Model and die material

PREPARED BY:
DR.RAHUL PATEL
M.D.S. PART 1

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

INTRODUCTION
Direct 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

REVIEW OF LITERATURE
 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

 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

 Disadvantage
1. 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 hours
3. 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


TO PLACE THE DOWELS AFTER THE
CAST HAS BEEN MADE.
•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.


•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

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

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


•Periphery of the cast should be trimmed.

•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 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.


•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.


•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
 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.


 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 Marking dowel pin locations
alignment fixture. on clear plate

Drilling holes for dowel pins Inserting dowels in the
as marked baseplate

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

Set cast is removed from baseplate

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 Impression is poured
base.

Base is inverted into the
stone

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

Sectioned cast
Precision saw aids
sectioning Rosensteil (2001) Contemporary Fixed Prosthodontics 3rd edition Mosby

BIBLIOGRAPHY
1. Philips (1992) Science of dental materials
11th edition W.B Saunders
2. Rosensteil (2001) Contemporary Fixed
Prosthodontics 3rd edition Mosby
3. 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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