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The old style of “cusp capping” is
wasteful of tooth structure, adds difficulties to the
restoration of occlusal height and is un-aesthetic.
This proposal offers strength to the occlusal surface sufficient to accept the
masticatory load and at the same time retains cusp height to facilitate
restoration
of the occlusal anatomy. It is also more aesthetic. |
The concept is to recognise the need in a given cavity where
the medially facing cusp incline is potentially under load
from mastication and the base of the cusp is at risk.
Leave
the bucco-lingual width of the cavity unchanged at the gingival
floor but lean the buccal and lingual walls outwards towards
the tip of the cusps. For non-working cusps there is generally
no need to shorten the cusp more than half a millimetre but
for working cusps shorten them about 1.5 to 2 millimetres.
Develop all retention in the gingival one third of the crown
of the tooth using ditches and grooves to engage the central
core of remaining dentine.
Cut the grooves with a 700 tapered
fissure bur so the amalgam can be packed fully into the groove.
Take care with matrix placement and be prepared to over-pack
the cavity and carve back to occlusal contour.
The diagram explains the basic principals and the following
laboratory case demonstrates the preparation procedures. |
AMALGAM RESTORATION
WITH CUSP PROTECTION - LAB |
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|
 figure1 |
The following
series shows this principle applied to a large cavity in an
upper molar, restored as a laboratory exercise. The first
illustration shows the cavity following removal of an old
failed amalgam. |
 figure2 |
A view from
the mesial of the lesion demonstrating the extent of the unprotected
medially facing incline on the two cusps which are obviously
subject to occlusal load and therefore to future splits at
the base of the cusp. |
figure3 |
The tapered diamond
bur is half way through the palatal cusp showing the extent
of the modification required for a load bearing cusp. Note
that there is no change to the width of the cavity at the
gingival floor. |
figure4
|
A similar modification
has been carried out on the buccal cusp but the amount of
protection is less. Now a standard tapered fissure bur is
being used to develop retention in under the buccal cusp.
|
 figure5
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The buccal and
lingual retentive grooves have been completed and now a small
dovetailed subsidiary lock is being placed in sound dentine
on the occlusal in some position between the two horns of
the pulp. |
figure6 |
The final cavity
is now complete. Note the retentive groove to the buccal under
the cusp and the subsidiary ditch at the end of the buccal
groove. |
figure7
|
A high strength
auto cure glass-ionomer has been placed in the central area
where there was some remaining demineralised dentine. This
is now expected to remineralise and heal. |
figure8 |
The cavity has
now been restored with amalgam. This is the material of choice
for a lesion of this size particularly in view of the expected
occlusal load and the need to protect the cusps from the potential
for splits. |
figure9 |
A view of the
mesial surface of the restoration illustrating the extent
of the protection offered by the amalgam over the palatal
cusp. |
AMALGAM
RESTORATION WITH CUSP PROTECTION - CLINICAL |
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|
figure1 |
A clinical case
showing a series of old amalgam restorations in the upper
right quadrant that require replacement because of the presence
of faulty margins, overhangs and over contour. |
figure2 |
The old restorations
have been removed and it is apparent that the disto-lingual
cusp on the molar, both buccal and lingual on the second bicuspid
and the lingual cusp on the first bicuspid required protection
against heavy occlusal load. |
figure3 |
The completed
cavity designs showing that these cusps have all been bevelled
to the extent that they can be covered as shown in the previous
diagram. Note the presence of 4 pins. This technique for
additional retention is no longer acceptable because of the
potential for corrosion leading to microleakage. |
figure4 |
The completed
restorations photographed at the polishing appointment. Note
the amount of amalgam coverage over those cusps that required
protection. |
figure5 |
The same restorations
approximately 8 years after placement. Note that the protection
appears to be effective. |
figure6 |
The same quadrant
approximately 15 years after placement. The buccal cusp of
the second bicuspid failed and it was decided to crown both
bicuspids in anticipation of catastrophic failure of either
or both bicuspids. |
| COMPOSITE
RESIN RESTORATION USING LAMINATION TECHNIQUE |
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|
figure1 |
A laboratory
simulation has been set up to show the stages required for
placement of a Site 2, Size 3 restoration using a lamination technique
with composite resin |
figure2 |
The completed
cavity design showing the typical cusp cover for the disto-lingual
cusp. Note the limited extension to the buccal of the disto-buccal
cusp. |
figure3 |
The entire cavity
has been restored with a high strength, auto cure, fast set
glass-ionomer. |
figure4 |
A composite
resin cavity has now been prepared leaving about 3.0mm of
space
on the occlusal to compensate for the relative flexibility
of the composite resin. |
figure5 |
The entire cavity
is now etched with 37% orthophosphoric acid for 15 seconds
to allow for a micromechanical union between the glass-ionomer,
the enamel margins and the composite resin. |
figure6 |
A thin layer
of an unfilled light activated resin enamel bond is
now painted over both the enamel and the GIC and light activated
to provide a bond between the different materials. |
figure7 |
A small section
of mylar strip can now be trimmed and contoured to act as
a matrix. It is then wedged firmly into place to develop some
degree of separation to enhance the contact area. |
figure8 |
The second increment
can now be placed against the lingual wall and again light
activated through the tooth structure to try to control the
direction of shrinkage. |
figure9 |
The finished
restoration. At this point the rubber dam can be removed and
the occlusion adjusted. Then apply a further light coat of
resin bond and light activate again to make sure the composite
resin is as fully converted as possible. |
figure10 |
As this was
a laboratory case it was possible to remove the tooth and
section it to show the ultimate relationship between the cavity,
the glass-ionomer and the composite resin. |
