Chairside Magazine Volume 2, Issue 1 - Glidewell Dental Labs

Q 5 : I have seen numbers published on the
mandibular block stating that up to 20% of
blocks are missed on the first attempt. Do you agree
with that?
AB: Yes, but it always seems to go in spurts.
Practitioners tell me, “I can’t miss a block for weeks
and all of a sudden I’m missing every one.” I published
a literature review paper some time ago and the range
I saw was 63% to 86%, with some studies reporting it
into the 90% range. Now that’s with the first injection. But
most of us get it with the second attempt. I think the true
incidence of failed anesthesia is well below 1%. But on the first
attempt, I’d say 15%, plus or minus 5%, is about average.
Q6: One of the most frustrating experiences most of us GP’s have
are with “hot teeth”. Any tips you can give us on accessory innervation
and how to anesthetize these patients?
AB: On a mandible, of course, the number one nerve to anesthetize
is the inferior alveolar nerve, number two is the long
buccal nerve. The long buccal has been shown to have a lot
of accessory innervation to the teeth, particularly the molars.
When you look at the retromolar pad area, there are a lot of
accessory foramina there. You may wonder are they there for
blood vessels, are they for nerves, or are they just air holes?
You cannot tell just by looking at the bone. But there are a
lot of holes there. By doing micro-dissection, the long buccal
nerve is seen to send little branches into the bone. It’s not
just the main pathway like we instructors have always taught.
There are a lot of accessory nerve branches coming off all
along the long buccal pathway.
The number three nerve to anesthetize is the mylohyoid
nerve. In anatomy, we teach that this is a motor nerve to
the mylohyoid muscle at the floor of the mouth and also
out to the anterior belly of the digastric under the chin. What
is not taught from the anatomy literature, is that there are
also pain and temperature fibers in that nerve. And those
pain fibers have been tracked through micro-dissection into
teeth. So yes, it is an accessory nerve pathway. All along
the pathway to the mylohyoid, it is giving off little branches
into the bone and many of those branches are accessory
innervation to teeth.
Q7: I recall being taught that the long buccal just innervated
buccal tissue and for crown preps it was necessary, but only
for soft tissue anesthesia. With all these nerves branching off, it
sounds like nature is not as simple and straightforward as we
want it to be.
AB: Exactly. That is a great summary. We teach the basic nerve
pathways, but we probably don’t do a decent enough job of
teaching that any nerve that exists in the neighborhood of a
tooth is likely to be carrying some accessory innervation to
that tooth. No nerve is purely sensory or purely motor. They
all have a mixture. Some of those fibers are proprioceptive,
but some of those are also primary pain fibers and going to
tooth structures. Unfortunately for us, as dentists and dental
hygienists, we have to be aware of all of the possible nerve
pathways in the oral cavity.
Q8: Say I come to your office and I need crowns on #18, #19 and
#20. Walk us through exactly what you’re going to do in terms of
local anesthesia.
AB: I would start with a Gow-Gates injection. It has the best
likelihood of anesthetizing the inferior alveolar, the lingual,
the long buccal and the mylohyoid nerves all with one injection.
I’ll use a 27-gauge long needle and I’m going to drop
a full cartridge of lidocaine. I could use Prilocaine or
Septocaine if I felt that you were a person who expressed
to me that you were very hard to get numb or you had a
history of getting numb but not staying numb very long, or
had a history of drug abuse. Then I might use one of the
“big boys,” the 4% solutions. Ideally, I’d just use lidocaine
because it’s pretty safe. I find that with the Gow-Gates
technique, I have a good success rate using one cartridge of
lidocaine, in the upper 80s to mid-90% range. Occasionally, I
will need to chase it with a full second cartridge in the same
location. The one nerve that is hardest to get consistently is
the long buccal. So I may sometimes have to inject that separately.
With a Gow-Gates injection, I’ve never had to give a
separate mylohyoid.
If you have a hot tooth, a tooth you’re going to extract or
that you need to do a root canal procedure on because it’s
abcessed, that’s a lot harder to get numb. I’m still going to do
the Gow-Gates and then I might use an intraosseous around
the tooth, or PDL injections to get it. But the Gow-Gates works
well because you’re so high up on the innervation pathway.
You target the anterior-medial aspect of the neck of the condyle.
With the mouth wide open, the condyle translates out
just immediately lateral to the foramen ovale. So you’re right
next to where this whole big nerve trunk is coming in to the
infratemporal fossa. If you drop your anesthetic bolus there
and keep the patient’s mouth wide open – Dr. Gow-Gates recommended
for a full 90 seconds after you finish the injection
— you keep that bolus right there next to the nerve. If there
are any accessory branches coming off of anywhere along the
trigeminal nerve pathways, you’re still catching them right at
the source.
Q9: How long do you wait after a Gow-Gates injection to test
for anesthesia?
AB: Gow-Gates has a slower onset because you’re approaching
such a large nerve trunk. The most peripheral fibers are
going to the back of the mouth. The fibers at the center of
that big nerve bundle are coming out to the tip of the tongue
and the lip, and so you must wait at least five minutes. The
study I like to quote, shows that it’s at ten minutes when the
Gow-Gates injection is really going to give you the absolute
best result. Within the five minute window I should be getting
some signs that the anesthesia has taken effect, and if so
I’m going to wait a little longer and double-check it for signs
of full anesthesia. If I’m not getting signs after 5 minutes,
I may conclude that I’ve missed it and give a second Gow-
Gates injection.
Q10: Some esthetic clinicians are advocating the use of the
Anterior Middle Superior Alveolar injection, the AMSA, because it
numbs all the maxillary anterior teeth. Do you use this injection
if you are working on 8 anterior teeth rather than going around
and giving numerous infiltrations? It seems counter-intuitive,
being a palatal injection. Tell us a little about it.
AB: There are actually two AMSA techniques, a facial approach
and a palatal approach. The palatal injection technique is
actually one that was first described in the 1920s. When
the Wand first came out they really pushed this palatal AMSA
technique but it has never really caught on. The whole principle
of this technique is that rather than doing the standard
facial approach AMSA injection, which is properly called the
infraorbital block injection given on the face just below the
eye, which is a true block, when you do the palatal approach
you’re further down on the pathway of the anterior and middle
superior alveolar nerves, at the junction where the vertical
process of the maxilla meets the horizontal hard palate.
If you take a line perpendicular to the midline palatal raphe
and extend it out to where it meets the two bicuspids halfway
along that line, you’ll be at that junction. Drop your anesthetic
there, a small amount, very slow injection, and you’ll
get anterior and middle superior alveolar anesthesia. Now the
beauty of this injection is that you don’t get lip anesthesia
like you do with the infraorbital, but you do get buccal soft
tissue anesthesia around the teeth. You get palatal, pulpal
and buccal anesthesia so you can do work from the second
bicuspid forward. It might be a little fuzzy at the second
bicuspid because you’re getting a little innervation coming in
from the posterior, the PSA, so I always give a little infiltration
behind there as well. By the way, infiltrations on the maxilla,
pretty much the only thing I’m giving these days is Septocaine.
Lots of times it gives me palatal anesthesia as well buccal.
Not on everybody, but most of the time.
Q11: You’re absolutely right about the Septocaine. It seems as
though I can pack cord on the lingual on nearly everybody without
any problems. Maybe once or twice every couple of months I
am not able to and need to give a little palatal soft tissue anesthesia.
So you like the AMSA injection?
AB: Well, with the palatal AMSA, you’ve got maxillary anterior
anesthesia without having the lip numb, which is helpful
for esthetic dentistry. But there are two drawbacks with it.
One, it’s a palatal injection, so you have to give it real slow
and #2 it doesn’t have as good duration because it’s not a true
block. It’s in between a block and an infiltration. For veneer
cases, where you want to keep the smile line and you’re not
going to be in there very long, it’s a real efficient way to do it.
But if you’re going to be doing crown preps from bicuspid Í
to bicuspid, in my opinion, I’d rather use the infraorbital and
the nasopalatine.
20 Questions with Dr. Alan Budenz