and now we need our axial depth cuts at the height of contour on the buccal
and the lingual and once we're done with that now we're ready to fly so the steps on a posterior
tooth as you can see here we're going to break the contacts on the mesial and the distal with our
56 carbide burr we're gonna place a double zero retraction cord in here again this is a plain cord
hasn't been soaked in anything we're gonna cut the two ends flush so that we don't have any overlap
and then we're gonna do our margination so we're going to take our 801 we'll just call this let's
say an 016 if we're doing like a zirconia crown and we're going to trace it from the mesial
facial line angle to the distal facial line angle and then the same on the lingual side
from the mesial lingual to the distal lingual sometimes with the smaller round burst the o14
and the o16 it'll actually fit in between the teeth like right over where you just made your
56 burst so if it'll fit there if you have room between the tooth you're prepping and the adjacent
tooth feel free to kind of go all the way through there um with that round bur and again anytime you
hold that round bur um parallel to the long axis of the tooth the shank of the bur acts as kind of
a self-limiting depth cutter on anterior teeth as you might have noticed the head of the handpiece
has to be held away a little bit so it angles the bur a little bit more which is good it gets
it into kind of its full depth and so you make your margin preparation on the buckle and the
lingual with your round bur then place your depth cuts in the central groove and the lingual cusps
and for the first couple times you do it just do the two buckle cuffs too just to
say that you did so you're going to end up with all your depth cuts on the occlusal
and now we need our axial depth cuts at the height of contour on the buccal and the lingual
and once we're done with that now we're ready to fly so we take a little extra time up front
but essentially again i refer to this as kind of like having gps or a surgical guide
for this preparation because you know when you're done so then i'm going to grab that 856025 bur
and literally just kind of hold it parallel to the occlusal surface while simultaneously pushing the
tip down to get to the bottom of that depth cut in the central groove and on the cusp tip you could
also use that football football bird the 379.023 if you wanted to here it really doesn't matter
what you use to do this gross reduction whatever floats your boat would be fine and then i'm going
to use the 856.025 or maybe the o21 based again if we're doing solid zirconia to prep an axial wall
there's taper built into that burst so really kind of try to hold that burst straight up and down
it's way more difficult to undercut a single tooth than you think it is i mean provided there's not
a big hole in the back of it from an amalgam that comes out of it so we're going to go around and
prep with our tapered bur our 856 burr and when you do this you're going to end up with
two sharp angles one on the buckle and one on the lingual on the occlusal surface as you see here
and don't use a bird to smooth those off it's much better to use a sandpaper disc like you see here
actually i asked the animator for a sandpaper disc and i got what looks to be a joe dandy so
i know that looks a bit like a very violent way to smooth off a 90 degree angle on a tooth and we're
going to smooth off those angles we used to do it because the all ceramics we had were too weak to
have a 90 degree angle a point a sharp point on the prep that's not true today with lithium nice
silicate with zirconia what is true is those are both milled restorations and all of our milling
units the burrs that are in the milling units have rounded tips so a milling unit cannot mill to a 90
degree angle like that so what it does instead is it over mills so it mills past it with that
round tip this kind of zone of safety around it so that it knows the crown will fit on the prep
if you leave that sharp edge which is fine that's a great strategy for the software to have
but if we're already at minimum thickness right on that spot on the occlusal surface
and then it over mills in that area it could violate that minimum material thickness so
a brux or crown that was supposed to be six tenths of a millimeter could now be four tenths of a
millimeter because of the milling strategy where it's going to mill beyond that to ensure that it
seats the point being round off any sharp edges of any milled restorations not because of the
strength of the material but because the mill uses rounded edge rounded-end burrs and needs
of that because it can't prep a 90 degree angles on the inside of a crown the next step once we
smooth off those angles is put the top cord in i put a 2e cord in that size two quarters the
top cord fits on maxillary anterior teeth it fits on lower molars very well it won't fit it
sometimes will fit on lower bicuspids but it will not fit on lower anterior so for lower anteriors
for example i put a double zero chord first and my top chord's probably going to be a zero
on lower bicuspids it's usually a double zero with a one chord on top and then on the molars
double zero chord with a two on top and then upper bicuspids because of the lack of attached
gingiva there it's usually a double zero cord that'll fit everywhere and then a zero cord or a
one just based on how thin and friable that tissue looks to be we don't wanna do any damage with this
so yeah i'd always love to have a ton of lateral retention of the tissue away from the tooth
but one of our goals in this is not to create any damage to the patient's biology to the connective
tissue so if i can only settle for you know a one cord instead of a two cord that's fine as long as
we have any lateral separation we're still going to make the technicians very happy and they're
going to be able to clearly see what we're doing if the patient's sensitive to epi and a local
anesthetic injection then don't use it in the core just use a plane 2 chord instead of a 2e chord
then we're going to place our anatomical copper cap on top and the patient's going to bite down
and on posterior teeth they can really crank on this so if you're doing a crown with some really
bad looking gingiva and it's frankly you shouldn't be taking the impression today but you are
because you want to put it into production sometimes the tissue is just too edematous
and boggy to even hold cord those are the cases where i go in with the diode laser and take the
tissue away and then we'll use something like traccinet or exfacil to help with the bleeding
and then we put the copper cap on top have the patient bite down for 10 minutes i come and why
10 minutes because that's how long it takes me to do a hygiene exam but no 10 minutes in this case
is to get all the blood out of there take it off rinse off whatever styptic material you're using
it will look like the patient had a gingival transplant i mean the gingiva looks so good
it will blow you away don't admire it too long because the blood's coming back from the capillary
bed and it's angry that it's been forced out for the last five minutes so take it off and
quickly take that impression but these anatomical copper caps can be lifesavers in dubious crown of
bridge situations especially on posterior teeth anteriors too but especially on posterior teeth
so i hope that through this prep sequence i've been able to share a couple things with you and my
passion on behalf of technicians worldwide for why we need to step our game up and actually prep to
the requirements for the materials we're choosing again it's hard for us to like die on the altar of
conservatism when we're not picking conservative materials and then under prepping them and saying
i'm conservative pick more conservative materials but still prep enough to get there so if i'm
prepping a crown for the first time i'm using reverse prep all day long because it's my way for
getting to a great prep i'm more challenged when i take off an old crown another dentist has done
and now i have to start shaping that prep but my guiding principle is again the same thing
i want to make sure i have enough reduction in the right areas and that's going to help give
me a good looking crown are you enjoying this instructional video i hope so if you'd like
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so if you want to be conservative that's a way to be conservative prescribe full strength solid
zirconia but then you gotta have the depth cutter you cannot eyeball six tenths of a millimeter on
a molar you just can't you can't stop trying to convince the computer stop trying to talk to me
and tell me that you can you cannot pull the cheek back close one eye and tell me what six
tenths of a millimeter looks like versus eight tenths or versus four tenths or five tenths
i mean it's just you can't i mean it's stop it it's magical thinking