This month’s Endo Newsletter topic: Supine vs Upright Position for Inferior Alveolar Nerve Block

Pivotal for successful treatment, profound anesthesia prior to endodontic therapy is not always easy to achieve, especially in the lower molar area. To improve the likelihood of success, various approaches have been proposed, such as using solutions with or without vasoconstrictors, increased volume or increased concentration of the anesthetic solution, buffered anes­thetic solutions, and Gow-Gates and Akinosi-Vazarani injection techniques. Studies have suggested that having the patient maintain an upright or semi-upright position after administer­ing the inferior alveolar nerve block (IANB) increases its success, because the anesthetic solution diffuses down along the ramus and is therefore more likely to hit the target.

To explore the effect of patient position on IANB success, Crowley et al from The Ohio State University recruited 110 healthy adults (55 women, 55 men; age range, 20–36 years) for a crossover-design study. Participants received 2 IANB injections of 2% lidocaine with 1:100,000 epinephrine at least 2 weeks apart, 1 while seated upright and the other while in a supine posi­tion. Researchers randomly decided whether the patient was to be seated upright or in a supine position during the first injection, making each par­ticipant his or her own control.

A total of 3.2 mL of the anesthetic solution was injected by a computer-controlled local anesthetic device over a period of 1 minute and 52 seconds.

All patients were repeatedly asked whether they felt profound lip numb­ness after the injections; if numbness was not achieved within 15 minutes, the block was considered unsuccess­ful. After each injection, the first and second molars, premolars, central and lateral incisors, and a contralateral canine (as a control) were stimulated with an electric pulp tester (EPT) in 4-minute cycles for 60 minutes. Success was defined as the patient maxing out on the EPT without feel­ing the stimuli for 2 consecutive times and sustaining the numbness for 60 minutes.

The authors found no statistical dif­ference between the 2 positions in achieving profound anesthesia for the molars and incisors, but the supine position significantly improved suc­cess for both premolars. There were wide differences in the success rates for the anesthesia: The second molars had a 65% to 73% success rate, but the central incisors had only an 8% to 11% success rate. Most importantly, neither position for IANB administra­tion consistently provided complete pulpal anesthesia.

Conclusion

This study found that the patient’s position is not critical to achieving profound IANB. It remains important to assess the patient’s level of anes­thesia prior to initiating therapy and, if numbness has not been achieved, then supplementary injections such as periodontal ligament or long buccal should be tried.

Crowley C, Drum M, Reader A, et al. Anesthetic efficacy of supine and upright positions for the inferior alveolar nerve block: a prospective, randomized study. J Endod 2017;doi:10.1016/j.joen.2017.09.014.