## 2 Materials and Methods
### DH Assessment  
DH assessment was performed through analysis of the response to different stimuli: evaporative (air) stimulus, tactile stimulus, thermic (cold) stimulus, osmotic stimulus, and acid stimulus. Sensitivity stimuli were applied on all molar teeth for each patient, and the overall score assigned to each patient corresponded to the dental elements with greater DH. A \"resting time\" of five minutes was introduced between stimuli in order to avoid any interference. The evaporative stimulus was evaluated through the Air Blast Test, consisting in the application of an air jet perpendicularly to the main axis of the tooth for 1 s, at a 10 mm distance from the cementoenamel junction on the vestibular region using the air/water syringe of the dental unit (at a pressure of 3-4 atm), while the adjacent teeth were isolated using the operator's fingers [35]. The same level of atmospheric pressure, calibrated at 4 bar, was used for all patients. The evaporative stimulus response was evaluated using the SCASS scale (Schiff Cold Air Sensitivity Scale) [36] and a 4-value index:  
* 0: the patient shows no response to stimulus. * 1: the patient responds to the stimulus but does not require the stimulus interruption. * 2: the patient responds to the stimulus and require the stimulus interruption or moves away from it. * 3: the patient responds to the stimulus, reports pain, require the stimulus interruption or moves away from it and still reports the continuation of pain even after the stimulus was interrupted. Regarding tactile, thermal, osmotic, and acid stimulus response evaluation, the VAS scale was used, ranging from 0 (no pain) to 10 (maximum intensity) according to patient reported pain quantification [37; 38]. The response to tactile stimulus was assessed using a blunt tip probe scratching a light pressure (10 g) along the cementoenamel junction for three seconds [39], while thermal, osmotic, and acid sensitivity evaluations were performed through a needle-free syringe with cold water, saturated saline (390 g dissolved in 1 L of water, 28%), and citric acid (pH value: 3), respectively. Finally, an omni-comprehensive sensitivity score ranging from 0 to 40 was calculated using the sum of each different DH stimuli response values (tactile, thermic, osmotic, and acid) obtained with the VAS scale for each stimulus applied. Additionally, at the baseline appointment (T0) after DH evaluation tests, a professional oral hygiene session was performed, followed by appropriate home oral hygiene instructions. The patients were also advised to use a toothbrush with soft bristles following the roller brushing technique, considered the most suitable since it is atraumatic and easily reproducible. At the end of T0, all patients were recommended to start desensitizing-devices application for home use at least twice a day during brushing and to apply the desensitizing products on sensitive molar teeth for at least two minutes. It was specified to apply wet desensitizer toothpaste on each tooth. In this observational study the desensitizing product choice between product A and B was made independently by each patient to help increasing patients' compliance. A second evaluation of DH by stimuli analysis was carried out at T1 (after 14 days), with the same modalities. The last evaluation (T2) was carried out two weeks after T1. Molar teeth that showed dental hypersensitivity at T0 were taken into account for comparison in the second and third evaluations. Periodontal analysis and sensitivity tests were performed by the same operator in each evaluation phase to minimize inter-operator errors. Furthermore, patients were instructed to perform the same oral hygiene habits which included: the use of dental floss 1 time/day, tooth brushing 3 times/day after the meals: in the morning, afternoon, and evening. Finally, a similar type of diet (3 meals/day with a small consumption of acidic foods 1 time/day) was suggested to the patients.