No tooth is the same. And if you’re considering joining the digital dentistry movement, you may need to make some adjustments when it comes to the type of crown margins you use.
Getting marginal design executed perfectly is critical so the digital scanner can pick up the prep scan accurately, says Jeannie Hughes, one of Dandy’s digital dental experts with 30 years of experience. “Digital scanners struggle with picking up knife/feather edge preps.”
In this article, we’ll cover which crown margin preparations are best for digital dentistry, the differences in shoulder vs chamfer, and why some, like the feather edge margin, aren’t ideal for best practices.
Types of marginal designs in crown preparation
Shoulder margin
The crown preparation technique called the shoulder margin is named that, because of its shape. The 90-degree angle resembles a shoulder and is one of the best marginal designs for digital dentistry.
Prep dimensions for shoulder margin: 1.0mm for zirconia, PFZ, PFM, and emax Lithium disilicate
Pros of the shoulder margin
It’s the easiest for the scanner to read, ensuring the restoration fits perfectly.
Cons of the shoulder margin
It can be difficult to put a shoulder margin crown on an anterior tooth. It can be challenging to do a shoulder margin in certain posterior teeth, too.
The shoulder margin is one of the best crown prep techniques for digital dentistry because the scanner can clearly see the prep, says Hughes.
Shoulder margin conclusion
“The shoulder margin is the best prep for zirconia crowns,” she says. Zirconia can be milled best with this prep style.
Chamfer margin
The chamfer margin crown preparation technique got its name because of the shape. It’s like a shoulder margin but with a slight angle.
Prep dimensions for chamfer margin: 1.0mm for zirconia, PFZ, PFM, and emax Lithium disilicate, 0.6mm for emax veneer
Pros of chamfer margins
They’re better for anterior teeth because they create a more seamless margin where it’s aesthetically noticeable.
Cons of chamfer margins
These can be more challenging to prepare.
Chamfer margin conclusion
The chamfer margin is acceptable in digital dentistry but it’s not as good as a shoulder margin due to the mill’s capabilities, making it a harder margin to mill.
Feather edge margin
The feather edge margin or “knife edge margin” is named such because it’s a very thin margin.
It’s not recommended in crown prep for digital dentistry because it can’t be 0.6mm thick, the value required for digital scans. “If you make a knife edge margin on a zirconia crown, it’s very likely going to break,” Hughes says.
It goes back to “minimum thickness,” a very common term in dentistry. We know that 0.6mm is the minimal amount of thickness that zirconia needs to be stable, Hughes says. The chamfer style prep limits the space needed to create adequate material thickness on the marginal region.
“When it’s less than that 0.6mm, it’s at risk for breakage and failure. If the margin in this case—the point where the lip of the crown and the tooth meet each other—is open,” says Hughes. That can lead to bacteria getting in and the crown is more susceptible to decay, infection, and other problems, she says.
With the feather edge margin, that thickness goes down to almost 0 and the scanner can’t read it. “When we’re trying to guess where that margin is, and a lot of times it’ll be too short, or too thin, and now we have an open margin, it leads to the crown having to be remade or it breaks,” says Hughes.
Chamfer vs shoulder margins
Now that you know you’re likely to use chamfer margins or shoulder margins with crown prep because they provide optimal room for the scanner to see the crown, you’re probably wondering the best case for using either one.
When do you do chamfer vs shoulder margins?
Ideally, the dentist should prep shoulder margin whenever possible in digital dentistry. This enables labs to create a restoration that flows with the remaining tooth structure with no bulge at the near margin, Hughes shares.
That being said, chamfer can make the transition from tooth-to-crown margin look more seamless with anterior teeth.
So how do you make the transition?
We get it. Not every tooth can be prepped for a perfect shoulder margin. To learn how to adopt a margin style you aren’t as familiar with, make sure you’re using the correct dental burs, suggest Hughes.
Once the crown margin is fully prepared with digital dentistry, make sure you pack cord so the designers can see the margin accurately.
And don’t be afraid to contact the Dandy team. Sure, you’ll have learned this with our trainers during the onboarding but, it’s easy to forget some details. The team is standing by and available for a private call before, during, and after the crown margin prep process.
Prep styles for zirconia crowns
Zirconia crowns are ideal for digital dentistry done with a shoulder margin prep, but they can be done with a chamfer style. They should be done at least 0.6mm thickness to be stable, Hughes suggests.
When prepping for a Zirconia Crown, keep in mind proper marginal finishing lines for clinical success. Intraoral scanners improve the accuracy and efficiency of the preparation process, reducing turnaround time compared to traditional methods.
Prepping crowns and digital dentistry
Why does a certain thickness matter so much when you’re doing restorations with digital dentistry?
Designing and milling a crown less than 0.6 mm minimal thickness can lead to fractures and chipping, says Hughes. “So if the doctors reduce 0.6mm or less, there could be an overhang, which leaves a trap for plaque and bacteria to get in. Then the doctor sometimes has to adjust the crown, And basically, so now we have something that’s overhanging and adjusted to fit, but now it’s too thin and is at a risk for breaking.”
Best practices for digital dentistry and crown prep involve using cord. “Make sure that you use gingival packing cord and move the tissue out of the way so the digital team can make you a great-fitting crown with digital precision,” says Hughes.
Verified by Dandy’s Clinical Support Leads: Brian Arias, Matt Hibert, Colin Kreinbrink
