## 2 Materials and Methods  
This study is a single-blind, randomized controlled trial and was conducted in the Department of Oral Medicine at the Faculty of Medicine and Odontology at the University of Murcia. The study sample was composed of patients with a xerostomia diagnosis who attended the Department of Oral Medicine. The study protocol was designed in accordance with the principles of the Declaration of Helsinki and was approved by the Ethics Committee from the University of Murcia (ACATA 10/2024/CEI). The study was registered at ClinicalTrials.gov (accessed on 24 November 2024) (ClinicalTrials.gov NCT06708195). All the patients participated voluntarily, having provided their Informed Consent after receiving detailed information about the study, and without receiving any economic compensation. The inclusion criteria were patients with a diagnosis of mouth dryness symptoms for more than three months and/or pathological sialometry. Age \(\geq\) 18 years with xerostomia of any etiology. Signed informed consent and commitment to attend the three intervention sessions. The exclusion were:  
Patients with resection of major salivary glands. Decompensated systemic disease. Medical conditions such as pacemaker implants, active skin infections, vertigo, continuous headaches, hearing problems, neuralgia or pregnancy, motor problems or inability to follow instructions. Participants:  
A total of 54 patients were included in the study, of which 4 were excluded due to travel-related reasons or not wanting to participate. Ultimately, 50 patients completed the study (25 in the treatment group and 25 in the sham (control) group). The patients were randomly assigned to the groups through a system of blocks (for example, AABB, ABAB, BABA) performed by a person not involved in the study. Sample size. The sample size was calculated based on previous studies ([PERSON] et al., 2022) ([PERSON] et al., 2022) ([PERSON] et al., 2022), in which 70% of the patients with xerostomia and diabetes showed an improvement with TENS. Assuming a similar improvement, with a significance level of \(\alpha\) = 0.05 and a power of 80%, including 25 subjects per group was deemed necessary. The study used a single-blind design in which only the patients were blinded. The clinical protocol was performed by the same technician (FR), who had been previously trained. The characteristics of the patients were recorded, including age, sex, toxic habits (tobacco and alcohol), index of oral hygiene (good, average, bad), and number of medications consumed. Before the collection of saliva, the patients were instructed not to eat, drink, smoke, chew, or perform oral hygiene at least 60 min before the intervention. Intervention with the TENS device:  
The treatment was performed with the use of the commercial electro stimulator TENS EMS TN23 (Sale&Service SL, Langenhagen, Germany). The electrodes were placed on both sides of the face over the parotid glands for effective stimulation. The intervention parameters were as follows: frequency: 50 Hz; pulse duration: 250 microseconds (\(\mu\)s); duration of each session: 15 min ([PERSON] et al., 2022, 2020). Three stimulation sessions were performed, with an interval of one week between them. At the end of each session, the patients were given a follow-up sheet to record the duration of the treatment effects every week. The control (sham) group was treated with an inactive TENS device (sham treatment) for 15 min, following the same protocol as the experimental group. In both groups, sialometry, VAS-X, and Xerostomia Inventory (XI) measurements were taken, and the impact on quality of life was measured with the OHIP-14 questionnaire. However, the patients in the control group only participated in a single session (Figures 1-3). Figure 1: Representation of the Schirmer oral test (RD Test), used to measure saliva production. Measurements.