Objective: The aim of this study was to assess the possible factors associated to root resorption, common to daily clinical orthodontics, especially parafunctional habits. Methods: A retrospective study of 600 patients (308 females and 292 males) previously treated orthodontically was conducted. The sample was divided into two groups related to the degree of root resorption at the ending of treatment according to Malmgren. Group 1 comprised 507 patients with a mean initial age of 14.21 years and who had absent or mild final external root resorption, characterized by grades 0, 1 and 2 of root resorption; Group 2 comprised 93 patients with initial mean age of 14.57 years and who had moderate or severe root resorption, characterized by grade 3 and 4. The groups were then compared in terms of age at the beginning and ending of the treatment, treatment time, gender, type of treatment (with and without extractions), parafunctional habits (bruxism, onychophagia, the habit of biting objects, tongue thrusting habit and thumb sucking habit), allergies and pretreatment root resorption. Results: The results show that the initial age, gender, type of malocclusion, parafunctional habits and allergies do not represent a statistically significant risk of root resorption. Conclusion: Treatment time and type (with and without extractions) and the presence of external root resorption at the beginning of the treatment showed significant differences.