Tooth preparation for class II
amalgam restorations and its
Amalgam although a brittle material, has been
adequately serving as a restorative material since 175
years, understanding of its properties and judgment
of the preparation design are the vital factors
controlling its use.
Class II Restorations.
It is defined as a cavity that is
present on the proximal surfaces of
premolars and molars.
( G.V .BLACK )
INDICATIONS for using amalgam as
Restorations that are not in highly esthetic areas of the mouth.
Restorations that cannot be well isolated.
Restorations that have heavy occlusal loads.
Temporary and caries control restorations.
Restorations that extends onto root surface.
Line angles and point angles
6 point angles
11 line angles
Tooth preparation walls-
Facial (proximal and occlusal portion)
Lingual (proximal and occlusal portion)
Distal / Mesial
Marking the occlusal contacts with articulating paper . These
contacts serve as guide in tooth preparation and restoration.
Recontouring of any opposing “plunging cusp" or other pointed
cusp to reduce the risk of fracture of the new restoration or the
cusp from occlusal forces.
For amalgam , the placement of rubber dam is generally
Burs used in class Ⅱtooth
Width 0.8 mm & Length 3 mm
INITIAL TOOTH PREPARATION
Tooth preparation for caries on proximal surface should have occlusal
outline such that it allow access to proximal lesion, remove
demineralized enamel and dentin, and remove enamel not supported
by sound dentin.
If an occlusal carious lesion is present, it should be treated with a
separated occlusal restoration.
If the proximal and occlusal lesions are in close proximity so that there
is minimal or no sound tooth structure separating the two
preparations, they should be joined.
Mesio-occlusal class II preparation
Occlusal outline form:
Enter the pit nearest the involved proximal
surface with a punch cut using a No. 245
Viewed from the proximal and lingual
aspects, the long axis of bur should be
parallel to the long axis of tooth crown
Bur position for
• Proper depth of the initial entry cut
is 1.5-2mm.The pulpal depth is
usually 0.1-0.2 mm in to the dentin.
While maintaining the same depth
and orientation ,bur is moved to
extend the outline to include the
central fissure and opposite pit ,if
Include all the carious occlusal pits and fissures in such a manner that
sharp angles in the marginal outline are avoided.
The isthmus width should be as narrow as possible, ideally should be
1/4th of the intercuspal distance
Enameloplasty should be used where indicated to conserve tooth
Enameloplasty .done by , Fine-grit diamond stone in position to remove fault. C,
Smooth surface after enameloplasty. D, Cavosurface angle should not exceed 100
degrees, and marginal-amalgam angle should not be less than 80 degrees.
Distal wall can be made occlusaly divergent by tilting the
bur ,if extension of distal margin would reduce the
dentinal support of marginal ridge
Maintaining the bur parallel to long axis of the tooth,
creates facial lingual and distal walls occlusaly
Dovetail prevents the proximal displacement of the
restoration. It is not required in outline form of single step
proximal box ,unless a fissure is radiating from the
occlusal pit .
Incline bur distally to make proper occlusal
divergence of distal wall
Before extending into the involved proximal marginal ridge, the
final location of the facial and lingual walls of the proximal box
relative to the contact area should be visualized ,to prevent
overextension of the occlusal outline form (i.e., occlusal step)
where it joins the proximal outline form (i.e., proximal box).
Visualization of final location of
While maintaining the established pulpal depth
and with the bur parallel to the long axis of the
tooth crown, the preparation is extended mesially, stopping
approximately 0.8 mm short of cutting through the marginal
ridge into the contact area.
Breaking proximal contact
The occlusal step in this region is made slightly wider
faciolingually than in the Class I preparation because
additional width is necessary for the proximal box.
This extension includes part of the mesial marginal ridge, it
also exposes the marginal ridge DEJ. The location of the
DEJ is an important guide in the development of the
Direction of mesiofacial and mesiolingual walls.
A, Failure caused by weak enamel margin.
B, Failure caused by weak amalgam margin.
C, Proper direction to proximal walls results in full-length enamel
rods and 90-degree amalgam at preparation margin
PROXIMAL OUTLINE FORM
Again we visualizes the desired final location of the facial and
lingual walls of the proximal box relative to the contact area.
The objectives for extension of proximal margins are to:
Include all caries, faults, or existing restorative material.
Create 90-degree cavosurface margins (i.e., butt joint margins).
Establish (ideally) not more than 0.5 mm clearance with the
adjacent proximal surface facially, lingually, and gingivally.
18 The initial procedure in preparation
of outline form is the isolation of the
proximal enamel by giving the
proximal ditch cut.
Allow the end of the bur to cut a
ditch gingivally along the exposed
DEJ, two thirds at the expense of
dentin and one third at the expense
of enamel. The 0.8-mm diameter
bur end will cut approximately 0.5 to
0.6 mm into dentin and 0.2 to 0.3
mm into enamel.
The ditch is extended gingivally just
beyond the caries or the proximal
contact, whichever is greater.
When extension places the gingival margin in cementum,
the initial pulpal depth of the axiogingival line angle should
be 0.7 to 0.8 mm (the diameter of the tip end of the No.
245 bur is 0.8 mm). The bur may shave the side of the
wedge that is protecting the rubber dam and underlying
Ideally the extension of facial and lingual margins of proximal
box should be such that ,it provides clearance of 0.2-0.3 mm
from the adjacent tooth.
but this clearance greater than 0.5 mm is excessive unless
indicated to include caries, undermined
enamel, or existing restorative material.
Ideally the gingival margin should
clear the adjacent tooth by only
0.5mm ,which may be measured
with the side of explorer.
Preparation of Axial wall-
It is an internal prepared wall that is parallel to the long
axis of the tooth & It is always placed in dentin to obtain:
It is always placed in the dentin to obtain:-
• Resistance & elasticity of dentin
• Bulk of the restoration.
• Placement of retentive locks.
Length of the axial wall :- 0.4-0.6 mm from the axio-
pulpal line angle to the axio-gingival line angle.
the axial wall should be straight or convex but it should
never be concave.
It should follow the contour of proximal surface .
PREPRATION OF GINGIVAL SEAT:-
It is an external cavity wall that is perpendicular to the long
axis of the tooth.
It is extended beyond the contact area or up to the proximal
lesion whichever is more. This also help in providing a
contact clearance gingivally.
It is made flat so that the masticatory forces are distributed
The width of gingival seat:- 0.6-0.8mm(premolars)
It consists of 2/3rd of dentin and 1/3rd of enamel.
GINGIVAL DIVERGENCE OF FACIAL AND LINGUAL
WAALS OF PROXIMAL BOX
The proximal ditch cut may be diverged gingivally to ensure that
the faciolingual dimension at the gingival is greater than at the
This gingival divergence :
- Increases the retention form .
- Provides desirable extension of the facial and lingual
proximal margins to include defective tooth structure or
old restorative material at the gingival level.
- Conserve the marginal ridge strength.
- Provides 90-degree amalgam at the
margins on this ridge .
In completing the proximal extensions, next make
two cuts, one starting at the facial limit of the
proximal ditch and the other starting at the lingual
limit, extending toward and perpendicular to the
proximal surface (until the bur is nearly through the
enamel at contact level).
The side of the bur may emerge slightly through
the surface at the level of the gingival floor.
a matrix band may be used around the adjacent tooth to prevent
marring its proximal surface.
The isolated enamel, if still in place, may be fractured out with a
spoon excavator or by additional movement of the bur.
Proximal enamel plate is broken by hand
Margins palned with
GMT or hatchet
To protect the gingiva and the rubber dam when extending the gingival
wall gingivally, a wooden wedge should already be in place in the
gingival embrasure to depress the soft tissue and rubber dam.
toothpick wedge Triangular wedge
Indicated in deep
With the enamel hatchet, the bin-angle chisel, or both, cleave away
any remaining undermined proximal enamel, establishing the proper
direction to the mesiolingual and mesiofacial walls. .
Proximal margins having cavosurface angles of 90 degrees are
PRIMARY RESISTANCE FORM
1. Pulpal & gingival walls being flat and
perpendicular to the forces directed to the long
axis of the tooth.
2. Restrict the extension of the walls to allow strong
cusps & ridges to remain with sufficient dentin
3. Restricting the occlusal outline form to areas
receiving minimal occlusal contact.
4.Reverse curve optimizing the strength of both the amalgam
and tooth structure at the junction of the occlusal step and
5. Rounding off the internal line angles.
6.Providing enough thickness of the restorative material.
When the direction of the mesiofacial wall is parallel to the
direction of the enamel rods, thus creating a ‘s’ shaped curve in the
It is created to:
Provide butt joint in the preparation margin.
To relieve the contact
To place the proximal margins in a self cleansing area.
PRIMARY RETENTION FORM
Occlusal convergence of facial & lingual walls
Dovetail design of occlusal step(when present).
FINAL TOOTH PREPARATION
Removal of any remaining defective enamel and infected carious dentin
Accomplished in the same manner as in the Class I preparation.
Infected carious dentin is removed with a slowly revolving round bur of
appropriate size or a discoid-type spoon excavator or both.
. A, Infected carious dentin extending beyond ideal pulpal wall position. B, Incorrect
lowering of pulpal wall to include infected carious dentin. C, Correct extension
facially and lingually beyond infectedcarious dentin.
The presence of infected carious dentin on a portion of either
the pulpal wall (floor) or axial wall does not indicate
deepening the entire wall.
. Infected carious
dentin on axial wall
does not call for
preparing axial wall
toward pulp as
shown by dotted
lines. It should be
removed with round
A partial extension of a facial or lingual wall is permissible if:
The entire wall is not weakened
The extension remains accessible and visible
Sufficient gingival seats remain to support the restoration
A butt joint fit at the amalgam and enamel margin (90-degree
amalgam angle and 90-degree cavosurface angle) is possible.
It is desirable to have approx 2mm bulk beneath the
pulp and metallic restoration which may be Dentin, Liner
or a Base.
Liner/Base- Mechanical, Chemical, Thermal Pulp
protection and act as a barrier that protects the dentin.
Remaining Dentin Thickness 0.5-1 mm -Zinc
Phosphate Cement, Glass Ionomer Cement base is
used followed by calcium hydroxide liner.
The base insulates the pulp from thermal changes,
bonds to the dentin, releases fluoride, and is strong
enough to resist the forces of condensation.
SECONDARY RESISTANCE AND
Using the gingival margin trimmer to bevel or round the axiopulpal
Proximal retention locks:
Placed on axiofacial and axiolingual line angles.
Terminate at axiopulpal point angle.
Prepared with No. 169L bur or No. ¼ bur
There are four characteristics or determinants of proximal
locks: (1) position, (2) translation, (3) depth, and (4)
Proximal retention locks
A, Position of No. 169L bur
and pulpally. B, Lingual lock..
C, Completed locks. D, Locks prepared
with No. '/, bur. E, Completed locks
Position refers to the axiofacial and axiolingual line angles of initial
tooth preparation It is important to note that the retention locks should
be placed 0.2 mm inside the DEJ, regardless of the depth of the axial
walls and axial line angles.
Translation refers to the direction of movement of the axis of the bur i.e.
parallel to DEJ.
Depth refers to the extent of translation (i.e., 0.5 mm at gingival floor level).
Occlusogingival orientation refers to the tilt of the No. 169L bur, which
dictates the occlusal height of the lock, given a constant depth.
Placed on axiofacial and axiolingual line
Extend from the gingival floor to the
Prepared with No. ¼ round bur with head
diameter of 0.5mm or No. 1/8 bur with
head diameter of 0.4mm
In preparation with deep proximal box
grooves should be in the proximal walls
just inside the DEJ and not in the corners
of the box
Prepared with No. 33 ½ inverted cone bur
0.5 to 1 mm deep inside DEJ
0.6 mm deep
C) Self threaded
As a rule one pin per missing axial angle should
be used .
Pin hole should be positioned no closer
than 0.5 to 1 mm to the DEJ or 1 - 1.5 mm
to external surface of the tooth.
Pinhole should be parallel to adjacent
external surface of tooth.
Depth of 1.5 to 2mm is adequate
Diameter 0.8 to 1mm
Prepared with No.1156, No.1157, No.330 or No.56 burs
Amalgam bonding agents:
Should have auto-polymerizing property as
amalgam does not allow light transmission
Ex: All bond-2, Amalgam bond plus, etc.
PROCEDURE FOR FINISHING
1. There should be no unsupported enamel and marginal irregularities
2. There should be a butt joint relation between the tooth & amalgam
3. Cavosurface bevel [20°] at the gingival margin can be given by G.M.T ,
to remove the unsupported enamel rods.
• When the gingival margin is positioned gingival to
the cementoenamel junction (CEJ) on the tooth
root, the bevel is not indicated.
Final procedures: cleaning,
First step includes removing all chips and loose debris and then drying
the preparation(not dessicating) and check for any infected dentin and
any unsound enamel margins.
Cleaning is to free the preparation of visible debris with warm water from
syringe and then to remove moisture with a few light surges of air
Varnishes should be applied on all the preparation walls to prevent the
GLUMA desensitizer can also be used to reduce the postoperative
Disinfection of the preparation walls can be done by silver nitrate,
phenol,ethyl alchol (short duration).
MATRICES Are used in class ii restorations.
It is defined as “a properly shaped piece of metal or non metal
which supports the restoration during its insertion and its
2. Help to re establish proper anatomic contour.
3. Help to re establish proper proximal contact.
4. To prevent over hang of the restoration and to maintain the
health of the interdental gingiva.
5. Easily removable.
6. Should neither adhere to ,nor react with the restorative material.
Many types of matrices are available:-
*Universal matrix *auto matrix
*Precontoured bands *compound supported matrix
UNIVERSAL MATRIXAUTO MATRIX
VARIATIONS OF ONE PROXIMAL SURFACE TOOTH
SIMPLE BOX PREPARATION
A proximal box that is prepared without occlusal step.
When restoring a small, cavitated, proximal lesion in a tooth with neither
occlusal fissures nor a previously inserted occlusal restoration, a proximal
box preparation without an occlusal step has been recommended
Indicated in narrow proximal contacts allowing minimum facial and lingual
Facial & lingual proximal walls converge occlusally.
Proximal retention locks-0.5mm at gingival point angles tapering to 0.3mm
at occlusal surface are prepared
The proximal preparation begins with the creation of a slot, cut with a
small bur in the center (mesiodistally) of the crest of the marginal
ridge and occlusal to the caries lesion.
The slot is deepened gingivally until the bur “falls” into the soft
The preparation is widened facially and lingually to eliminate all
demineralized tooth structure at the DEJ and to remove enamel that
is not supported by sound dentin.
SLOT PREPARATION FOR ROOT CARIES
When caries is present in the proximal aspect without involving
the marginal ridge.
Indicated in cases of gingival recession having root surface caries
gingival to the proximal aspect.
When the adjacent tooth is missing.
Preparation for Class II restorations with facial or lingual access
are sometimes referred to as Key Hole Preparations.
The tooth preparation is usually approached
from the facial and has the form of a slot.
Outline form extension to sound tooth structure is at a
limited depth axially (i.e., 0.75 to 1 mm at the gingival aspect
[if no enamel is present], increasing to 1 to 1.25 mm at the
occlusal wall [if margin in enamel]
The remaining infected carious dentin (if any) will be
removed during final tooth preparation.
• Prepare retention grooves with a No.
1/4, bur into the occlusoaxial and
gingivoaxial line angles, 0.2 mm
inside the DEJ or 0.3 to 0.5 mm
inside the cemental cavosurface
• The depth of these grooves is one
half the diameter of the bur head (i.e.,
0.25 mm), and the bur is directed to
bisect the angle formed by the
junction of occlusal (or gingival) and
Mandibular 1st premolar
The support of the small lingual cusp may be
conserved by preparing the occlusal step more at the
expense of tooth structure facial to the central groove
The lingual cusp may need to be reduced for capping
if the lingual margin of the occlusal step extends more
than two thirds the distance from the central fissure to
the cuspal eminence
58SLOPING PULPAL FLOOR.
This preparation is done in
the mandibular 1st premolar
because of a short lingual
cusp and also due to the
lingual inclination of the
This preparation coincides
with the occlusal
morphology of the tooth.
For a preparation that will not cross the transverse
ridge, prepare the proximal box before the occlusal
portion to prevent removing the tooth structure that
will form the isthmus between the occlusal dovetail
and the proximal box.
The bur axis is parallel to the tooth crown which is
tilted slightly lingually
The pulpal wall is facially inclined
Extension into the enamel oblique ridge is avoided
whenever possible to maintain the cross-splinting
strength it provides to the tooth
It may require extending through the oblique ridge to unite
the proximal preparations with the occlusal step.
Cutting through the oblique ridge is indicated only if:
(1) the ridge is undermined with caries,
(2) it is crossed by a deep fissure, or
(3) occlusal portions of the separate MO and DO outline
forms leave less than 0.5 mm of tooth structure between
Maxillary 1st premolar
A Class II preparation involving the mesial surface
requires special attention because the mesiofacial
embrasure is esthetically prominent.
The occlusogingival preparation of the facial wall of the
mesial box should be parallel to the long axis of the tooth
instead of converging occlusally to minimize an
unaesthetic display of amalgam in the faciogingival corner
of the restoration.
The facial extension of the mesiofacial proximal wall should be
minimal and margins may be placed lingual to the facial contact.
Tooth preparation for rotated teeth
follows the same principles as for
normally aligned teeth.
When the tooth is rotated 90 degrees
and the "proximal“ lesion is on the
facial or lingual surface or orthodontic
correction is declined or ruled out, the
preparation may require an isthmus
that includes the cuspal eminence.
If the lesion is small, consideration
should be given to the slot preparation.
• It is permissible to repair or replace a defective portion of an
existing amalgam restoration if the remaining portion of the
original restoration retains adequate resistance and retention
• Where the two restorations adjoin, care should be taken that
the outline of the second restoration does not weaken the
amalgam margin of the first.
• It includes replacing a defective portion of an existing
restoration , while remaining portion retains adequate
resistance and retention form.
• The intersecting margins of the
two restorations should be at
right angles as much as possible.
UNUSUAL OUTLINE FORM.
Usually seen in mandibular third
molars having unusual groove
central fissure segmented by
CLASS II AMALGAMRESTORATIONS INVOLVING
BOTH PROXIMAL SURFACES
THE CONVENTIONAL DESIGN
OR MESIO OCCLUSO DISTAL
A moderate to large sized lesion
involving both the proximal boxes in
which it becomes imperative to
involve the occlusal box for proper
accesibility of proximal lesion.
Requires extending grooves that are fissured,
capping cusps that are undermined, or extending
the outline form up the cuspal inclines.
Groove extension occurs at the same initial pulpal
floor depth (i.e., 1.5 mm) but follows the DEJ as
the groove is extended in a facial or lingual
This extension (and groove extension) will
usually require some alteration in the
orientation of the bur: a slight lingual tilt when
extending in a facial direction, and a slight
facial tilt when extending in a lingual direction.
Larger Class II restorations will often require larger proximal box
Extensive proximal boxes are usually prepared the same as a
more conservative proximal box, but may require modifications.
The increased dimensions of a large proximal box usually require
the use of retention locks or other secondary retention form
If the proximal box is extended onto the root surface, the axial
wall depth is no longer dictated by the DEJ.
Axial wall depth of approximately 0.8 mm.
The small distal cusp of mandibular first molars, the
distolingual cusp of maxillary molars, and the lingual cusp of
some mandibular premolars (especially first premolars) may
be weakened when normal preparations of surrounding
areas of the tooth are included.
This requires capping of these cusps
Cusp capping increases the resistance form of the tooth .
Cusp reduction for an amalgam restoration should
result in a uniform amalgam thickness over the
reduced cusp of 1.5 to 2 mm.
The thicker amount is necessary for functional
To reduce the cusp, orient the No. 245 bur parallel
to the cuspal incline and make several depth cuts
in the cusp (to a depth of 1.5 or 2 mm).
Use the bur to reduce the cusp, following the
mesiodistal inclines of the cusp. This results in a
Cusp capping reduces the amount of vertical
preparation wall heights and, therefore, increases
the need for the use of secondary retention
Maxillary first molar.
May require extending through the oblique ridge to unite the
proximal preparations with the occlusal step.
Cutting through the oblique ridge is indicated only if:
(1) the ridge is undermined with caries,
(2) it is crossed by a deep fissure, or
(3) occlusal portions of the separate MO and DO outline forms
leave less than 0.5 mm of tooth structure between them.
The remainder of the outline form is similar to the two-surface
Extending the facial or lingual wall of a proximal box to include the
entire cusp is done (if necessary) to include weak or carious tooth
structure or existing restorative material.
MANDIBULAR FIRST MOLAR
The distal cusp on the mandibular first molar may be weakened
when positioning the distofacial wall and margin.
When the distal cusp is small or weakened or both, extension of
the distal gingival floor and distofacial wall to include the distal
cusp places the margin just mesial to the distofacial groove.
Capping the distal cusp is an
alternative to extending the entire
distofacial wall when the occlusal
margin crosses the cuspal eminence.
Whenever possible, capping the distal
cusp is more desirable than extending
the distofacial margin because the
remaining portion of the cusp helps in
applying the matrix for the
development of proper embrasure
form. It also conserves tooth structure.
The cusp reduction should result in a
butt joint between the tooth structure
and the amalgam.
The successful and intelligent practice of operative dentistry is
based on a thorough knowledge of fundamentals of laws of
The wise operator who views each preparation with a discerning
eye can render the patient an excellent service!!
Theodore M. Roberson, Harald O. Heymann, Edward J. Swift,
Sturdevant’s Art and Science of Operative Dentistry; Fifth edition
James B Summit, J.W. Robbins, Richard S Schwartz,
Fundamentals of operative Dentistry a contemporary approach;