is filled Seat the cast on tray; in such a way that

cervical line of the prepared teeth should be approximately 4mm above the level of base.

Wipe off the excess stone. Allow the stone to set until it is hard and

dry . To complete the dies, the cast must be

removed from the tray.


•Then with a saw frame and a thin saw blade, cut between the prepared tooth and the adjacent tooth.•The saw cut should start in the interdental papilla area and extend downward on a very slight taper.•The occlusal saw cut should extend three-quarters of the way through the stone base.

•Disassemble the tray by lifting the back up, and then slide the buccal segment forward.

•Use finger pressure to break the die and attached teeth from the cast.


•Remove excess stone gingival to the finish line with a pear-shaped acrylic bur.

•Then cast and dies are reassembled in the tray.

•Then the cast and tray mounted on the articulator.

•When the stone has set, the articulated cast in the Di-lok tray is ready for the fabrication of the wax pattern.


WORKING CAST WITH SEPARATE DIE(MULTI-POUR TECHNIQUE) ADVANTAGES

SimpleSlightly more accurate.Minimum trimming.

DISADVANTAGESDifficult to transfer complex or fragile wax

patterns from cast to die.Seating the pattern on the cast may be

problematic.Technique can be used with elastomeric

impression materials.


The area of preparation is poured with the stones in small increments.

When set,it is separated.A second pour is then made of the entire arch.

•The first pour which is more accurate is trimmed into a die with a handle.

•A properly trimmed die handle is slightly larger in diameter than the preparation


•Improperly trimmed die with a handle that meets the preparation at an angle

•Handle should be 1 inch long

•The die is trimmed with an acrylic bur

•Shaping of the handle near the finish line is completed with a scalpel

•The die is smoothened below the finish line with the discoid end of a tanner carver

•The prepared finish line on the die should be outlined with a red pencil.

•Die relief agent is painted on the preparation-20 to 40 mm


DVA Model System:-

Trimmed impression on alignment fixture.

Marking dowel pin locations on clear plate

Drilling holes for dowel pins as marked

Inserting dowels in the baseplate


Impression is poured, stone placed around dowel pins & alignment fixture replaced over poured impression

Set cast is removed from baseplateRosensteil (2001) Contemporary Fixed Prosthodontics 3rd edition Mosby

Cast is trimmed Cast is sectioned

Trimmed working casts using the DVA Model System


ZEISER MODEL SYSTEM

Zeiser Model System Impression is leveled, blocked out with silicone putty,& positioned over

baseplate

Pin locations are determined & the pinholes drilled in the base.


Pins are inserted into the base.

Impression is poured

Base is inverted into the stone


Cast is separated from the impression when set & then separated from the base.

Precision saw aids sectioning

Sectioned cast


BIBLIOGRAPHY1. Philips (1992) Science of dental materials

11th edition W.B Saunders2. Rosensteil (2001) Contemporary Fixed

Prosthodontics 3rd edition Mosby3. Shillenberg (1981) Fundamentals of fixed

prosthodontics 3rd edition Quintessence 4. Silver plated dies marginal accuracy of

cast restorations J Prosth Dent 51;1984: 768-772

5. Comparision of surface detail reproduction of flexible die materials J Prosth Dent 1998; 80:485-9

6. An investigation of epoxy resin dies J Prosth Dent 1980;44:45-9

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