Effect of Cooling of Lidocaine with Epinephrine on the Anesthetic Success of Supplementary Intraligamentary Injection after a Failed Primary Inferior Alveolar Nerve Block: A Randomized Controlled Trial

OBJECTIVE: The purpose of this prospective, randomized clinical trial was to evaluate the effect of cooling a 2% lidocaine solution with 1:200,000 epinephrine, administered as a supplementary intraligamentary injection to overcome a failed primary inferior alveolar nerve block (IANB). METHODS: The study was preceded by a pilot study to evaluate the anesthetic efficacy of plain lidocaine solutions given as intraligamentary injections. In the subsequent randomized clinical trial, one hundred and thirty-eight patients received IANB with 2% lidocaine with 1:80,000 epinephrine for endodontic management of a mandibular molar with symptomatic irreversible pulpitis. Eighty-eight patients reported pain greater than 54 mm on a visual analog scale (Heft-Parker VAS) were categorized as unsuccessful anesthesia. These patients received either of the following intraligamentary injections: 2% lidocaine with 1:200,000 epinephrine at room temperature; or 2% lidocaine with 1:200,000 epinephrine at 4°C. Anesthetic success was again evaluated after re-initiation of the endodontic treatment. The heart rates of the patients were measured using a finger pulse oximeter. The categorical success rates were statistically analyzed with the Pearson chi-square test at 5% significance levels. The heart rate measurements were analyzed using a t-test. RESULTS: The intraligamentary injections with anesthetic solutions at room temperature presented a success rate of 59.1%, while the injections with a solution at 4°C gave a success rate of 52.27%. There were no significant differences between the success rates of the groups (χ(2)=0.41, p=0.52). Regarding the heart rates, there were no differences between the two solutions at baseline (T=1.2, p=0.2) or after injections (T=0.64, p=0.52). CONCLUSION: Reducing the temperature of 2% lidocaine with 1:200,000 epinephrine to 4°C does not affect the anesthetic efficacy of supplemental intraligamentary injections, given after a failed primary IANB.