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I haven’t been as diligent in picture taking this year. Partly due to a broken camera for the first month and partly due to time crunches in lab. When you are trying to pass off crown preps, wax-ups, provisionals, and get castings done for a porcelain fused to metal casting the last thing to think about is taking pictures. HOWEVER, I have been able to take a few pictures of some random things we are doing.
Last year in Restorative II we had a gold crown due as our final project. The final project in Restorative III is a porcelain fused to metal (PFM) crown. In short the steps of the PFM crown are similar to the gold crown. You do the crown preparation, make a custom tray, take an impression, pour up jade stone, drill pindex holes, form the base, mount on articulator, cut the jade stone, and then wax up the full crown. This is where it gets different from a gold crown.

Porcelain requires a certain thickness for strength, so instead of casting the whole wax crown you must cut back some of the crown so you can add porcelain to it AFTER it has been cast. The tooth is also prepared differently so after you remove some wax from the crown there is still enough wax left to make a strong enough metal base. The metals minimal thickness is .5mm while the minimum porcelain thickness is 1mm. This means that anywhere on the tooth where there is going to be porcelain you want to reduce it by 1.5-2mm.

Here is a shot of tooth #8, upper left central incisor with a temporary on it. If you look to the right you will see a chunk of acrylic on tooth #5 an upper 1st premolar. We are doing the porcelain on the opposite premolar, #12.

The next picture is of tooth #12 after the preparation, provisional, impression, jade stone, pindex, and articulator mount. It is ready to be waxed up. We wax up the tooth to look like the full tooth and then we remove wax in certain areas of the tooth (facial, occlusal, coronal 1/3 of the lingual, and the mesial and distal contact areas. Porcelain also has to meet metal at a 90 degree butt joint angle. The cut back also has specific dimensions. Here is the mounted articulator with #12:

I have made the wax cut back and sent it off for investing. It turned out nicely. I will be taking picture as we progress with this project. The next steps will be to add various layers of porcelain to the casting. There is an opaque layer which covers the color of the dark metal casting, a dentin layer to add natural tooth color and then a translucent layer to look like enamel. The steps include time in the oven at very hot temperatures after layers are added to bake the porcelain on. More to come on these details.

We have also been practicing doing PFM preps on various other teeth in the mouth. It is hard to believe that we will be doing this on patients in about 22 weeks. Here are some more pictures:

Pathology Lecture:

More information on PFM’s (I did a google search so you can browse these at your leisure, most are randome websites)

http://www.pjsdental.com/porcelain_to_metal.htm

http://www.smartooth.com/PFM%20Preparation.htm (Has some good preparation shapes and critiques)