The mandibular block is perhaps the most commonly delivered major nerve block injection in all of dentistry. Every dentist is an expert in administration of mandibular blocks since we have all delivered thousands of them. On the other hand, we have all run into patients for whom we could not produce the desired anesthesia using the standard technique. It happens rarely, but when it does, it is very, very frustrating.
Fortunately, an Australian dentist named Dr. George A.E. Gow-Gates invented an alternative to the standard mandibular block in the mid 1970's. This block is appropriately named the Gow-Gates and is delivered at the neck of the condyle just under the insertion of the lateral pterygoid muscle. The Gow-Gates has a number of advantages over it's more traditional alternative.
Unlike the mandibular block, the path the needle traverses during a Gow Gates block contains much less muscle tissue than is traversed by the needle in a standard mandibular block, and thus there is little release of bradykinins which are the chemicals which cause the aching that patients feel when receiving a mandibular block. Furthermore, the tissue through which the needle passes contains no nerve receptors, and thus there is little direct pain during the injection. It is not uncommon for patients to remark that they felt nothing during the injection.
The area where the Gow-Gates is delivered is less vascularized than the area adjacent to the location of injection in a standard mandibular block. Studies indicate that there is an 89-90% lower likelihood of giving an intra-vascular injection using this technique. In addition, because of the lower vascularization in the area, the anesthesia is less rapidly absorbed into adjacent blood vessels prolonging the presence of the anesthesia in the area, which means that mepivicaine without vasoconstrictor may be used to greater and longer lasting effect using the Gow-Gates. Some users of this technique recommend that no vasoconstrictor be used at all.
Finally, the Gow-Gates anesthetizes the nerve trunk before it splits into its three main branches; the lingual branch, the buccal branch and the alveolar branch. Thus the Gow Gates delivers three shots in one. A single shot does the work of three separate injections.
The image above shows the medial aspect of the right condyle and the relative position of the nerve trunk. The shaded oval indicates the area of the condyle where the tip of the needle should be placed. Note the proximity of the nerve trunk with respect to the general target.
In the image of the ear above, the little prominence in the front is called the tragus. The tragus is a useful landmark since it lies just distal to the temporomandibular joint. The little notch just below it is called the intertragal notch. Both of these landmarks are easily identified, and, more importantly felt with the finger. The intertragal notch is the landmark that is used as the "aiming point" of the needle when giving the Gow-Gates injection.
This intra-oral image shows the entry point of the needle. The patient's mouth must be WIDE open so that the condyle is fully translated over the articular eminence. The entry point of the needle is high and about a quarter inch distal to the distal palatal cusp of the second molar.
With the patient lying fully reclined in the chair, have the patient open his/her mouth as wide as possible. This technique is not possible if the patient is not able to open wide enough to allow the condyles to translate fully over the articular eminences.
Place your thumb in the patient's mouth retracting the cheek. The thumb should be relatively close to the site of the entry point of the needle noted in the image above.
Place the middle finger of the same hand over the intertragal notch. This landmark is easily felt with the finger. Thus the hand is held in a "C" with the thumb inside the mouth retracting the cheek and the middle finger outside the mouth placed firmly over the intertragal notch.
Using a long 27 gauge needle, and holding the handle of the syringe at about the level of the lower premolars, allow the needle to enter the buccal mucosa just distal and apical to the tuberosity. (See the arrow in the intra-oral imageabove.)
Now aim the tip of the needle toward the the intertragal notch. This is fairly easy because you can feel the notch under your middle finger, so in effect, you are simply aiming for your finger! Keeping the middle finger in this position, and using it as the aiming point makes giving the Gow-Gates block easy and predictable.
Proceed until the needle hits bone. The needle will enter about two-thirds to three-quarters of its length before hitting bone. If the needle does not hit bone, then you have missed the target and should withdraw and try again, aiming slightly laterally, or medially. It should be noted that this technique seems to produce very few misses. In any case, multiple tries do not lead to post operative pain since the needle has penetrated little or no muscle. Once you become familliar with the technique, missing the target becomes a rare event.
Once the needle hits bone, aspirate and then inject the entire carpule slowly.
After withdrawing the needle, ask the patient to remain open wide for about one minute after the shot.