TABLE CLINIC

Indirect band technique is valuable in saving your chair time and in sparing the patient the wear and tear of direct band fitting. The technique that I will show can easily be taught to your laboratory technician as in my case, or to your dental assistant, and permit them to make a very satisfactory set of bands.

First, two shimmed acrylic trays are made--one for the upper and one for the lower. The shim is made of hard "Beauty Pink" wax softened in warm tap water and placed over the teeth on the patient's study model with a double layer in the anterior region. The wax shim is extended 3-4 mm gingivally to the teeth (Fig. 1). The wax does not stick to the model or mar it in any way since the wax is water-softened and the model has already been given a soaped finish. No occlusal stops are prepared in the wax as you would for a partial denture or crown and bridge procedure, because it doesn't make any difference if the tips of the teeth contact the acrylic tray in the final impression. As a matter of fact, they rarely do. But it makes no difference if they do.

Making the acrylic impression trays

To make the acrylic impression tray over the wax shim, I use Lang's self-cure tray acrylic in blue. Why do I use blue? No reason. I like the color. It comes in blue, pink, and white. I get it in 5 lb lots -- the lab size-- and I get a better quantity price. It is also available in a 3 lb size. You can make about 20 trays to the pound. The material is inexpensive. As a matter of fact, I think it is cheaper to make this custom-made, shimmed acrylic tray than it was to take a compound impression as we used to and jiggle it around in the mouth. More importantly, this procedure uses lab time and lab technician's time and not my time. Also, it is easier on the patient. And better.

The finished acrylic tray should be made with a handle extension (Fig. 2) . Otherwise, removing the final impression would be very difficult. How do you make the acrylic tray? Follow Lang's directions. Nothing you haven't done before. As soon as the tray material has reached initial set, remove the wax shim and tray together from the model and scissor-trim the acrylic to the periphery of the wax. When setting is completed, remove the wax shim and finish trimming the tray.

The primary impression

Now you are ready for the impressions of the teeth. For this I use SIR silicone rubber impression material, both the tray type and the syringe type (Fig. 3).

About fifteen or twenty minutes prior to the patient's appointment, the acrylic trays are coated with the adhesive which comes with the SIR impression material (Fig. 4) . TP separators were placed mesial and distal to the first molars a day or two prior to the impression appointment. When the patient comes in for the impression appointment, rubber band separators are placed as needed

interproximally in the anterior segments (Fig. 5) and the posterior separators are removed. It is necessary to remove the posterior separators because otherwise the impression material would lock through the loop of the TP separators and the impression might pull away from the tray upon removal.

So now, with the rubber band separators still in place between the anterior teeth, the primary impression is taken using the tray type SIR impression material. The material is mixed according to the manufacturer's instructions with one exception. I use about twice the amount of accelerator as is recommended in the instruction sheet. This accelerates the setting time appreciably, so that the impression need stay in the mouth only two, perhaps three minutes as opposed to the ten minutes the manufacturer recommends. I have not found that this affects the accuracy or the stability of the impression and it does cut down substantially on the chair time required for the impression. Whether this would be desirable for impressions requiring the accuracy of an inlay or crown and bridge preparation is questionable, but for our purposes it introduces no discernible error.

The mixed tray type SIR impression material is buttered into the adhesive-treated acrylic tray and the primary impression is made. When this primary impression is removed from the mouth (Fig. 6) note the septi of the impression material. Now it is important for all interproximal impression material to be removed to make way for the final "wash" impression. All the septi are removed with iris scissors. In places where there are missing teeth, the impression material is scooped out to the level of the incisal or occlusal surfaces of the other teeth. Thus, the primary impression is trimmed so that there is one continuous trough in the tooth area (Fig. 7). You want no material that can trap air and cause bubbles.

The lingual flanges of the lower impression are trimmed completely down to the base plate so that when the second "wash" impression is taken, there is no difficulty encountered in seating the impression. This is very important. The trimming cannot be overdone and so, if there is any question in your mind whether to trim or not, by all means remove the material. Occasionally, if the rubber separators on the anterior teeth have been cut too long, they will fold and leave undermined, unsupported areas in the primary impression. These should be trimmed also to eliminate these undercut areas. I cannot emphasize enough the importance of trimming away anything that could interfere with the proper seating of the tray for the final impression.

The final impression

Now we are ready for the final impression. The rubber separators are removed. A small quantity of syringe type SIR impression material is mixed, again using about twice the quantity of accelerator that is called for in the instructions. This mix is buttered into the trough of the primary impression starting at one heel and continuing around to the other until the trough is completely full of the syringe type impression material. When I first started using this procedure, I was quite concerned about trapping air bubbles and having imperfections in the final impression. My experience has been that this almost never happens.

The SIR impression material is allowed to set (2 to 2½ minutes) and the impression is removed with a snapping or jerking motion. Upon removal you should see impression material interproximally between every tooth (Fig. 8) .

My reason for using the two types of impression material-- tray type for the primary impression and syringe type for the final "wash" impression-- is that the syringe type is thinner-bodied. Incidentally, it is called syringe type and in other techniques a syringe is used to dispense this material. However, no syringe is needed or used in our application of this impression material.

The advantage of the double impression technique is that you get extremely detailed impressions that are sharp and clear. The syringe type material is sort of plungered subgingivally into the free-gum margin so that an additional ½ mm or more of material is discernible. This all goes to make the grinding of the teeth and the preparing of the dies for the indirect band technique much easier. Certainly, as the computer engineers have said apropos of computers, "Garbage in, garbage out". The same applies to this impression technique and the work that you get back from your dental technician. If you give him garbage, you get back garbage. If you expect bands that will fit the teeth with the maximum degree of accuracy, you've got to give your technician something to work with. You can't rely on his guessing what the gingival anatomy or the subgingival contour of the tooth may be. If, on the other hand, you give him impressions such as are demonstrated here, and these-- believe me-- are routine and simply achieved, and then he doesn't give you good bands back, change your technician.

At this point you have now completed the chairside procedures. You can continue and complete the laboratory procedures in your own office with a simple, easily mastered technique.

Die material

I use die material called Plastic Steel B (Fig. 9). Type A is called the putty type by the manufacturer (the Devcon Corporation). Type B is called the liquid type. However, even the liquid type is not fluid enough to pour the impression and avoid bubbles. The secret of using the plastic steel is to use Devcon Thinner and a 10 cc syringe with an 18 gauge or, preferably, a 16 gauge needle.

The plastic steel is prepared using 2 tablespoons of the paste, 2 teaspoons of the hardener, and between ¾ of a teaspoon and a teaspoon of thinner. This is mixed in a glass jar and is then fluid enough so that it can be aspirated into the syringe. The syringe is loaded with the plastic steel and each tooth crown in turn is injected with the die material to fill the socket. The needle permits the die material to fill the tooth impressions from the incisal or occlusal tips and this avoids trapping air bubbles. The glass jar in which the material has been mixed and the syringe and needle are easily cleaned using soap and water.

The Devcon Corporation also makes a plastic aluminum (Devcon F-2) which can be used in the formula equally well and the plastic aluminum does have some slight advantage. The color is more pleasing-- it is an aluminum or silver color rather than the black of the plastic steel. Also, it will not

cause rust stains on the plaster index or core that is prepared later. These advantages are admittedly minor. However, if you are starting out and ordering the material and you can get plastic aluminum, I think you might be happier with it. A one-pound can of Devcon B or Devcon F-2 will suffice for 10 to 12 arches.

Pouring the dies

First, the heels of the impressions are boxed with baseplate wax and then die material is injected into the tooth areas. After that, the rest of the impression is simply poured (Fig. 10). The material cannot be vibrated into the impression even with the thinner being used. It is much too viscous. If you try vibrating, you will trap air bubbles and the bubbles cannot, as a rule, be removed. The instruction sheet that comes with the Devcon says that it hardens in two hours. I find that this is much too short a time. We leave it overnight.

The following morning the plastic steel cast is removed from the impression by levering them apart. The impression remains in its tray and is saved. The plastic steel cast is trimmed on the water wheel to shape its sides and flatten its base. Be sure to remove all the boxing wax before grinding because it may clog the carborundum water wheel. The plastic steel does not clog it. It behaves in this regard very little differently than plaster or stone.

Now the base of the plastic steel cast is notched from the gingival, both mesially and distally and across the base using an edge-cutting diamond disc 7/8" in diameter or larger if you can get one. This notching is made as deep as possible toward the occlusal and incisal without the arch coming apart. A hole about ¼" deep is drilled into the base of each tooth area using a #8 round bur. Preparation of the cast is now complete (Fig. 11).

Into each of the holes a brass dowel pin is placed. The brass pins have a small knurled portion at one end and a shaft with one side flat. The knurled end is glued into the hole using self-curing acrylic. This is the same stuff that is used for Hawley retainers. I came to use it almost by accident. I used to use household cement and one day I ran out of it. The acrylic works better and has one additional occasional advantage. Now and then you will drill your hole through the crown of the plastic steel tooth. This might especially be true on lower incisors. In this event, the acrylic used to cement the brass pin fills in the hole and is burnished flush on the surface. The way the acrylic is used is to pour a little powder into the hole in the base of the tooth area and drop in a drop of liquid monomer. Then the dowel pin is pushed into the hole and the excess acrylic is removed.

As the brass dowel pins are glued into the holes, the flats are set to face distally with two exceptions-- the two mandibular central incisors. For the two lower central incisors, one flat is faced to the buccal and the other is faced to the lingual. This is important, not because the two central incisors can be exchanged. If they were doweled like all the others and switched, one would face backwards. No, the reason for identifying the lower centrals in this special way is so that the lower central and lateral on the same side are not confused. To repeat, therefore, all dowel pins are inserted with the flats facing distally except for the two lower central incisors. These have one flat

facing buccal and the other lingual.

If care has been taken in drilling the holes for the dowel pins by keeping the handpiece in the same plane, all the pins will be essentially parallel. A horseshoe-shaped wafer of wax is formed and the ends of the dowel pins are embedded in the wax (Fig. 12).

Making the core

A boxing strip made of Ash metal (soft boxing strip metal) is formed (Fig. 13), filled with stone, and then the prepared, dowelled and waxed model is inserted into the stone with a gentle, vibratory motion. This is allowed to harden. The Ash metal boxing strip is removed. The plaster base is trimmed on the water wheel. The wax wafer is removed. This exposes the ends of the pins (Fig. 14).

If the pins have been inserted in essentially a parallel plane, the entire plastic steel cast with the pins can be removed from the stone base in one piece. If not, the plastic steel cast can be sectioned cutting through an edentulous area or a diastema, or through a tooth that is going to be extracted. Then the arch can be removed in sections.

If the notching that was done prior to the insertion of the pins was adequate, the individual teeth can be snapped apart and the arch snapped into individual dies (Fig. 15). If the notching was not adequate, I use a carpenter's nail-cutting plier which has rather large, broad beaks and will snap the dies apart.

Trimming the dies

Two Dedeco Chrome Finishing stones mounted on a single mandrel and ground into a truncated cone shape are most useful in trimming the dies (Fig. 16). These stones are extremely hard. I have one set which has been in constant use for about seven years and still shows practically no sign of wear. Prior to this, I used tungsten carbide laboratory burs of comparable shape, but found that these wore out very rapidly. The Dedeco Chrome Finishing stones are most efficient. However, you will have a problem shaping them to a truncated cone because they are so hard. I tried almost everything and wore out almost everything including the carbon steel tang of a wood file. About the best thing I found for shaping these stones was an old trueing stone for green stones. It is used against the mandrel-mounted stones chucked in the lathe. You might try to get one of them.

Using the double chrome finishing stones, the gingival margins of the plastic steel teeth are trimmed beyond the level to which the bands will seat (Fig. 17) .

Fitting the bands

In fitting the bands to the dies, I use preformed bands but not prewelds. My experience has been that quite often with the prewelds the optimum position for the band will result in an offset bracket. Also, using separate bands and brackets reduces our inventory and provides more versatility. So, the brackets are welded to the correct level after the bands are fitted (Fig. 18).

Storage

I use a special cabinet (Fig. 19) for storage because we store the dies in the stone core and also store the SIR impression. Storing the dies in the core makes it simple to pick out the required die if a band is lost or destroyed and a new band is needed. The SIR impression material keeps indefinitely. Therefore, I keep the tray with the final impression. If I want a lingual arch, the molar dies are reseated in the impression, luted in, and a plaster model is poured. We then have a model (Fig. 20) against which we can solder the lingual arch.

After the case has been retained for some time, I periodically go through the storage cabinet and eliminate the casts and impressions that are no longer useful. We do salvage the brass pins by simply heating them to soften the acrylic that is holding them and pull them out of the dies.