Background Adjunctive hyaluronidase has been widely used for ophthalmic anesthesia; however, in Dentistry, very few studies are available so far. Thus, the present study aimed to evaluate anesthetic outcomes of adjunctive hyaluronidase administration following buccal infiltration of articaine with epinephrine for anesthesia of mandibular first molars. Material and Methods Twenty-eight patients received a buccal supraperiosteal infiltration of 4% articaine with 1:100,000 epinephrine for anesthesia of the mandibular first molars, in a split-mouth approach. Afterward, randomly and using the same technique, they received either 1.0 mL of hyaluronidase (150 UTR/mL) or a placebo solution. Considering patients’ pain perceptions provoked by electric and mechanical stimulations, as well as using a pain scale, success rate, action onset time, duration of both pulpal and soft tissue anesthesia, and pain immediately after both punctures and on the 2nd day were assessed. Results The pulpal anesthetic success rate was 85.7% for hyaluronidase and placebo groups. Soft tissue anesthesia showed a shorter action onset time and a longer duration when hyaluronidase was used; however, there was no difference between the groups regarding action onset time and duration of pulpal anesthesia. Pain at the puncture sites did not differ between the groups, regardless of the time point evaluated. Conclusions Adjunctive hyaluronidase following buccal infiltration of articaine with epinephrine for mandibular first molars seems not to provide any advantage in anesthetic outcomes in which the nerve fibers are intraosseous (i.e., pulpal anesthesia). On the other hand, soft tissue anesthesia may be improved substantially by using this pharmacological strategy. Key words: Hyaluronidase, local anesthesia, dentistry.