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  • 1. # 26 MO/DO Class II Amalgam Preparation and RestorationDear colleague, I have decided to present to you this specific preparation and restoration since on thisexample I can show you the best all the do’s and dont’s of an amalgam preparation andrestoration. This exercise is one of the requirements that we have to meet before we areallowed to start treating patients. I have found this particular preparation as one of the more difficult ones because inorder to finish it both mesial and distal parts of the prep have to be well done. The firsttime I have attempted to do this preparation I started with the occlusal surface and thencontinued with the proximal box. However, at the end, my prep did not meet the specificrequirements because the box had a triangular shape and no reverse “S”. I was wonderingwhat I was doing wrong, but then during one of our lessons Dr. Gardner suggested to firststart working on the proximal box and finish it, then do the occlusal part of the prep andonly at the end to connect the two. During our next evening practice session I haveattempted this approach and right away I could see the difference!!! You might say thatthis was my break through moment and from then on I always start Class II preparations(amalgam and composite) with the proximal box. 1
  • 2. So if you like, I will walk you through the different steps of Ag Class II preparationsand restorations. It does not have to be particularly tooth #26 because you can apply thesame 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 thecritical requirements our preparation has to fulfill. However, even before we grab thehandpiece we have to draw a detailed sketch of the particular preparation that has to beevaluated by peers and instructor. You might think that this is not necessary and timeconsuming, but a few times my drawing helped me to prevent mistakes. This way weprepare a mental plan of the procedure and are less likely to make an error during theactual preparation. 2
  • 3. Pear shaped bur #330. As previously stated, I will usually start working on my proximal box. Before I use thehandpiece I will carefully look for the contact area and mark it with a pencil. This is aplace where my bur makes a first contact with the tooth. To prevent an iatrogenic damageto a neighboring tooth I’ll place a green wedge between 25 and 26 as well as matrix bandthat 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 thecritical requirements of Ag prep, occlusaly convergent walls. 3
  • 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 wouldbe 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 axisof the tooth and the bur is following the mesial contour of the tooth which ensures thatthe axiopulpal wall will be parallel to the gingival cavosurface (ensures better resistanceto displacement). However, at the same time I carefully move the bur in lingual – buccaldirection. My movements are very minimal because I do not want to open the contact toomuch in either direction. 4
  • 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 handpieceand start using hand instruments. Off angle hatchets (#44, #45) and gingival margintrimmers are ideal for this purpose. Hand instruments allow me to remove allunsupported enamel from the proximal box which could otherwise result in a fracture ofthe restoration. By using hand instruments I am able to just open the contacts (we usually 5
  • 6. check this if we are able to pass through the open contact the tip of the explorer; to checkif gingival contact is open enough we must remove the matrix band and the wedge andsee 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 criticalrequirement in this preparation. Since amalgam is corrosive, this step is crucial inprevention of secondary caries (Osborne, & Summitt, 1998). By opening the contacts wefollow G.V. Black’s principle of extension for prevention because corrosive Ag is rough whichcreates an ideal surface for plaque adhesion (Gardner, 2007). The use of hand 6
  • 7. instrumentation also ensures that the cavosurfaces are smooth which again prevents theadhesion of bacteria and removal of unsupported enamel as a prevention of fracture. Atthis 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 isachieved 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 toaccommodate amalgam condenser. If I am satisfied with the box preparation, I can moveon to the occlusal part of the prep. 7
  • 8. Measuring the depth with PQW probe.Using off angle hatchet to finish the buccal wall. 8
  • 9. Finished distal box of the preparation. Using the same bur I start at the central pit and move towards the mesial pit whilefollowing the central groove. During this part I am following the tooth’s surface to makesure 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 fracturesas well as extension for prevention. At this depth we are extending the prep into dentinand this way preventing recurrent caries (Gardner, 2007). 9
  • 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 thecentral pit following the facial groove to form a “dove tail”. This feature further enhancesthe mechanical retention of the material and also serves as an extension for preventionsince caries usually extend further following the grooves and fissures. Now I have onlyone thing to do: connect the proximal box with the occlusal prep by which I createreverse “S” that helps to circumvent the cusps and prevent unnecessary removal of asound tooth structure and therefore weakening the tooth. This connection has to havesmooth, rounded curves to prevent stress accumulation. It also gives bulk to amalgam andhelps to create cavosurface margins that are 90° (due to the angulation of enamel rods atthis area this ensures removal of unsupported enamel rods). 10
  • 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 withthe 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. 11
  • 12. Class II Ag restoration Before I start with the actual restoration I make sure that my preparation is clean andthere is no debris. Then I put a tofflemire matrix holder with a pre-shaped matrix bandaround the tooth. With a handle of a hand instrument I pre-shape the matrix band in sucha way that in the proximal areas it flares away from my prepped tooth towards theneighboring one. This ensures that in the proximal area I can condense amalgam reallywell and close the contact between the teeth. The placement of a green wedge betweenthe teeth pushes the teeth even further apart and once the wedge is removed the contactcloses much better. In our clinic we use 1 or 2 spill amalgam capsules. I prefer to use the 1 spill capsuleswhich I put into the amalgamator for 5 seconds. I add the first amalgam into the proximalbox and using bucco-lingual movements I pack it well into the box and against theproximal walls of the box. In a similar fashion I keep adding more amalgam into thewhole prep until it is quite full. I start with the smallest condenser, but as I amapproaching the surface I’ll switch to a larger size. I always make sure that my prep isoverfilled because this way I am sure that I do not overcarve and end up with voids. I domy rough carving using the Half Hollenback carver with the matrix still on. Using anexplorer at 45° angle to the tooth surface I start shaping the marginal ridge and removingexcess amalgam from the lingual and buccal surfaces of the proximal box. Then I loosenup the matrix band and with an explorer remove excess amalgam from the lingual andbuccal surfaces. When I am finished, I will remove the tofflemire matrix holder, but leavethe matrix band in place. I pull both loose ends of the matrix band away from the 26 andstraighten them. The next step can be tricky and extra caution at this step never hurts. To 12
  • 13. avoid pulling out the freshly packed amalgam from the prep I will put my index finger onthe top of the proximal box and with the other hand I gently pull out the matrix band andexhale if everything went smoothly. Removing excess amalgam with an explorer. 13
  • 14. With the pointed end of the beach carver I remove excess amalgam from theinterproximal 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 centralgroove I use the Half Hollenback carver, where with the flat part of the instrument Iclosely follow the tooth surface while the tip is centered between the facial and lingualcusps forming the groove. Then I switch to cleoid-discoid in order to place the mesial pit. Carving the mesial pit with cleoid – discoid carver. 14
  • 15. Properly carved distal pit. At this time the amalgam is quite set and does not “crumble” as easily which meansthat this is the best time to form the marginal ridge. Previously, I used the spoonexcavator and with gentle rounding strokes I went a few times over the ridge. Since wehave switched to a new type of spoon excavator that is not as suitable for this purpose asthe previous one I use the cleoid-discoid carver. 15
  • 16. Smooth, rounded marginal ridge at level with neighboring tooth.Marginal ridge has to be smooth without voids and following a tooth curvature whichwas challenging to achieve at the beginning because previously I was impatient andstarted to work on the marginal ridge too early. I trim the ridge until it is level withadjacent tooth which I check using a probe. 16
  • 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 distalpart to do) and do my final checks. I look whether my restoration is not over- orundercarved which will result in plaque accumulation, if I achieved proper position ofpits, cusps and their alignment. The surface of the entire restoration must be smooth withno 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 ofthese two teeth (similar as when you do bitewings X-rays) and check if there is a lightshining through (if it does  contact is not closed) or carry out the floss test. Before you 17
  • 18. do floss tests make sure that the amalgam is fully set because this way a few of myclassmates destroyed their restorations. You simply attempt to floss between 25 and 26. Ifthe contact is properly closed you must feel a resistance while pushing the floss in andout. As I got more efficient and faster I began to restore both the mesial and distal partsof the preparation at the same time. Closed contact. As the final stop on our road to a perfect restoration, is the occlusion test. Take thearticulating paper forceps (with articulating paper inserted!) and tell the patient to gentlyclose the mouth and tap his/her teeth a few times. If you are working on your mannequin 18
  • 19. head you have to do it yourself. It is very important to check the occlusion because if therestoration is too high and patient bites too strongly, the amalgam might fracture and theentire marginal ridge might fall off. If the preparation has areas that are too high simplycarve them down and repeat the occlusion test until you are happy with the result. Both contacts are closed. 19
  • 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 seeif I did not miss anything and confirm the esthetics of the restoration. I always ask myselfwhether I would put this restoration in my own mouth. At UBC we have high standardsin our SIM exercises because everyone wants to make sure that we are 100% ready forpatient care. 20
  • 21. If you have any questions with regards to any step of the procedure post it in our chatroom and I will try to clarify it to the best of my abilities. I am looking forward to readyour entry and compare the different approaches to dental procedures.Thank you for your time.Sincerely,Monika SchneiderovaDMD’09References:Gardner, K. (2007). Class II amalgam preparation handouts. Vancouver: UBC Faculty ofDentistry.Lussi, A. & Gygax, M. (1998). Iatrogenic damage to adjacent teeth during classicalapproximal box preparation. Journal of Dentistry, 26, 435-441.Qvist, V., Johannessen, L., Bruun, M. (1992). Progression of approxiaml caries inrelation of iatrogenic preparation damage. J Dent Res, 71, 1370-1373.Roberson, T., Heyman, H., Swift, E. (2006). Art and science of operative dentistry (5thed.). St. Louis: Mosby Inc.Summitt, J.B., Robbins, J.W., Hilton, T.J, & Schwartz, R.S. (2006) Fundamentals ofoperative dentistry: a contemporary approach (3rd ed.). Illinois: Quintessence PublishingCo.Sturdevant, C.M., (1995). The Art and Science of Operative Dentistry. St. Louis: Mosby 21

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