Chairside - Glidewell Dental Labs

that is we have to give the technician adequate reduction. I
would tell you from the experience of teaching a lot of handson
preparation courses — and I think every technician in
every laboratory I’ve ever talked to agrees with this — that
under-reducing is the classic problem in dentistry when we
do indirect restorations. When I work with dentists on prep
design, what I find is they mentally know how much tooth
reduction they want to send the laboratory. Where it breaks
down is they’re using their visual cues to try to assess how
much they have, instead of actually using hard facts like
depth-cutting diamonds to know how much they’re doing
their depth cuts and reduction, and then going back and
checking the amount of reduction.
I do a thing in my prep course where
I have everybody prep a tooth without
measuring. I have them write down
how much they want to prepare,
then prep the tooth. Then I go back
and show them how to measure, and
everybody, across the board, underreduces.
I do it! If I don’t measure,
I always under-reduce.
I do a thing in my prep course where I have everybody
prep a tooth without measuring. I have them write down
how much they want to prepare, then prep the tooth. Then
I go back and show them how to measure, and everybody,
across the board, under-reduces. I do it! If I don’t measure, I
always under-reduce. Now, one of the things that’s happened
after a couple of years of doing a prep design technique,
where I have been very meticulous about measuring my
reductions, is that now my eye is getting better because
I’m sort of training it. But I still don’t trust it. So one of
the classic things that I’ve gone back to, if I’m going to do
occlusal reduction on a posterior tooth, is placing depth
cuts. But you’ve got to know what you’re doing. Pull out
an old 330 carbide bur. Everybody has one of those in the
office somewhere. You don’t use them for anything because
they’re too wimpy for most preparations anymore, but
they’re exactly 1.5 millimeters from the tip of the bur to
where the shank starts. Just drop a bunch of pinholes in an
occlusal table. Go up on the cuspid. Go on the inclines. Go
on the central groove. And then connect the dots.
MD: Yeah, I had to do that when I started practicing in the
lab and we started filming everything. I realized I had to start
getting better in a hurry. I was a chronic under-prepper, too.
I stumbled onto these depth-cutting burs, these self-limiting
depth-cutting burs that come in different depths. There’s a
1.5 and 2 millimeter. I was shocked when I put a 2 millimeter
hole in the occlusal surface of a molar and then prepped until
I thought I was done. I had half the hole left the very first time!
And I thought, no wonder I was chronically under-preparing,
because if you’re not used to seeing 2 millimeters, it looks like a
really deep hole. It looks like an endo access.
LB: It does!
MD: But the weird thing is that dentists will never give us,
as a laboratory, 2 millimeters of occlusal reduction because
when you under-prep for so long, it feels like malpractice to
do 2 millimeters of occlusal reduction. But, meanwhile, they’ll
do 2 millimeters of occlusal reduction for a Class I amalgam
or composite, or a Class II amalgam or composite all day
long because every time you do a crown prep and make a
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