Dr. Lawrence I. Gaum DDS  FADSA  FICD          oral surgeon
 
 

The A.R.T. Mandibular Block

Gaum LI, Moon AC, The "ART" mandibular nerve block: a new approach to accomplishing regional anesthesia.

J Can Dent Assoc. 1997 Jun;63(6):454-9


ABSTRACT:

A new technique involving the use of a local block to anesthetize the inferior alveolar nerve (V3), a branch of the mandibular division of the trigeminal or fifth cranial nerve, is described. Clinicians fail to administer a successful mandibular block in as many as 15 per cent of all cases. 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 be reserved for isolated cases and not used on a routine basis. By avoiding or eliminating the reasons for mandibular block failure, and using the new block described in this paper, clinicians should be able to reduce the failure rate to much lower levels.


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. Monheim1 divided regional anaesthesia into four parts:

Topical

Infiltration

Field Block

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 afferent impulses from traveling 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 approach is the more common approach utilized in the practice of dentistry.

The mandibular branch, which contains both sensory and motor fibers, exits the cranium through the foramen ovale. The trunk divides into two branches, anterior and posterior. The posterior divides into the lingual and inferior alveolar nerves. The inferior alveolar nerve is the larger branch of the posterior division of the mandibular nerve. It enters 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 incisive2. When the intraoral mandibular or inferior alveolar nerve block is accomplished, its branches, the mental, incisive and the lingual nerve are all affected. As a result, the areas usually anesthetized are:

The body of the mandible and the lower portion of the ramus.

All mandibular teeth.

Floor of mouth.

Anterior 2/3rd of the tongue.

Gingivae on the lingual surface of the mandible.

Gingivae on the labial surface of the mandible.


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 matter3.

There are many reasons put forth as to why local anaesthesia and the mandibular nerve block fail. Dover4 suggests incorrect techniques such as injecting too high, too superficial, and too deep, are all reasons why dentists are having failures in accomplishing adequate block anaesthesia of the inferior alveolar nerve. Anomalies of the mandibular 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 methods. 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 patients experiencing pain during dental procedures. 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 consistent results, and in many instances result in complete failure of the technique7.

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:

Poor Technique.

Techniques that are too complicated and of high risk.

Gow Gates.

Akinosi.

Quality of local anaesthetic.

Quantity of local anaesthetic utilized.

Time allowed following administration of local anaesthetic for block to take effect.

Length and gauge of needle.


Poor Technique:
No matter what technique is utilized, there is an element of skill required in accomplishing 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:

Injecting too low, (The needle is inserted below the foramen and nerve.)

Injecting too deep, (The needle is inserted behind the foramen and nerve.)

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.

Techniques that are too complicated and of high risk:
Gow-Gates and Akinosi Techniques are complicated procedures 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 contains 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 needle and local anaesthetic into the anterior portion of the temperomandibular joint capsule could also produce damage and prolonged side effects in the form of severe joint dysfunctions. Dentists have had the frustrating task of treating these cases as they linger and drag on for many years.

The Akinosi technique9 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 experienced clinician in whose hands complicated techniques are routine. They should not be used on a routine basis in a dental office.

Quality of Local Anaesthetic:
There are many good quality local anaesthetics available today. Reputable companies 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 commitment 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 success 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 recall 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 anaesthetic 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 medications must always be discarded. Above all, one must purchase their products from a reputable dealer.

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 Co11. recommends up to 3.4 ml. of Ultracaine DS Forte for a block while Graham Chemical12 suggests up to 5ml. of Lidocaine 2%. In studies done by Lemay13, 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. Monheim1 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, regardless 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 mandibular teeth or restorative procedures.

Time allowed following administration of local anaesthetic:
Following the administration of the local anaesthetic, an important factor in the measure 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 membrane, 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 distressful outcome.

Size and gauge of needle:
To accomplish a mandibular block, Monheim1 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 possible 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. Monheim1 and Bennet14 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. (See Figure # 1)

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 direction away from point B. to point C. (See Figure # 1)

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 gauge1, 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 surgeon16, 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 litigation.
Some dentists are convinced that the larger gauge needle is more painful upon insertion 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)

Palpate the anterior border of the ramus with the thumb and find the greatest concavity, which is the coronoid notch. (See Figures # 2 and # 3). 
At the same time, use the middle finger and the thumb to determine the width of the ramus in its anterior-posterior dimension. Anatomically, the mandibular foramen lies in the middle of the ramus in this dimension. 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)

Inject the needle until bone in the coronoid notch is contacted. The syringe and needle at this stage are buccal to the posterior molars. (See Figures # 4 and # 5)

Use the thumb to guide the needle as it is advanced in a medial-posterior direction, inserting half the length of the needle (17-18mm.). (See Figures # 6 # 7 and # 8).  On occasion you may have a patient that has a larger or smaller ramus (as you will have determined in step #1). The length inserted must then be modified to compensate for this variance.

Turn the needle/syringe approximately 30 degrees in a horizontal plane, so that the syringe 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 mandibular foramen. It should sit slightly superior and medially to the foramen. (See Figures # 9 and # 10)

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:

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 dental office.

Good anatomical landmarks A very prominent and consistent 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.

Utilizing the LOWER portion of the Pterygomandibular Space::

Some mandibular block techniques utilize the upper portion of the Pterygomandibular Space. The "A.R.T." mandibular block utilizes the lower portion of this Space. Unlike 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 temperomandibular joint capsule. All of the complications associated with the upper space are therefore avoided.

The Needle Length The needle length and the average width of the ramus in the coronoid notch area are approximately 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:

1Monheim, L. Local Anesthesia and Pain Control in Dental Practice, 2nd. Edit. C.V. Mosby Co. 1961

2Carter, R.B., Keen, E.N. The intramandibular course of the Inferior Alveolar Nerve. J. Anatomy 103. 433-440 1971.

3Wong, M., Jacobsen, P. Reasons for local anesthesia failures. J.A.D.A. Vol.123 69-73, Jan.1992.

4Dover, W. R. The Mandibular Block Injection, why it sometimes fails. Oral Health 1971: 61: 12-14

5Grover, P.S., Lorton L. Bifid Mandibular nerve as a possible cause of inadaquate anesthesia in the mandible. J.O. M. S. 1983, 41; 177-179.

6Milles, M.: The Missed Inferior Alveolar Nerve Block, a new look at an old problem. Anesth. Progress 1984, 31: 87-90.

7Bremer, G.: Measurements of specific significance in connection with anesthesia of the Inferior Alveolar Nerve: Oral Surgery 5: 966: 988 1952.

8Gow-Gates, G. A. Mandibular Conduction Anaesthesia: A new technique using extra-oral landmarks. Oral Surgery 36: 321-326 1973

9Akinosi, G. A. A new approach to the mandibular nerve block: Br. J. Oral Surg. 15: 83-87 1977.

10A.A.O. M. S. Digest. Lidocaine Anesthetic Recalled, Astra Pharmaceutical Products, Inc. p 95, May1992

11Hoechst Inc. Product Monograph.

12Graham Chemical Product Monograph.

13Lemay, H., et al. Ultracaine in Conventional Operative Dentistry J. C. D. A. 1984:50 (No.9) 703-708

14Bennett, R. Monheim’s Local Anesthesia and Pain Control In Dental Practise 5th. Edit. C.V. Mosby Co. 1974

15Jastak, J. T., Yagiela, J. A., Donaldson, D. Local Anesthesia Of The Oral Cavity, W.B. Saunders Co. 1995 P166.

16Marks, 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

17Mima, T., et al. A broken needle in the pterygoid space. Osaka Daigaku Shigaku Zasshi. 34:418-422, 1989

18Menke, R.A., Gowgiel, J.M. Short-Needle block anesthesia at the mandibular foramen. J.A.D.A. Vol. 99, 27-30, July 1979