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For over 100 years, dentists have
endeavored to control pain in their offices by utilizing a method
that blocked the pathway of pain impulses to the brain. To
accomplish this blockade, a local anaesthetic is deposited in
proximity to a sensory nerve. In 1884, Dr. William S. Halsted
demonstrated that the injection of a nerve trunk in any part of
its course is followed by anaesthesia in its entire distribution.
As the anaesthetic is absorbed into the lipoid tissue of the
nerve, a state of depolarization ensues which then prevents
conduction of impulses along the nerve trunk to the Central
Nervous System. This state of depolarization initiated by a
chemical substance is referred to as regional anaesthesia. The
trunk or branch that Halsted first blocked was the mandibular
nerve.
Regional anaesthesia can be divided
into various sections, depending on the areas in which the
anaesthetic is deposited and the techniques employed. Monheim(1)
divided re-gional anaesthesia into four parts: 1. Topical 2.
Infiltration 3. Field Block 4. Nerve Block. For our discussion we
will concentrate on the latter or nerve block anaesthesia, wherein
the anaesthetic agent is deposited in proximity to the nerve trunk
to prevent af-ferent impulses from travelling to the C.N.S. from
the point of injection or block.
The Cranial nerve and its various
branches that are anesthetized when this block is accomplished, is
the fifth or trigeminal nerve. The mandibular or 3rd division (V3)
of the trigeminal can be anaesthetized by an intraoral or
extraoral approach. The intraoral ap-proach is the more common
approach utilized in the practice of dentistry.
The mandibular branch, which contains
both sensory and motor fibers, exits the cra-nium through the
foramen ovale. The trunk divides into two branches, anterior and
poste-rior. The posterior divides into the lingual and inferior
alveolar nerves. The inferior al-veolar nerve is the larger branch
of the posterior division of the mandibular nerve. It en-ters the
mandibular foramen in the ramus of the mandible to occupy the
inferior alveolar canal in the body of the mandible. As it
approaches the apex of the second bicuspid, it divides into two
terminal branches, the mental and the incisive(2). When the
intraoral mandibular or inferior alveolar nerve block is
accomplished, its branches, the mental, in-cisive and the lingual
nerve are all affected. As a result, the areas usually
anesthetized are:
A) The body of the mandible and the
lower portion of the ramus.
B) All mandibular teeth.
C)
Floor of mouth.
D) Anterior 2/3rd of the tongue.
E)
Gingivae on the lingual surface of the mandible.
F) Gingivae
on the labial surface of the mandible
G) Mucosa and skin of
the lower lip and chin
Most inferior alveolar nerve block
techniques come into play before the mandibular nerve enters the
mandibular foramen. In order for a specific technique such as this
block to be accomplished successfully, the dentist must have the
knowledge and ability to be able to deposit the local anaesthetic
at the exact anatomical site. It is this factor primarily that has
frustrated dentists for many years. Injecting the anaesthetic is
one thing, placing it by or as close to the nerve trunk as
possible is another matter(3).
There are many reasons put forth as to
why local anaesthesia and the mandibular nerve block fail.
Dover(4) suggests incorrect techniques such as injecting too high,
too superficial, and too deep, are all reasons why dentists are
having failures in accomplish-ing adequate block anaesthesia of
the inferior alveolar nerve. Anomalies of the man-dibular nerve as
suggested by Grover,(5) where there appears to be a bifid
mandibular nerve and mandibular foramen, does not allow proper
blockade by the traditional meth-ods. Poor anaesthesia in the
incisal area may indicate possible innervation of the anterior
teeth by the cutaneous colli branch of the cervical plexus.
Estimates as high as 15% failure rate
in attempts to accomplish adequate anaesthesia by blocking the
inferior alveolar nerve have been suggested.(6) These figures
represent numbers amounting to hundreds of thousands of inadequate
blocks administered, and pa-tients experiencing pain during dental
proceedures. Anatomical landmarks taught and suggested for
traditional block techniques such as the "apex of the buccal pad,
bisecting of the nail of the index finger or thumb," do not give
consistant results, and in many in-stances result in complete
failure of the technique.(7)
There are many reasons as to why a
mandibular block technique may fail, and some of the more
important ones are listed below.
REASONS FOR FAILURE:
#1. Poor Technique.
#2.
Techniques that are too complicated and of high risk.
A.) Gow Gates.
B.)
Akinosi.
#3. Quality of local
anaesthetic.
#4. Quantity of local anaesthetic
utilized.
#5. Time allowed following administration of local
anaesthetic for block to take effect.
#6. Length and gauge of
needle.
#1. Poor Technique:
No matter what technique is utilized,
there is an element of skill required in accom-plishing this task.
If the dentist does not possess this skill, or if they are unable
to fully master the techniques taught in dental school, the
failure rate will continue to rise.
Improper placement of the needle due
to poor technique, can be listed as follows:
#1. Injecting too low, (The needle
is inserted below the foramen and nerve.)
#2. Injecting too
deep, (The needle is inserted behind the foramen and
nerve.)
#3. Injecting too superficial, (The needle is
inserted in front of the foramen and nerve.
Placing the needle in any of the above
locations will cause the local anaesthetic to be deposited too far
away from the nerve and adequate absorption into the nerve fibres
will be impossible.
# 2 Techniques that are too
complicated and of high risk:
Gow-Gates and Akinosi Techniques are
complicated proceedures and present to the clinician greater
elements and degrees of risk. Gow-Gates advocates the use of an
intra- oral technique while utilizing extra-oral landmarks. The
dentist must inject in the mouth and at the same time visualize
the outside of the patient’s head and face regions, in order to
carry out this maneuver. Attempting to visualize the path of
insertion of the needle under these circumstances is by no means
easy to accomplish, and presents an additional element of risk to
the patient. The target for the needle point is the neck of the
condyle(8) which lies in the upper portion of the
pterygomandibular space. This upper portion con-tains many vital
structures that includes the maxillary and middle meningeal
arteries and veins, the sphenomandibular ligament and the otic
ganglion. Utilizing the Gow-Gates technique presents a risk of
inadvertently injecting the needle and local anaesthetic into
these vital structures with possible serious complications. In
addition, injecting the nee-dle and local anaesthetic into the
anterior portion of the tempero-mandibular joint capsule could
also produce damage and prolonged side effects in the form of
severe joint dys-functions. Dentists have had the frustrating task
of treating these cases as they linger and drag on for many
years.
The Akinosi technique(9) also
advocates placing the needle and local anaesthetic in the upper
portion of the pterygomandibular space. Coupled with this is the
disadvantage of not having any hard tissue landmarks that can be
utilized as the proceedure is carried out with the patient’s mouth
closed.
The Gow-Gates and Akinosi techniques
should be reserved for isolated cases that cannot possibly be
managed using routine block techniques. In these isolated cases,
one must operate with the greatest of caution and care,
administered by a skilled and experi-enced clinician in whose
hands complicated techniques are routine. They should not be used
on a routine basis in a dental office.
# 3 Quality of Local
Anaesthetic
There are many good quality local
anaesthetics available today. Reputable compa-nies continue to
manufacture the same high quality anaesthetics they have been
producing for many years. Some manufacturers of brand names do
enjoy a history of committment to the highest standards of quality
control and service to the dental profession. However, there are
circumstances and instances where a deterioration of the overall
efficacy of the product can take place. These altered local
anaesthetics can in turn interfere with the suc-cess of the
mandibular block.
If an anaesthetic is stored improperly
and subjected to extreme temperature changes such as freezing and
excessive heat, it will effect its chemical composition and
ultimately its efficacy. Blocks will fail not only because of
improper techniques but because of an impotent anaesthetic.(3)
Problems in maintaining the potency of the vasoconstrictor in the
anaesthetic are not unknown. In 1992, a major pharmaceutical
company announced a re-call of one of its products for this very
reason. They were unable to maintain the potency of epinephrine
over the full eighteen month shelf life in the formulation of
their anaes-thetic.(10) One must always pay heed to expiry dates
of the product and if the date has been reached do not accept the
anaesthetic from a dealer and do not use it. Expired medi-cations
must always be discarded. Above all, one must purchase their
products from a reputable dealer.
# 4 Quantity of Local
anaesthetic utilized
Over the years, a variety of
suggestions have been put forth as to the ideal amount of local
anaesthetic to utilize in accomplishing a mandibular block.
Monheim(1) suggested 1.5 to 2.0 ml.of solution. Hoechst Co.(11)
recommends up to 3.4 ml. of Ultracaine DS Forte for a block while
Graham Chemical(12) suggests up to 5ml. of Lidocaine 2%. In
studies done by Lemay,(13) recommended doses for block anesthesia
using Ultracaine DS and DS Forte, demonstrated amounts up to
3.6ml. The authors recommend a minimum of 2 carpules of Lidocaine
2% ( 3.6ml.) with 1/100,000 concentration of epinephrine for
mandibular block anaesthesia. Anything less may prove to be
ineffective in many cases. Monheim(1) stated that the inability of
an anaesthetic solution to diffuse throughout the large nerve
trunk in sufficient amounts and concentrations to block all of the
nerve fibers results in imperfect anaesthesia. Bearing this in
mind, one must use adequate amounts of anaesthetic solution in
order to block conduction of painful impulses. No matter how
successful the clinician judges the block to be, any pain
perceived by the patient, re-gardless of how minute the quantity,
must be classified as a failure none the less. If we are to err
then it is best to err by using more and not less, in order to
provide a painless and non-toxic environment for the patient.
Surveys conducted over a period of time by direct communication
with many dental colleagues seems to suggest that they are using a
maximum of 1 carpule of local anaesthetic or less, and have a high
rate of block failures. This amount is inadequate, regardless of
whether one is performing extraction of man-dibular teeth or
restorative procedures.
# 5 Time allowed following
administration of local anaesthetic
Following the administration of
the local anaesthetic, an important factor in the meas-ure of the
success or failure of the inferior alveolar block is the time the
practitioner waits for the agent to take effect. No matter how
accurate the technique utilized, if sufficient time is not
permitted to allow the agent to decrease the permeability of the
nerve mem-brane, the exercise will prove to be a failure.
Even when there is evidence of
subjective symptoms of anesthesia after three to five minutes of
waiting period, such as numbness and tingling of the lower lip,
the block may still not be profound enough to proceed with an
extraction or cavity preparation. The authors feel that a waiting
period of at least fifteen minutes should be allowed to provide
for adequate anesthesia and sufficient time for the anaesthetic
agent to work. This will give deep and profound anaesthesia
providing the technique utilized has been properly performed.
Reducing this waiting period and time factor will only reduce the
success of the block and produce a traumatic and painful
experience for a very unhappy patient. We cannot emphasize enough
the importance of waiting an adequate period of time to allow the
anaesthetic to do its work properly. Ignoring this factor will
only lead to a very dis-tressful outcome.
# 6 Size and gauge of
needle
To accomplish a mandibular
block, Monheim(1) suggests the use of a 15/8 inch, 23 gauge needle
and disagrees with anything smaller. Many authorities today
suggest the use of a 25 gauge, 13/8 inch needle, although some
schools advocate the use of a 27gauge. The authors do not agree
with any size smaller than 25 gauge, 13/8 inches for several very
important reasons:
# A. Intravascular
Injection
During the administration of a
mandibular block, no matter what gauge is being used, there is
always the possibility of placing the needle within a vessel.
Although it is possi-ble to aspirate with a 27 or 30 gauge
needle, their smaller lumen will significantly impede the flow
of blood, so that recognition of an intravascular injection by
the dentist may be hindered. Monheim(1) and Bennet(14) suggest
that larger gauge needles are less likely to penetrate the
smaller vessels. If the needle inadvertently enters a vessel on
insertion, and all or part of the solution is deposited, little
or no anaesthesia results. There is also the possibility of
precipitating a toxic reaction, which must be treated
immediately.
# B. Formation of
haematoma
Inadequate anaesthesia can also
result from the formation of a haematoma, due to the
traumatized, lacerated and bleeding vessel. Blood from the
haematoma may dilute the local anaesthetic solution, which to
some extent may inactivate and weaken its
potency.
# C. The larger the gauge, the more
accurate the block (25 gauge vs. 27 gauge)
i) Using a 25 gauge needle, 1 3/8
inches in length ( 35 mm.) In a straight line thrust, a 25
gauge needle will maintain its trajectory more accurately than
a 27 gauge. If a 25 gauge needle is inserted from point A., in
a straight line, it will usually reach its destination, point
B.
ii) Using a 27 gauge needle, 1 3/8
inches in length (35 mm.) A smaller gauge is not as rigid due
to its smaller diameter and greater flexibility, and when
inserted from point A. in a straight line thrust, will be
deflected from its path and deviate in a di- rection away from
point B. to point C.
If point A. is the point of
insertion in carrying out a mandibular block, and point B. is
the inferior alveolar nerve, than we can appreciate the fact
that a 25 gauge needle will provide a more accurate block, due
to its inherent rigidity. The inherent flexibility of a 27
gauge can result in less accurate placement of the needle and
thus a less potent or failed block. (15)
# D. Broken needle
There is a greater possibility of a
finer needle breaking as compared to one of a larger
gauge. (1,14) This presents another
complication that must be treated without delay. A broken needle
must be retrieved, which necessitates major surgical
intervention by an oral surgeon.(16,17) As can be appreciated,
we not only have an unhappy patient to say the least, who has
suffered pain and discomfort, but one that now requires
additional surgery in the confines of a hospital setting.
Situation such as this are potential sources of litiga-tion.
Some dentists are convinced that the
larger gauge needle is more painfull upon inser-tion when
compared to one of a smaller diameter. Studies have shown this
to be untrue, and the use of a 25 gauge needle in the
administration of a mandibular block, of good quality and
sharpness, can be inserted as painlessly as one of a 27 or 30
gauge, providing the technique is performed properly. (15)
THE "A. R. T." MANDIBULAR BLOCK ( ANTERIOR
RAMUS TECHNIQUE)
TECHNIQUE
The use of a 25 gauge
needle, 1 3/8 inches in length (35 mm.), is recommended.
1. Palpate the anterior border of
the ramus with the thumb and find the greatest concavity, which
is the coronoid notch. At the same time, use the middle
finger and the thumb to determine the width of the ramus in its
anterior-posterior dimen-sion. Anatomically, the mandibular
foramen lies in the middle of the ramus in this di-mension. The
average width of the ramus, including the thickness of the soft
tissue in the coronoid notch, is approximately 35mm., which is
also the length of the needle. (18)
2. Inject the needle
until bone in the coronoid notch is contacted. The syringe and
needle at this stage are buccal to the posterior molars.
3. Use the thumb to
guide the needle as it is advanced in a medial-posterior
direction, in-serting half the length of the needle (17-18mm.).
On occa-sion you may have a patient that has a larger or smaller
ramus (as you will have deter-mined in step #1). The length
inserted must then be modified to compensate for this
vari-ance.
4. Turn the
needle/syringe approximately 30 degrees in a horizontal plane,
so that the sy-ringe now rests on the anterior teeth of the same
side. The end of the needle should now lie medially and in
proximity to the inferior alveolar nerve as it begins to enter
the man-dibular foramen. It should sit slightly superior and
medially to the foramen.
5. Aspirate, and if
clear of all vessels, inject the full carpule of local
anaesthetic (1.8ml.). The administration of a second carpule is
recommended (1.8 ml. x 2). Repeat steps #1 - #4. A portion of
the second carpule can be used to anaesthetize the long buccal
nerve. The lingual nerve is usually anaesthetized when
performing the "ART" Mandibular Block Technique and a separate
procedure is usually not necessary.
Advantages Of The "ART"
Mandibular Block
#1. Simple to learn and easy to
accomplish:
The A. R. T. mandibular block is not
complicated and is simple to learn and easy to accomplish and
carry out. It is not associated with high risks or numerous
complications as some other techniques demonstrate, and can be
used as a routine procedure in the den-tal office.
#2. Good anatomical landmarks
A very prominent and consistant bony
landmark, the anterior border of the ramus, is utilized in this
procedure. Bisecting the fingernail or thumbnail, extra-oral
landmarks, the mouth being in a closed position and the teeth in
occlusion, are dispensed with.
#3. Utilizing the LOWER portion of the
Pterygomandibular Space
Some mandibular block techniques
utilize the upper portion of the Pterygomandibu-lar Space. The
"A.R.T." mandibular block utilizes the lower portion of this
Space. Un-like the Gow-Gates and Akinosi, there is no danger of
injecting the needle and depositing the local anaesthetic contents
into the maxillary artery and vein, the middle meningeal artery
and vein or the tempero-mandibular joint capsule. All of the
complications associ-ated with the upper space are therefore
avoided.
#4 The Needle Length
The needle length and the average
width of the ramus in the coronoid notch area are ap-proximately
the same. Inserting half the length of the needle will allow for
accurate placement of the tip in proximity to the nerve.
Summary:
Some of the more common reasons for
failure to accomplish a successful mandibular block have been
outlined and discussed. Suggestions are given as to how to reduce
or eliminate the many problems that they cause and at the same
time reduce the failure rate percentage to lower levels.
A new technique has been described to
anaesthetize and block the inferior alveolar nerve (V3), a branch
of the mandibular division of the Trigeminal nerve or 5th. cranial
nerve. The authors feel that utilizing this new block technique
will also contribute to the reduction of the failure rate as well.
References:
1. Monheim, L. Local
Anesthesia and Pain Control in Dental Practice, 2nd. Edit. C.V.
Mosby Co. 1961
2. Carter, R.B., Keen,
E.N. The intramandibular course of the Inferior Alveolar Nerve. J.
Anatomy 103. 433-440 1971.
3. Wong, M., Jacobsen, P.
Reasons for local anesthesia failures. J.A.D.A. Vol.123 69-73,
Jan.1992.
4. Dover, W. R. The
Mandibular Block Injection, why it sometimes fails. Oral Health
1971: 61: 12-14
5. Grover, P.S., Lorton
L. Bifid Mandibular nerve as a possible cause of inadaquate
an-esthesia in the mandible. J.O. M. S. 1983, 41;
177-179.
6. Milles, M.: The Missed
Inferior Alveolar Nerve Block, a new look at an old problem.
Anesth. Progress 1984, 31: 87-90.
7. Bremer, G.:
Measurements of specific significance in connection with
anesthesia of the Inferior Alveolar Nerve: Oral Surgery 5: 966:
988 1952.
8. Gow-Gates, G. A.
Mandibular Conduction Anaesthesia: A new technique using
extra-oral landmarks. Oral Surgery 36: 321-326 1973
9. Akinosi, G. A. A new
approach to the mandibular nerve block: Br. J. Oral Surg. 15:
83-87 1977.
10. A.A.O. M. S. Digest.
Lidocaine Anesthetic Recalled, Astra Pharmaceutical Products, Inc.
p 95, May1992
11. Hoechst Inc. Product
Monograph.
12. Graham Chemical
Product Monograph.
13. Lemay, H., et al.
Ultracaine in Conventional Operative Dentistry J. C. D. A. 1984:50
(No.9) 703-708
14. Bennett, R. Monheim’s
Local Anesthesia and Pain Control In Dental Practise 5th. Edit.
C.V. Mosby Co. 1974
15. Jastak, J. T.,
Yagiela, J. A., Donaldson, D. Local Anesthesia Of The Oral Cavity,
W.B. Saunders Co. 1995 P166.
16. Marks, R.B., Carlton,
D.M., McDonald, S. Management of A broken needle in the pterygoid
space: report of a case. J Am Dent
Assoc.,109:263-264,1984
17. Mima, T., et al. A
broken needle in the pterygoid space. Osaka Daigaku Shigaku
Zasshi. 34:418-422, 1989
18. Menke, R.A., Gowgiel,
J.M. Short-Needle block anesthesia at the mandibular fora-men.
J.A.D.A. Vol. 99, 27-30, July 1979
ABSTRACT
A new local anaesthetic
block technique to anaesthetize the inferior alveolar nerve (V3),
a branch of the mandibular division of the Trigeminal or 5th.
cranial nerve, is described.
The failure rate to
successfully administer a Mandibular Block may run as high as 15%.
This paper reviews and outlines some of the more common reasons
for this failure and how to avoid them. A short description of
other techniques are presented, some of which should only be
reserved for isolated cases and not utilized on a routine
basis.
It is possible that by
avoiding or eliminating the reasons for failure and the
utilization of this new block, one could reduce the failure rate
to much lower levels.
ABOUT THE
AUTHORS
Dr.Lawrence I. Gaum and Dr. Allan Moon
are both Oral and Maxillofacial surgeons and maintain a private
practice with offices in Toronto, Scarborough and Mississauga. Dr.
Gaum is on the teaching staff at the University of Toronto and
holds a Fellowship in the American Dental Society of
An-aesthesiology.
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