CLASS II AMALGAM RESTORATIONSCLASS II AMALGAM RESTORATIONS
Initial Clinical Procedures:
Tooth Preparation
Initial tooth preparation: Occlusal outline form (occlusal
step): The occlusal outline form of a class II tooth
preparation for amalgam is similar to that for the class I
tooth preparation. Using high speed with air-water spray,
enter the pit nearest the involved proximal surface with a
punch cut using a No. 245 bur.
Entering the pit nearest to the involved proximal surface
allow the mesial pit (in this case) not to be included if it is
sound. Proper depth of the initial entry cut is 1.5 to 2mm
(i.e., one half to two thirds the length of the cutting portion
of a No. 245 bur), 1.5mm as measured at the central
fissure, and approximately 2mm on the prepared external
walls
This pulpal depth usually 0.1 to 0.2mm into the dentin.
While maintaining the same depth and bur orientation,
move the bur to extend the outline to include the central
fissure and the opposite pit.
For the very conservative preparation, the isthmus width
should be as narrow as possible and no wider than one
quarter the intercuspal distance.
The pulpal floor should be prepared to a uniform
(previously described) depth (and is usually flat). However,
the pulpal floor of the preparation should follow the slight
rise and fall of the DEJ along the central fissure in teeth
with prominent triangular ridges.
During development of the distal pit area of the preparation,
extension to include any distofacial and distolingual
developmental fissures radiating from the pit may be
indicated. The distal pit area provides dovetail retention
form, which may prevent mesial displacement of the
completed restoration.
Before extending in to the involved proximal marginal ridge
visualize the final location of the facial and lingual walls of the
proximal box relative to the contact area.
Viewed from the occlusal a reverse curve in the occlusal outline
of a class II preparation, which often results when developing the
mesiofacial wall perpendicular to the enamel rod direction and
conserving the facial cusp structure.
Lingually, the reverse curve usually is minimal (if necessary at
all) because the embrasure form is larger.
While maintaining the established pulpal depth and with the
bur parallel to the long axis of the tooth crown, extend the
preparation mesially, stopping approximately 0.8mm (the
diameter of the end of the bur) short of cutting through the
marginal ridge in to the contact area.
The location of the DEJ is an important guide in the
development of the proximal preparation.
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 0.5mm clearance
with the adjacent proximal surface facially, lingually
and gingivally.
The Initial procedure in preparing the outline form of the
proximal box is the isolation of the proximal (i.e., mesial)
enamel by the proximal ditch cut. This is a very important
procedure in conservative tooth preparation.
With the same orientation of the bur, position it over the DEJ
in the pulpal floor next to the remaining mesial marginal ridge.
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 0.8mm diameter bur end will cut approximately 0.5 to
0.6mm into dentin and 0.2 to 0.3mm into enamel.
Extend the ditch gingivally just beyond the caries or the
proximal contact, whichever is greater. Because dentin is
softer and cuts more easily than enamel, the bur should be
cutting away the dentin immediately supporting the enamel.
A guide for the gingival extension is the visualization that
the finished gingival margin will be only slightly gingival
to the gingival limit of the ditch. This margin should clear
the adjacent tooth by only 0.5mm in a small tooth
preparation.
The location of final proximal margins. (i.e facial, lingual,
gingival) should be established with hand instruments (i.e.,
chisels, hatchets, trimmers) in conservative proximal box
preparations. Otherwise, these margins may be
overextended to achieve 90-degree cavosurface margins
with the No. 245 bur.
The proximal ditch cut should be sufficiently deep in to
dentin (i.e., 0.5 to 0.6mm) that retention locks, if deemed
necessary, can be prepared into the axiolingual and
axiofacial line angles without undermining the proximal
enamel.
G IH
A CB
BA
The proximal ditch cut may be diverged gingivally to ensure
that the faciolingual dimension at the gingival is greater than
at the occlusal.
The gingival divergence contributes to retention form and
provides for desirable extension of the facial and lingual
proximal margins to include defective tooth structure or old
restorative material at the gingival level, while conserving the
marginal ridge and providing for 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.
This weakens the remaining enamel by which the isolated
portion is held. If this level is judged to be insufficiently
gingival, additional gingival extension should be
accomplished using the isolated proximal enamel that is
still in place to guide the bur. This prevents the bur from
marring the proximal surface of the adjacent tooth.
If additional use of the bur is indicated, a matrix band
may be used around the adjacent tooth to prevent marring
its proximal surface.
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.
Primary resistance form is provided
The pulpal and gingival walls being relatively flat and
perpendicular to forces directed with the long axis of
the tooth;
Restricting extension of the walls to allow strong
cusps and ridges areas to remain with sufficient dentin
support
Restricting the occlusal outline form (where possible)
to areas receiving minimal occlusal contact.
The reverse curve optimizing the strength of both the
amalgam and tooth structure at the junction of the
occlusal step and proximal box;
Slightly rounding the internal line angles to reduce
stress concentration in tooth structure
Providing enough thickness of restorative material to
prevent its fracture under mastication.
Primary retention form is provided by the
occlusal convergence of facial and lingual walls and by
the dovetail design of the occlusal step, if present.
A B C
FINAL TOOTH PREPARATION:
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 is removed
with a slowly revolving round bur of appropriate size or a
discoid-type spoon excavator or both.
Stop excavating when a hard or firm feel with an explorer or
small spoon excavator is achieved.
Secondary resistance and retention
forms:
Secondary resistance form in final tooth preparation
involves both resistance of the remaining tooth structure
against fracture from oblique forces and resistance of
restorative material against fracture.
Restricting extensions of external walls provides the
former; the latter is enhanced by using the gingival margin
trimmer to bevel or rounden the axiopulpal line angle,
thereby increasing the bulk of and decreasing the stress
concentration within the restorative material.
The occlusal convergence of the facial and lingual walls and
the dovetail design (if needed) provide sufficient retention
form to the occlusal portion of the tooth preparation.
The occlusal convergence of the mesiofacial and mesiolingual
walls offers retention in the proximal portion of the
preparation against displacement occlusally.
To enhance retention form of the proximal portion,
proximal locks may be indicated to counter proximal
displacement.
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.
Ideally there should be a 90-degree cavosurface angle
(maximum of 100 degrees) at the proximal margin.
The occlusal line angle may be 90 to 100 degrees or
greater. This angle aids in obtaining a marginal amalgam
angle of 90 degrees (no less than 80 degrees).
Clinical experience has established that this “butt joint”
relationship of enamel and amalgam creates the strongest
margin.
Reverse Curve
Matrix systemMatrix system
AA matrix systemmatrix system provides and takes the provides and takes the place of the proximal tooth surface that place of the proximal tooth surface that was removed to restore the proximal was removed to restore the proximal contours and contact to their normal contours and contact to their normal shape and function.shape and function.
Posterior Matrix SystemPosterior Matrix System► Matrix bandsMatrix bands
Matrix bands are made of flexible stainless Matrix bands are made of flexible stainless steel and are available in premolar, molar, steel and are available in premolar, molar, and universal sizes and thicknesses.and universal sizes and thicknesses.
►The The largerlarger circumference of the band is circumference of the band is the the occlusal edgeocclusal edge and is always placed and is always placed toward the occlusal surface.toward the occlusal surface.
►The The smallersmaller circumference of the band is circumference of the band is the the gingival edgegingival edge and it is always placed and it is always placed toward the gingiva.toward the gingiva.
Posterior Matrix SystemPosterior Matrix System
► Universal retainerUniversal retainer Also referred to as the Also referred to as the Tofflemire retainerTofflemire retainer. .
This device holds the matrix band in This device holds the matrix band in position. The retainer is positioned most position. The retainer is positioned most commonly from the buccal surface of the commonly from the buccal surface of the tooth being restored. tooth being restored.
Matrix retainerMatrix retainer
Components of a Universal RetainerComponents of a Universal Retainer
Sectional MatricesSectional Matrices
► A thin polished A thin polished palodentpalodent-type band -type band and a tension ring produce a tight and a tension ring produce a tight anatomic contact for composite resin anatomic contact for composite resin materials for class II restorations.materials for class II restorations.
Sectional matrices.Sectional matrices.
Ivory matrix retainer 1 & 8Ivory matrix retainer 1 & 8
AutomatrixAutomatrix
Compound Supported matrixCompound Supported matrix
Copper BandCopper Band
WedgesWedges
► A A wedgewedge is either triangular or round is either triangular or round and made of wood or plastic. and made of wood or plastic.
► The wedge is inserted into the lingual The wedge is inserted into the lingual embrasure to position the matrix band embrasure to position the matrix band firmly against the gingival margin of the firmly against the gingival margin of the preparation.preparation.
A wedge correctly positioned.A wedge correctly positioned.