This document provides step-by-step instructions for preparing and restoring a Class II amalgam cavity. Key steps include: 1) Starting with the proximal box and ensuring open contacts before connecting to the occlusal surface; 2) Using pear-shaped burs and hand instruments to achieve smooth, convergent walls with even depth; 3) Checking for retention features like a "dove tail" and "reverse S" shape; 4) Condensing amalgam fully into the preparation and carving to achieve proper occlusion, contacts, and anatomy. The restoration is then checked thoroughly for quality.

1. # 26 MO/DO Class II Amalgam Preparation and Restoration
Dear colleague,
I have decided to present to you this specific preparation and restoration since on this
example I can show you the best all the do’s and dont’s of an amalgam preparation and
restoration. This exercise is one of the requirements that we have to meet before we are
allowed to start treating patients.
I have found this particular preparation as one of the more difficult ones because in
order to finish it both mesial and distal parts of the prep have to be well done. The first
time I have attempted to do this preparation I started with the occlusal surface and then
continued with the proximal box. However, at the end, my prep did not meet the specific
requirements because the box had a triangular shape and no reverse “S”. I was wondering
what I was doing wrong, but then during one of our lessons Dr. Gardner suggested to first
start working on the proximal box and finish it, then do the occlusal part of the prep and
only at the end to connect the two. During our next evening practice session I have
attempted this approach and right away I could see the difference!!! You might say that
this was my break through moment and from then on I always start Class II preparations
(amalgam and composite) with the proximal box.
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2. So if you like, I will walk you through the different steps of Ag Class II preparations
and restorations. It does not have to be particularly tooth #26 because you can apply the
same rules to any tooth as long as your material of choice is amalgam. Are you ready?
Buckle up and let’s do this together!
Class II Ag preparation
Open buccal Dove tail
contact
Axiopulpal wall
parallel to
gingival
cavosurface
Gigival contact
open
Lingual contact closed
Open lingual
contact
Any time we start working on a new procedure, we are given a sheet with all the
critical requirements our preparation has to fulfill. However, even before we grab the
handpiece we have to draw a detailed sketch of the particular preparation that has to be
evaluated by peers and instructor. You might think that this is not necessary and time
consuming, but a few times my drawing helped me to prevent mistakes. This way we
prepare a mental plan of the procedure and are less likely to make an error during the
actual preparation.
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3. Pear shaped bur #330.
As previously stated, I will usually start working on my proximal box. Before I use the
handpiece I will carefully look for the contact area and mark it with a pencil. This is a
place where my bur makes a first contact with the tooth. To prevent an iatrogenic damage
to a neighboring tooth I’ll place a green wedge between 25 and 26 as well as matrix band
that I pre-shape to follow the contour of distal part of 25.
In Ag preparations we use pear shaped bur #330 that helps to achieve one of the
critical requirements of Ag prep, occlusaly convergent walls.
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4. Buccal and lingual walls are convergent
Gingival and axiopulpal walls are parallel
Due to its properties, Ag requires this mechanical retention because otherwise it would
be displaced occlusaly and ultimately result in a failure of the restoration (Summitt et al.,
2006). As my bur touches the tooth surface I make sure that it is parallel to the long axis
of the tooth and the bur is following the mesial contour of the tooth which ensures that
the axiopulpal wall will be parallel to the gingival cavosurface (ensures better resistance
to displacement). However, at the same time I carefully move the bur in lingual – buccal
direction. My movements are very minimal because I do not want to open the contact too
much in either direction.
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5. Bur is parallel to the long axis
of tooth.
Fulcrum on the lingual of 26
& 25.
As soon as the contacts are just about to be open I stop working with the handpiece
and start using hand instruments. Off angle hatchets (#44, #45) and gingival margin
trimmers are ideal for this purpose. Hand instruments allow me to remove all
unsupported enamel from the proximal box which could otherwise result in a fracture of
the restoration. By using hand instruments I am able to just open the contacts (we usually
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6. check this if we are able to pass through the open contact the tip of the explorer; to check
if gingival contact is open enough we must remove the matrix band and the wedge and
see whether we can just barely see the rubber dam).
Using off angle hatchet to smooth out the buccal wall of the proximal box.
Opening of buccal, lingual and gingival contacts to a self cleansing area is a next critical
requirement in this preparation. Since amalgam is corrosive, this step is crucial in
prevention of secondary caries (Osborne, & Summitt, 1998). By opening the contacts we
follow G.V. Black’s principle of extension for prevention because corrosive Ag is rough which
creates an ideal surface for plaque adhesion (Gardner, 2007). The use of hand
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7. instrumentation also ensures that the cavosurfaces are smooth which again prevents the
adhesion of bacteria and removal of unsupported enamel as a prevention of fracture. At
this point, my proximal box is almost finished.
Making sure my preparation is wide enough by fitting an
amalgam condenser into the preparation.
Now I have to check if my internal line angles are rounded (for the most part this is
achieved due to the shape of the bur, but can be refined with gingival margin trimmer)
which prevents concentration of stress in one area and fracture of the restoration later on.
As a last step of a proximal box preparation I will check if my box is large enough to
accommodate amalgam condenser. If I am satisfied with the box preparation, I can move
on to the occlusal part of the prep.
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8. Measuring the depth with PQW
probe.
Using off angle hatchet to finish the buccal wall.
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9. Finished distal box of the preparation.
Using the same bur I start at the central pit and move towards the mesial pit while
following the central groove. During this part I am following the tooth’s surface to make
sure that the prep has even depth all around. The optimal depth for Ag preparation is 1.7
± 0.3 mm. This ensures that we get enough bulk of the material which prevents fractures
as well as extension for prevention. At this depth we are extending the prep into dentin
and this way preventing recurrent caries (Gardner, 2007).
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10. Checking for even depth on the occlusal part of the preparation.
After I got the basic shape of the occlusal part I extend my prep facially from the
central pit following the facial groove to form a “dove tail”. This feature further enhances
the mechanical retention of the material and also serves as an extension for prevention
since caries usually extend further following the grooves and fissures. Now I have only
one thing to do: connect the proximal box with the occlusal prep by which I create
reverse “S” that helps to circumvent the cusps and prevent unnecessary removal of a
sound tooth structure and therefore weakening the tooth. This connection has to have
smooth, rounded curves to prevent stress accumulation. It also gives bulk to amalgam and
helps to create cavosurface margins that are 90° (due to the angulation of enamel rods at
this area this ensures removal of unsupported enamel rods).
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11. At the end, I do a final check with a probe to see whether all my walls are convergent,
the surfaces are smooth with even depth and not undercuts. I repeat the same process with
the distal part of the preparation since same rules and restrictions apply.
Features of the Class II preparation: open gingival, lingual, buccal contacts; dove
tail; reverse “S”; convergent walls; even depth; smooth surfaces; no sharp angles.
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12. Class II Ag restoration
Before I start with the actual restoration I make sure that my preparation is clean and
there is no debris. Then I put a tofflemire matrix holder with a pre-shaped matrix band
around the tooth. With a handle of a hand instrument I pre-shape the matrix band in such
a way that in the proximal areas it flares away from my prepped tooth towards the
neighboring one. This ensures that in the proximal area I can condense amalgam really
well and close the contact between the teeth. The placement of a green wedge between
the teeth pushes the teeth even further apart and once the wedge is removed the contact
closes much better.
In our clinic we use 1 or 2 spill amalgam capsules. I prefer to use the 1 spill capsules
which I put into the amalgamator for 5 seconds. I add the first amalgam into the proximal
box and using bucco-lingual movements I pack it well into the box and against the
proximal walls of the box. In a similar fashion I keep adding more amalgam into the
whole prep until it is quite full. I start with the smallest condenser, but as I am
approaching the surface I’ll switch to a larger size. I always make sure that my prep is
overfilled because this way I am sure that I do not overcarve and end up with voids. I do
my rough carving using the Half Hollenback carver with the matrix still on. Using an
explorer at 45° angle to the tooth surface I start shaping the marginal ridge and removing
excess amalgam from the lingual and buccal surfaces of the proximal box. Then I loosen
up the matrix band and with an explorer remove excess amalgam from the lingual and
buccal surfaces. When I am finished, I will remove the tofflemire matrix holder, but leave
the matrix band in place. I pull both loose ends of the matrix band away from the 26 and
straighten them. The next step can be tricky and extra caution at this step never hurts. To
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13. avoid pulling out the freshly packed amalgam from the prep I will put my index finger on
the top of the proximal box and with the other hand I gently pull out the matrix band and
exhale if everything went smoothly.
Removing excess amalgam with an explorer.
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14. With the pointed end of the beach carver I remove excess amalgam from the
interproximal area, making sure that it is flush with no overhangs.
Using half Hollenback to place
the central groove.
At this point I start carving the occlusal part of my restoration. To place the central
groove I use the Half Hollenback carver, where with the flat part of the instrument I
closely follow the tooth surface while the tip is centered between the facial and lingual
cusps forming the groove. Then I switch to cleoid-discoid in order to place the mesial pit.
Carving the mesial pit with
cleoid – discoid carver.
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15. Properly carved distal
pit.
At this time the amalgam is quite set and does not “crumble” as easily which means
that this is the best time to form the marginal ridge. Previously, I used the spoon
excavator and with gentle rounding strokes I went a few times over the ridge. Since we
have switched to a new type of spoon excavator that is not as suitable for this purpose as
the previous one I use the cleoid-discoid carver.
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16. Smooth, rounded marginal ridge at level with neighboring tooth.
Marginal ridge has to be smooth without voids and following a tooth curvature which
was challenging to achieve at the beginning because previously I was impatient and
started to work on the marginal ridge too early. I trim the ridge until it is level with
adjacent tooth which I check using a probe.
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17. Checking the height of the marginal ridge using the explorer.
This brings me almost to the end of my restoration (of course now I have the distal
part to do) and do my final checks. I look whether my restoration is not over- or
undercarved which will result in plaque accumulation, if I achieved proper position of
pits, cusps and their alignment. The surface of the entire restoration must be smooth with
no scratches, overhangs or voids. I’ll clean up the restoration from amalgam shavings
(usually we use moist cotton pellet) and check if the contact between 25 and 26 is closed.
To do this I perform the light test when I look directly between the interproximal area of
these two teeth (similar as when you do bitewings X-rays) and check if there is a light
shining through (if it does  contact is not closed) or carry out the floss test. Before you
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18. do floss tests make sure that the amalgam is fully set because this way a few of my
classmates destroyed their restorations. You simply attempt to floss between 25 and 26. If
the contact is properly closed you must feel a resistance while pushing the floss in and
out. As I got more efficient and faster I began to restore both the mesial and distal parts
of the preparation at the same time.
Closed contact.
As the final stop on our road to a perfect restoration, is the occlusion test. Take the
articulating paper forceps (with articulating paper inserted!) and tell the patient to gently
close the mouth and tap his/her teeth a few times. If you are working on your mannequin
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19. head you have to do it yourself. It is very important to check the occlusion because if the
restoration is too high and patient bites too strongly, the amalgam might fracture and the
entire marginal ridge might fall off. If the preparation has areas that are too high simply
carve them down and repeat the occlusion test until you are happy with the result.
Both contacts are closed.
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20. Closed contact, smooth curvature, equal heights of marginal ridges and visible
is also properly placed central groove.
After I check the occlusion I will always look at my restoration one more time to see
if I did not miss anything and confirm the esthetics of the restoration. I always ask myself
whether I would put this restoration in my own mouth. At UBC we have high standards
in our SIM exercises because everyone wants to make sure that we are 100% ready for
patient care.
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21. If you have any questions with regards to any step of the procedure post it in our chat
room and I will try to clarify it to the best of my abilities. I am looking forward to read
your entry and compare the different approaches to dental procedures.
Thank you for your time.
Sincerely,
Monika Schneiderova
DMD’09
References:
Gardner, K. (2007). Class II amalgam preparation handouts. Vancouver: UBC Faculty of
Dentistry.
Lussi, A. & Gygax, M. (1998). Iatrogenic damage to adjacent teeth during classical
approximal box preparation. Journal of Dentistry, 26, 435-441.
Qvist, V., Johannessen, L., Bruun, M. (1992). Progression of approxiaml caries in
relation of iatrogenic preparation damage. J Dent Res, 71, 1370-1373.
Roberson, T., Heyman, H., Swift, E. (2006). Art and science of operative dentistry (5th
ed.). St. Louis: Mosby Inc.
Summitt, J.B., Robbins, J.W., Hilton, T.J, & Schwartz, R.S. (2006) Fundamentals of
operative dentistry: a contemporary approach (3rd ed.). Illinois: Quintessence Publishing
Co.
Sturdevant, C.M., (1995). The Art and Science of Operative Dentistry. St. Louis: Mosby
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