casts, dies and cast forming

CASTS, DIES AND CAST FORMING

Presented by:

Apurva ThampiMDS 1st year

Rudd an Morrow, dental laboratory procedures - complete dentures (volume I), 2nd edition

A Good Impression… Requires time and effort Ensures an accurate and detailed cast

Definations Cast : it is a life-size likeness of some

desired form

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

Glossary of prosthodontic terms

Pre – requisites of casts Void free Distortion free Reproduce both prepared and unprepared

surfaces Occlusal surface of all teeth must allow

articulation All relevant soft and hard tissue must be

involved The side walls should be vertical or slightly

tapered outwardRudd an Morrow, dental laboratory

procedures - complete dentures (volume I), 2nd edition

Peripheral roll : 3-4mm Edge of the cast : 3-4mm Base of the cast : 15-16mm at the

thinnest point Tongue space should be flat nad smooth

Rudd an Morrow, dental laboratory procedures - complete dentures (volume I),

2nd edition


Types of casts

Diagnostic casts

Working casts

Refractory casts

Diagnostic casts : A life size production of a part or parts of the oral cavity and/or facial structures for the purpose of study and treatment planning

Working casts: A cast formed of a prosthesis for the purpose of mounting on an articulator

Refractory casts: A cast made of a material that will withstand high temperatures without disintegrating (investment cast)

Glossary of Prosthodontic terms

CAST FORMING

PRELIMINARYIMPRESSION

FINAL IMPRESSION

INVERSION METHOD INVERSI

ON METHOD

WAXBOXINGMETHO

D

DENTALPLASTER

& PUMICE METHOD

CAULKINGCOMPOUN

D & PADDLE BOXING METHOD


Preliminary impression materials Alginate

Impression compound


2nd edition

Alginate impressions Used to make diagnostic cast and

removable partial dentures

Impressions to be poured soon after taking the impression


2nd edition

Procedure Examine the

impression Run cold tap water

and clean it gently Trim excess alginate Weigh the stone and

mix it with the recommended W/P ratio

Vibrate the tray gently and add the stone in increments

Create undercuts in the first pour Rudd an Morrow, dental laboratory


After initial set, soak in slurry water from 3-5 mins

Mix stone and place on glass slab, shape to approx. size and thickness

Invert the stone cast onto this Remove excess, and shape until surface

is flat


2nd edition


PROBLEM CAUSE SOLUTION

Voids in impression Voids in impression material during making of impression.

Obtain another impression.

Impression separated from tray

Too much time between impression and pouring.

Pour as soon as possible.

Cast surface chalky and soft

Impression not separatedfrom cast within 1hrafter pouring.Incorrect water powderratio, making mix too thin.

Separate within 1 hr. Weigh stone and mixwith required amount ofwater.

Voids on surface of cast Mechanical spatulatornot used.Stone poured intoimpression too quickly

Mix it in mechanicalSpatulator. Pour slowly into only onedistal corner.


Cast too thin or thick Cast trimmed improperly.

First pour of stone notchecked for thickness.

Trim with care to prevent over trimming.

If first pour stone is too thick trim it before pouring base.

Critical areas of cast trimmed away

Trimmed improperly. Check cast frequently when trimming.

Cast broken easily Improper water powderratio.

Cast trimmed too thin.

Use recommended water

powder ratio.

Do not over trim


2nd edition


Modelling plastic impressions Thermoplastic material

Rigid, hydrocolloid – less subject to distortion

Procedure Examine the impression Place it in a holder and

make a mix of stone Gently tap while pouring

mix After initial set, pour base

(inversion method) After 45min – 1hr, dip in

warm slurry water Lift the modelling plastic

off the cast Examine the cast and

trimRudd an Morrow, dental laboratory


PROBLEM CAUSES SOLUTION

Cast broken during separation from impression.

Modeling plastic not softened adequately before removal.

Immerse poured impression in warm water to soften before separation

Modeling plastic stuck to cast at time of separation.

Modeling plastic overheated when placed in water that is too warm.

Do not over soften modeling plastic, place in warm water only long enough to soften and remove.

Cast too thin or thick. Cast poured ortrimmed too thin.

Thick base as a result

of first pour being toothick.

Pour cast to properthickness do not trimtoo thin.

Check thickness offirst pour beforepouring base , trim oncast trimmer ifneeded.


2nd edition


Cast forming in final impression Wax boxing method

Dental plaster and pumice boxing method

Caulking compound and paddle boxing method

Wax boxing methodEffective for zinc oxide paste impressionBeading Grip wax, Orthodontic tray wax, and

utility wax are used for beading an impression


2nd edition

Procedure Place the impression such that ridge

portion is parallel to the bench top Fill the tongue space with wax and seal it

3-4mm below the border Adapt 4mm wide beading wax 3-4mm

below the border


2nd edition

Warm boxing wax until flexible Seal the ends to the underlying layer of

wax Check the boxing for adequate width,

height, border and sealing Check for leaks Pour the impression


2nd edition

Problem Cause SOLUTION

1. Borders of cast too narrow or wide

Beading wax too narrow or wide

Make beading wax approximately 3- 4mm wide.

2. Border of cast not high enough to preserve thickness of impression flange

Beading wax placed too high

Adapt beading wax 3 – 4mm below border of impression.

3. Border of cast too high Beading wax placed too lowPlace beading wax 3 – 4mm below border of impression.

4. Base of cast too thin Boxing strip not extended too high

Extend boxing strip 13mm above highest area of impression.

5. Base of cast too thick Boxing strip extended too high

Keep boxing strip approximately 13mm above impression.

Dental plaster and pumice boxing Excellent for rubber based silicones


2nd edition


Procedure Mix a 1:1 mix of dental

plaster and pumice Place a patty of it on a

glass slab Settle the impression

into the patty till 3-4mm below border

Remove excess material Border is 4mm wide Adapt boxing wax

( height – 13mm above the highest point on the impression


Paint plaster surface with separating medium

Check for leaks Pour the impression with stone After setting place in warm water Adjust the dimension on a cast trimmer



1. Border of cast too high or low

Plaster of paris and pumice not trimmed to proper level

Trim it until 3 – 4mm below border of impression

2. Borders of cast too narrow or wide

Plaster of paris and pumice border of wrong width

Make border 4mm wide

3. Cast unable to be separated

Separating medium not applied Apply separating medium

4. Base of cast too high on one side and low on another

Impression not oriented properly before boxing

Place the impression parallel to bench top

5. Base of cast too thick or too thin

Height of boxing strip wrong

Place boxing strip 13mm above highest point on impression


Caulking compound and paddle boxing method The impression is boxed on a paddle

and wax and caulking compound is used for beading

The beading should be 4-5mm wide Fold a metal boxing strip around the

impression Secure with rubber band


Procedure Strips of caulking compound rope to bead

impressions (3-4mm below border) The beading should be 4-5mm wide Fold a metal boxing strip around the

impression (13mm above highest point on impression)

Secure with rubber band Seal the caulking compound to the boxing

strip Pour the impression with stone



1. Borders of cast too high / low

Beading placed at wrong level

Place it 3 – 4mm below border of impression

2. Borders of cast too narrow / wide

Beading too narrow / wide. Cast over trimmed

Beading approximately 4mm wideExercise care when trimming

3. Base of cast too thick / thin Boxing wax at wrong height Place it 13mm above

border of impression

Pre-requisits of a Die Void free Distortion free Trimmed to ensure access for carving

wax pattern margins Reproduce tooth exactly Remaining unprepared tooth structure

should be 0.5 – 1mm visible

Rosenteil, contemporary fixed prosthodontics, 3rd edition


Material sciences

Dimensional accuracyResistance to abrasion

Both these criteria are achieved by GYPSUM

Rudd an Morrow, dental laboratory procedures – Fixed Partial dentures (volume II), 2nd edition

Gypsum (CaSO4.2H2O) Available in 5 forms : type I – V When subjected to a temperature of

110C – 120C, water of crystallisation is driven out and produces CaSO4.1/2H2O

CALCINATION

Differences between various types of gypsum are attributed to Calcination

•Beta form(Plaster)•Irregularly shaped and extremely porous crystals

Calcination in open kettle

•Alpha form (type I stone – Hydrocal)•Dense non-porous crystals, regularly shaped and cuboidal

Under steam pressure in autoclave

•Alpha form(Type II stone – Densite)•Crystals are dense and larger than in type I

Boiling in 3-% solution of

calcium chloride

Rudd an Morrow, dental laboratory procedures – Fixed Partial dentures

(volume II), 2nd edition

Physical properties of Dental stone

Setting expansion

Setting time

Compressive strength



Setting expansion of dental stone Linear expansion occurs during conversion

from hemihydrate to dihydrate due to the outward thrust of needle-like crystals

Expansion ranges from 0.06% - 0.5% Can be controlled by:

Smaller w/p ratio Longer mixing time Hygroscopic expansion Accelerators and retarders



Setting time of dental stone Manufacturers

Accelerator: 2% K2SO4 - decreases

Retarders : 2% Borax - increases

Powdered CaSO4.2H20 mixed with hemihydrate - increases

Operators Increase amount

of water - increases

Longer and faster mixing time - decreases

Exposure to high humidity - decreasesRudd an Morrow, dental laboratory procedures – Fixed Partial dentures


Compressive strength of dental stone Inversely proportional to the water powder

ratio Presence of accelerators and retarders

decrease compressive strength Increasing spatulation time increases

strength Compressive strength of:

Dental plaster : 1800 p.s.i Type I stone (hydrocal) : 4500 p.s.i Type II stone (Densite) : 5500 p.s.iRudd an Morrow, dental laboratory

procedures – Fixed Partial dentures (volume II), 2nd edition

Strength

Wet strength Dry strength

Gypsum product has excessWater than that required for the hydration of the hemihydrate

Excess water present in the Gypsum Product is driven off

• Dry strength is usually twice that of the wet strength• Accelerators and retarders decrease compressive strength• Increasing spatulation time increases compressive strength



Alternative die and cast material Resins

Electroplated die

Flexible die materials

Rosensteil, Contemporary fixed prosthodontics,#rd edition

Resins (Epoxy resin) Advantages

Overcomes low strength and abrasion of stone

Cures at room temperature without expensive equipment

Dimensionally stable Abrasion resistant

Disadvantages More expensive

than gypsum Undergoes

shrinkage Some impression

materials are not compatible with resin

Rosensteil, Contemporary fixed prosthodontics,3rd edition

Electroplated dies Deposition of a coat of pure copper or silver on

the impression Insert cathode wire in the border of the

impression in the metallised area Fill the preparations with electrolytic material Completely submerge the impression into the

plating solution Plate for initially 5mA per tooth for 1 hr. re-

submerge and plate for12hrs at 10mA Wash and dry, and use dental stone for the

construction of working castsRudd and Morrow, dental laboratory

procedures –volume II, 2nd edition

Advantages Overcome poor

abrasion resistance of gypsum

When done properly, it can be as accurate as a stone die

Disadvantages Distortion

commonly occurs Time consuming Time required to for

a film is enough for the development of dimensional changes

All impression materials are not suitable due to low surface energies


Flexible die material It is similar to heavy bodies silicone or

poly ether impression Selection of compatible impression and

die material is very important to achieve good surface details

It is more rapid setting Easy to remove


Die systems Working cast with removable die

Straight dowel pin Curved dowel pin Pindex system Di-lok tray

Working cast with separate die DVA model system Zeiser model system

Shillingburg, Fundamentals of fixedproshodontics, 3rd edition

Working cast with removable die Dies that can be removed from the

working cast Convenient to use It should satisfy the following

requirements Must return to their exact positions Must remain stable even if inverted Should be easy to mount on an articulator


Straight dowel pin

The brass dowel pin is one of the most accurate dowel types

It resists horizontal displacement and vertical deviation


Procedure Dowel is positioned over each

prepared tooth Place it between the arms of

a bobby pin Push a straight pin between

the arms of the bobby pin and into the impression

Pin should be placed parallel to the long axis of the prepared tooth

Pour die stone into the impression covering the knurled end of the dowel

Paperclips can be used to add retention to the base Shillingburg, Fundamentals of

fixedproshodontics, 3rd edition

Once the stone has set, remove the straight pins from the impression

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

Cut a V-shaped bucco-lingual orientation groove or a round dimple on each die to aid in reseating the die completely

Lubricate around each dowel with separating medium for easy separation from working cast

Pour the base leaving peaks and curls to facilitate retention for the mounting


Once the stone is dry, use a saw with a thin blade to cut through the layer of die stone on the mesial and distal sides of he prepared tooth

The cuts should taper towards each other from occlusal to gingival

Trim the die with no.25 blade and mark the finish line with a red pencil


Curved pin dowel Procedure

To install pins before pouring the impression, use finger pressure to insert a curved dowel, tip first into an opening in the positioning bar

The dowel extends 1-2mm into the impression of the prepared tooth, and the tail points facially


Insert a straight pin into one of the three holes in the facial aspect of the bar onto the impression

It should not touch the impression and should be approx. parallel to the long axis of the tooth.

Vibrate a mix of die stone into the impression until it covers the heads of the dowels and 1-2mm of the thicker hexagonal bodies.

After the stone has hardened, extract the straight pins and side the position bar off each dowel


Cut a 2mm deep hole on either side of the dowel with an acrylic bur

Paint the stone and the exposed parts of the dowel with petrolatum.

Box the impression with wax allowing the tails to extend slightly.

Fill the boxed impression with yellow stone


Remove boxing wax and make vertical saw cuts on either side of each die

Separate each segment from the working cast by tapping on the exposed end with a knife handle


To place the dowels after the cast has been made: Pour the impression with die

stone to form a horse shoe shaped working cast

Trim the bottom to a height of 10mm from the necks of the teeth

Drill a 5mm deep hole on the bottom of the cast directly under the centre of each prepared tooth.( with a 2mm bur)

Clean the hole with a drill if necessary

Cement the dowels into the holes one at a time placing a drop of cyanoacrylate cement into each (tails of the dowel point facially) Shillingburg, Fundamentals of


Brush a thin layer of petrolatum on the flat surface of the cast

Box the cast, pour the base, and separate the dies


Pindex system


Procedure Pour the impression, adding

approximately 20mm of stone. Wet the cast prior to trimming Use a model trimmer to flatten the heels

of the cast It should sit perfectly flat on a tabletop,

and its thickness must be a minimum of 15mm.



Trim the periphery of the cast 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.

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 around the cast. Base is poured with the die stone.


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

Saw cuts are pre-marked 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.

Procedure 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. Shillingburg, Fundamentals of


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.


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

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.

use finger pressure to break the die and attached teeth from the cast. Shillingburg, Fundamentals of


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

Then cast and dies are reassembled in the tray.

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 casts with separate die ADVANTAGES

Simple Slightly more

accurate. Minimum

trimming.

DISADVANTAGES Difficult 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.

Rosensteil, Contemporary prosthodontics, #rd edition

Procedure 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 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 40mm


DVA system

Trimmed figure on alignment fixture

Marking dowel pin locations on a clear plate


Drilling holes for dowel pins as marked

Inserting dowels in the base plate

Impression Is poured, stone is placedAround the dowel pins and the alignmentFixture is placed over the poured impression


Drilling holes for dowel pins as markedDrilling holes for dowel pins as markedDrilling holes for dowel pins as marked


Cast is removed

Cast is trimmed

Cast is sectioned using a thinblade saw

Trimmed working cast using the DVA model system


Zeiser model system

The Zeiser model system

The impression is leveled, blocked out’With silicone putty and positioned overThe base plate


The pin locations are determined

Pinholes drilled in place


Pins are inserted into the base

Impression is poured

Base inverted into the stone


Cast is separated from the impression when set


Precision saw aids in sectioning

The sectioned cast


Summary

Accurate working casts and dies are essential to successful restorations. There are various techniques and materials that provide an extremely precise reproduction of the prepared tooth. The die of the prepared tooth can be made removable by the use of dowels or other more convenient system. Alternatively, a solid working cast and separate die can be used. Whatever system is chosen, it must articulate precisely with an accurately made opposing cast

Bibliography Rudd and Morrow, dental laboratory

procedures – Volume I, 2nd edition Rudd and Morrow, Dental laboratory

procedures – volume II, 2nd edition Rosenteil, Contemporary fixed

Prosthodontics, 3rd edition Shillingburg, fundamentals of fixed

prosthodontics, 3rd edition Philips Glossary of prosthodontic terms

Thank You!

casts, dies and cast forming

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