When doing proximal reductions on a porcelain fused to metal, you will connect the chamfer and shoulder margins. There will be a gradual change of width in this area. Unless, if you are asked a “winged” prep wherein there is a distinct demarcation between these margins. A separate section will be designated for a winged prep, so be sure to check that page if your program asks for one.
Step by Step
The buccal, occlusal and lingual portions on this upper molar tooth were done already, if you want to have a review, please refer to these following pages.
LINK Upper Molar Occlusal Reduction
LINK Buccal and Lingual Porcelain Fused to Metal
Step 1: Break the Proximal Contacts
Tilt your bur in a buccolingual direction to use the bur in a see-saw action if needed. Just be careful not to over-taper which is a common mistake. Also make sure to leave a shell of enamel.
Add video here
No need to follow the contour of the tooth here, just go straight through because your main objective here is just to break the contact.
Step 2: Connect the Margins
Once the contacts are broken, a 014 diameter bur will fit without damaging the adjacent tooth. If not, work with the interproximal bur some more until it does, but as soon as you can fit in a larger bur, please do so.
Widening the Interproximal Area Demo Video
There are other instances when you can barely fit a 014 diameter and you can go ahead on using that just to widen the clearance a little bit from the adjacent tooth. Then after, you may use a larger bur (the bur that you used to make the shoulder margins). Don’t worry if it the shoulder bur could barely fit within the clearance because you may pass it through while reducing the axial wall. Just remember to keep your bur upright to avoid over tapering of the walls.
One advantage of this technique is that you can widen the clearance without nicking the adjacent tooth. Also as you increase to a larger bur, you can still have time to check whether your taper or the location of the margins are still good. When there are adjustments, you may do so with the larger bur.
Connecting the Margins Demo Video
However, there are some who forget to change to larger bur and continue to use the previous thinner burs to make and place the margins. This is a bad habit because thinner burs have the tendency to gouge and make rough margins. So be sure to use the shoulder burs to connect margins.
Make sure to bring the margin down gingivally to match the rest of the margin location, 1mm supragingival. It’s so easy to either keep it higher up or even leave a triangular shape un-reduced enamel area interproximally, so always double check!
Also, don’t over-taper here, another common mistake. I said that already, didn’t I? It’s that important!
This is a wingless variation of a metal-ceramic crown preparation, the shoulder gradually narrows toward the lingual chamfer margin. So when you think you are done with the shoulder margin part of the interproximals, shift to your chamfer bur and use it to pass through from the lingual towards the buccal. This will create a very nice and smooth transition from shoulder to a chamfer margin.
Now that we are done, we can proceed to refinement and hand instrumentation.
LINK to Hand Instrumentation and Refinement