Transcript USC/RKH AEGD PROGRAM PRECLINICAL ENDODONTIC …

 Dental
amalgam
has
been
used
in
operative dentistry for not less than 150
 years.
Almost
80%
of
single
tooth
restorations are fabricated from amalgam,
 in
view of its numerous advantages,
which include:
Advantages
1- Good adaptability to cavity walls and margins 
i.e. provides good seal that prevents:
1) Recurrence of caries.
2) Irritation to dentin and pulp.
2- High compressive strength → minimum 80 MN /
m2.
3- Low coefficient of thermal expansion when
compared to other restorative materials: →
 Amalgam → 25 x 10-6.
 Tooth → 11.5 x 10 -6.
Advantages
4- Indestructible in oral fluids → i.e.
maintains marginal seal, proximal contact
and contour.
5- Biologically compatible with oral tissues.
6- Convenience of manipulation.
7- Could take and maintain high surface
polish that increases the strength.
8- Low coast.
Disadvantages
4- Thermal conductivity.
5- Dimensional changes during setting → 
20  / cm.
6- Poor esthetic.
Fracture
INDICATIONS
Amalgam
should
be
considered
together with posterior composite and
cast gold as a restorative for classes I,
II, the distal surface of cuspids and
class V in posterior teeth. Material
selection in such cases will depend on:
A) THE EXTENT OF THE LESION:
 The
most suitable indication for amalgam
is the small and medium sized class I and
II cavities especially those with four walls
and a floor, where the amalgam will be
confined and not subjected to tensile
loads.
 Extensive
lesions
especially
those
including undermined cusps will require
cusp capping and tooth supported against
high loads including tensile, where cast
gold will serve better.
B) ESTHETICS:
 For
will
esthetic-conscious patients, amalgam
be
objectionable
particularly
in
conspicuous areas of teeth and posterior
composites may be favored.
C) CARIES INCIDENCE:
 Amalgam
may be favored if repair or
remake is likely to include extensions for
original cavities and for patients with
moderately high caries incidence; being
less costly and having good sealing ability.
D) ECONOMICS:
 Although
amalgam restorations cost far
less than cast gold restorations yet costing
per se may not be in favor of amalgam in
the long run if the restoration has to be
repeatedly be made. Amalgam can also
be used for core build-up under full
crowns.
Cavity preparation
 Cavity
preparation for amalgam restoration
is characterized by: →
 CSA 90C.
 Cavity walls parallel or perpendicular to
the direction of occlusal force.
 Enough depth to provide bulk to the
material.
Cavity preparation





If a cusp is undermined and is to be capped
with amalgam, it must be reduced minimum of
2 mm, to provide enough bulk of the amalgam
enables it to withstand the tensile stresses.
The isthmus area shows: → Minimal buccolingual width.
→ Axio-pulpal line
angle beveled, rounded or saucerized to
provide:
a) Elimination of stress concentration
area.
b) Bulk of amalgam.
B) DESIGNS OF CLASS I CAVITY
PREPARATION
 Cavity
preparation for Class I lesions for
amalgam restoration. It may be either:
 A-
Class I simple cavity.
 B-
Class I buccal pit cavity.
 C-
Class I extension cavity.
Definition:
These are pit and fissure type cavities
that involve the occlusal surfaces of
molars and premolars, the occlusal 2/3
of buccal and lingual surfaces of molars,
and the palatal pits in maxillary anterior
teeth.
 These are self-cleansable areas.
However, they may get involved by
caries due to their inherent defective
structure as areas of imperfect
coalescence of lobes of calcification
of these teeth. These areas are
retentive for food and thus invite
caries.
These lesions are
clinically characterized
by:
1. A small surface opening which may remain
unnoticed until the lesion becomes of a
considerable size.
2. A conical spread in both enamel and
dentin, with the bases of cones at the
Amelo-Dentinal Junction, "A. D."J.
3. Its rapid burrowing at the dento-enamel
junction. These lesions may involve one or
more surfaces and hence a simple or
compound cavity should be prepared.
Simple occlusal cavities
Designing the Outline Form.
The outline form of a routine class I cavity
should describe a symmetrical design running in
sweeping curves along all pits, fissures, and
angular grooves between the cusps and with a
minimum width.
The mesial and distal margins are
placed midway between the bottom
of the proximal fossae and the
crest of the proximal ridges and in a
direction parallel to these ridges.
 The mesial and distal wall should
have a slant or slight divergence
from the pulpal floor outward to
avoid undermining the marginal
ridges.
In a bucco-Iingual direction, the cavity
is extended just sufficient to eliminate
the defective and susceptible tissues.
The lingual and the buccal wail should
be parallel to the respective tooth
surface.
 It must be reemphasized that the
outline form for class 1 cavities
should be very conservative since
they involve cleansable areas.
It is governed only by the extent of
caries in both enamel and dentin and
the amount of extension or need to
eliminate pits and fissures to secure
smooth margins.
Again:

The outline form for simple design of Class
I cavity preparation should include all
carious and undermined enamel, all pits and
fissures and extended to area self-cleansable
in the shape of multi curves without any
 sharp line angles.

Bucco-lingually, it should not extend
beyond the intercuspal line except if there is
caries with minimal width of the cavity
about 1/4 - 1/3 the inter-cuspal distance.
Mesio-distally, it should be extended mid
way between the triangular fossa and the
crest of the marginal ridge.
The resistance form

Achieved by maximum conservation of
sound tooth structure. Also, considering the
amalgam as a brittle material, cavo-surface

margin configuration of 90oC provides both
the enamel margins and the amalgam
restoration with enough bulk at margins to
resist the fracturing forces

Minimal cavity width and providing bulk of
the restoration through a cavity depth at
level of 0.2-0.5-mm beyond the DEJ will
provide minimal surface area of the
restoration exposed to the occlusal loading
force with bulk strength through the depth.

Flat and smooth pulpal floor parallel to the
occlusal
plane
will
help
in
proper
distribution of occlusal forces and provides
stability that deletes the wedging action of
the restoration upon the tooth structure.
Roundation of axial line angles also
eliminates stress concentration.
Retention form:

Only retention against axial displacement is
needed in the form of mechanical undercuts
in dentin by converging the cavity walls
occlusally about 5 - 15° from the tooth long
axis.
Convenience form

In simple Class I cavity design, no need for
convenience in as it is easily seen and
instrumented.

Only, accentuation of cavity walls, line and

point angles and selection of suitable sized
instruments is considered as a satisfactory
convenience.
Removal of Carious
Dentin
 In small size cavities, the carious dentin
should have been removed during making the
cavity extensions.
 In moderately deep and deep cavities, the
carious dentin is peeled off carefully at the
sides using large spoon excavators, and then
scooped out in few and large pieces.
 Only light pressure in a direction parallel to
that of the pulp is utilized. This is continued
until a sound dentin floor is reached.
Planning of Enamel
Walls
The enamel walls of the cavity should be
finished free from any loose, short, or
undermined enamel, and trimmed to meet the
tooth surface at a right cavo-surface angle.
This may be done by sharp and regularedged chisels and hatchets, plane fissure
burs, stones, or sand-paper discs.
All sharp corners in enamel must be rounded,
as they may contain short enamel rods.
Performing of the toilet
of the cavity
A sharp explorer is then used to check
the details of the prepared cavity and to
loosen the tooth debris which are then
blasted out with warm air.
Procedure
The outline form is performed by first
gaining access through the enamel to
the carious dentin floor of the cavity
followed by making the necessary
cavity extensions.
In case of initial carious lesions, access
is obtained by employing a small sized
round bur.
 In big carious lesions, access is
obtained easily by breaking down the
undermined enamel overlying the carious
dentin, using a suitable size chisel.
 In either case, access is started at the
most defective area of enamel, i.e., a
carious pit or fissure.

 The bur is held at a right angle to
the involved surface of, the tooth and
light pressure in an in-and-out
direction is exerted. Cutting is
continued until the amelo-dentinal
junction (A.D.J.) is reached.
 The
necessary cavity extensions
through pits, fissures, and deep
developmental grooves are made using an
inverted cone bur held at right angle to the
surface of the tooth.
The bur is rotated, and carefully
introduced through the opening just
obtained, so that its weak corners do not
touch the enamel and get dulled.
With the bur seated in the cavity just
below the amelo-dential junction ½ -1 mm.
gentle pressure is applied in the direction
of required extension.
During cutting, the bur should be kept
moving in-and-out of the cavity and at
right angle to the tooth surface. In this
way, the bur will undermine and lift the cut
enamel, and at the same time unclog itself.
Provision of ample resistance and
adequate retention through boxing of
the preparation could be obtained.
This is obtained by using a fissure bur
held perpendicular to the surface of the
tooth. All the line angle in dentin must
be squared up hoe excavators.
Buccal Pit Cavities
The outline of these cavities usually
describes a triangle with its base faming
the gingival wall and its sides forming
the mesial and distal walls.
The gingival wall is placed at or
slightly occlusal to the height of contour
of the tooth.
All walls are extended just enough to
eliminate defective enamel and dentin.
The enamel walls are planed in the
direction of enamel rods and
perpendicular to the axial wall.
Hoe excavators are used to smooth
the axial wall and make it parallel with
the external surface of the tooth.
It should be re-emphasize that the
shape of the cavity will be governed by
the extension of caries, accordingly
the outline of these cavities may be a
rounded or oval in shape.
Class I extension cavity:
• Compound or complex Class I cavity
design is an extension of the occlusal
cavity to buccal or/and lingual surfaces
It is indicated in:
• 1. Deep caries in buccal or / and lingual
pits.
• 2. Deep fissure or groove extended from
the occlusal to the lingual or / and buccal
surfaces.
• 3. Fissure crossing the oblique ridge in
upper molars.
• 4. When the remaining oblique ridge in
upper molars or transverse ridge in lower
premolars is weak (Fig. 4-4, A and B), it is
a must to be included in the cavity outline
to avoid its fracture.
The outline form:
• The outline form of compound or complex
Class I design is the she same as simple
Class I cavity preparation in addition to
extension to include the carious or
retentive area either buccal or/and
lingually.
• It may be extended with step, forming axial
wall and gingival floor, or without step, in
• cases showing extended caries or fissure
at the level of the pulpal floor.
• The formed step will provide inclusion of
the carious or retentive area without
• endangering the pulp.
Resistance form:
• The same features of resistance form as
simple Class I is performed in addition to:
roundation of axio-pulpal line angle to
prevent
stress
concentration
and
to
provide bulk to the restoration at this
critical area.
• The axial wall direction should be parallel
to the corresponding external tooth
• surface,
i.e. convex, in order to prevent pulp exposure
and
provide
restoration.
uniform
thickness
of
the
• Axial retention in the form of mechanical
undercuts in dentin, the same as simple
Class I, in addition to occlusal lock against
lateral
displacement.
Extension
for
retention to the other opposing surface to
• provide
cavities.
lateral
retention
in
extensive
Convenience form:
• When
the
cavity
design
becomes
compound or complex Class I preparation
no need for extra convenience than that of
simple Class I cavity as the extension
portion is also easily seen and reached.
Finishing of enamel walls
• The enamel wall should take the same
direction
of
enamel
rods
without
undermining or weakening with cavosurface margin of 90°.
• The mesial and distal walls of the
extension will be completely parallel to
each other and to the long axis of the
tooth,
• while the gingival floor of the extension
portion will be slightly slanting gingivally to
be in the same direction of enamel rods.
Designs of Class II cavity
preparation
• Class II cavity preparation for amalgam
restoration mat be:
• 1. Class II compound or complex cavity
with proximal step.
• 2. Class II compound or complex cavity
without proximal step.
• 3. Class II simple cavity.
1. Class II compound or complex cavity
with proximal step:
• Compound or complex Class II cavity
preparation with step consists of three
portions, occlusal, isthmus and proximal
portion.
• The isthmus portion is defined as the
narrowest
connection
between
the
occlusal and proximal portions of class II
compound or complex cavity.
• The outline of the isthmus portion should
be extended to involve all the carious
enamel and dentin and place the cavity
margins
in
area
self-cleansable
freeing of the proximal contact area.
with
• According to the occlusal anatomy of the
tooth, the position and size of the proximal
contact area and width of the embrasure,
the isthmus outline form may follow one of
the following Ingrham’s lines
• These lines may be straight; in case of
small contact area,
• uniform; in case of normal sized contact
area .
• or reverse curve; in case of broad or wide
contact area.
• The reverse curve outline will be followed
in the buccal wall more than the lingual as
the contact area is much more shifted
buccally.
• The width of the cavity at isthmus should
be narrow bucco-lingually as much as
possible, about 1/4 the inter-cuspal
distance. The occlusal outline is similar to
that of Class I cavity preparation
• The proximal outline should be extended
enough to ensure involvement of all
carious enamel and dentin, freeing the
proximal surface out of contact lingually,
buccally and gingivally and placing the
cavity margins in the embrasures to be in
area selfcleansable.
• The axial wall is about 0.5 – 0.8-mm away
from the DEJ to provide enough bulk of
the restoration.
• The axial wall should be in a direction
parallel to the external proximal tooth
surface,
– i.e. it will be either straight or convex to
provide enough uniform bulk of the restoration
and protection of the pulp against traumatic
exposure.
• It is preferable to complete the proximal
outline before breaking the marginal ridge
and proximal enamel plate (Proximal ditch
cut) (Fig. 4-6,
• 7 and 11, A and B).
This will provide:
• 1. A guide to proximal design.
• 2. Protection of the proximal surface of the
adjacent tooth from rotary instrument.
• 3. Save time and effort.
• 4. Reduce heat generation as cutting in
enamel
produces
generation.
much
more
heat
• 5. Enamel wall in the direction of enamel
rods.
• 6. CSA 90°.
• 7. Freeing of the contact area with
maximum
structure.
conservation
of
the
tooth
Resistance form:
• Resistance of isthmus portion is achieved
by minimal width of the cavity bucco-
lingually about ¼ the inter-cuspal distance.
– This will provide decrease in the surface area
of restoration subjected to the occlusal
stresses.
• Roundation, beveling or saucerization of
the axio-pulpal line angle, to provide
removal of sharp axio-pulpal line angle
that acts as stress concentration area and
increased bulk of restoration at isthmus
area
• Reverse curve in case of wide proximal
contact
area
will
provide
maximum
conservation of the sound tooth structure
during freeing of the contact, removal of all
undermined enamel and correct cavosurface configuration of 90°
• Resistance of proximal portion is achieved
by performing cavosurface configuration of
90°.
• The gingival floor should be smooth, flat
and parallel to the pulpal floor and the
occlusal plane.
• The axial wall should be parallel to the
external proximal tooth surface and be at
0.5-0.8-mm away from the DEJ, To
provide uniform bulk of the restoration.
• The buccal and lingual walls should be
parallel
to
corresponding
the
direction
surfaces
of
to
the
avoid
weakening of cusps.
• In general, the proximal portion should be
a box form.
Retention form:
• Axial retention features includes,
• 1) mechanical undercuts by preparing the
cavity walls slightly converging occlusally,
2) the inverted truncated cone shape of
the proximal portion,
• 3) proximal axial grooves
• 4) pin retention in extensive cavities
placed in the gingival floor.
Retention form:
• lateral retention features includes
• 1) dove tail, which is considered as
extension for retention in premolars,
considered extension for prevention that
provides retention also in molars
• 2) occlusal lock.
• 3) proximal axial grooves.
• 4) pin retention in extensive cavities.
• Proximal axial grooves are cut in the axiobuccal and axio-lingual line angles, in the
expense of buccal and lingual walls rather
than the axial wall to avoid pulp exposure.
They should extend from the gingival floor
in occlusal direction up to the level of the
pulpal floor.
• These grooves are wider internally than
externally
and
wider
gingivally
than
occlusally.
• They are prepared using small round bur
or small tapered fissure bur
Convenience form:
• Cutting an occlusal cavity is considered as
a
convenience
form
as
it
provides
accessibility to the proximal portion.
• The axial wall should be parallel to the
tooth long axis in occluso-gingival direction
to allow instrumentation up to the depth of
the proximal portion..
• Also, accentuation of cavity walls and
margins, roundation of line angles and
selection of suitable sized instruments are
important convenience features
Buccal and Lingual
Extensions
In case of occluso-buccal and occlusolingual cavities extensions are made
through the fissures and towards the
respective surfaces.
The cutting is done in dentin at the
amelo-dntinal junction using a #56 bur
until the ocdusal ridge is undermined
and removed.
If the caries is still gingival to the
level of the pulpal seat, a step is
indicated: a #330 or 56 but is used
to cut the dentin at the amelodentinal junction, applying pressure
in a gingival direction and at the
same time moving the bur mesiodistally.
The enamel thus undermined, is broken
down with chisels.
Retention grooves are then cut in
dentin along the axio-mesial and axiodistal line angles. The cavity walls and
margins are finished as previously
described.
In case of deeply-seated caries,
where removal of the carious dentin
will leave a round cavity floor,
flattening of which to obtain the
required resistance form, will expose
the pulp.
The following
technique is used:
a) The cavity floor is covered with
a sub base of calcium hydroxide,
followed by a base of glass
ionomer cement which fills it to
the routine cavity depth.