Article by Michael C. DiTolla, DDS, FAGD
BruxZir® Solid Zirconia crowns & bridges were originally designed by Glidewell Laboratories as a replacement for
posterior cast gold or metal occlusals, when the patient did not want any metal showing in his or her mouth. As
dentists began placing BruxZir restorations and were repeatedly satisfied with the results, they started to prescribe
BruxZir for bicuspids, as well. The lab realized that if dentists wanted to prescribe BruxZir in the anterior, the translucency
of this material needed to increase. Our R&D team worked on this quietly and finally told me when they were
ready to test it. They asked me for an esthetic challenge, so I decided to give them the tough one we all face: the
single-unit central incisor crown adjacent to a natural tooth. This photo essay shows the clinical steps for placing an
anterior BruxZir crown. For a crown that is 100 percent zirconia with no ceramic facing, the lab pretty much nailed it.
Figure 1: Tooth #9 is going to be prepped for a BruxZir crown. I
chose this case for a couple of reasons. First, tooth #8 is a natural
tooth, and it will be a good test of how the light interacts with the
BruxZir restoration versus the natural tooth. Second, tooth #7 is an
all-ceramic crown, which will be replaced later, and tooth #10 and
#11 are a PFM cantilever bridge. So, we will be able to compare
the BruxZir crown to those two restorations, as well.
Figure 2: I place PFG topical anesthetic gel (Steven's Pharmacy;
Costa Mesa, Calif.) into the sulcus using an Ultradent syringe. I
used to use a cotton-tipped applicator, but this made it difficult to
get PFG into the sulcus. Because I am using single-tooth anesthesia
for this case, the needle is going into the sulcus, so that's where
the topical needs to go. The tufted tip on the syringe makes it easy
to place the topical subgingivally.
Figure 3: The 30-gauge extra short needle of the STA™ System (Milestone Scientific; Livingston, N.J.) is placed in the sulcus. I
prefer using the Rapid Anesthesia Technique for injections, and
a few drops of anesthetic are given as I penetrate the base of the
sulcus and contact bone. I started using this technique
for single mandibular molars to avoid blocks, until I realized
patients hate anterior infiltrations just as much. So I began using
single-tooth anesthesia here, as well.
Figure 4: I use the Reverse Preparation Technique to prep the
tooth. The
first step of this technique is to break the proximal contacts.
Because we are only preparing tooth #9, we are going to do this
with a thin 56 carbide bur on both the mesial and distal. The goal
is to break contact with the adjacent teeth just enough to place our
first retraction cord.
Figure 5: The first retraction cord is an Ultrapak® Cord #00 (Ultradent; South Jordan, Utah). It is a hollow, braided cord that has
no EPI and has not been soaked in any medicament. The cord is
flossed into place on the mesial and distal, and the two loose ends
are grabbed on the lingual and pulled until the cord rests against
the facial surface of the tooth. A non-serrated cord packer is used
to pack the cord on the facial, and the two ends are cut on the
lingual to be flush in the lingual sulcus.
Figure 6: Now that the first cord has retracted the tissue approximately
0.5 mm, it's time to prep the gingival margin. I call this technique
the Reverse Preparation Technique because we prep the
gingival margin first, not last (as I was taught in dental school). We
use an 801-021 bur to trace around the gingival margin, taking this
bur to nearly half its depth, about 1 mm. It cuts a perfect half circle
into the gingival third.
Figure 7: Crowns often look fake in the gingival third, but this
gingival depth cut ensures that we will deliver an esthetic crown.
Because the depth cut is a perfect half circle, we will be left with a
perfect quarter circle – which is a precision deep chamfer or shallow
shoulder – after we do our axial reduction. There is no easier
way to prep a perfect margin.
Figure 8: I prepare a 2 mm depth cut in the incisal edge because
we are restoring the tooth to its original length. I typically place two
of these cuts, which help me quickly reduce the incisal edge while
keeping it level. Under-reduction of incisal edges leads to crowns
that are facially prominent in the incisal third, which gives them a
bulky look.
Figure 9: With the depth cut bur perpendicular to the facial surface
of the tooth, at the junction of the incisal third and the middle, we
make a 1.5 mm depth cut. This depth cut should be just apical to
the incisal edge depth cuts. Depth cuts ensure that we get enough
facial reduction to have an esthetically pleasing crown that is the
same size as the adjacent natural tooth. This is difficult to achieve.
Figure 10: At this point, all depth cuts are finished. This allows me
to fly through the rest of the prep because the gingival is essentially
done. The incisal edge takes about 15 seconds, and the facial
reduction is marked with a depth cut. There is no guessing about
how much to reduce.
Figure 11: The 856-025 bur is the workhorse of the Reverse Preparation
Technique. I find this bur extremely easy to cut with because
of its coarse grit and wide surface area. As I move the bur mesiodistally,
I am doing the facial reduction to the bottom of the depth
cut. I am really not doing any reduction in the gingival third. The tip
of the bur almost floats in space as I make the facial depth cut and
blend it with the gingival.
Figure 12: I turn the 856-025 bur perpendicular to the incisal edge
and connect the two 2 mm depth cuts I made in
Figure 8. As the bur
moves mesiodistally, it is pretty easy to make quick work of incisal
edge reduction. Because the tip of the bur is pointed at the lingual,
I roll the tip of the bur about 20 degrees toward the lingual margin.
Figure 13: I now do the lingual reduction using a 379-023 football
bur. This bur is convex and cuts a concave surface, which is the
shape of the lingual surface of a natural tooth. You don't really need
to place a lingual depth cut because you have the opposing tooth
to use as reference, but you could certainly place a 1 mm depth
cut here, if you wished.
Figure 14: This image explains why I will never switch from an electric
handpiece. I am able to turn down the handpiece speed to
5000 RPM, which allows me to turn off the water. Even with the
water turned off, I will not generate excessive heat because the bur
is only spinning at 5000 RPM. This is the only way I can really dial
in and smooth the margins. With the water turned off, it is easy to
see what I am doing.
Figure 15: The prep is essentially done. I now place the top cord,
an Ultradent Ultrapak Cord #2E. The first cord (#00) retracts the
tissue for the prep and also helps ensure we get a slightly subgingival
margin. This means we never have to take a bur subgingival,
which often causes bleeding.
Figure 16: The top cord (#2E) is now placed. This cord is
responsible for displacing the tissue laterally, to make room for
the impression material. The #2E cord can't be used in all clinical
situations because it is simply too big for many lower anteriors or
upper bicuspids with minimal attached tissue. For those cases,
a smaller top cord, such as Ultrapak Cord #1, can be used to
achieve similar results.
Figure 17: With the top cord in place, you have one final opportunity
to get a great look at the prep. Typically, I spend about 45 seconds
polishing the prep, especially the gingival margin. I again turn
the handpiece down to 5000 RPM and the water off, and I use a
red-striped fine grit 856-025 bur to give the prep a mirror-like finish.
Figure 18: Here is an incisal view of the finished prep. The top cord
is in place with just a small tail protruding on the lingual for easy
removal. The gingival margin is smooth and uniform all the way
around the preparation. This is due to the use of the round bur early
in the procedure, when the hard tissue landmarks were still in place.
Figure 19: The last step of the preparation sequence is to place
a
ROEKO Comprecap anatomic (Colténe/Whaledent; Cuyahoga
Falls, Ohio) on the prep. Slightly wet the inside of the Comprecap
before placing it to keep the tooth moist and to prevent the cotton
from sticking to the prep. Comprecap compression caps help keep
the retraction cord in place and prevent the patient's tongue from
dislodging the cord.
Figure 20: The patient bites down on the ROEKO Comprecap
anatomic for 8-10 minutes. This ensures you have plenty of retraction.
The other day, I pulled the Comprecap after just two minutes
to take the impression. I did not have a wide-open sulcus. It is
important to leave the Comprecap in place for 8-10 minutes.
Figure 21: The result of waiting 8-10 minutes is a sulcus that cannot
be missed with an intraoral tip. I could fling alginate into the
sulcus from the other side of the operatory and still get a good
impression. When your assistant pulls the top cord, look down
from the incisal with a mirror to see what I mean. The impression
material will flow into the sulcus.
Figure 22: Blood or other gingival fluids have not contaminated
the impression because the bottom cord (#00) was left in place.
As a result, you will also get an impression of the 1 mm of tooth
structure apical to the gingival margin. This allows the dental technician
to precisely see the exact gingival margin and enables him
or her to build a proper emergence profile into the restoration —
an important determining characteristic for whether the crown will
have a natural and lifelike appearance.
Figure 23: I try in the BruxZir crown on tooth #9 and find the fit
to be acceptable. The patient has approved the esthetics, so we
clean it out prior to cementation. I decide to cement the restoration
rather than bond it into place because I have sufficient prep
length and it is not overtapered. I use RelyX™ Luting Plus Cement
(3M ESPE) because of its natural bond to dentin and simple cleanup.
An orange pinewood stick is used to provide pressure while
the cement sets.
Figure 24: Here is the final BruxZir restoration on tooth #9, on the
day of cementation. It probably won't be mistaken for a natural
tooth, but it blends well with the adjacent natural tooth, tooth #8.
When I compare it to the existing all-ceramic and PFM crowns in
the anterior segment, I think it looks better, although those other
crowns are a few years old. While I don't recommend that you
jump into prescribing BruxZir for single-unit central incisors, I think
BruxZir is one step closer to being a material that is as well suited
for anterior restorations as it is for posterior restorations.
