Shoulder bevel vs chamfer preps?

Some dentists live and die by the chamfer and some swear allegience to the shoulder bevel prep. To me the difference is much to do over nothing. Both preps allow a dentist to have a "ramped finish line" instead of a butt joint. For the unitiiated a butt joint finish line refers to a preparation that ends in a flat surface (a shoulder) that runs perpendicular to the rest of the prepped tooth. It is designed to allow for maximum thickness of the restoration at its gingival termination . Although the width of a shoulder can vary, I usually try to keep it between .75 mm -1mm).  Some dentists advocate even deeper shoulders but I try to avoid them since they can weaken the remaining tooth structure or make it more likely that a tooth will need a root canal because the resulting preparations come to close to the pulp.

The reason that chamfers and bevels are used is to change the angle of the finish line so that it ends up being between 45- 25 degrees in relation to the rest of the preparation. This can be beneficial because the tooth at the finish line is less prepped and therefor somewhat more resistant to fracture and also restorations with these preparations tend to fit more precisely at their finish line (the gap between the restoration and the tooth tends to be smaller )

I personally use a bevel preparation when I am planning to make a ceramometal crown and a chamfer preparation when I will make a zirconium preparation, but I am sure a chamfer preparation would be ok with a ceramometal restoration as well. I like the bevel because I can make the final part of the preparation at a more acute angle than 45 degrees as well as vary it along the preparation as needed. Some parts of the preparation may have a 45 degree bevel and some parts the bevel is more acute. also I can make some parts of the bevel longer and some parts shorter, so I find that bevel allows me more flexibility in my preparation. That being said, I like chamfer preparations as well and many fine dentists use chamfer preparations instead of shoulder bevels. To make this discussion more confusing I often use a chamfer and bevel in combination for longer tooth preparations since I believe the a shallow chamfer preparation leave the tooth stronger than a "rounded" shoulder/bevel preparation.

Ultimately, it really doesn't matter much. Now I am a seriously geeky about dentistry and lately I have been combining my techniques. I start by making a preparation using a rounded shoulder diamond of .75 diameter at the tip. I rough out my preparation to ensure that I have a rounded shoulder of  at least .75 mm all around. Then I take a black diamond chamfer stone and "chamferize" my entire preparation. I find that it tends smooth out my prep and reduce any unintended  undercuts that I made while creating my shoulder preparation ( I find it difficult to lock my  wrist while preparing a well placed shoulder). I then go over the preparation lightly with a fine chamfer bur and finish with a bevel made by a very small flame shaped diamond bur. I use a bevel so that my final preparation will result in a finish line with a less than 45 degree angle.

from Ask Dr. Spindel - http://lspindelnycdds.blogspot.com/2018/05/shoulder-bevel-vs-chamfer-preps.html - http://lspindelnycdds.blogspot.com/

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