## 2 Materials and Methods  
The vestibular surfaces of the teeth of 58 subjects (34 females and 24 males aged 22 to 68 years), afferent to the Conservative Dentistry Unit (Dental Materials Section) of the Dental Clinic of the University of Campania \"[PERSON],\" from October 2019 to March 2022, complaining of DH, were examined by an experienced clinical operator using a probe tip and an \(\times\)4 magnifying lens. The tip of the probe was held perpendicularly to the tooth surface and inserted up to the bottom of the gingival sulcus crossing the cement-enamel junction (CEJ). Any irregularity in the cervical enamel and at the CEJ of the teeth was considered a NCCL. All subjects signed an Informed Consent after verbal and written information on the study was provided. This study was conducted in accordance with the ethical standards of the committee responsible for human experimentation (institutional and national) and with the Helsinki Declaration of 1975, as revised in 2013. The research was approved by the Ethics Committee of AORN of Ospedali dei Colli with N. 1374/2019. The first operator, after identifying 151 NCCLs responsible for DH, used exclusion criteria to filter those not suitable for this study. Tooth with NNCLs with these characteristics were excluded from the study: (1) association with periodontal pockets or gingival recession; (2) presence of carious lesions or restoration; (3) evidence of cracks; (4) primary teeth, and (5) presence of subgingival NCCLs. The second clinic researcher further selected NCCLs to be enrolled in this study based on the pain intensity elicited by each NCCL after a stimulus using the Evaporative Air Test (EAT). For this type of inclusion criteria, each patient evaluated the pain intensity associated with every NCCL at baseline (t0) using a visual analog scale (VAS) and recorded the perceived pain level using a numeric scale from 0 to 10, where 0 indicated the absence of pain, and 10 indicated the maximum pain ever felt. Only 102 patients who reported a pain intensity between 4-7, were considered suitable for this study. Using these restrictions, only 121 NCCLs belonging to 48 patients (26 females and 22 males from 22 to 65 years) were enrolled in this study. Evaporative Air Test (EAT): the degree of tooth sensitivity was determined using an air stimulus defined as a 3 s cold air blast (temperature range of 19-20 \({}^{\circ}\)C) at a distance of 2-3 mm from the test site. The tooth under examination was isolated using cotton rolls and by shielding the neighboring teeth with the gloved fingers of the operator. All patients were asked to report their degree of pain for each NCCL after the EAT using the VAS scale at each point of the timeline previously described. The third examiner, who was not a clinician, divided the 48 patients into 4 study groups, each of 12 patients, using a random distribution software, and each group was assigned a different treatment protocol for DH that was administered by the fourth operator (an experienced clinician) after isolating each tooth with NCCL from the saliva using cotton rolls and after air-drying gently for 3 s [18]. Study group 1: 27 NCCLs (total VAS of 142, mean 5.29 and DS 1.09) were subjected to a protocol based on the topical application of fluoride (0.33% acidified sodium fluoride gel, MEDICAL, Treviso, Italy) for 12 s on the surface of each cervical lesion. Study group 2: 34 NCCLs (total VAS 179, mean 5.26 and DS 1.11) were subjected to a therapeutic protocol based on the topical application of fluoride for 60\" on the surface of each cervical lesion and then of irradiation by a diode laser (DL) (Creation, Soft Touch; 810 nm, 5 W) for the following 60\". The parameters of the DL were: power of 0.2 Watt in continuous emission and fiber of 400 \(\upmu\)m diameter. The tip of the fiber was kept immersed in the topical gel, avoiding touching the surface of the tooth for 60 s and performing rapid movements at the apical-coronal and mesiodistal surfaces to treat the whole surface of the dental lesion.