Background/Objectives: External root resorption is an undesirable complication of orthodontic treatment, characterized by the loss of dental root structure. The aim of this study was to identify the biological and dental risk factors involved in the development of external root resorption at the end of orthodontic treatment. Methods: A retrospective observational study was conducted on a sample of 120 patients who underwent orthodontic treatment. External root resorption was assessed using pre- and post-treatment panoramic radiographs. Correlations were established between the severity of external root resorption and various biological and dental risk factors. Results: Out of a total of 2639 teeth analyzed, 52.14% exhibited external root resorption, with most cases being mild to moderate (<3 mm). The maxillary central incisors were the most affected teeth. Age showed a statistically significant correlation with the severity of external root resorption in the lower anterior region (p < 0.01). No significant differences were observed in relation to gender, facial growth pattern, or type of dento-maxillary anomaly. Conclusions: External root resorption is a common consequence of orthodontic treatment, most often presenting with low severity. The type of tooth and the patient’s age influence the severity of root resorption, while factors such as gender, facial growth pattern, and type of dento-maxillary anomaly did not prove to be significant in this context.