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Patient does not get numb
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Joint Hypermobility Syndrome
Joint Hypermobility Syndrome (JHS) also called HyperMobility
Syndrome (HMS), is one of a group of
inherited conditions which affect the connective tissues of the body.
It is estimated that 10%-15% of normal children have hypermobile joints,
or joints that can move beyond the normal range of motion. Patients
with these conditions are more prone to joint injuries than patients
without. The problems associated with JHS seem to diminish with age,
and persons born with less severe forms of HMS may be unaware of their
condition.
The most severe variant of HMS is called Ehlers-Danlos syndrome.
Persons with this rare variant generally are well aware that they have a
connective tissue problem.
Studies have suggested that as many as half of JHS
patients have enhanced pain perception as well as noticeable pain in
multiple sites in the body. Many seem to respond poorly to local anesthetics
(i.e., at the dentist or during surgery) and require larger dosages for
effective pain control. Most of the evidence for the lack of efficacy
of local anesthetics in patients suffering from less severe form of HMS is
anecdotal, so it is difficult to say with certainty that a patient who seems
refractory to local anesthetics is in fact suffering from a side effect of
an undiagnosed case of JHS. If a refractory patient has had a lot of
accidental joint injuries, or knows he or she is "double jointed", this
would be a reasonable avenue to explore.
In patients suffering from the various forms of HMS, the local anesthetic will produce numbness, but it
may be of insufficient intensity or duration to complete the dental
procedure without repeated injections. The reason probably involves the rapid absorption of
the anesthetic solution into the bloodstream due to the defective nature
of the connective tissues in the surrounding blood vessels. If the
anesthetic solution cannot remain in place long enough to take effect,
then the patient will not get numb. The only known way to overcome
this problem is to give repeated, frequent injections during the procedure.
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Alcohol and alcoholics
There is a general consensus in dentistry that patients
directly under the influence of large amounts of alcohol, as well as
recovering alcoholics can be quite difficult to get numb in the dental
office. A few
studies have confirmed this supposition
with respect to alcoholics in hospital settings, although most of the
evidence suggesting that alcohol directly affects the efficacy of local
anesthetics appears to be anecdotal.
The mechanism for the direct effect of alcohol on the
ability of anesthetic solution to produce numbness would be a combination of
systemic acidosis and reduced circulatory resistance due to the vasodilative
properties of alcohol.
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High alcohol intake produces a state of metabolic acidosis
which affects all the tissues of the body. Metabolic acidosis is due
to lactic acidosis, ketoacidosis and acetic acidosis. An acidic
environment at the site of the injection reduces the ability of the
anesthetic to cross the cell membrane into the nerves, thus limiting its
effects. A good discussion of this is found on
page 4 of
this course, and I advise persons who want to know more about the physiology
of nerves and local anesthesia to read the entire page, but the specific
reference to acid/base balance is found
here.
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Alcohol acts as a vasodilator. In other words, it
causes relaxation of the smooth muscles that line the blood vessels, at
least during the initial stages of inebriation. This causes them to
widen (dilate) and increases the volume of blood that flows through them.
One obvious sign that this is happening is the tendency of persons who are
drunk to have flushed faces. Vasodilation also occurs at deeper
levels, and the increased blood flow at the site of the injection carries
away the anesthetic bolus more quickly than would otherwise be the case.
This reduces the time during which the anesthetic solution is available to
produce its effect.
- Patients without connective tissue disorders or alcohol related
anesthetic failures
No
one is immune to the effect of local anesthetic! If the patient
suffers from one of the various forms of HMS, they may require much more
anesthetic with repeated injections, but they can usually be made
sufficiently numb to proceed with dental work if enough anesthetic is
injected. When a patient does not get numb for a procedure in spite of a dentist's
best efforts, the reason is generally that the anesthetic has either not
reached the nerve, or has not penetrated into the nerve. Remember that
a dentist never intentionally gives a shot directly into a nerve trunk.
He/she simply delivers the anesthetic solution into close approximation with
the relevant nerve fibers and hopes that the material diffuses through the
intervening structures, surrounds the nerve fibers and then diffuses into
them. In order to understand how failures in anesthesia happen, it is
helpful to understand a bit about the techniques of delivery of the shots.
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Field blocks: A
field block is often called an "infiltration". It is a shot
that is delivered into the gums directly beside the tooth or teeth that
the dentist wants to anesthetize. Since the introduction of
articaine (Septocaine), which is quite good at diffusing through bone,
field blocks have become useful on 26 of the 32 teeth (lower molars are
the exception). The
needle is inserted a very short distance into the movable buccal or
labial tissue at
about the level of the tip of the root, and the anesthesia is delivered
there. The solution then diffuses through the periosteum (the thin
covering of the bone) and then through the thin layer of bone that surrounds
the tip of the root where the nerve enters the tooth. Using articaine which diffuses through bone very well, this
procedure is effective on all premolars and anterior teeth regardless of
location in upper or lower arch. The advantage of a field block is
that there is never a question in the dentist's mind about the location
of the spot where the anesthesia should be delivered, or about the depth
of the shot. The needle enters the tissue at about where the
dentist estimates the tip of the root lies, and penetrates no more than
1/8 inch. Hence there in never a likelihood of "missing" the block.
There are only two things that may interfere with the
production of numbness during a field block:
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Very thick or dense bone--Even articaine
cannot diffuse through very dense or very thick bone. This is
most likely to be a factor in lower molars and lower canine
teeth. If dense or thick bone is the factor preventing the
induction of anesthesia, then the dentist must resort to a major
nerve block to anesthetize these teeth.
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Acidic tissue--Infected tissue tends to be
acidic. Acidic tissue does not anesthetize easily. See
my discussion of
PKa for a better
understanding of this phenomenon. This is a function of
chemistry. It is generally best to treat an infection
prior to giving a shot in the area to be anesthetized mostly
because injections into injections into infected tissue are
not only painful, but often ineffective.
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Major nerve blocks--Major
nerve blocks are necessary to anesthetize all molars, and there is a
major nerve block available for each of the other teeth as well, even
the ones generally anesthetized with field blocks. When giving a
major nerve block, the dentist aims for a deeply placed bundle of
nerves, or a nerve trunk which contains fibers from the area he wants to
anesthetize. The nerve trunk also contains fibers from adjacent
areas, so the area of numbness may encompass the entire lower jaw, or even the entire side of the
head depending on the target of the block. The main reason that
patients may not get numb when anesthetized with a major nerve block
involves variations in individual internal anatomy.
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Major nerve blocks require the use of longer needles
and are somewhat more dependent on local anatomic variations in the
patient's anatomy. Everyone has two eyes, a nose and a mouth,
but variations in the anatomy of these gives everyone a unique
appearance. We are like that internally too. Since a
vast majority of people have anatomy that fits within certain norms,
dentists use techniques that generally guide the tip of the needle
to the target using external anatomy as a guide to the hidden
anatomy underneath. Unfortunately, some patients have hidden
internal anatomy that does not fit within the standard variation,
and therefore, a dentist may "miss" the block simply because of this
anatomic variation.
Furthermore, the longer needle is more likely to
deviate from a straight path direct to the target structure causing
a missed block. This happens because of the flexibility of the
needle combined with the "aerodynamic" characteristics of the bevel
of the needle which acts like a rudder causing the tip of the needle
to deviate from the straight path.
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The Gow-Gates Block
The most commonly delivered major nerve
block is the mandibular nerve block. It is the shot
that normally makes one half of the entire lower jaw numb,
along with half the tongue. It is one of the most
important major nerve blocks in dentistry, and,
unfortunately, also one of the most commonly "missed
blocks". Failure to obtain good anesthesia with a
mandibular block is very frustrating to both the dentist and
the patient. The most common reason for failure of
this block is variation in patient anatomy.
A great alternative to the standard
mandibular block was invented by an Australian dentist named
Gow-Gates. When properly delivered, it is painless,
and nearly 100% effective with a very fast onset of
anesthesia. The dentist aims the tip of the needle for
the neck of the condyle, aspirates and delivers the entire
carpule. No lingual, long buccal, or any other
accessory injection is necessary since the mandibular nerve
is anesthetized before any of these branches split off.
The only problem with this block has been
that until now, there has been no reliable method for
"finding" the target. Over a period of years, I have
developed a very simple technique which reliably finds the target and
has vastly simplified the practice of dentistry for me.
I have written a page for other dentists that demonstrates
my technique. If you try it and can improve on it, let
me know. |
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Can severe anxiety on the
part of the patient cause the local anesthetic not to work??
To my knowledge, there isn't much research on this subject,
so what follows is based on my own observations. Any dentist,
physician or academic is welcome to email me with their views.
I believe that severe anxiety on the part of a patient
can affect the effectiveness and duration of local anesthetic, although,
even extremely anxious patients can be made numb if enough anesthesia is
injected. The following are the factors that I believe may be involved
in causing this phenomenon:
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Anxious patients are likely to have abnormal body PH.
It may involve alkalosis if the patient is hyperventilating, or
acidosis due to hyperactivity of the skeletal musculature. Any
deviation of local PH from normal can affect the ability of the
anesthetic radicals to penetrate the nerve cell (axon) membrane. Please see my
explanation of PKa
above for a better understanding
of this phenomenon. This would affect both
field blocks and
major nerve
blocks.
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People who are anxious in the dental chair are
likely to be
bruxers (people
who unconsciously grind or clench their teeth). People who brux
are likely to have extremely sensitive teeth, and again, though research
in this area is scant, I believe the reason for the extreme sensitivity
is due to inflammation of the
hammock ligament at the tip of the root caused by the constant
stress placed on it by the bruxing habit. Inflamed tissue remains in a state of acidosis which would prevent diffusion of the
anesthetic into the nerve bundle at that point. This would limit
the effectiveness of field blocks
(infiltrations).
Under any circumstance, severely anxious patients may be
better served, and better anesthetized, if prescribed diazepam (Valium)
tablets, 10 - 15 mgm to be taken an hour before presenting to the office.
Patients so sedated should never drive under the influence and should be
accompanied by an adult driver in transit to and from the office.
Serious pain during
the injection
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 Hitting a nerve (direct
injection into a nerve trunk)
Most injections are not especially painful. We are not
actually trying to "hit" a nerve when we penetrate, and since the
majority of the pain sensors are located in the surface mucosa, the use of a
topical anesthetic can be quite helpful in preventing most sensation.
The techniques are designed to allow needle penetration with the least
trauma to known existing structures under the mucosa. Unfortunately, variations
in internal anatomy can occasionally place a sensitive structure in the path
of the needle. When we give a lower nerve block, the needle penetrates
beside the lingual nerve. If variations in anatomy place the lingual
nerve directly in the path of the needle, the patient will often feel a
burning jolt in the tongue. It is very quick, but quite surprising and
sometimes scary. It generally does not cause serious injury, however, the
patient may experience prolonged numbness or paresthesia (burning or
tingling sensation) in the tongue for up to three weeks (sometimes a number
of months) after the
procedure. This same phenomenon may happen to other nerves causing a
jolt to radiate into the lower jaw, down the neck or behind the ear.
Once again, no damage done. Just an unwanted complication.
It has been my experience that the probability of hitting a nerve
increases if the patient is especially thin. When one gains or looses weight,
the neurovascular bundles (blood vessels and nerves run together in bundles)
do not increase or decrease in diameter. It is a modern social
convention today that "you can't be too thin", however thin people
lack bulk in the muscle and fat surrounding the spaces where the injection
is aimed. This makes the relative size of the neurovascular bundle
larger with respect to the rest of the target. The nerve becomes a
"larger needle in a smaller haystack", and thus more likely to be
struck directly by the needle.
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Injection into an
artery
If the tip of the needle enters an artery, the patient may
experience pain and blanching on the skin of the neck and face. This
is due to the fact that most injections use vasoconstrictor. The
anesthesia is swept along the distribution of the artery into the arterioles
and capillaries of the skin and muscle and the vasoconstrictor causes these
blood vessels to temporarily close down causing ischemia (lack of blood
flow) in the tissue. Ischemia is a painful, but temporary
condition. If this happens, the dentist generally stops the
injection. No permanent damage is done, but the patient may lose some confidence
in the dentist. In order to avoid this complication, the dentist
generally develops an injection technique in which he "aspirates"
(pulls back on the plunger of the syringe) in order to see if any blood
enters the carpule. If this happens (very rarely) he changes the
position of the needle and aspirates again
Prolonged Pain, Numbness or
Paresthesia (burning or tingling) after the procedure
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Make no mistake. Local anesthesia is serious
medicine, and a dental injection is a serious surgical procedure.
Some people are more susceptible to negative local toxic effects of the
anesthetic agent or the associated vasoconstrictor than most, and these
people may suffer some local negative and (generally) temporary side
effects from the agents. Injection directly into a nerve trunk may
unintentionally happen after the patient is already numb and unable to
feel the intrusion. Injection directly into a neurovascular bundle
(nerve trunk) may cause physical damage due to the expansion of the
anesthetic bubble, local toxic effects of the agent and ischemia in the
nerve from the vasoconstrictor. The vast majority of these
complications slowly heal and are gone over a period of several weeks or
months. Upon rare occasion, they can last quite a bit longer (over
a year), but if the patient waits it out, the injury will generally heal
eventually. Local anesthetic agents that come in higher
concentrations such as
articaine and
prilocaine have been implicated in a very slightly higher
incidence of this complication. This most
commonly occurs in major nerve blocks of the lower jaw. At this
time, no one knows why this happens, but it is a fairly rare
complication.
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Injection
under the periosteum
Sometimes the tip of the needle may penetrate under the
periosteum which is the thin, tough covering of the bone.
When this happens, the periosteum is separated from the surface of the
bone and serious pain can result when the anesthesia wears off. In
spite of the severity of the pain, the damage is temporary and generally
is gone within 12 hours.
Feelings of nervousness, fast
heart rate, "head rush"
It is not uncommon for patients to feel nervous with a fast
heart rate immediately after receiving a shot of local anesthetic.
This generally happens when an anesthetic with a vasoconstrictor is being
used. In these cases, the vasoconstrictor is
entering into larger veins and going into general circulation. The
vasoconstrictor is the same as the naturally occurring "fight or flight"
hormone adrenaline, and it is acting just like the release of natural
adrenaline would to produce a heightened sense of awareness, nervousness and
an increased heart rate. This is a short lived reaction and is
generally not dangerous. The feeling fades after a minute or two and
the patient feels much better.
<==How anesthesia makes you numb
Allergies to
local anesthetics==>
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