Dr. Someshukla Sarkar

CONTENTSy INTRODUCTION y MODEL MATERIALS y DESIRABLE QUALITIES OF DIE MATERIALS y TYPES OF DIE MATERIAL y COMPATIBILITY OF DIE MATERIALS WITH IMPRESSION

MATERIALSy COMPARISON OF THE VARIOUS DIE MATERIALS y SUMMARY y CONCLUSION y REFERENCES

y In dentistry replicas of the hard and soft tissues are used

for diagnosis and treatment of oral tissues. These replicas are called study models, casts, or die.

y STUDY MODELS :A positive full scale replica of teeth, soft

tissues, and restored structures used as a diagnostic aid for construction of orthodontic and prosthetic appliances. They are used for observation of the patients oral structure for e.g. orthodontists use study models to evaluate the crowding of teeth or progress in correcting that crowding.y CAST: Is a working model.

Acc to GPT: A life size likeness of some desired form. It is formed within or is a material poured into a matrix or impression of the desired form.

y DIE: These are extremely accurate replicas of a single tooth

and are generally used to make crowns or inlays. Acc. to PHILLIPS it is a reproduction of a prepared tooth made from a gypsum product, epoxy resin, a metal, or a refractory material. Acc. to GPT: the positive reproduction of the form of a prepared tooth in any suitable substance. It is the reproduction of the form of a prepared tooth in a suitable hard substance.(JPD 1968; 20, 5)

DIE

CAST

MODEL MATERIALS The most commonly used model materials are gypsum products. Gypsum is a mineral found as white to milky-yellowish mass in nature. Plaster and stone products are produced by calcining calcium sulphate dihydrate or GypsumCaSO4 . 2H2O 110 - 130 C CaSO4 . H2O (plaster or stone)

(gypsum)

Calcium sulfate dihydrate: CaSO4. 2H2O GYPSUM

Heat in open vessel at 120C

Heat in autoclave, steam pressure 120C130C

Heat ground gypsum in autoclave : sodium succinate additive, 1400C

Heat in boiling 30% solution of CaCl2 or MgCl2

Calcined calcium sulfate hemihydrate ( -hemihydrate)

Autoclaved calcium sulfate hemihydrate ( -hemihydrate)

Calcium sulphate hemihydrate (sometimes called densite; similar to autoclaved material (CaSO4)2 H2O

Calcium sulfate hemihydrate CaSO4 H2O

Heat at 200C

Hexagonal calcium sulfate; soluble anhydrite

Orthorhombic calcium sulfate; insoluble anhydrite

Anhydrous calcium sulfate : CaSO4

SETTING REACTIONy The he ihydrate is

ti es

re s l le i reacti

ater tha is the dihydrate ear ca e derst d as f ll s:

r

te

erat re ( ). The setti

he the he ihydrate is a d wor a le. This sat rated

i ed with water, a s s e si sol tion,

is f r ed that is fl id in dihydrate,

e ihydrate dissol es he ihydrate s dihydrate

til it for s a sat rated sol tion. s ersat rated reci itates out, solution is no

reci itates out dihydrate.

longer saturated with the he ihydrate, so it continues to dissol e.issolution of he ihydrate and precipitation of dihydrate proceeds as either

new crystals for

or further growth of already present crystals happen. This

is continuous and continues till no dihydrate precipitates out.

CaSO4 (1/2)H2O] + [(3/2)H2O] ----------> CaSO4 (2)H2O + HEAT P l a s t e r , Stone, Die Stone + Water ----------> Gypsum + HEAT

Calcium Sulfate Hemihydrate

Calcium Sulfate Dihydrate

PHYSICAL PROPERTIES

y The water/powder ratio is 0.28 0.30. y Mixing time is 20-30 seconds mechanically and around one

minute through hand spatulation.y The working time is 3 minutes. y Setting time is 124 minutes. y The compressive strength of the mixture in 1 hour is 20.7 MPa

Chemical Name FormulaPowder Shape

-calcium sulfateCaSO4-(1/2)H2O

-calcium sulfateCaSO4-(1/2)H2O

-calcium sulfateCaSO4-(1/2)H2O

IrregularPorous Plaster, impression plaster

UniformModerately denseStone

UniformDenseImproved stone

DensityDental Products

Common Names

Plaster of Paris

Investment [eg, Hydrocal]

Die stone [eg, Densite]

MANIPULATIONy Storage: In closed containers to prevent reaction with moisture from the

atmosphere which can cause formation of the dihydrate which can accelerate the setting time.y Correct water / powder ratio

To attain maximum strength and resistance to abrasion it is necessary to use the current water to powder ratio when preparing dies made of gypsum products. Reducing or increasing w:p ratios, the powder to liquid ratio below that recommended by the manufactures result in not only reduced strength and abrasion resistance but also a deviation from the expected setting expansion.y The w/p ratio for gypsum die materials is 0.22 to 0.24 i.e. 100 gm of material is

mixed with 22 ml of water.

SPATULATION Measured amounts of water and powder are added to a flexible rubber mixing bowl. The water is dispensed in the bowl first the powder is added and allowed to settle in to the water for approximately 30 sec. Spatulate using stiff blade. Mixing for one minute. Use of automatic vibrator. Time and rate of spatulation.

SETTING PROCESSy Initially a mix of hemihydrate and water can be poured. y Next the material becomes rigid but not hard this is called

initial setting. At this stage the material can be carved but not molded.y The final set follows when the mix becomes hard and strong.

However at this stage the hydration reaction is not necessarily complete nor has optimum strength and hardness necessarily been achieved.

y Heat is given out during setting since the hydration of the

hemihydrate is exothermic.y Dimensional changes also takes place. A setting expansion of

0.05 0.3% is observed for dental stones. This is caused by the outward thrust of the growing crystals of dehydrate. If the material is placed under water at the initial set stage a greater expansion on setting occurs. This is hygroscopic expansion.

DESIRABLE QUALITIES OF DIE MATERIALSy Ability to reproduce fine detail and sharp margins. y Dimensional accuracy and stability should show little

dimensional change on setting and should remain stable.y Mechanical properties

High strength to reduce the likelihood of accidental breakage.

Abrasion resistance so that the die can withstand the manipulative procedures during carving of wax pattern.

y Compatibility with impression materials: There should be no

interaction between surface of impression and die.y Good color contrast with other materials being used for ex.

Inlay wax or porcelain.y Biological safety: non-injurious to health by touch or

inhalation.y Economical y Easy to use.

TYPES OF DIE MATERIALSy Gypsum products Model plaster Dental stone Improved stone Gypsum bonded

investment Phosphate bonded

investment

y Metals Amalgam Electroplated copper Electroplated silver Metal sprayed dies

y Cements Silico phosphate cements

y Polymers and filled polymersSelf curing acrylics Epoxy resins Polyesters

and epiamines

y Ceramics y Divestments

COMPATIBI ITY OF I MATERIAL WITH IMPRESSION MATERIAL IMPRESSION MATERIAL DIE MATERIALy Gypsum type IV y Gypsum type V y Divestment y Silver plated dies y Metal sprayed die y Amalgam

For all impression material For all impression material For silicone, polysulphide and alginate impression material Used with elastomeric impression material Impression compound ,silicone rubber impression Used with inelastic impression material

y Epoxy polymer

y Ceramic die materials y Flexible die material

Used for all impression material EXCEPT for HYDROCOLLOID impression material. Silicone and polysulphide impression material. Used with all EXCEPT polyvinyl siloxane impression material.

HIGH STRENGTH DENTAL STONEy Both Type IV gypsum and Type V gypsum are known as high

strength dental stones.y ADA specification no is 25. Both are calcium sulfate alpha

hemihydrate.y The crystals are denser and have prismatic shape with a

reduced surface area , which makes them suitable as a die material.

y Water /Powder ratio:

the W/P ratio is an important factor in determining the physical and chemical properties of the final gypsum product,y The ideal W/P ratio for gypsum products,

Type IV (die stone)

- 0.22- 0.24 -0.18 -0.22

Type V (high strength & expansion)

Effects of Impression and Die Stone Variables A. IMPRESSION MATERIAL VARIABLES: 1. Blood and Saliva 2. Plasticizers 3. Hydrophilicity 4. Disinfection Procedures B. STONE AND DIE STONE VARIABLES 1. W/P Ratio 2. Disinfection Procedures 3. Additives a. Accelerators: K2SO4; Gypsum Particles b. Retarders: Borax (Na2B4O7-10H2O); Colloids c. Fillers: Silica; Resin

Advantages:y Generally compatible with all impression materials. y Have the ability to reproduce fine detail and sharp margins. y Dimensional accuracy and stability are good. y Produces consistent results. y Easy to use.

Disadvantages: Susceptibility to abrasion during carrying of the wax pattern

especially with Type IV Gypsum die.

To overcome the poor abrasion resistance, the following methods can be used: Gypsum hardeners, such as aqueous colloidal silica or soluble

resin restorations, can be used instead of water during mixing of the stone. This increases the abrasion resistance by 100%. Impregnate the surface of the die with a low viscosity resin

such as cyanoacrylate (fine film not thick). (Mason et al JPD23:96;1970)

Use of gum arabic, calcium hydroxide mixture that reduces the

amount of water necessary to mix gypsum products.

USES: As individual dies for full gold crowns and porcelain fused to

metal and cobalt chromium crowns. Used for constructing cast metal denture framework.

DIVESTMENTDie stone investment combination (divestment) is a combination of die material and investment media. A commercial gypsum bonded material called divestment is mixed with colloidal silica liquid. The die is made from this mix and wax pattern constructed on it then 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 investment. The setting expansion of the material is 0.9% and thermal expansion is 0.6% when heated to 677C. because divestment is a gypsum bonded material it is not recommended for high fusing alloys like metal ceramic restorations. It is highly accurate technique for conventional gold alloys especially intracranial preparations.

ELECTROPLATED DIES/ ELECTROFORMED DIESy Used to overcome the poor abrasion resistance of gypsum. y It involves electro deposition of silver or copper or gold on the

impression that gives a hard metallic surface to the cast.y Advantages

High strength, Hardness Abrasion resistance

The first step in the procedure is to treat the surface of the

impression material so that it conducts electricity. This process is referred to as METALLIZING. In this process,

a thin layer of metal, such as silver is deposited on the surface of the impression material. AMMETER :- The current passed is of 10mA / tooth area for 12 hrs. It should not exceed 50mA. Plating tank glass or hard rubber with well fitting cover to prevent evaporation.

Metallizing agents are : 1. Bronzing powder suspended in almond oil 2. Aqueous suspensions of silver powder 3. Powdered graphite Requirements for electroplating : The impression to be coated is made the cathode. Anode is the metal to be deposited either silver or copper Anode and cathode holder. Electrolyte is the solution through which the electric current is passed. The ions are deposited from the anode to the cathode.

COMPOSITION OF ELECTROPLATING BATH : Copper : Copper sulfate (crystals) 200g Sulfuric acid (concentrated) 30 ml Phenol sulfonic acid 2 ml Water (distilled) 1000 ml Silver : Silver cyanide 36g Potassium cyanide 60 g Potassium carbonate 45g Water (distilled) 1000ml

PROCEDURE : a) Copper plating :

The surface of the impression is rendered conductive by coating it with fine particles of copper or graphite.

The coated impression is made the cathode (negative electrode)

of a plating bath, with an anode (positive electrode) of copper. The electrolyte is an acid solution of copper sulfate (about

250g/l.

A current is passed, causing slow dissolution of the anode and movement of copper ions from anode to cathode, so plating the impression

5.

Dental5.

Dental stone is then cast into the plated is then cast stone impression. into the plated

impression. for the elastomeric

The technique is often not considered Thesuitable for the elastomeric materials technique is often not considered suitable

materials

b) Silver plating: Polysulfide and silicone impression materials can be silver plated by the same general technique except 1) The impression is coated with silver or graphite powder. 2) The anode is silver. 3) The electrolyte is an alkaline solution of silver cyanide

y ADVANTAGES: a) Gives excellent clinical result b) Hard and most abrasion resistant c) High strength d) Better marginal definition e) Imparts smooth surface to the wax pattern in contact f) Does not absorb oil or water.

y DISADVANTAGES: a) Limited to non aqueous impression materials b) Expensive, time consuming and special equipment required c) Health hazard d) Difficult to trim e) Adaptation of wax pattern is not so good as die stone, pattern

tends to lift from the marginsf) Impression materials and electrodeposits can contribute to die

inaccuracies

EPOXY DIES OR POLYMERS OR FILLED POLYMERSy Resins are used as die materials to overcome the low strength

and abrasion resistance of die stone.y These are self curing acrylic material or polymeric materials

with fillers.y Epoxy die material can be used with polyether, polysulphide

or silicone epoxy to which filler may be added. CH2 CH R CH CH2 O O

y Advantagesy More abrasion resistance. y Less brittle than die stones. y Can be carved at room temperature.

y Disadvantagesy Shrinkage on polymerization y Less dimensional stability y Expensive.

Composition:It has two parts : RESIN and HARDNER The first part contains: Epoxynovoclac polymer

50-60% 30-50% 0-20%

Vinyl 3 cyclo hexene diepoxide 3,4 epoxy cyclo hexene methyl

The second part contains: Partially hydrolyzed 3,4 benzophene tetra carboxylic acid dianhydride 20% Partially hydrolyzed pyrometallic acid dianhydride not less than 50% and

preferably 90% or more.

The setting reaction is condensation polymerization cross linkage reaction. Catalyst : tertiary amine 0.03 parts by weight mixed just before using the

material. As activator is toxic, the material should not come in contact with the skin

and cannot be used in mouth. The shrinkage value is 0.1%, which is very low but hardening takes up 24 hours. Fast setting epoxy material is supplied in auto mixing system. Epoxy resin in one cartridge and catalyst in another. Forcing the 2 pastes through the static mixing tip thoroughly mixes the epoxy material, which can be directly injected into a rubber impression. This hardens so rapidly that die can be waxed up in half an hour after injecting into the impression.

Properties:y Working time 15 min. y Setting time 1 to 12 hours depending on the product. y Knoop hardness number is 25 KHN 15 less than that of high

strength stone (77 KHN).y Compressive strength after 7 days is 16,000 psi. y Abrasion resistance is superior to stone dies.

y Dimensional change due to shrinkage during polymerization is

between 0.03% and 0.3% and continues to occur for upto 3 days.y Epoxy materials are very viscous when poured hence porosity

can occur.y Epoxy resin cannot be used with water containing agar and

alginate materials because water retards the polymerization of the resin. They are compatible with polyether, polysulphide or silicon impression materials.

AMALGUM DIESy They are made by packing amalgam into impression made of

impression compound.y Advantages

Dies made of amalgam exhibit superior strength resistance to abrasion and reproduce fine details and sharp margins

Although a material of choice a number of years ago it has been largely replaced by electroplated dies. Which are also resistant to abrasion the property of amalgam dies has declined for a number of reasons.y Can be packed only into a rigid impression like that of impression compound. y (Because of the tech necessary to produce a sound die) dimensional accuracy

may vary from one die to the next.y Time required for fabricating an amalgam die is lengthy. Although the die

packing procedure may take only 30 minutes amalgam requires 12 to 24 hours of hardening before it can be manipulated as a die.y It has high thermal conductivity and so can cool a wax pattern rapidly which

may lead to distraction of the pattern. This can be overcome by warming the die.

SILICO- PHOSPHATE CEMENTy It is similar to the filling and cementing material. The powder is a

mixture of silicate powder and zinc oxide liquid contains phosphoric acid.y Advantages: Strength and surface hardness are superior to those of

die stone.y Disadvantages: This material contracts during setting and may be

dimensionally inaccurate. There is loss of water on standing since the viscosity of these material is relatively high. Presence of surface voids can occur.

METAL SPRAYED DIES: A bismuth-tin alloy, which melts at 1380c, can be sprayed directly on to an impression to form a metal shell, which can then be filled with dental stone. Advantage -A metal coated die can be obtained rapidly from elastomeric impression materials. Disadvantage -The alloy is rather soft, care is needed to prevent abrasion of the die.

CERAMIC DIE MATERIALS:Two ceramic die materials are available -A material for the production of dies on which porcelain restorations are to be fabricated, without the use of a platinum foil matrix. To form the dies heating to over 10000c is necessary. -A ceramic material, supplied as a powder and liquid, and mixed to a putty like consistency. After 1 hour the material is removed from the impression and fired at 6000c for 8 minutes to produce a hard strong die.

FLEXIBLE DIE MATERIAL :

-Similar to silicone or polyether impression material.-Used to make provisional restorations or indirect composite resin inlays . eg; polyvinyl medium viscosity impression material Advantages: -More rapid setting -ease of removal of provisional or inlay Disadvantages: -expensive

COMPARISONS OF THE VARIOUS DIE MATERIALS

y Moser et al in 1975 found that the epoxy resins reproduced

details better than stoney Nomura et al in 1980 concluded that the detail

reproduction of epoxy resin dies was comparable to stoney Bailey et al in 1984 found no difference in the accuracy of

stone, epoxy resins and electroplated silver dies.

y Derriem et al in 1995 reported that the detail reproduction of stone

was inferior to epoxy and polyurethane resins. Stone cannot reproduce details smaller than 20 nm as the gypsum crystal size ranged formal 15 to 25 nmy Chaffe et al in 1997 reported that epoxy resins reproduce a single

die with a degree of accuracy similar to gypsum material usedy According to Craig: The epoxy resin dies reproduce detail the

best followed by metal die and high strength dental stone.

Dimensional stability:y Nomura et al in 1980 and Mose et al in 1975 demonstrated that the

epoxy dies were under sizedy Derriem et al in 1995 were able to show that the dies exhibited slight

shrinkage as compared to stone, which exhibited slight expansion. This required the epoxy dies to be coated with several layers of spacersy Chaffee et al in 1997 concluded that the improved dental stone dies

were significantly larger in occluso-gingival dimension than epoxy resins.

Abrasion resistance and strengthy Chaffee et al in 1997, Derriem et al 1995 ,Nomura et al in 1980 and Moser et al

in 1975 concluded that metal formed dies have superior abrasion resistance ,epoxy dies have good resistance and the high strength dental stones have the least resistance to abrasiony Philip Duke et. al in 2000 conducted a study of the physical properties of type

IV gypsum, resin containing and epoxy die materials. The results were all gypsum products expanded where as the epoxy resin material contracted during setting. The epoxy resin exhibited much better detail reproduction, abrasion resistance, transverse strength than gypsum materials. In general the epoxy resin exhibited the best properties of the materials studied

Jacinthe M et al in 2000 conducted a study on the dimensional accuracy of an epoxy resin die material using two setting methods and concluded that retarding the setting reaction of an epoxy resin die material improved its accuracy. Epoxy resin die materials had a net shrinkage but the gypsum based materials had a net expansion.

SUMMARYy Detailed reproduction of die materials for fixed partial

prosthesis affects the accuracy of working casts and is related to the compatibility between the die and impression materials.y Hence an accurate working cast and die are essential in making

successful cast restoration.y Different types of materials and techniques are available that

will give an extremely precise reproduction of prepared teeth .

y Dental stone is compatible with majority of impression

materials.y This material is inexpensive easy to use and generally

compatible with all impression material.y Resistance to abrasion of the material can be effectively

increased by using gypsum hardner, such as aqueous colloidal silica or soluble resin .y Epoxy resin and electroplated dies are good alternatives

CONCLUSIONy A good impression and an accurate die are the first step

towards the fabrication of an accurate restoration whether its inlay, onlay or crown. Proper selection of the die material and its manipulation are paramount to achieve accuracy in the die.y In conclusion, a wise choice of material, combined with proper

handling and meticulous approach to the details of each step of fabrication will bring us that much closer to perfection .

REFERENCES

y Fundamentals of fixed Prosthodontics:Shillingberg.

Contemporary fixed Prosthodonticsy Philips science of dental materials

:Stephen F.Rosenstiel :Anusavice

y Dental material -properties and manipulation :Craig ,powers y Notes on dental materials- E C Combe y Restorative dental materials- Robert G Craig

IJP 2000 Vol 13, No: 3 pp: 214-220. JPD 2000 Apr; Vol 83 No: 4 pp: 466-473. JPD 2000 Mar; Vol 83 No. 3 pp: 301-305. JPD 1998 Oct; Vol 80 No. 4 pp: 485-489. JPD 1968 Apr; Vol 20, No 5 pp; 35-38 JPD 1995 Aug;Vol 74 No. 2 pp:198-201 JPD 1988 Mar; Vol 59, No 3 pp: 326-333 JOP 2005 Mar; Vol 14, No 1 pp: 25-31