Dentaltown February 2022 - 24

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Cons:
* Diffi cult to follow both on tooth and die, axial reduction fades out instead of terminating
a defi nite fi nish line.
* Thin margin that fi ts fi nish line diffi cult to wax and cast.
* Overcontoured restorations.
* Diffi cult to view on impression.
* Diffi cult to prepare as margins become wavy, because there is no defi nitive stop for the bur. ■
12/3/2018
drewdg21
Member Since: 04/15/13
Post: 53 of 222
Thanks for the info, Matt. I've seen a lot of these vertipreps lately online and wasn't sure on
the exact details of them. They're not for me right now in my career, but defi nitely think they're
the way of the future. Appreciate the photos and explanations. Nice preps and crowns. ■
12/3/2018
velogeek
Member Since: 04/15/10
Post: 56 of 222
OK, let's start with the premise that we are dealing with a large lab and not a sole proprietor
setup. First, most of the milling will be done with a larger-diameter bur with more than enough
internal relief to compensate for die spacing. In this case, you want as much as a horizontal
margin as possible for the best seating and sealing of the margin. (See following comment.) If
you are going to prep a knife edge, understand the milling won't allow for the correct emergence
contours Matt is showing.
There must be enough bulk for the milling. The fi nal contouring must be done after sintering
by hand, or you will have a bulky margin. You will not get this from a large lab charging
under a hundred bucks a crown. Now, if you do wish to pay a good lab to hand-fi nish the
contours and want to prep a knife edge/vertiprep, understand the concept of slip joint/µ (MEE)
angle with such a brittle material may cause huge fracture issues down the line. If you are going
to do this, you want your internal relief to be more at the gingival third of the prep; this will
prevent wedging of the crown against the axial walls when seating causing internal stress at the
margin-think about it for a moment. ■
12/3/2018
avees
Member Since: 01/21/03
Post: 61 of 222
fl yfi shdr
Member Since: 02/26/04
Post: 64 of 222
According to my lab, a chamfer is ideal for the scanner to capture than a shoulder.
What would be an ideal chamfer bur? ■
12/4/2018
Also, a chamfer can be diffi cult to carry interproximal if the teeth are close together. As you
mention, a person can get a 1mm chamfer on buccal and lingual using a 2mm diameter bur.
But it can be diffi cult to impossible to carry a 2mm bur interproximal to achieve the same
1mm chamfer interproximal. My view is that there are two solutions: a smaller chamfer interproximal
by using a narrower diameter bur or changing to shoulder interproximal, which uses
the full width (not half) of the bur so a 1mm shoulder is created by a 1mm diameter bur. ■
12/4/2018
fatbillybob
Member Since: 09/10/02
Post: 107 of 222
In 35 years, I have never met a tech who could guess at margins or read my mind. When
they do guess, they guess wrong. The chamfer/shoulder fi nish line is defi nitive. They teach that
in school for a reason. In the days of amalgam, we were accused of placing restorations in a sea of
sepsis. Some docs claimed kids didn't get tartar and other docs said they weren't looking. Time
marches on and new good things come to the fore but pencil-sharpener preps should be a tool
in the tool bag for limited use. ■
12/6/2018
24 FEBRUARY 2022 // dentaltown.com

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