Introduction: Breast cancer treatment includes the use of antiresorptive agents aimed at increasing bone density in early stages and reducing skeletal events in advanced disease with bone metastases. Its prolonged usage is associated with the risk of medication-related osteonecrosis of the jaw (mronj), a condition that can affect patients' quality of life. Objectives: To describe the incidence of medication-related osteonecrosis of the jaw and the clinical characteristics of patients with breast cancer treated with bone-antiresorptive agents during the period 2020–2024. Materials and methods: A retrospective, observational, descriptive cohort study based on a review of clinical records from the dentistry department of the Breast Cancer Foundation, A.C. (fucam a.c., its acronym in Spanish) was conducted. All female patients over the age of 18 with a diagnosis of breast cancer and an indication for bone-antiresorptive treatment who were seen between January 2020 and December 2024 were included. Absolute frequencies and measures of central tendency were calculated. Results: Clinical records of 1,643 patients with breast cancer who underwent dental assessment prior to the initiation of antiresorptive treatment were analysed. Of these, 930 were considered candidates to initiate it. Seven cases of mronj were confirmed, corresponding to a cumulative incidence of 0.75% during the observation period. All cases occurred in patients with bone metastases treated with intravenous zoledronate. The temporal distribution of diagnoses showed an absence of new cases from 2023 onwards. Conclusions: The incidence of mronj in the studied cohort was low. All confirmed cases occurred in patients with bone metastases and prolonged exposure to zoledronate. The pre-treatment dental evaluation and periodic follow-up are practices focused on prevention prior to the start of treatment.