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Problem 1: Anatomical Variation
Local anesthetic ("freezing") is always effective if it is injected in the correct anatomical area and given sufficient
time to take effect. It works by blocking the nerve supply to the particular region under treatment.
However, there is huge anatomical variation between people - and some people have such an unusual anatomy that the "standard"
dental block used by 99% of dentists doesn't work. However, this is very very rare - more commonly, all that's required is
to inject into another place to get the aberrant nerve (see Problem 2 - Poor Local Anaesthesia Technique - below).
Unusual anatomy can be a problem with the lower jaw, because here, the dentist uses a "nerve block" as opposed
to infiltration in the upper jaw. This is because the nerves run differently in the lower and upper jaw. The dental nerve
in the lower jaw is buried within dense bone, while the nerves supplying the upper teeth run on the surface before diving
in to the teeth. The upper jaw is more poreous (sponge like) meaning that when anaesthetic is injected next to a tooth, it
can get through to the root, making the tooth go numb. The lower jaw is denser and an injection next to the tooth is usually
not enough on its own to make that tooth numb enough for dental procedures. Therefore the main nerve which supples sensation
to that half of the jaw is frozen.
So around upper teeth, the local anesthetic can be "infiltrated" around the tooth/teeth to be numbed, whereas
in the lower jaw, the nerve which innervates the teeth on one side of the jaw is blocked by the injection (near the cheek).
This will numb your tongue and lip on the side of the injection as well, because the Inferior Dental Nerve and Lingual Nerve
become frozen.
The reason some people don't go numb very well on the lower jaw is because the opening to the canal isn't in the usual
place.
Everyone CAN be successfully numbed, but it may be necessary to use a different technique for numbing than the "standard"
inferior dental block: either a Gow-Gates block or an Akinosi block, or supplemental techniques such as intraosseous or intraligamental
injections. Here's the catch: these are considered "advanced" techniques and not commonly taught to undergraduates
at dental school, but are taught in some post-graduate courses. Most dentists who are familiar with these techniques learn
them from their supervisor or tutor.
If you do have this very rare problem (see this story, for an example), you will want to find a dentist who is familiar with these techniques. How to find them? You could always
explain your situation and ask if they are familiar with advanced local anaesthesia techniques like Gow-Gates and Akinosi,
but this may get you labelled a smart-ass... if you're stuck, why not post on our dental phobia message board and ask for help with finding a dentist? We've got access to some inside info!
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Problem 2: Not Freezing at the First Attempt OR Poor Local Anesthesia Technique
Some dentists are not very good with local anaesthesia but don't think they have a problem or don't care that they do. These
dentists are best avoided. While they are not that numerous, they do exist.
If you don't go numb straight away, this doesn't mean that the dentist isn't good at their job. There can be occasions
when the local anaesthetic doesn't work first time. If that's the case, your dentist should be able to explain to you why
it has happend and be able to do something about it (inject in a different place, use a different technique, prescribe antibiotics
if there is an abscess etc.). In case this page sounds scary to you - the initial injection isn't terribly difficult, and
90% of lower blocks (which can be harder to achieve than numbing in the upper jaw) work at the first attempt when using the
most common local anaesthetic (lidocaine aka lignocaine with epi) (Matthews et al, 1997).
As always, word-of-mouth is a good way of finding a dentist who's good at local anaesthesia.
Some common problems include:
* rushing things and not waiting until the local has kicked in sufficiently
* not injecting in the right place (this can happen to any dentist, all that needs to be done is try again in a different
place - don't grin and bear it!)
* some patients are resistant to the effect of certain local anaesthetics (e. g. lignocaine/lidocaine), the answer is
simple - use a different LA solution.
You should discuss past problems with getting numb with your dentist and ask what measures can be taken to prevent it from
happening again. If you're not happy with the answers, look for another dentist who CAN give you a reassuring explanation
and/or answer.
Problem 3: Anxiety (local anesthetic doesn't kick in for ages or wears off too quickly)
When someone is highly stressed or anxious, the local anesthetic may not work as well as when you're relaxed. The hormones
related to anxiety (such as adrenaline aka epinephrine) can prevent local anaesthetic from working properly in some people.
The effect of the local may be delayed, not pronounced enough, or it may wear off too quickly.
To the best of my knowledge, the actual neurophysiological mechanism by which stress hormones prevent LA from working properly
is still unclear. The "Gate Control Theory" (Melzack & Wall, 1965) proposes that the body cannot produce a stress response
and a relaxation response simultaneously. According to the theory, as a pain impulse is generated it goes through the spinal
cord to the brain where it is interpreted as painful or not painful. The spinal cord is the "gate". The gate sends the signal
to the brain and simultaneously, a signal is sent from the brain to the gate to either open or close the gate. If someone
is expecting pain, their brain signals the gate to be wide open, and they will then react to the smallest pain impulse. According
to the theory, if a patient can learn effective relaxation methods, has confidence their dentist, and uses positive self-talk,
they can make their brain signal to the gate to close. This will allow anaesthetics to work more effectively. Please note
that this is just a theory and the actual mechanism described is unproven.
Whatever the physiological mechanism may be, sedation can help with pain prevention. By lowering anxiety levels, sedation
gives the local a much better chance of working properly. "Laughing gas" (or RA, short for relative analgesia, in dentist speak) tends to be the method of choice.
The following article, written by a dentist who suffers with dental anxiety himself, is well worth a read if you reckon that
anxiety prevents you from getting completely numb: Treating Anxious Dental Patients Like Me. This article may describe your situation perfectly, however, it contains some generalizations that won't appeal to everyone.
If you're not too enamoured with the article, please note my comments at the end.
Problem 4: Infections ("Hot Tooth")
A localized infection or "abcess" can prevent local anaesthetic from working effectively (as an interesting aside,
this is why "root canals" have such a bad reputation - most are completely painless, but when an infection is present,
it can be a different story... see below!).
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What is an abscess, and what causes it?
"Sometimes, due to trauma or decay the "nerve" inside the tooth dies off. Any passing bacteria find this a
source of nourishment and proceed to munch on the dead nerve and have lots of babies :D.
Your body can't do anything about this infection because along with the nerve dying, the blood supply to the tooth dies
off too, so the body can't send in some antibacterial cells (white blood cells) to attack the bugs.
Eventually, the bugs start to spill out of the tooth and into the tiny space between the tooth and the jawbone. This starts
an abscess, the body reacts to the invasion by pouring in defensive cells, which kill most of the bugs in the area, but still
can't get to the source of the problem, which is in the tooth. If the bugs are hard to kill, the battle rages on for a while
and because the area is very tiny, the pressure becomes high and it becomes extremely painful. This is called an acute abscess.
Anyway, to sort this mess out, the dentist has two choices, extract the tooth and remove the bugs that way or do a root treatment.
In a root treatment the inside of the tooth is cleaned and sterilised and then a plug is put in to bung up the space inside
the tooth and stop more bugs getting in..." (description courtesy of Gordon Laurie, BDS)
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Freezing (i. e. numbing) depends on the pH of the tissue. When there is an abscess (an acute area of infection), the pH drops
and the environment becomes acidic. Local anaesthetic is very pH sensitive. Even in a normal environment, it seeps into nerve
fibers slowly, which is why anesthetics don't kick in immediately. In an acid environment, the nerve fibers look to the anesthesia
molecules like they are coated with wax and thus diffusion into the fibers is very slow (this info comes from www.doctorspiller.com).
As a result, the anaesthetic may not have as powerful an effect. Extra anaesthetic can sometimes (but not always) do the
trick in making sure things are as comfortable as possible. As Mike (one of "resident dentists") says: "Don't
be afraid to ask for more - it's not that expensive!!! Also if things are too sore at the time you can always abort and reappoint
- might annoy an impatient dentist, but certainly isn't the end of the world!! It's your mouth - you are in control!"
Most of the time, it's possible to bring the infection under control using antibiotics first. In that case, the pH in
the tissue rises again, and the local anaesthetic will work.
What do I do if the antibiotics don't work?
Often you'll be prescribed penicillins of some sort (e. g. amoxicillin), or an equivalent antibiotic if you're allergic to
penicillins. Usually, they're very effective, but not always. These antibiotics kill off some bacteria, typically the aerobic
(oxygen-breathing) bugs. But sometimes it can be necessary to kill off anaerobic bugs which contribute to the infection as
well (and may indeed be a more common cause of dental infections). A different antibiotic with an activity spectrum effective
against anaerobes (such as Metronidazole) should be helpful.
It may not always be possible to get rid of the infection completely, but it may have reduced enough to allow for comfortable
treatment. If things don't get any better (and you're scared of giving things a try if there's any possibility of feeling
pain), you may want to look into sedation options. Laughing gas can help by lowering your anxiety level, thus allowing the
LA to work more effectively, while IV sedation has the added benefit of inducing partial or complete memory loss for the procedure
(if that sounds appealing to you).
With a painful abscess, the rule is to establish drainage. Opening up into the abscess, will produce almost immediate rapid
relief of pain and and can be better than waiting for 12-24 hrs for antibiotics to kick in. It's a bit of a "gotta be
cruel to be kind" scenario, but if you're in unbearable pain anyway...
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