Extra-oral Mandibular Nerve Block: Comparative Evaluation of Local Anesthetic Distribution Using Ultrasonography

Background and Overview:  Compared to local anesthetic success rates in most other parts of the body, the incidence of failure to achieve pulpal anesthesia of the mandibular teeth using the traditional techniques is quite high.  Failure rates have been reported by several authors to be 15-20%¹.  As a result there is continued interest in striving for an alternative mandibular nerve block offering the potential of greater success.  In dentistry mandibular nerve blocks are commonly performed using an intra-oral technique while other areas of medicine typically use an extra-oral technique.  The Akinosi-Vazirani technique is such an alternative intra-oral technique to the Halstead used for achieving a mandibular nerve block.  The goal of this injection technique is to fill the pterygomandibular space thus bathing the inferior alveolar, lingual, and mylohyoid nerves with anesthetic².  This technique has been shown to have both higher and comparable success rates when compared to the Halstead technique.  The goal of the extra-oral technique by Kantorowicz is also to deliver local anesthesia within the ptergyomandibular space adjacent to the mandibular foramen.   This technique offers a number of benefits such as reducing the need for patient cooperation: the path of injection also more closely approximates that of the nerve itself and may offer a greater contact between local anesthetic solution and nerve trunk.  If the Kantorowicz technique can be shown to reliably deliver local anesthesia within this space it may achieve comparable anesthesia success.  Such an alternative could then be a valuable and routine adjunct in dental education.

 Methodology: Following approval from the Ohio State University IRB. 80 ASA I and II patients requiring bilateral mandibular tooth extractions under general anesthesia and deep sedation were enrolled over a period of 6 months.  All patients received bilateral mandibular nerve blocks; on one side the Kantorowicz technique, on the other the Halstead technique.  Patients were randomly assigned to group A or B. Group A received the Halstead injection on the right, group B this technique on the left.   An Acuson p50 ultrasound (7L3 high-frequency linear wideband array transducer) confirmed the location and deposition of the local anesthetic within the pterygomandibular space.  The volume administered was 3.0 ml of 2% Lidocaine with 1:100,000 parts of epinephrine.  Syngo US Workplace software was used to measure the planar dimensions of the local anesthetic.  A dependent paired t-test was used to compare the depth, width, and ratio of depth to widths of the two injection techniques.  

Results: Using ultrasonography we confirmed the Kantorowicz technique fills the pterygomandibular space with local anesthetic.  The traditional Halstead technique was shown to also fill the pterygomandibular space. Using a dependent paired t-test we were able to show there was no statistical difference in the depth, width, or ratio of the depth and width in the distribution of the local anesthetic bolus between the two techniques. 

Conclusions: Other mandibular nerve block techniques such as the Akinosi-Vazirani aim to fill the same pterygomandibular space with local anesthesia and have shown high success rates.  By accomplishing the same goal of filling the pterygomandibular space with local anesthesia the Kantorowicz technique provides dentistry with an extra-oral technique for achieving anesthesia of mandibular teeth.  With the reduced need for patient cooperation, this is a technique that dental students would benefit from being taught.

Future research: Determine the volume needed within the pterygomandibular space to achieve pulpal anesthesia.

  References:

1. Malamed SF. Handbook of local anesthesia. 5^th ed. St. Louis: Mosby Year Book; 2004:227
2. Haas DA. Alternative mandibular nerve block techniques: A review of the Gow-Gates and Akinosi-Vazirani closed-mouth mandibular nerve block techniques. JADA 2011; 142 suppl 3): 8S-12S