inlay
TRANSCRIPT
CAST INLAY RESTORATION AND WAX PATTERN FABRICATION
Contents:
• Introduction
• History
• Definitions
• Advantages and disadvantages
• Indications and contraindications
• Materials for cast restorations
• Mouth preparation prior to cast restoration
• Principles of cavity/tooth preparation for cast restoration
• Tooth preparation for cast inlay restoration
o Indications
o General shape
o Internal anatomy
• Tooth preparation for class II cast metal inlay o Initial preparation o Final preparation o Preparation of bevels and flares
• Variation in proximal marginal designs
o Box o Slice o Auxiliary slice o Modified flare
• Modifications in inlay tooth preparations
• Preparation of wax pattern o Direct technique o Indirect technique
• Removing the wax pattern • References • Conclusion
INTRODUCTION:
Submitted by: Dr. Anshuman Khaitan Post – graduate student Department of conservative dentistry and endodontics College of Dental sciences, Davanagere
Many of the restorative problems that need solution cannot be resolved using amalgam or
composite resin. A cast restoration is usually the restoration of choice when there is no
support for materials like amalgam, direct filling gold or resin.
The cast metal restoration is extremely versatile and is especially applicable to class II
preparations. The restoration procedure requires meticulous care both in cavity preparation
and in proper manipulation of dental materials.
HISTORY:
Dr. John Murphy (1837) first tried to form cast restorations by platinum foil matrix
technique.
Ames and Swasery (1880) used burnished foil tech for fabrication.
Dr Philbrook (1897) first introduced the technique of investing and casting an inlay,
reported to the IOWA STATE DENTAL SOCIETY.
But it was Dr. Taggart (1907) who permanently changed the practice of restorative
dentistry by introducing pneumatic pressure casting technique and other refinements. He gets
the credit of introducing Lost wax tech for castings and presented to the New York
Odontological group.
He described the inlay as “an honest filling”
DEFINITIONS:
CAST RESTORATIONS: Cast restorations may be defined as intra or extra coronal
restorations which is fabricated outside the mouth and then cemented in the cavity.
(Vimal K. Sikri)
• An inlay is primarily an intra coronal cast restoration that is designed mainly to restore
occlusal and proximal surfaces of posterior teeth without involving the cusps and rarely
the proximal surface anterior teeth.
• Onlay is a combination of intra coronal and extra coronal cast restoration when one or
more cusps are covered.
• Full veneer crown is an extra coronal cast restoration where all cusps are covered.
According To Sturdevant
Inlay
• Class II Inlay involves the occlusal and proximal surface(s) of posterior teeth and
May cap one or more but not all of the cusps.
Onlay
• The class II Onlay involves the proximal surface(s) of a posterior tooth and caps all of
the cusps.
ADVANTAGES:
• Yield strength, compressive strength, tensile strength and shear strength of alloys
used for cast restorations are far greater than those of any materials used intra orally.
• Cast alloys have five times the ultimate strength of amalgam.
• It impart resistance to the tooth rather than depending on tooth structure to provide
resistance form to the restoration.
• Are capable of reproducing precise form and minute detail.
• As the cast inlay contains one or more noble metals, they are not significantly
affecting by tarnish and corrosion process.
• Restorations can be finished and polished outside the oral cavity there by producing
surfaces with maximum biological acceptance.
DISADVANTAGES:
• Being a cemented restoration, several interphases will be created at the tooth cement
casting junction, thus the chances of microleakage is high especially gingivally than
the other parts of the restoration.
• Restorations necessitates extensive tooth involvement in the preparation, which creates
possible hazards for the vital dental tissues.
• The cathode nature of cast dental alloys towards amalgam may lead to galvanic
deterioration of amalgam, if these two restorations are placed adjacent to or opposite
to each other.
• The procedure is lengthy and requiring more than one visit and the procedure is
technique sensitive.
• Much more expensive than other restorative materials.
• Some cast alloys have a very high abrasive resistance caused wear of opposing
natural tooth.
INDICATIONS:
• Extensive tooth involvement; restorations are efficient in replacing lost tooth structure
and also for supporting remaining tooth surface.
• Fractured amalgam restorations.
• Adjunct to periodontal therapy to correct tooth anomalies, which predisposes to
periodontal problems.
• Restoration of endodontically treated teeth.
• Retainers for fixed prosthesis.
• Subgingival lesions: properly finished and polished gold alloys are more compatible
with the periodontium.
• Patients with low incidence of plaque accumulation.
CONTRA INDICATIONS:
• Physiologically, young dentition with large pulp chambers and incompletely
mineralized dentin are contra indications.
• Developing and deciduous teeth
• High plaque / caries indices patient with rampant caries and poor oral hygiene should
not be given cast restoration.
• Should not be used in-patient with severe occlusal interference or other defects in the
stomatognathic system.
• Dissimilar metals: gold-based castings are avoided in patients already having silver
restorations.
MATERIALS FOR CAST RESTORATIONS:
The ADA Sp. #5 requires 75% of gold and platinum group metals to be present in alloys for a
cast restoration.
According to Marzouk:
Class I – Gold and platinum group based alloys.
They are Type I, II, III, IV gold alloys.
a) Type I- Soft, VHN = 50-90
b) Type II- Medium, VHN= 90-120
c) Type III- Hard, VHN= 120-150
d) Type IV- Extra hard, VHN>150
Class II – Low gold with gold content less than 50%. Some may contain as less as 5% gold.
Class III – Non-gold palladium based alloys.
Class IV – Nickel-chromium based alloys.
Class V – Castable, moldable ceramics.
MOUTH PREPARATION PRIOR TO CAST RESTORATION:
1. Control of plaque - Due to the vulnerability of the cast/cement/tooth structure
junction, patients to receive a cast restoration should exhibit the ability and
willingness to adopt plaque control measures.
2. Control of caries - restorative procedures should be employed until the patient
demonstrates the ability to control plaque, and, subsequently, demonstrates little or no
incidence of caries.
3. Control of periodontal problems - It is ideal to start cast restoration fabrication with a
sound periodontium, unless, of course, these restorations are part of the periodontal
therapy and maintenance. In the latter case, the periodontal disease should be under
control.
4. If irreversible pulpal changes are present, then endodontic therapy should be done
prior to cast fabrication
5. Equilibration of occlusion - Prior to preparing teeth for cast restoration, is vitally
important to equilibrate the natural dentition. There must be no interfering or
premature contacts.
6. Full arch study models should be made. They help in the fabrication of both the
temporary and final restoration.
PRINCIPLES OF CAVITY/TOOTH PREPARATION FOR CAST RESTORATION
Unlike amalgam, cast alloys and ceramics can restore teeth via both intra and extra-
coronal preparations.
• Intra-coronal preparations are mortise shaped having definite walls and floors joined
at line angle and point angle.
• Extra coronal preparations are created by occlusal and axial surface reduction, in
many cases ending gingivally with no definite flat floor.
Most single-tooth restorations are combinations of these intra- and extra-coronal types.
The general principles of cavity-tooth preparation may be applied without deviation to cast a
restoration:
1) Outline form
2) Retention form and resistance form
3) Removing carious dentin
4) Convenience form
5) Finishing enamel wall and margin
6) Cleaning and critical appraisal of the cavity.
Besides all the general principles of a cavity and tooth preparation, cast restoration should
have the following features:
1) Preparation path
2) Apico-occlusal taper of the preparation
3) Preparation features of the circumferential tie
4) Mechanical problems and preparation design solutions
1. Preparation path
The preparation will have a single insertion (draw) path, opposite to the direction of
the occlusal loading. This path is usually parallel to the long axis of the tooth. So that the
completed cavity will have draft (no undercut).
2. Apico-occlusal taper of the preparation:
• For maximum retention in a cast restoration, opposing walls and opposing axial surfaces
of a tooth preparation should be perfectly parallel to each other.
• Since exact parallelism can create technical problems, a slight divergence of opposing
axial wall intra-coronally and a slight convergence of opposing axial surfaces extra-
coronally are essential to facilitate cast fabrication with minimum errors.
• This taper should be an average of 2-5° from path of preparation.
• It can be decreased or increased according to the following factors :
1. Length of the preparation wall /axial surface.
Greater the wall – more taper will be necessary although it should not exceed
10°. Less the length, less the taper will be.
2. Dimensions and details of surface involvement and internal anatomy in the
preparations.
The greater the surface involvement is, and more detailed the internal anatomy
is, the greater will be the frictional component between the preparation and the
materials contacting it. To diminish friction, the taper is increased.
3. The need for retention.
The greater the need for retention is, the more will be the need to approach
parallelism (i.e.) less taper.
If anatomical conditions dictate two different types for opposing walls, it is
preferable to create two planes for each involved wall, i.e., inner planes
parallel to each other and outer planes, satisfying the needs compelling the
different tapers. The inner plane assures the single path of insertion of
preparation.
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)
3.Preparation features of the circumferential tie:
The peripheral marginal anatomy of the preparation is called circumferential tie. This
should have the following features advocated by Noy for an ideal cavity wall namely:
1. Enamel must be supported by sound dentin.
2. Enamel rods forming the cavosurface margin should be continuous with sound
dentin.
3. Enamel rods forming the cavosurface margin should be covered with the
restorative material.
4. Angular cavosurface angles should be trimmed.
For the occlusal and gingival walls in intra-coronal cavity preparation, the tooth
circumferential tie will be in the form of a bevel, which is a plane of a cavity wall or
floor directed away from the cavity preparation.
Types and design features of occlusal and gingival bevels:
A. Partial bevel – involves part of enamel wall, not exceeding 2/3rds its
dimension.
B. Short bevel – includes entire enamel wall, but not dentin. This bevel is
used with class I alloys especially for type 1 & 2.
C. Long bevel – includes all enamel and upto ½ of the dentinal wall. Most
frequently used bevel for the first 3 classes of cast material. Its major
advantage is that it preserves the internal ‘boxed-up’ resistance.
D. Full bevel – includes all of the dentinal and enamel walls of the cavity wall
or floor. Its use should be avoided except in cases where it is impossible to
use any other form of bevel.
E. Counter bevel – when capping of cusp is done to protect and support them,
this type of bevel is used, opposite to an axial cavity wall, on the facial or
lingual surface of the tooth.
F. Hollow ground (concave) bevel – All the types of bevels are in the form of
a flat plane, but any of them especially the last three can be prepared in a
concave form. This allows more space for cast material bulk, to improve
materials castability, retention and better resistance to stresses.
Function of Occlusal and Gingival Bevel:
• Bevels are the flexible extensions of a cavity preparation, allowing the inclusion
of surface defects, supplementary grooves, or other areas on the tooth surface.
• Bevels create obtuse angled marginal tooth structure, which is the bulkiest and the
strongest configuration of any marginal tooth anatomy and produce acute angled
marginal cast alloy. This configuration will be most amenable to burnishing for
that alloy.
• Bevels are major retention forms for cast restorations.
• Reduce the error factor to three or more folds at the margins.
• Some bevels like hallow ground and counter bevel, are used for the resistance
form of the tooth-restoration complex, by encompassing cusps.
Types and design feature of facial and lingual flare:
For the facial and lingual proximal walls in intra-coronal cavity preparation for
castings, flares are used, which are the flat or concave peripheral portions of the facial and
lingual walls.
There are 2 types of flares;
- The Primary Flare
- The Secondary Flare
Primary Flare
- Is the conventional and basic part of the circumferential tie facially and lingually
for an intra-coronal preparation.
- It is very similar to a long bevel formed of enamel and part of dentin on the facial
or lingual wall.
- Primary flares also have a special angulation i.e. 45° to the inner dentinal wall
proper.
They bring the facial and lingual margins of the cavity preparation to cleansable
finishable areas. They are indicated for any facial or lingual proximal wall of an intra-
coronal cavity preparation.
Secondary flare:
- It is almost always a flat plane super imposed peripherally over a primary flare.
- It is usually prepared solely in enamel.
- Unlike primary flares, secondary flares may have different angulations,
involvement and extent depending on their function.
Indicated in very widely extended lesions bucco-lingually and in very broad contact areas or
malposed area.
Flare
PRIMARY FLARE SECONDARY FLARE
Conventional and basic part of the Not always used
circumferential tie facially and lingually
Similar to a long bevel on A flat plane superimposed
on facial / lingual proximal walls. peripherally to primary flare.
Formed of enamel and dentin Usually prepared in enamel,
may sometimes contain dentin.
Have a specific angulation ie 45o to - May have different angulat-
the inner dentinal wall proper. ions, involvement and extent.
Function:
Brings the facial and lingual margins of the cavity preparation to cleansable – finishable
areas.
TOOTH PREPARATIONS FOR CAST INLAY RESTORATION:
Definition of Inlay:
The class II inlay involves the occlusal and proximal surfaces of a posterior tooth and
may cap one or more cusps but not all of the cusps.
Indications(Marzouk):
These are purely intracoronal restorations, which have limited indications. These are;
1. A cavity’s width does not exceed one third the intercuspal distance.
2. Strong, self-resistant cusps remain.
3. Indicated teeth have minimal or no occlusal facets and if present, are confined to the
occlusal surfaces.
4. The tooth is not to be an abutment for a fixed or removable prosthesis.
5. Occlusion or occluding surfaces are not to be changed by the restorative procedures.
General shape:
The outline of the occlusal portion of this preparation is dove-tailed. The proximal
portion is usually boxed in shape.
Location of margins:
Occlusal portion:
The facial, lingual and sometimes proximal margins are located on the inclined planes
of the corresponding cusps, triangular ridges or the marginal ridges – the most
peripheral margins of the preparation are located away from contact with the opposing
tooth surfaces during centric closure.
All adjacent wear facets, supplementary grooves, and areas of decalcifications, or any
defect in the adjacent parts of the occlusal surface should be included in the beveled
part of the cavity preparation only.
Proximal portion:
The facial and lingual margins are each in the corresponding embrasures. The more
inaccessible this portion of the tooth preparation, the more should be this proximal
extension, but it should always stop short of the axial angle of the tooth.
Extensions should be made in and with the flared portion, not with the wall proper.
Extension gingivally should be accomplished with the bevel and not with the wall
proper.
Internal anatomy:
Occlusal portion:
The facial and lingual walls and sometimes the proximal walls will be formed of 2 parts.
1. The wall proper, constituting about the pulpal 2/3 of the facial or lingual wall is
formed completely of dentin.
These walls should taper from each other on the average of 2-5° or be parallel to each
other. Each wall should make a right angle or a slightly obtuse angle with the pulpal
floor.
2. The occlusal bevel, which is a long bevel constitute almost one-third of the facial and
lingual walls.
• This beveled outer plane of the walls will have an average angulation of 30-45° to
the long axis of the crown. This angulation should increase with the width of the
cavity preparation in order to:
- Accommodate more bulk of cast alloy.
- To be able to resist increased stresses near the cusps on the inclined
planes.
• The angulation of the bevel should decrease with the increased steepness of the
cusp. Bevels are not needed at all in very steep cusps, especially in a very narrow
preparation. An increased angulation is necessary also for a direct wax pattern as
compared to a cavity preparation for an indirect pattern as more marginal bulk is
required for the direct wax pattern technique.
• This bevel is extended to include wear facets and occlusal defects or
decalcifications, if they are confined to the occlusal surface. They are also
extended to include supplementary grooves and to move the margin away from
the occlusal contact.
• In wider cavities and in deeper ones they are extended to improve the taper and
reduce frictional components for easier material manipulation.
• In the inlay cavity preparation, the pulpal floor should be flat over most of its
extent.
According to Marzouk the conventional pulpal depth should be little more than that
for amalgam in order to create more length for surrounding walls. According to
Gillmore the depth is limited when compared with the amalgam restoration because
bulk is not necessary to resist fracture. The depth of the cavity should be 1 - 1.5 mm
from the DEJ. The pulpal floor should meet all surrounding walls in a definite line
angle, except at its junctional with the axial wall, where the joint should be rounded.
Proximal portion:
• The axial wall should be either flat or slightly rounded in the bucco-lingual direction,
and either vertical or slightly divergent (5-10°) towards the pulpal floor in the gingivo
occlusal direction.
• The depth axially should be 1 - 1.5 mm from the DEJ. However different depths may
be necessary according to the cariogenic pattern of the dentinal lesion proximally.
• Proximally the facial and lingual walls are comprised of two planes.
§ In the axial half it is formed completely of dentin and meets the axial
wall at a right angle relationship. This is the main resistance and
retention feature of that part of the cavity preparation.
§ The proximal half of the facial and lingual walls is formed of a primary
flare, comprised of enamel and dentin with a 45° angle to the wall
proper.
• Sometimes it is necessary to impose a 3rd plane in the form of secondary flare, placed
on enamel peripherally. This serves to simplify impression and wax pattern
manipulation. Secondary flare should not be used if a direct wax pattern technique is
to be used.
• The gingival floor proximally should be flat in the bucco-lingual direction.
In the axioproximal direction, it is formed of 2 planes.
§ The axial half consists of gingival floor (wall) proper, being perfectly flat,
formed of dentin, and making either a right angle or slightly obtuse angle
with the axial wall.
§ The proximal half should be beveled in the form of a long bevel inclining
gingivally. This bevel is usually angulated on the average of 30-45° to the
wall proper.
• The junction between the occlusal bevel and the secondary or primary flare
proximally and also the junction between the primary or secondary flares proximally
and the gingival bevel should be very rounded and smooth.
In modifications of Class II cavity preparation for esthetics the secondary flare is omitted for
esthetic reasons on the mesio-facial proximal wall. The wall is completed with minimal
extension by using hand instrument only.
TOOTH PREPARATION FOR CLASS II CAST METAL INLAY:
Initial Preparation
• Carbide burs used to develop the vertical internal walls of the preparation for cast metal
inlays and onlays are plane cut, tapered fissure burs. Recommended dimensions and
configurations of the burs to be used are No. 271 and the No. 169L (Brassier USA, Inc.,
Savannah, Georgia). The marginal bevels are placed with a slender, fine-grit, flame
shaped diamond instrument, such as the No. 8862 (Brassier USA, Inc., Savannah,
Georgia).
• Throughout preparation for a cast inlay, 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.
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.
• 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.
• 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.
• 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.
• 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.
Final Preparation
Removal of Infected Carious Dentin and Pulp protection.
• After the initial preparation has been completed, evaluate the internal walls of the
preparation visually and by tacile sensation (with an explorer) for indications of
remaining carious dentin.
• Use a slowly revolving round bur (No. 2 or No. 4) or spoon excavator to remove the
carious infected dentin.
• 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.
• 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
nonretentive, (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, (i.e., there is some breach in the junction of the material \with the
adjacent tooth structure that may indicate caries under the material).
Preparation of Bevels and Flares.
• After the final cavity preparation and placement of a cement base (where indicated) is
completed, the slender, flame-shaped, fine-grit diamond instrument is used to bevel the
occlusal and gingival margins and to apply the secondary flare on the distolingual and
distofacial walls. This should result in 30- to 40-degree marginal metal on the inlay.
• This cavosurface design helps seal and protects the margins and results in a strong enamel
margin with an angle of 140 to 150 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.
While cutting the gingival bevel reduce the rotational speed to increase the sense of touch;
otherwise over beveling may result.
• The gingival bevel should be 0.5 to 1 mm wide and should blend with the lingual
secondary flare.
• Complete the gingival bevel, and then prepare the facial secondary flare.
• When access permits, a fine-grit sandpaper disc may be used on the facial and lingual
walls and margins of the proximal preparation, especially when minimal extension of the
facial margin is desired.
• In the flaring and beveling of the proximal margins, as described in the previous
paragraphs, the procedure began at the lingual surface and proceeded to the facial surface;
however, the direction may be reversed, starting at the facial surface and moving toward
the lingual surface, depending on the operator preference.
• The gingival bevel serves the following purposes:
• Weak enamel is removed. If the gingival margin is in the enamel, it would be weak
if not beveled because of the gingival declination of the enamel rods.
• The bevel results in 30-degree metal that is burnishable (on the die)
• A lap, sliding fit is produced at the gingival margin. This helps improve the fit of
the casting in this region. With the prescribed gingival bevel, if the inlay fails to seat
by 50 µm, the void between the bevel metal and the gingival bevel on the tooth may
be as small as 20 µm; however, failure to apply such a bevel would result in a void
(and a cement line) as great as the failure to seat.
LAP SLIDING FIT
• The secondary flare is necessary for several reasons:
(1) The secondary flaring of the proximal walls extends the margins into the
embrasures, making these margins more self-cleansing and more accessible to
finishing procedures during the inlay insertion.
(2) The direction of the flare results in 40-degree marginal metal. Metal with this
angular design is burnishable; however, metal shaped at a larger angle is
unsatisfactory for burnishing; metal with an angle less than 30 degrees is too thin and
weak.
(3) A more blunted and stronger enamel margin is produced because of the secondary
flare.
• The secondary flare is omitted for esthetic reasons on the mesiofacial proximal wall of
preparations on premolars and first molars of the maxillary dentition.
The flame-shaped, fine-grit diamond instrument also is used for occlusal bevels. The width of
the cavosurface bevel on the occlusal margin should be approximately one fourth the depth of
the respective wall.
• The resulting occlusal marginal metal of the inlay should be 40-degree metal; thus the
occlusal marginal enamel is 140-degree enamel.
• Beveling the occlusal margins in this manner increases the strength of the marginal
enamel and helps seal and protect the margins.
• While beveling the occlusal margins, a guide to diamond positioning is to maintain an
approximate 40-degree angle between the side of the instrument and the external enamel
surface. This also indicates when an occlusal bevel is necessary. For example, if the cusp
inclines are so steep that the diamond instrument, when positioned at a 40-degree angle to
the external enamel surface is parallel with the enamel preparation wall, then no bevel is
indicated.
• The diamond instrument also is used to lightly bevel the axio-pulpal line angle. Such a
bevel provides a thicker and therefore stronger wax pattern at this critical region.
Thus the desirable metal angle at the margins of inlays is 40 degrees, except at the
gingival margins, where the metal angle should be 30 degrees. This completes the
preparation.
VARIATIONS IN PROXIMAL MARGIN DESIGN:
The design of the proximal margins will vary with
1. The extent of tooth tissue loss,
2. The location of that loss,
3. Tooth form,
4. The positional relationship with adjacent teeth,
5. The need for retention form, and
6. Convenience
Several basic designs are used to finish and extend walls and margins of the proximal
box. Each design may have a specific advantage because of the factors present. These
designs include the box, slice, auxiliary slice and modified flare.
1. Box preparation:
• There are two common methods by which cast gold restorations may be fabricated.
With the direct method the wax pattern is formed directly in the mouth. The indirect
method requires that an impression of the prepared cavity be taken, from which a die
is constructed.
• A wax pattern is formed on the die.
• The direct wax technique requires a proximal margin be designed for ease of wax
manipulation in the mouth. Margins are prepared to permit as great a bulk ofwax
required for subsequent finishing and adaptation.
• The buccal and lingual proximal walls are finished so that the cavosurface angle
formed by the proximal flare and tooth surface will be at right or slightly obtuse
angles.
• A cervical bevel is required. The bevel is placed most often with hand instruments,
thus forming a lap joint with a bulk of wax.
The box design is principally used with the proximo-occlusal preparation for the direct
method of wax pattern formation.
2. Slice preparation:
• Historically, a slice referred to the placement of extra-coronal taper using a disk of
adequate diameter to contact nearly the entire proximal surface. A slice
establishes a cervical finish line for the preparation and also eliminates much of
the proximal anatomic undercut which facilitates taking an impression with a non-
elastic material, dental compound.
• With the introduction of the elastic impression materials such as gross reduction
of the proximal contour was unnecessary.
• Presently, the slice preparation involves conservative disking of the proximal
surface to establish the buccal and lingual extent of the finish lines and provide a
lap joint for finishing.
• These slices are generally placed on the buccal and lingual proximal surfaces
independently. The slice may extent to the cervical floor, or more frequently will
terminate at some point occlusal to the cervical floor.
• The preservation of tooth tissue is a major factor in deciding the cervical extent of
the slice.
• Tooth form, as observed intra-orally and radiographically, will suggest how much
cervical extension is required.
• In general, teeth with square tooth form will permit the use of a slice that extends
to the cervical floor. Convenient external outline is reached with minimal loss of
tooth tissue when such flattened areas are disked. Teeth with tapering or ovoid
forms generally will indicate a slice preparation extending short of the cervical
floor. Excessive tooth tissue would be removed if disking were carried further
cervically.
Square teeth Tapering/ovoid teeth
Placement of a proximal slice for the indirect inlay produces excellent definition for
the finishing line. Beveling of the proximal cavosurface with the slice not only
assures a sound enamel margin but also yields a casting margin that is adapted and
finished with relative ease.
3. Auxiliary slice:
• Slice preparation provides external support to the weakened tooth structure and
areas subjected to high stresses during function.
• The auxiliary slice, 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.
• The auxiliary slice can also be employed to provide external retention form. An
auxiliary slice around the lingual proximal line angle of a tooth, for example, will
aid in preventing a buccal displacement of the casting.
• In a like manner an auxiliary slice around a buccal line angle will provide an
external cavity wall to aid in preventing the lingual displacement of the casting.
4. Modified Flare Preparation:
• The modified flare preparation is somewhat of a hybrid between the box and slice
preparations.
• Buccal and lingual proximal walls are initially formed with minimal extension, and
then disked in a plane that only slightly reduces the proximal wall dimension.
• Excessive disking will reduce the retention of these walls.
• The obtuseness of the cavosurface angle is enhanced.
MODIFICATIONS IN INLAY TOOTH PREPARATIONS
1. Mesioocclusodistal Preparation.
If a marginal ridge is severely weakened because of excessive extension, the preparation
outline often should be altered to include the proximal surface. The decision to extend the
preparation in this manner calls for clinical judgment as to whether the remaining marginal
ridge can withstand the occlusal forces without fracture. Also caries present on both the
proximal surfaces would result in a MOD preparation and restoration.
2. Modifications of class II cavity preparation for esthetics:
For esthetic reasons, minimal flare is indicated for the Mesio-facial proximal wall of
maxillary first premolar and first molar. To accomplish this, secondary flare is omitted, and
the wall and margin are developed with a chisel or enamel hatchet and final smoothing done
with fine grit or a narrow diamond or bur.
3. Facial and lingual groove extension:
Frequently a faulty facial groove on the occlusal surface is continuous with a faulty facial
surface groove in mandibular molars; or a faulty distal oblique groove on the occlusal surface
is continuous with a faulty lingual surface groove in maxillay molars. This indicates
extension of the cavity outline to include the fissure to its termination.
4. Class-II cavity preparation for abutment teeth and extension gingivally to include root
surface lesions.
Extending the facial. Lingual and gingival margins maybe indicated on the proximal surfaces
of abutments for RPD to increase the surface area for development of guiding planes.
In addition the occlusal outline form must be wide enough faciolingually to
accommodate any contemplated restoration preparation without involving the margins of the
restoration. Also further gingival extension is indicated to include a root surface lesion on the
proximal surface.
5. Maxillary first molar with unaffected strong oblique ridge.
When a maxillary first molar is to be restored consideration should be given to
preserve the oblique ridge if it is strong and unaffected especially if one proximal surface is
carious.
If a distal surface cavity appears subsequently to an insertion of a Mesio-occlusal restoration,
the tooth should be prepared for a disto-occluso-lingual inlay. This is preferable to the disto-
occlusal restoration because it caps the DL cusp and prevents the miniature disto-lingual cusp
from subsequent fracture.
6. Fissures in the facial and lingual cusp ridges or marginal ridges
In class II inlay preparations, facial and lingual occlusal fissures may extend nearly to or
through the respective facial and lingual cusp ridges, but not onto the facial or lingual
surface.
Proper Outline form dictates that the preparation margin should not cross such fissure but
include them. For the occlusal step of the preparation, the preparation can be extended with a
No.271 carbide bur until only 2mm of tooth structure remains between the bur and the tooth
surface(buccal, or lingual). If this extension almost includes the length of the fissure,
additional extension is achieved later with the help of the occlusal bevel to eliminate the
fissures.
7. Capping cusp
• The facial and lingual walls on the occlusal surface frequently must be extended toward
the cusp tips to the extent of existing restorative materials and to uncover caries.
• When the occlusal outline is extended up the cusp slopes more than half the distance from
any primary occlusal groove (central, facial, or lingual) to the cusp tip, capping the cusp
should be considered.
• If the preparation outline is extended two thirds of this distance or more, capping the
cusp is usually necessary to: (1) protect the weak, underlying cuspal structure from
fracture caused by masticatory force and (2) remove the occlusal margin from a region
subjected to heavy stress and wear.
• Before reducing the surface, prepare depth gauge grooves (depth cuts) with the side of the
No. 271 carbide bur. Such depth cuts helps to prevent thin spots in the restoration.
• With the depth cuts serving as guides, complete the cusp reduction with the side of the
carbide bur. The reduction should provide for a uniform 1.5 mm of metal thickness over
the reduced cusp. On maxillary premolars and first molars, the reduction should be
minimal (i.e., 0.75 to 1 mm) on the facial cusp ridge to decrease the display of metal. This
reduction should increase progressively to 1.5 mm toward the center of the tooth to help
provide rigidity to the capping metal.
• A bevel is placed on the margins of a reduced cusp with the flame-shaped, fine-grit
diamond instrument (with the exception of esthetically prominent areas). This bevel is re-
ferred to as a reverse bevel or counterbevel. It should be at an angle that results in 30-
degree marginal metal.
• The exception is the facial margin on maxillary premolars and the first molar where
esthetic requirements dictate only a blunting and smoothing of the enamel margin.
Cusp reduction appreciably decreases retention form because of decreasing the
height of the vertical walls; consequently, proximal retention grooves usually are recom-
mended.
8. Including Portions of the Facial and Lingual Smooth Surfaces Affected by Caries or
Other Injury.
When portions of both a facial or lingual smooth surface and a proximal surface are
affected by caries or some other factor (e.g., fracture), the treatment may be a large inlay, an
Onlay, a three-quarter crown, a full crown, or multiple amalgam or composite restorations.
Generally, the choice of restoration depends on the degree of tooth circumference involved.
A full crown is indicated if both the lingual and facial smooth surfaces are defective. When
only a portion of the facial or lingual smooth surface is carious, an inlay or onlay is chosen
over crown.
PREPARING THE WAX PATTERN
There are two methods of making a wax pattern for an inlay: the direct method (fashioned on
the tooth) and the indirect method (fashioned on a die).
1. Direct Method
Indications:
• A tooth is in an area of easy accessability
• Cavity preparation with minimal proximal extension
• Cavity preparation where the walls are flat, internal line angles are sharp and gingival
bevel is definite.
Advantages:
• The pattern is carved on the tooth and not on a model which may not be a perfect
replica of the t ooth because of possible inaccuracies during each stage of
preparation of the model.
• Less laboratory work
• Time saving
Disadvantages:
• Greater skill and patience required
• Wax manipulation is difficult in the mouth
• Maginal discrepancies are difficult to detect
Manipulation of the inlay wax:
• The stick of inlay wax can be softened in hot water or using dry heat. When wax is
softened directly over a flame, care must be exercised to ensure thorough heating of
the wax stick.
• The wax should be kept moving till it becomes shiny and then removed from the
flame. It should then be compressed between the fingers and again wanned. The
process is repeated until the wax is warm throughout.
• Plastic mass should be inserted in to the prepared cavity immediately and the surface
is cooled with running water.
• The pattern should be prepared in such a manner that no addition of wax would be
required, as wax, which is added after the initial cooling, introduces stresses which
will distort the pattern.
The wax pattern by direct method can be prepared with and without the application of matrix
band.
Wax pattern prepared with a matrix band:
• The retainer and band are placed on the tooth, making certain that the gingival
margins are covered by the band before fitting and applying a wedge.
• The internal surfaces of the band are lightly lubricated with a separating medium such
as castor oil.
• Wax is placed on the cavity and a finger is used as a plunger to confine the wax
within the prepared cavity. Pressure is maintained till the wax is cooled and hardened.
• The excess wax is trimmed, matrix band and retainer is removed and trial removal of
the pattern is done.
• If internal anatomy of the preparation is satisfactory on trial removal, carving is done
or else, the procedure is repeated.
• The pattern is seated on the cavity and carving is done with the help of plastic
instruments.
• The occlusion is checked and high points are removed with the help of warm carvers.
• The occlusal surface is then polished with the help of wet warm cotton pellet and the
proximal surface is polished with the help of linen strip.
Wax pattern prepared without a matrix band:
• Here, the wax is softened and pressed into the cavity. Thumb and forefinger is used to
press the wax into the embrasure space.
• Excess wax is removed occlusally. Wax is softened with the help of warm water
delivered via syringe and the patient is asked to bite, to locate the occluding cusps.
• The occlusal surface is then carved. Excess wax from the embrasure is then removed
with the help of curved probe.
• A silk thread is passed through the contact to remove the remaining excess proximal
wax followed by final finishing of the proximal surface with linen strips.
2. Indirect method:
• In this, an impression of the cavity is made and a die is prepared.
• After die preparation, a lubricant is applied on the walls, inlax wax is softened,
molded and pushed into the cavity and carving is done similar to the direct wax
pattern technique.
• It is indicated for large cavities and in cases where the tooth is inaccessible for direct
wax pattern preparation.
Removing the pattern from the cavity:
The pattern must be removed without distortion and maintaining the path of removal parallel
with the direction of the cavity walls.
The sprue former should be attached to the pattern while it is still on the tooth or die to
minimize distortion
The sprue former of proper size and shape is selected, sticky wax is applied to one end of the
sprue and is attached to the pattern.
The pattern is then carefully removed, inspected for any defects and then sent to the lab for
casting.
REFERENCES
1. Gerald T. Charbeneau. Principles and practice of operative dentistry. 3rd Edition.
Varghese Publishing. 351-356.
2. William H. Gilmore. Operative Dentistry. 4th Edition. B.I. Publication Pvt. Ltd.
260-268.
3. Lioyd Baum. Textbook of Operative Dentistry. 3rd Edition. W.B. Saunders
Company. 470-484.
4. Theodore M. Robertson. Herald O. Heyman. Sturdevants art and science of
operative dentistry. IV Edition. Mosby Company. 801-826.
5. Vimal K.Sikri. Textbook of operative dentistry. CBS Publishers. 243-256.
6. M.A. Marzouk., A.L. Simonton., R.D. Gross. Operative dentistry modern theory and
practice. All India Publishers and Distributors.
CONCLUSION:
Although various aesthetic options available at present has reduced the use of gold in oral
cavity, cast restorations meet the needs of patients who require replacement of a large amount
of tooth tissue. It is well said that “old is gold” but the reverse i.e. “gold is old” is not true.