1. Tooth preparation of class II
Inlay for cast restorations
Guided by- Presented by-
Dr. W. N. Ghonmode Dr. Shubhangi
Warake
Dr. Sathish Abraham
Dr. Pradnya Nagmode
2. According to Mc- Gehee,” an inlay may be defined as
a restoration, which has been constructed out of the
mouth from gold, porcelain, or other material and then
cemented into the prepared cavity of a tooth.”
An inlay is an intracoronal restoration fabricated in
the laboratory and cemented into prepared cavity.”
According to Sturdevant, the class II gold inlay
involves the occlusal and proximal surface(s) of
posterior tooth and may cap one or more but not all the
cusps.
Inlay
3. INDICATIONS FOR CAST RESTORATIONS
Acoording to M. A. Marzouk-
A cavity’s width does not exceed one-third the intercuspal
distance
Strong , self- retentive cusps remain.
Indicated teeth have minimal or no occlusal facets and if present
are confined to the occlusal surfaces.
The tooth is not to be an abutment for a fixed or removable
prosthesis.
Occlusion or occluding surfaces are not to be changed by the
restorative procedure.
5. ADVANTAGES
Strength - high tensile, compressive and shear strength.
Low wear.
Controls of contours and contacts.
Biocompatibility.
Can be finished and polished outside the oral cavity.
6. DISADVANTAGES
Longer chair side time.
Number of appointments required are more.
Temporary restoration required between cavity preparation
and delivery appointments.
Expensive.
Technique sensitive.
Wedging forces
7. LOCATION OF MARGINS
OCCLUSAL PORTION
In the occlusal portion of the cavity, the facial, lingual and
sometimes proximal margins are located on the inclined planes of
the corresponding cusps, triangular ridges or the marginal ridges, so
that buccolingual width of the cavity does not exceed one-third the
intercuspal distance.
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. These features fulfill the requirement of extension
for prevention.
8. PROXIMAL PORTION
The facial and lingual margins should lie in the
corresponding embrasures so that the full length
of an explorer can pass in an occluso-gingival
direction; and all undermined enamel, surface
defects and undercuts are eliminated.
The more inaccessible is this portion of the
tooth preparation, more should be the proximal
extension, but it should always stop short of the
axial angle of the tooth.
Gingival margins should be extended to involve
any surface defects and undercuts. Extension
gingivally should be accomplished with the
bevel.
9. INTERNAL ANATOMY
Occlusal portion is formed by two parts:
- Wall proper
- Occlusal bevel
1. Wall proper:
Formed completely of dentin
• The walls should preferably be parallel to the
long axis of the crown or have a taper 2-50
10. 2. Occlusal bevel:
• Constitutes almost one-third of the facial and lingual proximal walls
• Average angulation: 30-45° to long axis of crown.
• Angulation should increase:
-as width of cavity preparation increases
-to accommodate more bulk of cast alloy
-resist increased stress near cuspal inclines
-direct wax pattern (as more marginal bulk is required
for direct wax pattern)
-to include superficial defects, supplementary grooves,
decalcifications on occlusal surface.
• Angulation should decrease: with increased steepness of cusps.
11. 3. Pulpal floor:
Should be flat, or in case of caries may have different
levels, but the peripheral portions should be flat.
Depth- 1-1.5mm from the dentino-enamel junction.
Pulpal floor should meet all surrounding walls, except the
axial wall at definite line angles.
Junction with axial wall is rounded.
12. 4. Axial wall:
Should be flat or slightly rounded in buccolingual
direction.
Either vertical or divergent (5-10°) towards pulpal
floor.
Should meet the pulpal floor at an extremely rounded
junction. This prevents stress concentration in the tooth
and in the casting.
The depth is 1-1.5 mm from the dentinoenamel
junction. Depth may vary depending on caries
extension.
13. 5. Facial, lingual walls:
Proximally, the facial and lingual walls are comprised of two
planes-
Axial half (i.e. facial, lingual wall proper) is formed completely
of dentin and meets the axial wall at right angle.
Proximal half is formed of primary flare, comprised of enamel
and dentin with an unchanged 45° angle to wall proper.
Sometimes a third plane in the form of secondary flare may be
placed on enamel peripherally.
This serves to simplify impressions, wax pattern manipulations.
Not used when direct wax pattern technique is employed.
14. 6. Gingival floor:
Flat in bucco-lingual direction,
It is formed of two planes in axio-proximal direction:
• Axial half : consists of gingival wall (floor) proper,
perfectly flat,
formed of dentin.
• Proximal half : bevelled in the form of long bevel inclining
gingivally, average angulation 30-450 to wall proper.
15. 7. Junction between occlusal bevel and primary or
secondary flare should be round and smooth.
Also junction between the primary/secondary flare and
gingival bevel should be rounded and smooth.
18. DISTO-OCCLUSAL CAVITY PREPARATION:
INITIAL PREPARARTION
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.
A punch cut to a depth of 1.5 mm is
established in the depth of the pulpal wall. In
initial preparation the depth should not be
exceeded regardless of whether the bur end is
in dentin, caries, old restorative material, or
air.
19. Long axis of the bur is kept parallel to
the long axis of the tooth crown at all
times.
Gingival to occlusal divergence of walls :
2 ° – 5 ° from line of draw
For mandibular molars and premolars
whose crowns tilt slightly lingually, the bur
should tilt slightly (5-10 degree) lingually
to conserve the strength of the lingual
cusps.
20. With the 1.5 mm initial depth and
the same bur orientation, extend the
preparation into the uninvolved
pit/fossa (mesial) keeping
faciolingual width minimum &
marginal ridge strong
If a fissure extends on the mesial
marginal ridge, It is treated by:
a) Enameloplasty or by
b) bevelling
Enameloplasty
Bevel
21. Extension to include faulty
facial & lingual fissures
radiating from mesial pit
Slender No. 169L bur is
used so that tooth structure
can be conserved
This provides the desired
“Dovetail retention form”
which resists distal
displacement of inlay
22. The facial and lingual walls of the occlusal step
should go around the cusps, and the prepared
isthmus in the transverse ridge ideally should be
only slightly wider than the bur, thus conserving
dentinal protection for the pulp and maintaining
strength of the cusps.
The occlusal step is extended distally into the
distal marginal ridge sufficiently to expose the
junction of the proximal enamel and the dentin,
The preparation is progressively widened while
extending distally to the desired facio-lingual
width till proximal surfaces clear adjacent
teeth by 0.2 – 0.5 mm.
23. Proximal Box:
Continuing with No. 271 carbide bur, the
distal enamel is isolated by cutting a proximal
ditch.
Mesiodistal width of the ditch should be 0.8
mm, and prepared approximately two thirds
(0.5 mm) at the expense of dentin and one third
(0.3 mm) of enamel.
While penetrating gingivally, the proximal
ditch is extended facially and lingually beyond
the caries to the desired position of facio-axial
and linguo-axial line angles.
24. Ideal extension gingivally, eliminates caries
on the gingival floor and provide 0.5-mm
clearance from the gingival margin of the
adjacent tooth.
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.
25. 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 towards the
enamel surface.
These cuts are extended until the bur is
nearly through the marginal ridge enamel
(the side of the bur may emerge through the
surface at the level of the gingival floor)
The remaining wall of enamel often breaks
away during cutting. If the isolated wall of
enamel is still present, it can be fractured out
with a spoon excavator.
26. Proximal & gingival walls are planed using hand instruments
to remove remaining undermined enamel
Hand instruments such as straight
chisel, binangle chisel, enamel
hatchet can be used.
When proximal caries is minimal,
ideal facial and lingual extensions
at this step result in margins that
clear the adjacent tooth by 0.2-0.5
mm.
27. FINAL PREPARATION:
Removal of Infected Carious
Dentin and Pulp Protection.
If infected but shallow carious dentin
remains, it is removed with a slowly
revolving round bur (no. 2 & 4) or a
spoon excavator.
Light cured Glass Ionomer Cement
may be placed in these areas to get
the form of ideally prepared surface.
28. If carious lesion is closely approaching the pulp:pulp
space therapy / direct pulp capping is indicated.
Place calcium
hydroxide liner
Place retention coves in peripheral
dentin to provide mechanical
retention for Glass Ionomer base
Completed base
29. Preparation of Bevels and Flares.
Slender, flame shaped, fine-grit diamond instrument is used:
to bevel the occlusal and gingival margins
to apply the secondary flare on the distolingual and distofacial
walls
The bevel should result in 30-40° marginal metal on the inlay.
This cavosurface design helps seal and protect the margins and
results in a strong enamel margin with an angle of 140-150°.
30. There are two types of flares :
1. Primary flare
2. Secondary flare
The proximal walls
(distofacial/distolingual/mesiofacial/mesiolingual)
extends from the respective proximal lineangles to the
respective embrassures in two planes.
The first is termed the Primary flare and the second is
termed the Secondary flare.
31. Instruments used (for preparation of secondary flare) :
1. Fine-grit, Flame-shaped diamond instrument
2. No 169L carbide bur
3. Fine grit sandpaper disc
32. During preparing distolingual secondary flare : the long
axis of the instrument is held nearly parallel to the line of
draw, with only a slight tilting mesially and lingually for
assuarance of draft.
During preparing distofacial secondary flare : the
instrument is tilting mesially and facially.
33. The secondary flare is necessary for several
reasons :
1. Extends the margins into the embrassures, making
these margins more self-cleaning and more accessible
to finishing procedures.
1. The direction of the flare results in 40 degree marginal
metal which is burnishable.
2. A more blunted and stronger enamel margin is
produced.
34. 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 wall is completed with minimal extention by using
either hand instruments followed by sandpaper disc or
very thin rotary instruments.
35. Gingival bevel
It is prepared by moving the instrument facially along
the gingival margin, slightly tilting it mesially to
obtain the desired steepness and marginal metal of 30
degree. The gingival bevel should be 0.5 to 1 mm
wide and should blend with the lingual secondary
flare.
36. The gingival bevel serves the following purposes :
Weak enamel is removed.
The bevel results in 30 degree metal that is
burnishable (on the die).
A lap, sliding fit is produced at the gingival
margin.
37. Occlusal Bevel
During beveling occlusal margins, diamond instrument is
positioned to maintain an approximate 40 degree angle
between the side of the instrument and the external enamel
surface.
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, no bevel
is indicated.
38. Proximal marginal ridges always require a cavosurface
bevel.
Failure to apply a bevel in these regions leaves the enamel
margin weak and subject to injury by fracture.
39. Beveling of the axiopulpal line angle.
Provides a thicker and stronger wax pattern at this critical
region.
40. MODIFICATIONS IN INLAY TOOTH PREPARATION
1. Mandibular bicuspids.
Mandibular 1st premolar:
- prominent buccal cusp,
- small lingual cusp,
- central groove positioned lingual to midline.
Preparation:
- two third of occlusal width to be removed from tooth tissue buccal
to the central groove, one third from the lingual area.
- pulpal floor slanted to lingual side.
41. Mandibular 2nd premolar:
-central groove has variable forms: ‘H’,
‘U’, ‘Y’.
Preparation:
- ‘U’, ‘Y’ types require special
consideration so as to not weaken the
lingual cusps.
- two third of occlusal width to be
removed from tooth tissue buccal to the
central groove, one third from the
lingual area.
- lingual extension into lingual groove
may at times be necessary.
42. 2. Mesio-occluso- distal Preparation:
Indication:
Caries present on both proximal surfaces.
If a marginal ridge is severely weakened because of excessive
extension.
43. 3. Modifications of Class II Preparation for
Esthetics:
Minimal flare is desired for the mesiofacial
proximal wall in the maxillary premolars and
first molars.
The mesiofacial margin is minimally extended
facially to such a position that the margin is
barely visible from a facial view.
To accomplish this, the secondary flare is
omitted, and the wall and margin are developed
with either: a hand instrument(a chisel or enamel
hatchet) or a narrow diamond bur.
44. 4. Facial or Lingual Surface Groove
Extension.
A faulty groove (fissure) on the occlusal surface
may be continuous with a faulty facial surface
groove (mandibular molars), or
A faulty distal oblique groove on the occlusal
surface may be continuous with a faulty lingual
surface groove (maxillary molar).
This requires extension of the preparation outline
to include the fissure to its termination.
45. For extension on the facial surface, no 271
carbide bur is held parallel to the line of
draw.
When a facial or lingual groove is included,
it must also be bevelled.
Mesial & distal margin bevel should be
continuous with the occlusal bevel
Axial wall depth = 1mm
Bur should be tilted lingually as it is drawn
occlusally to develop uniform axial wall
depth.
46. 5. Class II preparation for abutment teeth & extension
gingivally to include root-surface lesions
The occlusal outline form must be wide enough
faciolingually to accommodate rest preparation.
Extending the facial, lingual, and gingival margins
may be indicated on the proximal surfaces of
abutments for removable partial dentures to increase
the surface area for development of guiding planes.
These extensions may be accomplished by simply
increasing the width of the bevels.
If gingival extension is essential, it is accomplished
by increasing the length of the gingival bevel,
especially when preparing a tooth that has a longer
clinical crown.
47. 6. Maxillary first molar with unaffected, strong oblique
ridge:
When a maxillary first molar is to be restored, consideration should
be given to preserving the oblique ridge if it is strong and
unaffected, especially if only one proximal surface is carious.
48. 7. Fissures in facial & lingual cusp ridges or marginal ridges
If fissure can be eliminated
with bevel; wide occlusal bevel
used to eliminate fissure or
Enameloplasty can be
performed to eliminate the
fissure
49. 8. Reduction of the cusps for capping
Depth gauge grooves are placed
with No. 271 bur to ensure
uniform reduction
1.5mm thickness of the metal
should rest over the reduced cusp
If only lingual cups included
reduction should extend to
include lingual groove
50. Bevel prepared on facial / lingual
margin of reduced cusp to result in
30° marginal metal
In esthetic areas, blunting /
smoothening off, of the enamel
margins done by holding
instrument at right angle to facial
surface
51. VARIATIONS IN PROXIMAL MARGIN DESIGN
Design of the proximal margins varies with:
Extent of tooth tissue loss,
Location of that loss
Tooth form
Positional relationship with adjacent teeth
Need for retention form
Convenience
DESIGNS INCLUDE
Box Preparation
Slice Preparation
Auxiliary Slice Preparation
Modified Flare Preparation
52. BOX PREPARATION
Indication: Proximo-occlusal preparation for
direct wax pattern method.
Design features:
Proximal walls- Finished at nearly right
angles to outer tooth surface or slightly
obtuse angles.
Cavosurface angle - right angle or slightly
obtuse
Cervical bevel /Gingival bevel
- Forms lap joint
53. SLICE PREPARATION
Disking of proximal surface to establish
buccal and lingual extent of finish lines.
Provides a lap joint.
Placed on buccal, lingual surfaces
independently.
May or may not extend to cervical floor.
Establish cervical finish line.
Factors determining cervical extent of
the slice-
1. Preservation of tooth tissue
2. Tooth form(square form permits extent to
cervical floor; tapering/ ovoid forms-
short of cervical floor).
54. AUXILIARY SLICE PREPARATION
Indication: When a buccal/ lingual proximal wall is difficult to
establish due loss of tooth tissue from caries or fracture.
Wraps partially around proximal line angle, provides additional
tooth support.
Provides external support to:
-weakened tooth tissue
-areas subjected to high stress
during function.
Advantage: though minimal bulk of tooth is lost, resistance form is
greatly enhanced, minimising tooth fracture.
55. MODIFIED FLARE PREPARATION
Hybrid between box and slice preparation.
Buccal and lingual walls are initially formed with minimal
extension, then disked in a plane that only slightly reduces the
dimension.
Advantage: Obtuseness of cavosurface angle is enhanced.
56. CONCLUSION
Cast restorations form an integral link in the dental
restorative chain.
They are an excellent choice in many demanding
situations.
Understanding the principles of tooth preparations
and the intricacies of cast restorations will enable
the dentist to optimally utilize this excellent option
when the clinical situation demands.
57. References
Sturdevant’s Art & Science of Operative Dentistry
Operative Dentistry – M.A. Marzouk
Fundamentals of Operative Dentistry – J.B. Summit
Fundamentals of Tooth Preparation – H.T. Schillinburg
Operative dentistry- Charbeneu
Textbook of operative dentistry- Vimal Sikri
