Background: The pH of lidocaine with epinephrine in dental cartridges ranges between 2.9 and 4.4. In this pH range, less than 0.1% of the anesthetic is in the de-ionized or "active" form. The acidity of the anesthetic may delay onset and contribute to injection pain.
Objective: The study compared anesthetic latency and injection pain for alkalinized versus non-alkalinized anesthetic in inferior alveolar nerve blocks (IANBs).
Methods: The study buffered the anesthetic directly in the cartridges using a mixing pen device. The study included 20 participants, each receiving one control and one test IANB injection. The control solution was non-alkalinized 2% lidocaine/epinephrine 1:100,000 at pH 3.85. The test solution was 2% lidocaine/ epinephrine 1:100,000 alkalinized to pH 7.31. Latency was measured using endodontic ice confirmed with an electric pulp tester (EPT), and injection pain was measured using a visual analog scale (VAS). ONSET TIME: With the alkalinized anesthetic, 71% of participants achieved pulpal analgesia in 2 minutes or less. With non-alkalinized anesthetic, 12% achieved pulpal analgesia in 2 minutes or less (P = 0.001). The average time to pulpal analgesia for the non-alkalinized anesthetic was 6:37 (range 0:55 to 13:25). Average time to pulpal analgesia for alkalinized anesthetic was 1:51 (range 0:11 to 6:10) (P = 0.001). INJECTION PAIN RESULTS: 72% of the participants rated the alkalinized injection as more comfortable, 11% rated the non-alkalinized injection as more comfortable, and 17% reported no preference (P = 0.013). Forty-four percent of the patients receiving alkalinized anesthetic rated the injection pain as zero ("no pain") on a 100-mm VAS, compared to 6% of the patients who received non-alkalinized anesthetic (P = 0.056).
Conclusions: Alkalinizing lidocaine with epinephrine toward physiologic pH immediately before injection significantly reduces anesthetic onset time and increases the comfort of the injection.
Clinical implications: Clinicians can begin procedures more quickly and give a more comfortable injection by alkalinizing their lidocaine/epinephrine immediately before delivering the injection.