The goal of this prospective clinical trial is to evaluate the possible superiority of a treatment compared to the gold standard of reference in Orthodontics.

Apical external root resorption is defined as the loss of dental hard tissues such as dentine, cement and alveolar bone. This is considered an irrevocable effect associated to different factors, among which dental movement during orthodontic treatment is related.

This study suggest to compare root resorption after the use of two different types of alignment and levelling arches in orthodontics. Consecutive patients randomly chosen will be analysed after going through one of the two arches sequences:

1. Gold standard group: using arches that provide the same amount of force in all sections . 3M United® nickel-titanium arches (0.012, 0.014, 0.016 x 0.016, 0.020 x 0.020, 0.018 x 0.025 y 0.019 x 0.025)
2. Intervention group: using some arches that provide individual sectional forces for each dental group (incisors, premolars and molars). 3M United® nickel-titanium 0.012 and 0.014 arches and BioForce PLUS® arches (0.016 x 0.016, 0.020 x 0.020, 0.018 x 0.025 y 0.019 x 0.025).

All patients will be treated with multi-braces fixed appliances (0.022" technique and VictoryTM brackets).

Root resorption will be compared through CBCT (Cone Beam Computed Tomography) images made before the beginning of treatment (T0), after 8-9 months of the beginning of treatment (T1) and at the end of treatment (T2). Root resorption will be measured by the root volume and surface root morphology in each of the times scheduled.

Study Population: patients undergoing orthodontic treatment in Orthodontic Department at Dental School of Universidad Complutense de Madrid.

Inclusion Criteria:

1. Completed permanent dentition (third molars are excluded)
2. Completed root formation
3. Need of orthodontic treatment

Exclusion Criteria:

1. Tooth agenesis in the anterior region (incisors)
2. Included or ankylosed teeth in the anterior region (incisors)
3. Periodontal pocket >3 mm in any anterior teeth (incisors)
4. Need of a combined surgical and orthodontic treatment
5. Root resorptions observed at the initial CBCT (in more than 3 teeth)
6. Delay of the treatment due to a external reason or complication during treatment
7. Systemic disease or cranio-facial malformation
8. Tooth fracture or restoration in the anterior region (incisors) at the beginning of treatment
9. Problems from roots such as lacerated root, trauma or fractures during treatment 10 Severe occlusal attrition