Background: Alkalinization or buffering of dental local anesthetics to raise the pH of these acidic solutions is a well-documented technique that results in clinical benefits such as decreased injection pain, reduced onset time, and the need for less overall volume of local anesthesia.
Objective: In a previous study, two options available for buffering local anesthetics in dentistry were compared, one using the Onpharma® mixing system (Onpharma), and the other by hand mixing with 8.4% sodium bicarbonate using a "remove and replace" technique. The results of that study showed no statistically significant difference in buffering outcomes between the two methods. This follow-up in vitro study introduces and examines a less complex, direct injection, chairside hand-mixing approach using four commercially available dental local anesthetic preparations.
Materials and methods: The authors prepared multiple buffered samples of four different commercially available local anesthetic solutions. The buffered samples were mixed to 9:1, 19:1, and 18:1 ratios (local anesthetic to 8.4% sodium bicarbonate). Sample pH was recorded using a pH meter. Two samples of each local anesthetic at each ratio were prepared and sequentially pH tested. The pH was recorded via the same pH meter, which was cleaned between each test.
Results: The pH change between unbuffered solutions and all buffered samples was statistically different (P < .01, CI 99%). There was no final pH difference between the 9:1 and 19:1, and 19:1 and 18:1 buffering ratios (P > .01); however, a statistical difference was seen between the final pHs of the solutions resulting from the 9:1 and 18:1 buffering ratios (P = .006, CI 99%). After correction for multiple comparisons, the difference between the 9:1 and 18:1 ratio was marginally significant (P = .048).
Conclusions: Each of the buffering ratios tested can be used to alkalinize dental local anesthetic solutions. For practical purposes, a direct injection chairside of 0.1 mL of 8.4% sodium bicarbonate into any of the four local anesthetics tested is easy, simple, and safe compared to the more complex remove and replace method. Further studies are needed to evaluate if a clinically significant difference exists between the 9:1, 19:1, and 18:1 ratio solutions.
Clinical implications: The potential benefits of buffering local anesthetic solutions prior to injection, such as decreased injection pain, faster onset, and greater depth of anesthesia, may be particularly advantageous in patients who have difficulty achieving profound anesthesia for clinical dentistry, and for anesthetizing infected areas. Dentists can effectively buffer local anesthetic preparations using commercially available mixing systems or by utilizing a hand-mixing technique. Rather than using a remove and replace technique, practitioners may consider a direct injection technique, adding 0.1 mL of 8.4% sodium bicarbonate directly into any local anesthetic cartridge regardless of local anesthetic concentration.