A retrospective study was performed to verify if the number of admissions for urgent dental care in the Urgent Dental Care Service of San Paolo Hospital in Milan (Italy) was directly related to the different phases of the COVID-19 pandemic. Different periods were analyzed: March 25–April 5, 2019 (pre-COVID); March 23–April 3, 2020 (lockdown); June 8–June 19, 2020 (reopening); and November 9–November 20 (second wave). Raw data regarding admissions, diagnoses, and treatments were extracted. Descriptive and bivariate analyses were performed. The survey included 901 admissions, 285 in pre-COVID, 93 during lockdown, 353 in reopening, and 170 in the second wave. In each time period, statistically significant differences were found in the prevalence of each kind of diagnoses (X2(3) = 20.33 p = 0.01 for endodontic emergencies, X2(3) = 29.05 p < 0.01 for cellulitis/phlegmon, X2(3) = 28.55 p < 0.01 for periodontal emergencies, Fisher’s Exact Test p < 0.01 for trauma, and X2(3) = 59.94 p < 0.01 for all other kinds of diagnosis). A remarkable increase in consultations (+186.36%) and other treatments (+90.63%) occurred during reopening. Tooth extraction was the most frequently delivered treatment, but suffered the largest reduction during lockdown (−79.82%). The COVID-19 pandemic has highly affected dental activity in north Italy, underling the weaknesses of a private dental system in a pandemic scenario. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.