INLAY CAVITY PREPARATION seminaar.pptx

INLAY
PRESENTED BY:
Dr.Neha Dubey
MDS 2ND YEAR
1
GUIDED BY:
DR. RAHUL MARIA
Professor and HOD

CONTENTS
 Introduction
 Definitions
 Indications
 Contraindications
 Advantages
 Disadvantages
 Material for cast
restorations
• General shape
• Location of margins
• Bevels
• Flare
•Internal anatomy
• Variations in proximal
margin design
•Impression technique
1- Direct technique
2- Indirect technique
•Sprue
•Reservoir
Charbeneau page no 351-359
2

INTRODUCTION
 For restoration of extensively damaged teeth with vital pulp so as
to restore remaining tooth structure, cast gold inlays or onlays
are a good option.
 Cast gold restoration has a long history of success as they are
strong, inert and reproduce precise details.
Summit 4th edition
3

 The cast metal restorations are versatile and the procedure requires meticulous
care in preparation and laboratory procedures.
 Dr. Phil Brook in 1897, was the first to introduce Inlay in dentistry who gave the
concept of forming an investment around a wax pattern, eliminating the wax and
filling the created mold with a gold alloy.
 In 1907 Taggart changed the practice of restorative dentistry by introducing his
technique of cast gold dental restorations.
4

DEFINITIONS
 GPT 9- A ﬁxed intracoronal restoration; a dental restoration made outside of a
tooth to correspond to the form of the prepared cavity, which is then luted into the
tooth.
 Summit 4th ed -Inlays are entirely intracoronal restorations, most commonly with
occlusal and proximal extensions .
 Mosby’s Dental Dictionary- A restoration of metal, fired porcelain, or plastic
made to fit a tapered cavity preparation & fastened to or luted into it with a
cementing medium
 Sturdevant’s 4th ed- An inlay may cap none, or may cap all but one cusp.
5

 William HO McGhee - An inlay may be defined as a restoration which has been
constructed out of mouth from gold, porcelain, or other material & then cemented
into the prepared cavity of a tooth.
 Shillingburg - Inlays may be used as single-tooth restorations for proximo-
occlusal or gingival lesions with minimal to moderate extensions.
 Sturdevant 7th ed- Class II inlay involves the occlusal and proximal surfaces of a
posterior tooth and may cap one or more, but not all of the cusps.
6

FACTORS AFFECTING THE DESIGN OF THE CAVITY
 Length of clinical crown.
 Anatomic contours of the occlusal, proximal,
buccal and lingual surface.
 The position of tooth in arch.
 The occlusal and proximal relations.
 Unusual esthetic conditions, if any.
 The condition of soft tissues around the tooth.
 The extend and location of carious lesion.
7
Pulp
chamber

8
 Box preparation and flat floor.
 Parallelism: internal walls must be almost parallel
 Dovetails : occlusal dovetails aid in retention
 Surface area- frictional retention
 Masticatory loads directed to seat the restoration.

INDICATIONS
Charbeneau page no 351-359 9

A cavity’s width does not exceed one-third the
intercuspal distance.
Strong, self-resistant cusps remain.
Patients with low caries index.
Marzouk MA, Simonton AL, Gross RD. Operative Dentistry- Modern Theory & Practice, 1st Edition. Page no -323
10

Restorative procedure – does not change
the occlusion or occluding surfaces.
For restorations of large abraded surfaces.
Tooth – not to be used as an abutment
for fixed or removable prosthesis.
11

Restoration for endodontically treated
teeth..
Retainers for fixed prosthesis.
Correction of occlusion
12

Low incidence of plaque accumulation
Cracked teeth (vertically, horizontally
or diagonally).
Partially subgingival restorations
Marzouk MA, Simonton AL, Gross RD. Operative Dentistry- Modern Theory & Practice, 1st Edition.page no 323
13

CONTRAINDICATIONS
High Caries Rate Young Patients
Studevant’s Art and science of operative dentistry – 7th edition page no 309
14

Esthetics Small Restorations
Studevant’s Art and science of operative dentistry – 7th edition page no 309
15

Developing and
deciduous teeth Occlusal disharmony
Dissimilar metals
Marzouk MA, Simonton AL, Gross RD. Operative Dentistry- Modern Theory & Practice, 1st Edition.
16

ADVANTAGES
Control of Contours
and Contacts Strength
Biocompatibility Low Wear
Studevant’s Art and science of operative dentistry – 7th edition
17

Can be finished
and polished
outside the oral
cavity
Not affected by
tarnish and
corrosion process.
Imparts resistance
to tooth

Number of
Appointments
and
Higher Chair
Time Temporary
Restorations
Cost
Technique
Sensitivity
Splitting
Forces
DISADVANTAGES
Studevant’s Art and science of operative dentistry – 7th edition19

MATERIAL FOR CAST RESTORATION
 ADA Specification - Requires a minimum total gold plus-platinum-
metals content of 75 weight percent (wt%).
 Acc to Sturdevant
(1) Traditional high-gold alloys,
(2) Low-gold alloys,
(3) Palladium–silver alloys, and
(4) Base metal alloy
20

 Acc. to Marzouk
1) Class I – Gold and Platinum based alloys
2) Class II- low gold alloys <50%
3) Class III- non Gold, Palladium based alloys
4) Class IV- Nickel-Chromium based alloys
5) Class V – Castable and moldable ceramics
21

Preparation
path
Apico-occlusal
taper of a
preparation
Circumferential
tie
Basic designs of cast metal restoration
Flares
Bevels

Preparation path
Preparation should have single insertion path
opposite to the occlusal load and parallel to the
long axis of tooth. This helps in retention of
the restoration.

Apico-occlusal taper of a preparation
To have unhindered removal and placement of the wax
pattern and seating of the final casting, intracoronal and
extracoronal tooth preparation should have some taper.
Ideally, an intracoronal tooth preparation should have
slight diverging walls from gingival to occlusal surface. This
is the concept of taper.

The optimal taper lie in
the range of 2° to 5° per
wall.
 A 2° to 5° of taper provides
optimal retention for inlay.
MAXIMUM- 10°

Degree of taper
3 – 12o (Ward, 1926)
6o (Shillingburg et al, 1974)
10 – 14o (Tylman, Malone 1978)
3 - 5o (Dykema et al 1986)
Ideal convergence angle - 2 – 10o
Clinically acceptable convergence angle - 10 – 20o (Goodacre et
al 2001)

Giving more than
required taper in
preparation walls
results in reduced
retention of inlay.

Uneven taper of
preparation walls will
result in failure of inlay.

When to
increase or
decrease the
taper?

Circumferential Tie
Circumferential tie refers to the design of
cavosurface margin of an inlay tooth
preparation.
For the success of restoration, the margins of
restoration should be designed so as to achieve its
maximum adaptation to tooth structure.
32

What is the
weakest
portion of an
inlay and how
can we modify
it?

Cavosurface margins of an inlay preparation
can be of two types:
1. Bevels
2. Flares.
34

Bevels
Bevels are the “ flexible
extensions” of a cavity
preparation, allowing the
inclusion of surface defects,
supplementary grooves, or other
areas on the tooth surface.
- MARZOUK
35

Functions of bevels
• Weak enamel is removed
• Beveling produce obtuse angled
tooth margins (140 – 150 degrees)
and acute angled metal margins
(35°-45°).
• Increases retention, resistance,
aesthetics and color matching for
composite resin restoration.

• Improves junctional
relationship between the
restorative material and tooth.
• Bevels are the flexible
extensions, i.e. they allow
inclusion of faults, wear facets,
etc. without overextending the
preparation margins.
Because of beveling, the
gingival margin has a lap
sliding fit which provides
better fit at this region

Figure showing an equal bevel of 40
degree given on both the wall
Mesial bevel directed
correctly to result in
40 degree marginal
metal.
Unbeveled mesial margin
is incorrect because it
results both in weak
enamel margin and
unburnished marginal
metal.

Failing to bevel gingival
margin resulting in
undermined rods and
difficulty in burnishing.
Butt joint (90) with metal
margin.
Sliding lap joint with metal
margin.
Properly directed
gingival bevel resulting
in 30 degree marginal
metal.

FLARES
Flares are concave or flat peripheral portions of the facial
or lingual proximal walls. They are of two types:
PRIMARY
SECONDARY

PRIMARY FLARE
• It is the conventional &
basic part of
circumferential tie
Facially & lingually.
• Similar to long bevel, 45°
to the inner dentinal wall
proper

Functions & Indications
• Bring the facial & lingual margins to cleansable
– finishable areas.
• Indicated for any facial or lingual proximal wall
of cavity preparation.

• It is a flat plane superimposed
peripherally to the primary
flare.
• It may have different
angulations, involvement and
extent depending upon
requirement.
• Secondary flare is not given in
the areas where esthetics is
more important.
SECONDARY FLARE

Indications of secondary flares:
• When broad contact area is present.
• To include the faults present on facial and lingual
walls beyond primary flare.
• To include the undercuts present at cervical aspect of
facial and lingual walls in ovoid teeth.
• When caries is widely extended in buccolingual
direction.

Advantages
• Secondary flare ensures cavo-surface margins to
extend into embrasures (self-cleansing area).
• Permits easy burnishing and finishing of the
restoration.
• Produces more obtuse angled and stronger cavo-
surface margin.

Reverse Secondary Flare
These are extension of secondary flare.
Reverse secondary flare
upon secondary flare
Reverse secondary
flare upon primary
flare

Indications
• To include facial or lingual defects beyond the axial angle of tooth.
• To eradicate severe peripheral marginal undercuts which have not
been removed by maximum angulations & extent of secondary flare.
• Needed to add to the retention capability of restoration proximally.

• Fulfill objective of secondary flare in extremely wide
cavities or contact areas.
• For encompassing an axial angle for reinforcing and
supporting reasons.

TOOTH PREPARATION FOR
CLASS II CAST METAL
INLAY

A, Proposed outline form for disto-occlusal preparation.
B, Dimensions and configuration of No. 271, No. 169L, and No. 8862 instruments.
C, Conventional 4-degree divergence from line of draw (line xy).

• The cutting instruments used to develop the vertical walls are oriented to a
single "draw" path, usually the long axis of the tooth crown, so that the
completed preparation will have draft (no undercuts).
• The gingival-to-occlusal divergence of these preparation walls may range
from 2 to 5 degrees per wall from the line of draw.
• If the vertical walls are unusually short, a maximum of 2 degrees occlusal
divergence is desirable to increase retention potential.
• As the occlusogingival height increases, the occlusal
divergence should increase because lengthy preparations
with minimal divergence (more parallel) may present
difficulties during pattern withdrawal, trial seating and
withdrawal of the casting, and cementing.

A and B, Bur after punch cut to a depth of 1.5 mm.
C, For maxillary posterior teeth, the long axis of the bur should parallel the long axis of the
tooth crown (line yz).
D, For molar and second premolar teeth of mandibular dentition, the long axis of the bur
should tilt slightly lingually to parallel the long axis of the tooth crown (line wx).
Occlusal Step
• With the No. 271 carbide bur held parallel to the long axis of the tooth
crown, enter the fossa/pit closest to the involved marginal ridge, using a
punch cut to a depth of 1.5 mm to establish the depth of the pulpal wall.
• In initial preparation do not exceed this specified depth, regardless of
whether the bur end is in dentin, caries, old restorative material, or air.

• A general rule is to maintain the long axis of the bur
parallel to the long axis of the tooth crown at all times.
• For mandibular molars and second premolars whose
crowns tilt slightly lingually, this rule dictates that the bur
should tilt slightly (5 to 10 degrees) lingually to conserve
the strength of the lingual cusps.

E and F, Extending the mesial wall, taking care to conserve dentin that
supports marginal ridge (s).
G, The marginal bevel can provide additional extension.
H, Improper extension that has weakened the marginal ridge.

•Maintaining the 1.5-mm initial depth and the same bur orientation,
extend the preparation outline mesially along the central groove/fissure
to include the mesial fossa/pit.
• The facial and lingual extension in the mesial pit region should provide
the desired dovetail retention form, which resists distal displacement of
the inlay.
• Continuing at the initial depth, extend the occlusal step distally into
the distal marginal ridge sufficiently to expose the junction of the
proximal enamel and the dentin.

• While extending distally, progressively widen the preparation
to the desired faciolingual width in anticipation for the
proximal box preparation.
• The increased faciolingual width enables the facial and
lingual walls of the box to project (visually) perpendicularly to
the proximal surface at positions that will clear the adjacent
tooth by 0.2 to 0.5 mm.

Proximal Box
• Continuing with the No. 271 carbide bur, isolate the distal enamel by cutting
a proximal ditch.
• The Mesio-distal width of the ditch should be 0.8 mm (the tip diameter of
the bur) and prepared approximately two thirds (0.5 mm) at the expense of
dentin and one third (0.3 mm) at the expense of enamel.

A, After exposing the junction (j) of proximal enamel and dentin.
B, Sectional drawing of A.
C, Cutting the proximal ditch.
D, Sectional drawing of C.
• While penetrating gingivally, extend the proximal ditch
facially and lingually beyond the caries to the desired position
of the facioaxial and linguoaxial line angles.
• Ideal extension gingivally will eliminate caries on the gingival
floor and provide 0.5-mm clearance of the unbeveled gingival
margin with the adjacent tooth.

E, Proximal view of D.
F, Occlusal view of the proximal ditch with proposed ideal
clearance with the adjacent tooth.

• Guard against overcutting the facial, lingual, and gingival walls, which
would not conserve tooth structure and could result in:
(1) overextension of the margins in the completed preparation,
(2) a weakened tooth, and
(3) possible injury of the soft tissue.

• The axial wall should follow the contour of the tooth
faciolingually.
• Any carious dentin on the axial wall should not be removed at
this stage of preparation.
• Then with the No. 271 carbide bur, make two cuts, one at the
facial limit of the proximal ditch and the other at the lingual
limit, extending from the ditch perpendicularly toward the
enamel surface (in the direction of the enamel rods).

• Extend these cuts until the bur is nearly through the marginal ridge
enamel (the side of the bur may emerge slightly through the surface at
the level of the gingival floor).
• At this time, however, the remaining wall of enamel often breaks away
during cutting, especially when high speeds are employed. If the
isolated wall of enamel is still present, it can be fractured out with a
spoon excavator.

H, Proximal ditch extended distally. x, penetration of enamel by side
of bur at its gingival end.
I, Breaking away isolated enamel.

• Planing the distofacial, distolingual, and gingival walls by hand
instruments to remove all undermined enamel may be indicated.
• When proximal caries is minimal, ideal facial and lingual extension at
this step in the preparation results in margins that clear the adjacent
tooth by 0.2 to 0.5 mm.
• Shallow (0.3 mm deep) retention grooves may be cut in the facioaxial
and linguoaxial line-angles with the No. 169L carbide bur. These grooves
are indicated especially when the prepared tooth is short.

A–D, Using modified palm-and-thumb grasp
(A) to plane distofacial and distolingual walls
(B and D) and to scrape gingival wall (C).
E, Before cutting retention grooves.
F, Cutting retention grooves.

Moderately deep caries.
A–C, Extending the proximal ditch gingivally (B) to a sound floor free from
caries (C).
D, Remaining caries on the axial wall.
E, Section of C in plane yy

• Light-cured glass-ionomer cement may be mixed and applied with a suitable
applicator to these shallow (or moderately deep) excavated regions to the
depth and form of the ideally prepared surface.
• If removal of soft, infected dentin leads directly to a pulpal exposure
(carious pulpal exposure), then root canal treatment should be accomplished
before completing the cast metal restoration.
• If the pulp is inadvertently exposed as a result of operator error or
misjudgment (mechanical pulpal exposure), then it must be decided whether
to proceed with root canal treatment or attempt a direct pulp capping.

F, Removing the remaining infected dentin. c, inserted retraction cord.
G, Section of F.
H, Inserting glass ionomer base with periodontal probe.
I, Completed base.

Remaining old restorative material on the internal walls should be
removed if any of the following conditions are present:
(1) the old material is judged to be thin and or non-retentive,
(2) there is radiographic evidence of caries under the old material.
(3) the pulp was symptomatic preoperatively. Or
(4) the periphery of the remaining restorative material is not intact,

D–F, Diamond instrument preparing lingual secondary
flare. Large arrow in F indicates the direction of the
translation.
Preparation of Bevels and Flares

Properly directed gingival bevel resulting in 30-degree marginal metal.
Failure to bevel the gingival margin results in a weak margin formed by undermined rods
(note the easily displaced wedge of enamel) and 110-degree marginal metal, an angular
design unsuitable for burnishing.
Lap, sliding fit of prescribed bevel metal decreases the 50-µm error of seating to 20 µm.
A 50-µm error of seating produces an equal cement line of 50 µm along the unbeveled
gingival margin.

Occlusal marginal metal is approximately 40 degrees in cross-section, making the enamel angle 140
degrees.

• Using the flame-shaped diamond instrument, rotating at high speed,
prepare the lingual secondary flare.
• Approach from the lingual embrasure, moving the instrument Mesio-
facially.
• Bevel the gingival margin by moving the instrument facially along the
gingival margin.

D–F, Diamond instrument preparing lingual secondary
flare. Large arrow in F indicates the direction of the
translation.

PRIMARY Retention features
 Primary Retention forms:
 Box preparation and flat floor.
 Parallelism: internal walls must be almost parallel
 Dovetails : occlusal dovetails aid in retention
 Surface area- frictional retention
 Masticatory loads directed to seat the restoration.

SECONDARY RETENTION FEATURES
Additional Retention and Resistance forms include:

Retention Grooves
• Located completely in dentin.
• Can be located at the mesial
& distal wall/the gingival floor
of the facial or lingual portion
of a cavity preparation.

• Prevent the lateral displacement the of restoration.
• Grooves are prepared using a tapered fissure bur (168 or 699).
• They should not exceed 2mm in depth and should be at the
expense of the side of walls or axial surfaces of the preparation.

INTERNAL BOX
Internal boxes are indicated in
shallow cavities and short teeth
preparations when occlusal dovetail
cant be prepared because of cavity
involvement of occlusal surface.

• Are prepared using a 168 or 699 bur to a dimension
compatible with the size of the restoration.
• Should have a minimum size of 2mm in three
dimensions.
• Has high locking power- it is advisable to place internal
boxes at the very peripheries of the cavity preparation.
• If placed in the middle- uneven immobilization of the
casting with ends less resistant than the middle part.

Slots
• Slot is preferred over preparing a
box in the distal surface because
(1) the former is more conserving
of the tooth structure and of the
strength of the tooth crown, and
(2) the linear extent of marginal
outline is less.
• Slot should have a 2 to 3 mm
depth

• Use a No. 169L carbide bur with its long axis parallel to the line of draw
(this must be reasonably close to a line parallel with the long axis of the
tooth).
• The slot is cut in dentin so that it would pass midway between the pulp
and the DEJ if it were to be extended gingivally.
• The position and direction of the slot thus avert
(1) the exposure of the pulp,
(2) the removal of the dentin supporting the distal enamel, and
(3) the perforation of the distal surface of the tooth at the gingival
termination of the slot.

The slot should have the following approximate dimensions:
(1) the width (diameter) of the bur mesiodistally;
(2) 2 mm faciolingually; and
(3) a depth of 2 mm gingival of the normally positioned pulpal wall.

Collar preparation
•A facial or lingual “collar” or both may
be prepared increase the retention and
resistance when preparing a weakened
tooth for a mesioocclusodistal onlay to
cap all cusps.
•They help in retention of shortened
teeth.

Collar preparations are of two types:
• Cuspal Collar: involves the facial & lingual
surfaces of one cusp only in multi-cusped tooth.
• Tooth Collar: involves entire facial and lingual
surface of the tooth.

• Skirts are thin extensions of the facial
or lingual proximal margins of the cast
metal onlay that extend from the
primary flare to a termination just past
the transitional line angle of the tooth.
• They are a conservative method of
improving the retention and resistance
forms of the preparation.
• Usually, are prepared entirely in
enamel.
Skirt preparation

Modifications of Inlay cavity preparation
SLICE PREPARATION
MODIFIED FLARE
BOX
PREPARATION
AUXILLARY
SLICE

• The box design is principally used with the proximo-occlusal preparation
for the direct method of wax pattern formation.
• A cervical bevel is required in the proximo – occlusal cavity for ease of
wax manipulation in mouth.
• The bevel is placed most often with hand instruments, thus forming lap
joint for the bulk of wax suitable for direct carving.
Box Preparation

Slice preparation
A slice refers to the placement
of extracoronal taper using a
disk of adequate diameter to
contact nearly the entire
proximal surface.

• Involves conservative disking of the proximal surface
to establish the buccal & lingual extent of the finish
lines.
• Teeth with proximal contours of the square tooth form
- extends to the cervical floor.
• Assures a sound enamel margin & also yields a casting
margin that is adapted & finished with relative ease

• Wraps partially around the
proximal line angles, thus
providing additional tooth
support.
• Minimal bulk of tissue is lost,
yet resistance form is greatly
enhanced, reducing the
possibility of tooth fracture.
Auxiliary Slice
Auxiliary slice around the lingual proximal line
angle of a tooth, for example, will aid in
preventing a buccal displacement of the casting.

Modified flare Preparation
Hybrid between the
box & slice
preparations.

• Buccal & lingual proximal walls are initially formed with
minimal extension, then disked in a plane that only slightly
reduces the proximal wall dimension.
• Extensive disking will reduce the retesion of these walls.
• The obtuseness of the cavosurface angle is enhanced.

IMPRESSION TECHNIQUES
Impression
technique
Direct
technique
Open method-
with matrix
band
Closed
method-
without matrix
Indirect
technique
Anusavice, Shen, Rawls. Phillips’ Science of Dental Materials, 11th Edition
Types
1. Type I – medium wax – direct technique
2. Type II – soft wax – indirect technique

PKT instruments
 No. 1 and no. 2 are wax addition instruments
 No. 3 is a burnisher for refining occlusal anatomy
 Nos. 4 and 5 are wax carvers.

Tissue
compatible
lubricant is
placed in the
internal surface
of the prepared
tooth and
adjacent tooth
Piece of wax is
placed is flamed
to achieve
hanging drop
and band is
immediately
place on tooth
and pushed 2-
3mm cervically
Whenever
subsequent
layers of wax are
added the
previous layer
which was
applied should
be remelted or
folds would form
on fitting surface
Adequate bulk
should be
provided at
proximal and axial
surface in order to
prevent distortion
while removal
Principles and practice of operative dentistry – Gearld T.
Charbeneau – 3rd edition
Anusavice, Shen, Rawls. Phillips’ Science of Dental
Materials, 11th Edition

The pattern is again seated in the
cavity. A heated instrument is held
lightly against the copper staple,
thus facilitating its removal
Pattern is then carved. Prepared tooth &
opposing tooth is isolated and dried with
cotton rolls. With camel hair brush,
talcum powder is dusted on the occlusal
surface of the wax and the patient is
instructed to close the teeth lightly
Cuspal contact with the wax pattern is
indicated by a shiny burnished spot on
the pattern. The spots of hyperocclusion
are carved away using warm carvers Textbook of operative dentistry –Vimal K
Sikiri - 4nd edition 267
Principles and practice of operative dentistry –
Gearld T. Charbeneau – 3rd edition

ADVANTAGE
• Proper margin seal in
gingival area
• Good isolation
• Make a proper contour
in proximal surface
DISADVANTAGE
• Great skill & patience is
required
• Greater tendency for wax
pattern to get distorted.
• Indirect vision is required.
• Discrepancies at the gingival
margin is difficult to detect
• If the casting fails patient has to
be recalled

Indirect patterns:
• The wax should be allowed to cool
thoroughly before the pattern is
removed from the die.
• A constant light grip is maintained
on the pattern by the thumb and
forefinger of one hand while
pressure is applied against them
with the thumb and forefinger of the
other hand, which also holds the
die
Disadvantages
• The model may not be the exact
replica of the tooth.
• Time consuming procedure.

Types of Sprue
• According to material used:
• Wax sprue former (for large restorations E.g.. RPD
frameworks)
• Plastic/Resin sprue former (smaller restorations)
• Metal sprue ( smaller restorations E.g.. Crown)
• According to process:
• Prefabricated
• Custom made
• According to shape:
• Solid
• Hollow (Round)
• According to the diameter of teeth:
• For molars: 2.5mm (10-gauge)
• For anteriors and pre-molars: 2.0mm (12-gauge)
10
3

Materials Used In Sprue
10
4
• Special wax supplied as rope form (rolls) of different diameters (gauges) for
selection.
• Hollow stainless steel wires of different diameters and lengths.
• These are to be coated with thin layer of inlay wax by dipping in molten wax.
• This is done for easy removal of sprue former after setting of investment.
Anusavice (phillips) 11th edition page no 321
104

Length & Diameter of The Sprue
10
5
• The length of the sprue former should be adjusted so that the pattern is
approximately 6 mm from the open end of the ring.
• The sprue former should be atleast 1.7mm in diameter unless the pattern is
extremely small.
• Sprue formers upto 2.5mm in diameter is used for very large patterns and
bulky full crowns.
105

Spruing Principles AndTechnique
• The first step in the production of refractory mould is termed as spruing the pattern, whereby the
wax pattern is attached to conical base by extension of wax, plastic, or metal.
• This connector is known as sprue former, which should be properly selected in respect to size
and configuration.
10
7
107

Location Of Sprue
• Sprue is attached to the bulkiest, non-critical part of the pattern.
• Away from the margins and occlusal contacts.
• Normally it is attached to largest non-functional cusp used.
Wrong
10
8
Correct

Sprue Former Direction
• It is attached at 45 degrees to the walls
of the mould, which decreases the
turbulence of molten alloy.
10
9
109

RESERVOIR
Reservoir is a small amount of
additional wax which is added to the
sprue former near the junction of wax
pattern It prevents localized
shrinkage porosity as the alloy in this
part solidifies last after the
solidification of metal in mold
Philip's 11th edition page no:320
110

• If bulky pontics are placed at the heat center of the
mould without a reservoir, porosity is very likely to
occur in the pontic itself, resulting in a weak bridge.
• Where a dental casting contains both thick and thin
elements, porosity can be minimized by the addition
of chill vents.
• Chill vents accelerate the cooling of the pontic
relative to the parts of the casting external to the
dental unit itself.
Addition of chill vents to bulky dental units may speed
solidification and minimize porosity in the thick pontic
or connector areas.
Venting
11
1

Thin film of cleaner on pattern reduces surface
tension of wax better “wetting” of wax pattern by
the investment.
Some of the commercially available debubblizing
agents can be used.
 The wax pattern should not stand for more than
20-30 min before being invested. So, it is best
to invest the wax pattern as soon as possible

REFERENCES
 Strudevants 4th edition
 Philip's 11th edition
 Marzouk
 Charbeneau 3rd edition
 G.H. Mount
 Mc Ghee 1st edition.
 Shillingburg
 Vimak sikri, textbook of endodontics
114

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