that's one of the lateral lateral incisors that we prepped for this and hopefully you'll notice
some things here this is kind of the picture that i want you to have in your mind it's a a
dramatic version kind of of an ideal impression because this patient did have a deep sulcus and
so it makes it easier to point out some of what's going on here we'd like to see a half
a millimeter to a millimeter of an impression material an impression of the root structure
that not only shows the technician exactly where that margin is that point in space but as you get
the impression of that root structure now all of a sudden the technician can really blend the
emergence profile of that crown and on an anterior crown like this that is really important so we've
seen some not so ideal impressions let's talk about the eight characteristics or requirements
for an ideal impression how do you even articulate you know i followed one of those tiny impressions
down to the plaster department because i wanted to see how they poured up do they have a tiny green
bowl and a tiny spatula where they put a tiny bit of yellow stone in there and mix it up on a
tiny vibrator and then pour it in and have a tiny articulator that it's going to go on i mean how
do you even work with that as a crown and bridge impression it's just it's just compromise from
left to right from start to finish and the way i was taught to take impressions in dental school
was to place one retraction cord in the sulcus then we'd wait our five to eight minutes
and then we'd pull that retraction cord out and anytime the last retraction cord comes out of a
sulcus and in a one chord technique there's only one so that is the last one when you pull it out
there will be blood they will be bleeding i don't care how healthy your patient sulcus is or when
their last cleaning was when you pull that last cord out of the sulcus there will be blood and so
the game was always tell my assistant don't pull it yet you know so i'm getting behind her with
the impression syringe ready and go ahead pull it out and i'm like racing behind her trying to beat
the blood into the sulcus as though if i got there first the blood would see the polyvinyl cylox and
i go whoa whoa whoa boys he beat us this time back let's go back into the capillaries we lost this
battle we'll get him next time the blood didn't care the blood continues to kind of come out
and compete for space in that sulcus with the impression material and the blood always seems
to win you end up with thin little friable pieces of impression material uh in the sulcus and so
it's incompatible with blood um in the sulcus that 75 percent of the cases that come into glidewell
are single unit crowns and another 11 are two single units often next to each other so that's
86 of the cases coming in here roughly are one and two unit crown and bridge cases and that's
about the same amount that 86 85 86 of the case is coming in that we see in double large trace
here in the laboratory so it's a it's a big number and it represents a lot of the cases that comes
in and since we most of us tend to do dentistry or at least crown a bridge one or two units at a time
really making sure that we know our double arch technique and that our lab does as well goes a
long way to getting success with this so let's talk about predictable impressions and what
benefits we can get from the two chord technique um this happens to be the chord that i've used
uh most of my career the ultra pack chord from ultradent it's not until we put our
double zero in and it's sitting there we get the vertical retraction and now we put a top cord in
the vertical retraction's already gone where we now can get this lateral retraction of the
tissue because it moves in two dimensions so we have to move it down before we can move it out
the only other way to do it is we had like maybe a size 12 or some huge retraction cord
that would do both things at once you'd push it in and assuming it didn't tear the tissue away
from the underlying periosteum you could get vertical and horizontal or lateral retraction
of the tissue at the same time that really doesn't happen very much though as you know
and so as we look now at this picture that you see on the screen you can see i've teased the double
the number two chord up out of the sulcus and you can see the black double zero chord at the base of
the sulcus still there's no skill here i mentioned it earlier there's no skill when it comes to great
impressions what's the skill in putting a double zero chord none it's simple where's this skill
in a number two chord it's slightly harder than a double zero but is it hard it's not hard does it
take time it does take time and that's why for me it's not a skill thing it's more of a heart thing
you know caring enough to get great impressions for your your technician where you're going to
spend the time to put a second cord in for some reason of all these things we do in
dentistry dentists really find cord packing to be annoying and will do almost anything they can to
avoid doing it meanwhile it is clearly the most effective in the gold standard way for getting
great retracted impressions like this that lead to amazing models to have crowns be made on and
look at all that space we have here you can see a wide space between the sulcus
and the two structure itself sometimes you might even find a patient's car keys or a
credit card they lost in there that's we're looking deeply into the sulcus and here it is
just schematically in a drawing so the drawing on the left you can see the green double zero cord
in place during the impression you can see the purple impression material all along the tooth
and then down into that sulcus and then when you remove that impression the double zero cord
stays in place in the sulcus like you see on the image on the right and then the image on the left
now the in par inside part of the impression material has been turned kind of a gold color
and here's just another example again of a two chord uh impression you can just see it very
easily by the excess material beyond uh where the gingival preparation for the restorative margin
has been done and then the thick top to that wall where it was in contact with the double zero cord
this once you take a stone model out of a polyvinyl impression you might think you can
put it back in again but it will never seat all the way so you blow the accuracy of that bite
if you do it that way you need to make sure they're pouring one side mounting it pouring the
other side mounting it on the articulator however they want to do that and then and only then
separate those two arches from the double arch tray so you got to have both arches poured and
have it articulated and everything's set before you separate those two models from the impression
then you have the most accurate bite in dentistry and what we're trying to do is avoid remakes and
so i i usually you know we talk about remakes as a percentage in this section but we also want to
talk about the true cost of a remake for example so the lab fee may or may not be covered um here
at glidewell you probably already know there's a no fault remake policy so whether the crown breaks
when you try it in or the patient doesn't like how it looks or you doesn't want you don't like
how it looks the labview will be covered and glide will send you a new restoration free of
charge because if you schedule a patient to redo a crown that didn't fit next tuesday at 10 am
you're doing that for free you're redoing and remaking that crown for free at 10 am next tuesday
and you'll never have that hour back to produce that twelve hundred dollars um so you might say
well it's not that well it is you're really losing the ability to be able to um have that
twelve hundred dollars so now it's twelve hundred dollars plus the three hundred dollars in overhead
which makes it difficult about so again we want to lower these remakes as much as possible and it
really comes down to the impression whether or not we're going to have these remakes we can work with
preps that aren't perfect it's almost impossible to work with impressions that aren't perfect
so let's talk about some of the most common impression errors that we see
in the laboratory as we walk through and look at cases i've made all these mistakes
on multiple multiple occasions over time and hopefully aren't making these anymore
because you don't have to kind of make these the first one is in regards to margins
critical bubbles we see a lot of bubbles like this it really is ironic you know you'll look
at full arch impressions it might be a full arch impression for like a single unit crown
and i swear to you nine times out of ten the only bubble you'll see on that entire impression
is on the prep tooth this seems cruel and unusual it certainly wants to push you towards doing
digital impressions marginal tears ooh that one on the right i used even when i started here at
glidewell i used to have that happen a lot and it was happening when i was still doing a one chord
technique before the two chord technique so i was able to sneak some impression material subgingival
but then it was tearing when i went to take the impression material out
this also might happen with the two core technique if you're using material that doesn't have a high
an impression material that doesn't have a high tear strength and so it's possible to
do the two core technique pull the top cord have your laterally retracted sulcus squirt
the impression material in seat the tray let it set for five minutes now when you go to remove
that impression you're pulling this direction right you're pulling out of the mouth and down
here in the sulcus we have this double zero cord sitting here and it's stuck in place more or
less and it's kind of pulling on the impression material as you try to pull it out of the mouth
are you enjoying this instructional video i hope so if you'd like to receive additional
clinical instruction with agd and ada approved ce credits all at no charge be sure to visit
glidewelldental.com forward slash education where in addition to over 60 on-demand clinical courses
you can also access our weekly webinars along with other valuable content