This prospective randomized clinical trial aimed to evaluate the effects of different anesthesia protocols on anesthetic success and intraoperative pain during root canal treatment of mandibular premolars diagnosed with symptomatic irreversible pulpitis. A total of 100 systemically healthy patients were randomly allocated into four groups: infiltration anesthesia alone, inferior alveolar nerve block (IANB) alone, infiltration anesthesia combined with cryotherapy, and IANB combined with cryotherapy. Cryotherapy was applied intraorally for 5 minutes immediately after anesthetic administration.

The effectiveness of anesthesia was confirmed using electric pulp testing and cold testing prior to treatment. Root canal therapy was completed in a single visit by a calibrated operator. Intraoperative pain was assessed during access cavity preparation using a visual analogue scale (VAS). Anesthetic success was defined as the presence of no or mild pain, whereas moderate or severe pain indicated anesthetic failure and required supplemental anesthesia.

The primary objective of the study was to determine whether the adjunctive use of cryotherapy improves anesthetic success and reduces intraoperative pain in mandibular premolars with symptomatic irreversible pulpitis. The null hypothesis was that no significant differences would be observed among the study groups in terms of anesthetic success or intraoperative pain intensity.

Inclusion Criteria:

• Systemically healthy patients classified as ASA I or II, aged between 18 and 60 years,
• Presence of a restorable mandibular premolar tooth diagnosed with symptomatic irreversible pulpitis,
• History of spontaneous pain or lingering pain elicited by thermal stimuli,
• Positive response with lingering pain to cold testing (Endo Ice; Coltene, Altstätten, Switzerland),
• Positive response at low current levels to electric pulp testing (Parkell Inc., USA),
• Teeth with closed apex and no radiographic evidence of periapical pathology (intact periodontal ligament space and absence of periapical radiolucency),
• Patients presenting with moderate or severe preoperative pain, as assessed using the visual analogue scale (VAS).

Exclusion Criteria:

• Patients who had taken analgesic, anti-inflammatory, or opioid medication within the last 12 hours before treatment,
• Patients with systemic conditions that may affect pain perception, inflammatory response, or healing,
• History of antibiotic use within the previous month or requirement for antibiotic prophylaxis,
• Teeth presenting with clinical or radiographic signs of pulp necrosis or apical periodontitis (Pain on percussion or palpation, presence of sinus tract or swelling, presence of periapical radiolucency),
• Teeth with root resorption, immature apices, severe coronal destruction preventing proper isolation, or calcified canals,
• Teeth that had undergone previous endodontic treatment, including pulpotomy or root canal filling,
• Patients with neurological or psychiatric conditions that could interfere with pain perception or accurate pain reporting,
• Inability to achieve adequate isolation with a rubberdam.