Purpose <p>To evaluate whether daily postoperative irrigation combined with suction drainage is associated with improved clinical outcomes compared with suction drainage alone in patients with odontogenic submandibular deep neck abscess.</p> Methods <p>This retrospective cohort study included adult patients treated between January 2019 and April 2025. Among 112 screened patients, 60 with odontogenic submandibular abscess larger than 3&#xa0;cm were included and allocated using an alternating sequence to irrigation plus drainage (Group A, <i>n</i> = 30) or drainage alone (Group B, <i>n</i> = 30). Postoperative daily irrigation with diluted povidone–iodine followed by saline plus suction drainage vs. suction drainage alone. Primary outcomes were length of hospital stay and postoperative complications (reoperation, mediastinitis, or tracheostomy). Secondary outcomes included evolution of inflammatory markers.</p> Results <p>Baseline characteristics were comparable between groups. Mean hospital stay was shorter in Group A (5.6 ± 3.4 days) than in Group B (7.5 ± 3.0 days; <i>p</i> &lt; 0.05). Postoperative complications occurred in 10.0% vs. 36.7% of patients, respectively. Irrigation was associated with a reduced risk of complications (risk ratio, 0.27; 95% CI, 0.09–0.79), corresponding to an absolute risk reduction of 26.7% and a number needed to treat of 4. Inflammatory markers declined more rapidly in the irrigation group. Multivariable analysis confirmed irrigation as independently associated with lower complication risk.</p> Conclusions <p>Postoperative irrigation combined with suction drainage was associated with improved clinical outcomes compared with drainage alone. These findings support irrigation as a potentially valuable adjunct in the management of odontogenic deep neck abscesses.</p>