Chairside - Glidewell Dental Labs

ago to less than a quarter of the crowns we make here today.
You would almost think that a bunch of research came out
saying PFMs are causing cancer or something because of the
way dentists are turning and running from them. But, really,
it’s these high-strength, cementable all-ceramics like IPS e.max,
and a product that is a little less researched and a little uglier
than IPS e.max, the full-contour zirconia material BruxZir ®
Solid Zirconia — the one that we’re doing here at Glidewell.
It’s amazing. We totally underestimated how much more the
average American dentist was concerned about strength than
they were about esthetics. So with what I’ve seen here in the
laboratory, it has evolved to the point where I’m doing mainly
BruxZir restorations in the posterior and the less esthetic
areas, and mainly IPS e.max in the anteriors. I don’t do that
many single-unit PFMs anymore. For me, the PFM has just
really become a bridge material. Is that what you find for
PFMs as well?
LB: Exactly. I cannot think of the last single-unit PFM that
I did. Actually, I can. I had a patient who had some of the
worst discolored teeth — combinations of secondary dentin
and old metal post/cores — and we just decided to go with
PFMs with metal cutbacks to try to maximize the esthetics.
But that was a very unique situation. Single-unit PFMs in
the posterior? I can’t remember the last time I did one. And,
yes, Glidewell is right on the cutting edge of developing
those materials.
I guess it doesn’t surprise me how it’s been adopted, simply
because I think a lot of dentists, like me, have the experience
of recommending a crown for a person and having them get
this weird look on their face. If you actually stop and ask
them about their reaction, they ask if the crown is going to
have this “black line”? And they point someplace in their
mouth to an old PFM that was done with a metal margin. It’s
amazing to me how patients find that so offensive, where
they can see that metal margin, way more so than having to
have the exact shade of a posterior tooth match. It’s really
rare for me with a patient, especially when you are doing
single teeth, to have the patient say, “Oh no, I don’t want
you to cement that one because it’s slightly darker than my
tooth or slightly brighter than my tooth.” I actually show
them. I will actually hand them a mirror and say, “I want
you to look at the color before it’s fully cemented in.” And
they usually look at me and say, “Why are you asking me
this?” But that metal margin, they just hate. So my guess is
that other folks’ experiences are similar. And then you know
you have a material that’s strong, which has always been
the PFM’s claim to fame. Why wouldn’t you use something
that’s all-porcelain? You also have patients who say to you
that they don’t want any metal in their mouth.
MD: I’ve had a couple of patients over the years get really
demonstrative about that, and they did happen to be women
— probably because they pay more attention to themselves
than men do! Once most men get married, we just give up
and stop caring about how we look. But I had a woman get
really upset because she could see a lingual metal margin on
an upper second molar. I told her no one was ever going to see
it, and she said, “You can see it if I’m lying on my back with
my mouth open.” I had to ask her what she did for a living. I
mean, how often does someone find themself in this situation?”
I saw a patient who had a gold stud in her nose, but shuddered
when I mentioned placing gold in her mouth on a lower second
molar where I didn’t think I would be able to get enough
occlusal reduction. So there is something weird. Gold is highly
acceptable around your neck, hanging from your ears, stuck
through your nostril, for some people, but you put it next to a
tooth and it’s a cardinal sin.
LB: I agree. I think that’s been a huge boon to it. I also think
the other part of it is it allows us to be more conservative,
if we don’t have to put all of the margins subgingival. And
dentists love saving a half-millimeter or a millimeter. I think
that’s one of the things I love about our profession, how
concerned we are about preserving tooth structure.
MD: Well, OK, I’ll give you that. I know that you’re conservative
and you want to do that, but many of us under-reduce
and when called out on it, we say we were trying to be
conservative. If a dentist prescribes a PFM, for which our lab
and the manufacturers of the materials have always asked
for 2 millimeters of occlusal reduction, and they give us threequarters
of a millimeter, I’m not going to say, “Oh, doctor,
you’re so conservative.” If you’re that conservative, prescribe
a cast gold crown because you’re under-preparing. It’s either
laziness or not having a system to reduce enough. But I hear
what you’re saying because one of the things about BruxZir,
or any solid zirconia for that matter, is it can be made thinner
than, for example, an IPS e.max crown, especially if it’s not on
a posterior tooth. You can’t go below a half-millimeter with a
contoured zirconia restoration on a posterior tooth, but on an
anterior tooth, you can get away with a half-millimeter, maybe
a little less.
I’m going to start experimenting with minimally invasive
crowns, where we remove the least amount of material possible
and see what it looks like to put one of these super-thin, highstrength
crowns on top of it. We’re not going to start selling
those anytime soon, but we are going to start experimenting
with those. It would allow us to be more conservative, like we’ve
seen for veneers. When I went through LVI, we were not only
prepping veneers into dentin, but prepping into deep dentin.
Have you noticed over the years the change in the way that you
prepare veneers, in terms of the depth?
LB: Oh, absolutely. I am much more conservative now. I
make decisions about the amount of tooth reduction based
on things like how much I am going to change the shade of
the tooth. I don’t want to tie my technician’s hands behind
his back and say, “I’ve given you 0.3 millimeter of reduction,
but can you take this from an A5 to an OM3 please?” Part of
Interview with Dr. Lee Ann Brady49