Written by Thomas E. Jacobsen, DDS Monday, 31 July 2006 19:00
Many dentists have taken silver amalgam off their menu of offered services. Accordingly, the question will sometimes arise, "What do I use to restore an extensively destroyed tooth when a laboratory-fabricated restoration is not possible due to time or financial considerations?" With silver amalgam out of the picture, many practitioners will have only resin remaining as a directly placed option. This means that a large, possibly multicusped restoration will have to be built up and placed in its totality completely at chairside, a difficult task at best.
Since I stopped placing amalgams about a decade ago, I have devised a procedure to handle this difficult restorative challenge. I'd like to say I developed this technique on my own, but I actually drew on many different sources to arrive at the present technique. We call it our Semi-Direct or Heat-Hardened alternative. Hereís the executive summary: cut the prep, place the resin, and light-cure. Remove the restoration from the prep, heat-cure it, and bond it back into the preparation. The details follow.
SEMI-DIRECT TECHNIQUE: CASE REPORT
Figure 1. Initial presentation.
Figure 2. Core Paste buildup.
Figure 3. Onlay preparation.
Figure 4. Rubber Sep placed.
Figure 5. Placement of thin increment of composite at gingival margin.
Figure 6. Restoration placed in curing oven.
Figure 7. Sandblasting with Danvilleís Microetcher.
Figure 8. Onlay seated into preparation lined with Danvilleís Starfil.
Figure 9. Completed restoration.
The patient presented with an extensively broken down posterior tooth (Figure 1). As always, gold was offered as the best restorative option. That plan was rejected by the patient, who wanted something done that could be accomplished in one visit. Advantages and disadvantages of all options were discussed, and the Semi-Direct restoration was agreed upon.
Anesthetic was administered, the rubber dam was placed, and the existing amalgam and decay were removed. No attempt was made at this point to produce the onlay shape; just prepare the tooth down to clean, bare dentin and donít worry about undercuts yet. The walls of the prep must be scrubbed clean of all black discoloration; if left in place it will show through the final restoration and compromise the aesthetic result. Some leathery decay may be left over the pulp chamber if necessary to avoid an exposure, but all decay must be scrupulously removed in the vicinity of the gingival margin.
The dentin was then treated in a manner known to produce no sensitivity. In our hands, this means a total-etch (Clearfil SA Primer and Clearfil Photo Bond [Kuraray]) followed by a buildup with Den-Matís Core Paste (Figure 2). We know from more than a decade of experience that dentin treated in this manner will not produce sensitivity. But any proven dentin bonding and buildup protocol could be used here; the objective is to cover all the dentin using a technique that will keep the tooth comfortable.
In this case, due to the deep decay down the mesial root surface, we decided that the most reliable bond between resin and dentin at the gingival margin would be obtained with the buildup material contained and isolated by a matrix band. We therefore relocated the gingival margin coronally in that area.
Now the onlay preparation can begin. Make a deep enough reduction to be able to allow for an adequate thickness of resin restoration, but do not go through the buildup into the dentin. The walls must be very divergent with no undercuts; flare them enough so that your operative instructor in dental school would have given you an F for too much draw. Remember, we must be able to recover the onlay from the prep in order to heat-cure it. The more complex the "coastline" of the occlusal margin, the more divergent the walls must be. The onlay will not rely on nearly parallel walls for its retention; it will be retained by a strong bonding method. Once bonded in, the only way to remove it will be with a bur, regardless of the amount of divergence of the walls. When the prep is finished, all the dentin should still be protected with the build-up material, and only the enamel at the cavosurface margin should be exposed (Figure 3).
Before starting to form the restoration in our prep, a releasing agent was applied so that no bonding would take place at this time between the restoration and the walls of the prep. We like to use a latex separator for ease of removal (Figure 4). A sectional matrix band was then placed and wedged.
Have you ever been curious about just how much a large bolus of resin would shrink if cured unencumbered by any bond to the walls of the prep? If you make the mistake of bulk loading the prep with one mass of resin, youíll soon find out. After curing, the gingival margin will be open wide enough to get a half Hollenbeck in sideways. Instead, place a very thin initial portion of resin at the gingival margin (Figure 5), cure, and then build the remainder of the restoration in several increments. Don't worry about the occlusal anatomy yet. Overfill slightly at the margins and leave a large ìlove handleî of resin either buccally or lingually to provide a purchase point for a tapper to effect the removal. It will be polished off later. Now use a tapping instrument to release the restoration from the preparation. Peel out the latex liner and try the restoration back in to check the contacts.
Here is the opportunity to take advantage of the biggest benefit of the indirect restoration; namely, perfecting the proximal contours that are inaccessible if placed direct. If the contacts are too light or the surface rough, sandblast the proximal surface and brush on some bond. Cure and then add a thin layer of resin. Cure again and polish smooth. Perfect proximal contours and contact can be readily achieved using this method.
The restoration can now be light-cured and heat-cured in the oven (Figure 6), brought back to the patient, and bonded in. After curing, we sandblast both the internal surface of the restoration and the external surface of the preparation (Figure 7). Total-etch the prep. Place a dual-cure bonding agent on both the internal surface of the restoration and the surface of the prep and do not cure. We like Clearfil Photo Bond. Place a dual-curing resin (Danville's Starfil or similar) in the prep and quickly seat the restoration (Figure 8). Clean off the excess before it sets, then light-cure from all sides. Perfect the anatomy with raptor burs, 7404s, and 7901s. You will notice that the surface is much harder and more resistant to the polishing burs than directly placed resin, thanks to the heat-hardening (Figure 9). Polish, take off the dam, check the bite, and you're done.
You will now have a restoration with the following advantages:
• No sensitivity. The den-tin has been protected with a technique known to be comfortable.
• The composite has been heat-hardened for optimal hardness.
• Contours and contacts of proximal surfaces have been perfected.
• Almost all shrinkage of the composite has occurred before bonding to the walls of the preparation.
In our hands, total chair time to produce a Semi-Direct restoration is the same as we would spend prepping and seating a laboratory-fabricated unit. Of course, the expense of the lab bill and operatory costs for a second patient visit have been avoided. We have priced this service midway between a 4-surface composite and a PFM crown.
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