The concentration of 16% carbamide peroxide is the highest concentration that European regulations allow for use in home whitening (Council directive 2011/84/EU). This concentration allows for faster results, but instead patients may suffer more frequently from dental sensitivity. The most commonly described side effect of all whitening procedures is the appearance of dentin hypersensitivity, hence the efforts to counteract or overcome this adverse effect.

The objective of the study is to clinically evaluate the difference in dental hypersensitivity produced by home dental whitening treatment using 16% carbamide peroxide in a tray for two hours daily applied daily or every other day for three weeks.

Volunteers will be instructed to use the whitening gel once a day for 2 hours, completing a total of 3 weeks of whitening procedure. Depending on the randomization, the bleaching procedure will be performed every other day or daily. In the upper arch, the teeth to be whitened will be from 15 to 25. The evaluations of efficacy, dental sensitivity and satisfaction will be carried out in the upper and lower arch. The color will be recorded before, weekly for 1 month, 6 months and 12 months after finishing the treatment. Shade assessment using the subjective method will be recorded with the Vita Classical color scale (Vita Zahnfabrik, Bad Säckingen, Germany), it will also be determined with the Vita 3D-MASTER scale (Vita Zahnfabrik, Bad Säckingen, Germany). For objective evaluation, the Vita Easyshade spectrophotometer (Vita Zahnfabrik, Bad Säckingen, Germany) will be used, according to the CIEL*a*b* system.

Inclusion Criteria:

• Patients older than 18 years.
• Patients with vital teeth without restorations, single crowns, implants and/or bridges at the level of the anterior teeth.
• Absence of cavities in the teeth to be whitened.
• Patients with satisfactory oral hygiene and periodontally healthy, who are not undergoing periodontal maintenance and who do not use chlorhexidine mouthwashes. Patients with recessions without presenting sensitivity will be included.
• Absence of sensitivity, measured with the application of air with the dental team's syringe.
• Patients whose canines have at least an A2-A3 shade (VITA Classic® Guide).

Exclusion Criteria:

• Patients who have previously undergone whitening (less than 5 years).
• Patients undergoing orthodontic treatment.
• Patients with white spots or alterations in the development of enamel or with stains.
• Patients with a history of trauma to anterior teeth.
• Patients who require internal whitening.
• Smokers.
• Pregnant or lactating.
• Patients with allergies to any whitening component.
• Patients presenting alterations of the oral mucosa (desquamative gingivitis, oral lichen planus, leukoplakia, etc.).
• Patients with medical conditions considered by the researchers that may compromise the study or the individual safety of the patient.
• Patients with poor oral hygiene.
• Patients with previous hypersensitivity.

The results obtained will only be shared once they have been published in an impact journal.

The present study presents blinding of both the evaluator and the person who will carry out the statistical analysis, and therefore double-blind. The evaluators are considered blind in this study because they do not know the randomization of the patients, being a blind study. The operator and patients know the groups in which they are assigned, due to the delivery and placement of the splints.

A block randomization of the treatment applied to the patients will be carried out, to ensure that the sample size is similar in both groups. The operator will open an envelope for the group's allocation. The assignment of the groups will be carried out using opaque, sealed and sequentially numbered envelopes. The operator will open the envelope when the splints are delivered, and will give the pertinent explanations to the patient. Data will be collected from each patient that may influence treatment results such as age, sex, initial color, systemic pathologies and pharmacological treatments.