The aim of this study was to evaluate the effect of nanohydroxyapatite associated with low potency laser therapy in eliminating or reducing dentin hypersensitivity in a randomized placebo-controlled clinical trial. Volunteers 18 to 50 years old with hypersensitive teeth were randomized into 4 groups: GPLACEBO - positioning of the laser tip without light emission + placebo dentifrice; GnHAP - positioning of the laser tip without light emission + nano-hydroxyapatite; GLASER - laser tip positioning with light emission + placebo substance; GLASERnHAP - positioning by laser beam with light emission + nano-hydroxyapatite.

GLASER received the laser application using the infrared light spectrum with wavelength of 808 nm with its active AsGaAl medium in two points of the vestibular face of the hypersensitive teeth. It was applied at each point 60 J / cm², for 16 seconds. The laser was applied in 2 sessions with a time interval of 24 hours. GLASERnHAP first received laser application and then the application of nanohydroxyapatite according to the manufacturer's recommendations. Before initiating laser therapy, the equipment was calibrated with a tester (MMOptics Ltda®, São Carlos, SP, Brazil).

The GnHAP volunteers were submitted to the application of Desensibilize Nano P on the vestibular surfaces of hypersensitive teeth with the aid of a Microbrush applicator (Microbrush, 3M ESPE, São Paulo, Brazil) for 10 minutes. Then, a rubber cup (Unid Microdont, São Paulo, SP, Brazil) mounted on a low speed handpiece (Dabi Atlante, Ribeirão Preto, SO, Brazil) was used to scrub the desensitizing gel on teeth for 20 seconds in each tooth, according to the manufacturer's specifications. GPLACEBO followed the same protocol used in Gn-HAP. In addition to the desensitization treatment, all GnHAP and GPLACEBO volunteers received the positioning of the laser tip to mimic the light emission produced in GLASER and GLASERnHAP. The noise emitted by the laser device during mimicry was simulated through the sound reproduction of a smartphone application (HD Voice Recorder - iPhone 6s, Apple®, Cupertino, California, USA).

Inclusion criteria:

- The presence of at least one hypersensitive tooth;

Exclusion criteria:

• patients with systemic diseases;
• patients with pulpitis;
• patients with carious lesions;
• patients with defective restorations;
• patients with cleft enamel;
• patients with active periodontal disease;
• patients with analgesic medication;
• patients with pregnant or lactating women
• patients who have received professional desensitizing treatment in the last three months.

For this double-blind study, the evaluator and the patient were blinded. Only one evaluator assessed pain sensitivity, who did not participate in the randomization process, and also did not know in which group the patient was. The volunteers evaluated in the experiment also were not aware of the treatment to which they were submitted. Both the Nano-P desensitizer and the placebo toothpaste have the same coloration and similar visual appearance. The desensitizers were placed in equal containers so that patients were not identified as to the application of the product.