Context:Dexamethasone has been frequently used in oral surgical procedure and accepted by oral and maxillofacial surgeon community worldwide. However, this is the first clinical trial that used dexamethasone as adjuvant with lignocaine in dental nerve block (DNB).Aims:The purpose of this double-blind, randomized control trial (RCT) was to compare the effect of dexamethasone with normal saline (NS) in a lignocaine DNB.Settings and Design:This prospective, double-blind, RCT was carried out after obtaining approval from the Institutional Ethical Committee.Subjects and Methods:In forty patients, the present placebo-controlled clinical trial was conducted; allocated randomly into two groups: study group (SG) or control group (CG). The single-dose submucosal dexamethasone or NS injection was administered immediately after 2% lignocaine with epinephrine 1:2,00,000 nerves block during mandibular third molar surgery (TMS). Visual analog scale score, number, and exact time nonsteroidal anti-inflammatory drugs were administered were used to measure postoperative analgesia in 2nd and 7th days.Statistical Analysis Used:All the data were entered into the Spreadsheet (Excel, Microsoft) and Chi-square test, Mann–Whitney U-test, Student's paired and unpaired t-test, and Fisher exact test were used.Results:This study found maximum duration of DNB in SG was 248.88 min and in CG was 175.44 min, whereas minimum duration in SG was 197 min and in CG was 140.78 min.Conclusions:Dexamethasone prolongs the action of lignocaine 2% in DNB for TMS.