tooth preparation/ dental implant courses

CLASS II AMALGAM
TOOTH PREPARATION
• Class II Restorations are the
Restorations on the proximal surfaces of
posterior teeth.
INDIAN DENTAL ACADEMY
Leader in continuing Dental
Education
www.indiandentalacademy.com

The stages and steps in tooth preparation are:
• Initial Tooth Preparation Stage
Step 1: Outline form and initial depth
Step 2: Primary resistance form
Step 3: Primary retention form
Step 4: Convenience form
• Final Tooth Preparation Stage
Step 5: Removal of any remaining infected dentin &/or
old restorative material, if indicated
Step 6: Pulp protection, if indicated
Step 7: Secondary resistance and retention forms
Step 8: Procedures for finishing external walls
Step 9: Final procedures: cleaning, inspecting, sealingwww.indiandentalacademy.com

STEP 1: OUTLINE FORM AND INITIAL
DEPTH
• The first step in initial tooth preparation is
determining and developing the outline form while
establishing the initial depth.
• The preparation is extended internally
no deeper than 0.2 mm into dentin for pit &
fissure lesions and
0.2 to 0.8 mm into dentin for smooth surface
lesions

• sound external walls should have a pulpal depth
of approximately 1.5 to 2 mm and usually a
maximum depth into dentin of 0.2 mm
• When two pit-and-fissure preparations have less
than 0.5 mm of sound tooth structure between
them, they should be joined to eliminate a weak
enamel wall between them.

RULES FOR ESTABLISHING OUTLINE FORMS FOR
PROXIMAL SURFACE TOOTH PREPARATIONS
1. Extend the preparation margins until sound
tooth structure is obtained and no
unsupported and/or weakened enamel
remains.
2. Avoid terminating the margin on extreme
eminences such as cusp heights or ridge
crests.
3. Extend the margins to allow sufficient access
for proper manipulative procedures.

4.Restrict the axial wall pulpal depth of the proximal
preparation to a maximum of 0.2 to 0.8 mm into
dentin
5.The isthmus width should be as narrow as possible
& should not be more than 1/4th
of the intercuspal
distance or 1-1.5 mm wide
6. Usually, gingival margins of tooth preparations
are extended apically of the proximal contact to
provide a minimum clearance of 0.5 mm between
the gingival margin and the adjacent tooth.

7. Likewise, the facial and lingual margins in
proximal tooth preparations usually are extended
into the respective embrasures to provide specified
clearance between the prepared margins and the
adjacent tooth.
The purpose of this clearance is to place the
margins away from close contact with the
adjacent tooth so that the margins can be better
visualized, instrumented, and restored .

Factors that dictate proximal box are :
• Extent of caries
• Adjacent tooth contact

PROXIMAL OUTLINE FORM
(PROXIMAL BOX)
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.

REVERSE CURVE

STEP 2: PRIMARY RESISTANCE FORM
• Box shape with a relatively flat floor, which helps
the tooth resist occlusal loading by virtue of being
at right angles to those forces of mastication that
are directed in the long axis of the tooth;
• Enough thickness of restorative material to
prevent its fracture under load
• A slight rounding (coving) of internal line angles
to reduce stress concentrations in tooth structure;
• The reverse curve optimizing the strength of both
the amalgam and tooth structure at the junction of
the occlusal step and proximal box

• Internal and external angles within the
tooth preparation are slightly rounded
(coved) so that stresses in the tooth and
restoration from masticatory forces will not
be as concentrated at these line angles .
• Rounding internal line angles (those with
apices directed internally) reduces the
stress on the tooth, thus resistance to
fracture of the tooth is increased.
• Rounding external angles (those with
apices directed externally [e.g., axiopulpal
line angles]) reduces the stress on some
restorative materials (amalgam and
porcelain), thus increasing resistance to
fracture of the restorative material.

• Restorative material thickness affects the
ability of a material to resist fracture.
• Amalgam requires a minimum occlusal
thickness of 1.5 mm for adequate strength
and longevity in relation to wear.

STEP 3: PRIMARY RETENTION FORM
• For amalgam restorations in Class II conventional
preparations, the material is retained in the tooth by
developing external tooth facial and lingual walls of the
occlusal portion of the preparation, as well as the
proximal portion converge toward the occlusal surface.
• The cavosurface angle where the proximal facial and
lingual walls meet the marginal ridge is a desirable 90°
because of the occlusal convergence of the preparation.
• In Class II preparations involving only one of the two
proximal surfaces, an occlusal dovetail may aid in
preventing the tipping of the restoration by occlusal
forces.

STEP 4: CONVENIENCE FORM
• On occasion, obtaining this form may necessitate
extension of distal, mesial, facial, or lingual walls
to gain adequate access to the deeper portion of
the preparation.
• Extending proximal preparations beyond proximal
contacts is a type of convenience form.

FINAL TOOTH PREPARATION STAGE
Step 5: Removal of Any Remaining Enamel Pit or
Fissure, Infected Dentin, and/or Old Restorative
Material, if Indicated.
• Large areas of soft caries usually are best removed with
spoon excavators by flaking up the caries around the
periphery of the infected mass and peeling it off in
layers. The bulk of this material is thus easily removed
in a few large pieces.

• Pulpal damage may result from the creation of
frictional heat with the use of a bur while removal
of the harder, heavily discolored dentin.
The ideal method of removing this material would
be one in which minimal pressure is exerted,
frictional heat is minimized, and complete control
of the instrument is available.
• Examination of the area with an explorer
following the removal of infected dentin is
advisable, but should be done judiciously to avoid
perforation into the pulp.

• Removal of remaining old restorative material,
when indicated, also is accomplished with use of a
round carbide bur, at slow speed (just above stall-
out) with air or air water coolant.
• The water spray (along with high-volume
evacuation) is used when removing old amalgam
material to reduce the amount of mercury vapor.

STEP 6: PULP PROTECTION, IF
INDICATED
• When the thickness of the remaining dentin is
minimal [1.5 mm ], heat generated by injudicious
cutting can result in a pulpal burn lesion, an
abscess formation, or pulpal necrosis. Thus a
water or air-water spray coolant must be used
with the highspeed rotary instrument.
• liners or bases are used to protect the pulp or to
aid pulpal recovery or both.
• Liners and bases in exposure areas should be
applied without pressure.

• Both zinc oxide-eugenol and calcium hydroxide
liners (chemosetting types that harden) in
thicknesses of 0.5 mm or greater have adequate
strength to resist condensation forces of
amalgam and provide protection against short-
term thermal changes.
• As a general rule, it is desirable to have
approximately a 2mm dimension of bulk
between the pulp and a metallic restorative
material.
This bulk may include remaining dentin, liner,
and/or base.

STEP 7: SECONDARY RESISTANCE
AND RETENTION FORMS
• Because many preparation features that improve
retention form also improve resistance form, and
the reverse is true, they are presented together.
• The secondary retention and resistance forms are
of two types:
(1) mechanical preparation features and
(2) treatments of the preparation walls with
etching, priming, and adhesive materials.

Mechanical Features
Retention locks and grooves
• Vertically oriented retention locks and retention grooves
are used to provide additional retention for proximal
portions of some tooth preparations; the locks are for
amalgams and the grooves are for cast metal
restorations
• Retention locks in Class II preparations for amalgam
restorations are generally thought to increase retention
of the proximal portion against movement proximally
due to creep.
• Also, they are believed to increase the resistance form of
the restoration against fracture at the junction of the
proximal and occlusal portions.www.indiandentalacademy.com

Pins, slots, steps, and amalgam pins
• The use of pins and slots increases both
retention and resistance forms
Enamel wall etching
• Enamel walls are etched for bonded
restorations that use porcelain, composite,
or amalgam materials.

STEP 8: PROCEDURES FOR FINISHING THE EXTERNAL
WALLS OF THE TOOTH PREPARATION
• Nevertheless, when a preparation has extended onto
the root surface (no enamel present), the root-surface
cavosurface angle should be either 90 degrees (for
amalgam, composite, or porcelain restorations) or
beveled (for intracoronal cast metal restorations).
• The 90-degree root-surface margin provides a butt
joint relationship between the restorative material and
the cementum/dentin preparation wall, a configuration
that provides appropriate strength to both.

• line angles formed by the junction of
enamel walls should be slightly rounded
whether they are obtuse or acute.
• when extending the facial and lingual walls
to remove extensive occlusal caries, tilting
the bur is often indicated to conservatively
extend the margins and provide a 90 to 100
degree cavosurface angle.

• When amalgam is used, bevelling also is
contraindicated, except on the gingival floor of a
Class II preparation when enamel is still present.
• In these instances, it is usually necessary to place
a slight bevel (approximately 15 to 20 degrees)
only on the enamel portion of the wall to remove
unsupported enamel rods.
• This is necessary because of the gingival
orientation of enamel rods in the cervical area of
the tooth crown.

• The degree of desired smoothness or roughness is the
second consideration in finishing external walls.
• Hand instruments such as enamel hatchets and
margin trimmers may be used in planing enamel
walls, cleaving enamel, and establishing enamel
bevels.
• The restorative material used is the primary factor
dictating the desired smoothness or roughness of an
enamel wall.
• when using amalgam restorative materials, a more
rough surface prepared wall markedly improves
resistance to marginal leakage.

STEP 9: FINAL PROCEDURES:
CLEANING, INSPECTING, AND SEALING
• Final procedures in tooth preparation
include the cleaning of the preparation,
inspecting the preparation,and applying a
sealer when indicated.

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