Adrenaline dilution in dental local anesthetic: a preliminary study to prevent coring in cartridges

Many patients with underlying medical conditions are treated with local anesthetics in dental clinics. Dental local anesthetic cartridges contain the vasoconstrictor adrenaline, which can affect the cardiovascular system. For this reason, the adrenaline in the cartridge (2% lidocaine + 1:80,000 adrenaline) is sometimes diluted in order to avoid hemodynamic changes in these patients. However, at the same time, considerations have to be made for coring. Coring is a process in which a piece of rubber is scraped off when a needle is inserted into a rubber stopper, and the rubber is mixed with the drug solution. Particles generated during the coring process contaminate local anesthetic solutions. In this study, we closely observed the puncture site of a 33G dental needle inside a cartridge to investigate a safe dilution method that considers coring. The puncture site was located within 1.50 ± 0.08 mm (mean ± SD) of the diameter from the center of the rubber stopper of the cartridge head. Punctures were made with a 0.75-mm outer diameter metal needle outside the 1.50-mm diameter range from the center of the rubber stopper to reduce the overlap between puncture sites and minimize the risk of coring. After discarding half of the cartridge, 2% lidocaine without adrenaline was injected by piercing the end of the rubber stopper at the cartridge head with a 22-27G metal needle (outer diameter approximately 0.4-0.7 mm). This method minimizes the risk of rubber displacement and coring while ensuring a safe and effective dilution process. Providing a safer method for adrenaline dilution reduces the risk of coring and contamination in dental anesthetic cartridges.