The authors, using a crossover design, randomly administered, in a single-blind manner, 3 sets of injections: an inferior alveolar nerve block (IANB) plus a mock buccal and a mock lingual infiltration of the mandibular first molar, an IANB plus a buccal infiltration and a mock lingual infiltration of the mandibular first molar, and an IANB plus a mock buccal infiltration and a lingual infiltration of the mandibular first molar in 3 separate appointments spaced at least 1 week apart. An electric pulp tester was used to test for anesthesia of the premolars and molars in 3-minute cycles for 60 minutes. Anesthesia was considered successful when 2 consecutive 80 readings were obtained within 15 minutes following completion of the injection sets, and the 80 reading was continuously sustained for 60 minutes. For the IANB plus mock buccal infiltration and mock lingual infiltration, successful pulpal anesthesia ranged from 53 to 74% from the second molar to second premolar. For the IANB plus buccal infiltration and mock lingual infiltration, successful pulpal anesthesia ranged from 57 to 69% from the second molar to second premolar. For the IANB plus mock buccal infiltration and lingual infiltration, successful pulpal anesthesia ranged from 54 to 76% from the second molar to second premolar. There was no significant difference (P > .05) in anesthetic success between the IANB plus buccal or lingual infiltrations and the IANB plus mock buccal infiltration and mock lingual infiltration. We conclude that adding a buccal or lingual infiltration of 1.8 mL of 2% lidocaine with 1:100,000 epinephrine to an IANB did not significantly increase anesthetic success in mandibular posterior teeth.