Aim: This randomized clinical trial compared the anesthetic efficacy of buccal infiltration (BI) with 4% articaine (AR) and inferior alveolar nerve block (IANB) with 2% lidocaine (LI), both with 1:100,000 epinephrine, in symptomatic mandibular molars with irreversible pulpitis. Likewise, we compared the efficacy of the primary infiltration (BI or IANB) with one supplemental injection (intraligamentary infiltration with articaine for AR and BI with articaine for LI). The influences of buccal cortical bone thickness and root distances to buccal cortical bone on articaine performance (AR) were also evaluated using cone-beam tomography. methodology: Volunteers presenting symptomatic mandibular molars with irreversible pulpitis were randomly divided into two groups (30 for AR and 20 for LI). Success was recorded when complete pain-free treatment was achieved after primary injection or when one supplemental injection was needed for emergency endodontic procedures.