In my crowns and bridges lab, we are learning how to make metal crowns. Metal crowns are used because of how strong they are and how long they last. metal crowns aren’t the only crowns available. There Porcelain and Ceramic crowns as well. Porcelain crowns are just like the metal crowns. They are very durable and long lasting. The most popular crown however is the Ceramic crowns. These crowns are popular because not only are they strong, but they look very realistic.

Besides the different materials that the crowns are made up, there are different types of crowns that one can make. An inlay crown, a onlay crown, a partial crown and a full crown. The last two are self explanatory, but an inlay crown is a type of restoration that fits inside a tooth. An only crown is a restoration that fits on top of whatever is remaining of a tooth.

In lab i am working on a metal, onlay crowns for the central, bicuspid and a molar. The first thing we did was pour stone into impression molds. Before pouring the stone we spray the maxillary and mandible molds we debubblizer.  Debubblizer helps smooth the surface tension, which helps the stone flow more easily through the mold and it prevents bubbles from forming. Bubbles prevent the stone from hardening and create potholes on the model that could lead to the model breaking.

The Maxillary was poured using die stone, because it’s one of the hardest stone and it’s our working model. The mandible was poured using buff stone. Of course if this was a real case from a real dentist, we would receive the impression and carefully open the package while wearing the necessary protection. The necessary protection would be lab coat, gloves and   Then we would sterilize it with idophor. We, the lab technician, need to sterilize the cases in order to protect ourselves and others in the lab from dangerous infections.

We would pour the stone onto the model on one side, letting the stone flow throughout the model. The model of course will be on a vibrator while we are pouring. After the models are completely filled with stone we let them set for about forty five minutes. After the forty five minutes we would carefully remove our casts from the molds. After this we are ready for pindexing.

Pindexing is when we drill holes onto our casts in order to be able to put pins into our molds. These pins will help hold our casts in place when we place them on a base that is made of buff stone. The holes on the casts should be parallel to each other and should be in the middle of the teeth we are working on. Once the holes are created, we take our pins and put glue on the tip that is going to be inserted into the stone. Once we insert the pin with the glue we spray an accelerator. The accelerator helps the glue dry faster. Once all the pins are inserted into the mandible and maxillary casts, and the pins are lined up parallel to each other, we insert sleeves on the pins. These sleeves will be use to position the casts onto the base that we will create.

The base models are made using buff stone. We pour our stone mix into a pre-made mold, following the same procedure we used when pouring our casts. Once the molds are filled with buff stone mix, we take our maxillary and mandible casts, with the pin and sleeves attached to them, and place them into the base models. This will allow the base model to harden around the pins and sleeves. Don’t forget to put separator on the bottom of the maxillary and mandible casts, before butting them into the base mold. Separator will help the casts separate from the base easily, without breaking it. Once you align the cast’s midline with the base molds center, you let it set for about forty five minutes.

Once it hardens, you carefully remove the casts from the base molds. If everything was done carefully, you are able to separate them with any cracks or damage to the casts. The sleeves should be inside the base, following the outline of the cast and the pins attached to it. You might need to use some force to separate them, but if you put enough separator you should be able to do it easily. Now, you are ready to cut out each die that you are working on. You can use a hand saw or hand piece, depending on what you are comfortable with. Be very careful when cutting the dies. Try not to damage the margins. Protect the margins at all times. The margins guide you to how far the crown is supposed to go. Once you have separated the dies, in this case the maxillary dies, you can start trimming and ditching. Trimming is cutting the excess from the working dies. This helps make it easier to remove and work on the die. Using a hand piece, carefully go around the die, trimming the excess stone. Do not touch the margins and do not make the die too skinny. The next step is ditching. Ditching involves exposing the margins by carefully using a hand piece to create a small ditch underneath the margin. This helps make the margin more visible. Before you ditch, use a red pencil to highlight the margin. Holding the pencil on its side gently glide it across the margin.

After the ditching and trimming is done, you attach an articulator. This articulator is deposable articulator. It is very basic in its function, which is to mimic the opening and closing of the patient’s mouth. You use glue to attach the articulator to the back side of the maxillary and the mandible. Use accelerator to make the glue harden.  Now you apply die hardener, this makes the die stronger. Now you are ready to begin waxing up the crown.

Before wax up begins, use must put separator on the die. This helps you remove the wax up from the die. The reason for this is to help you check the margins and you are going to need to remove them from the dies in order to invest and cast them. Waxing up a crown requires patience and a steady hand. You must make sure that the anatomy of the tooth is correct and the margins are smooth and not too short. After you are happy with your wax up, you can begin to invest and cast the wax up. We will take our two wax ups, the bicuspid and the molar, and attach it to the casting ring. You must first attach the wax up to waxing screws. This is done by taking baseplate wax to one end of the screw and attaching to the thickest part of the wax up. Then you take baseplate wax and form a small ball. This ball attaches to the center of the casting ring. This ball will help you attach the screws with the wax up to the casting ring. Then you must make sure that the wax ups are at a forty five degree angle and aren’t in the heating zone. After that is done, have to mix the Hi- Temp, Two packets for each casting ring, mix with 14.5 ml of the manufacturer’s special liquid. Before adding the Hi- Temp mixture to the casting ring you must spray debubblizer to the casting ring, so that once the investment hardens you can remove it easily from the casting ring. After using a vibrator to add the investment into the casting ring, you must put it into a pressure pot. The pressure pot will help it harden by removing air and adding pressure. After 15 minutes you can remove it from the pressure pot . Now you are ready to cast the wax up into metal. I am not up to this part and would rather wait and see how it is done before describing it.