Due to the high prevalence of malocclusions in Mexico and the existing concern to improve aesthetics, function (chewing), or both, patients resort to orthodontic treatment. The patient may experience pain during treatment due to the release of different chemical mediators such as RANK-L. Analgesic and anti-inflammatory medications such as acetaminophen and ketorolac are used to control pain during orthodontic tooth movement. These drugs can inhibit the expression of RANK-L which can affect tooth movement, inhibiting bone remodeling. The orthodontist should indicate the drug that is safest for the patient without affecting treatment or tooth movement.

Objective: To evaluate the association of RANK-L levels with the administration of paracetamol and ketorolac in patients starting orthodontic treatment.

Material and methods: A double-blind clinical trial will be carried out with a placebo control group and random drug allocation. Patients who begin orthodontic treatment in the Orthodontic Specialty of the Comprehensive Dental Clinics of the University Center for Health Sciences and who decide to participate in the study with the signing of informed consent will be included. Three groups will be formed with 8 patients in each one.

The first group will be administered with Placebo (calcined magnesia), the second group with Ketorolac and the third group with Paracetamol, for all groups the medication will be one capsule every 6 hours for 5 days all study subjects will be sampled Gingival Crevicular Fluid (LGC), Visual Analogue Pain Scale (APS) and Intermolar Space (IS).

Measurements will be made four times; baseline, 24 h, 48 h, and on day 5 of initiation of treatment.

Inclusion Criteria:

• Patients of both sexes between 18 and 27 years of age
• Periodontally and systematically healthy
• Attended the Orthodontic Clinic of the University of Guadalajara
• Who required the use of dental spacers in at least one quadrant were included

Exclusion Criteria:

• Patients who have previously had orthodontic treatment or are under orthodontic treatment
• Who have an allergy to ketorolac or paracetamol
• Who are under pharmacological treatment and/or using contraceptives
• Pregnant or lactating women, as well as those who consume alcohol were not included or tobacco.

Blinded, the orthodontist performing the clinical intervention and the investigator