|Year : 2015 | Volume
| Issue : 1 | Page : 16-19
The effects of transcutaneous electric nerve stimulation (TENS) on salivary flow: A study
Dipti Singh1, Sudhanshu Agrawal2, Mathod C Shashikanth3, Neeta Misra4
1 Department of Oral Medicine and Radiology, Chandra Dental College and Hospital, Lucknow, Uttar Pradesh, India
2 Department of Periodontist, Chandra Dental College and Hospital, Lucknow, Uttar Pradesh, India
3 Department of Oral Medicine and Radiology, Rungta College of Dental Sciences, Bhilai, Chhattisgarh, India
4 Department of Oral Medicine and Radiology, Babu Banarsi Das College of Dental Sciences, Lucknow, Uttar Pradesh, India
|Date of Submission||15-Nov-2014|
|Date of Acceptance||15-Sep-2015|
|Date of Web Publication||12-Oct-2015|
48, MIG, Shekhupura, Awas Vikas Colony, Aliganj, Lucknow, Uttar Pradesh
Source of Support: None, Conflict of Interest: None
| Abstract|| |
Aim: This study was undertaken to evaluate the effectiveness of transcutaneous electric nerve stimulation (TENS) as a means of stimulating salivary function in healthy adult subjects. Materials and Methods: Fifty healthy adult subjects with no history of salivary gland disorder were enrolled in the protocol. The TENS electrode pads were placed externally on the skin overlying the parotid glands. Unstimulated saliva was collected for 5 min into graduated tubes. TENS unit was then activated and the stimulated saliva collected for an additional 5 min. Statistical Analysis Used: A paired "t" test was applied to look for statistically significant differences as a group between the amount of unstimulated and TENS-stimulated samples of saliva. Results: Forty-three out of 50 subjects demonstrated increased salivary flow when stimulated via the TENS unit. The mean unstimulated salivary flow rate was 0.354 ml/min (SD 0.19) and the mean stimulated salivary flow rate was 0.49 ml/min (SD 0.24). Statistical analysis of flow rates utilizing the paired t test demonstrated the difference to be statistically significant (P < 0.001). Conclusion: The TENS unit was effective in increasing the salivary flow in two-thirds of healthy adult subjects. A further study in a cohort of patients with salivary gland disorders is warranted.
Keywords: Saliva, salivary flow, transcutaneous electrical nerve stimulation
|How to cite this article:|
Singh D, Agrawal S, Shashikanth MC, Misra N. The effects of transcutaneous electric nerve stimulation (TENS) on salivary flow: A study. J Indian Acad Oral Med Radiol 2015;27:16-9
|How to cite this URL:|
Singh D, Agrawal S, Shashikanth MC, Misra N. The effects of transcutaneous electric nerve stimulation (TENS) on salivary flow: A study. J Indian Acad Oral Med Radiol [serial online] 2015 [cited 2019 Jul 20];27:16-9. Available from: http://www.jiaomr.in/text.asp?2015/27/1/16/167068
| Introduction|| |
Saliva is a critical fluid necessary for oral health. The three major pairs of salivary glands along with 300-500 minor salivary glands produce about 1.5 l of whole saliva daily.  Resting saliva is primarily secreted by the submandibular glands (approximately 65%); in contrast, stimulated high flow rates drastically change the percentage contribution from each gland, with parotid contributing more than 50% of total salivary secretions. 
In humans, saliva is a fluid in the mouth possessing several functions involved in oral health and homeostasis, with an active protective role in maintaining the oral health. Saliva helps in bolus formation by moistening food, protects the oral mucosa against mechanical damage, and plays a role in the preliminary digestion of food through α-amylase and other enzymes. It also facilitates taste perception. Saliva also has a role in maintaining teeth enamel mineralization. Saliva has defensive functions against pathogenic microorganisms; salivary defense proteins react in specific (immunoglobulins) or non-specific (lysozyme, peroxidase, cystatins, lactoferrin, hystatins, and others) ways, inhibiting the growth of microorganisms. 
Xerostomia is a real or perceived decrease in the amount of saliva. Some practitioners restrict the use of the term xerostomia to refer to a subjective complaint or oral dryness, and use the term hyposalivation to describe an objective decrease in volume. There are multiple causes of salivary hypofunction, including oral disorders, systemic diseases, prescription and non-prescription medications, chemotherapy, and head and neck radiotherapy.
The general approach in treating patients with xerostomia is directed at palliative treatment for the relief of symptoms and prevention of oral complications. It includes topical agents such as ice chips and saliva substitutes, increased water intake, application of lip balm, chewing sugar-free gums, sucking sour lemon drops, paraffin and citric acid containing lozenges and rinses. Patients need to be counselled to avoid mouth breathing, smoking, carbonated beverages, alcohol-based drinks and mouthwashes, and to change or discontinue drugs causing dry mouth. 
Transcutaneous electrical nerve stimulation (TENS) is a well-known physical therapy, which is useful for pain relief. Electrostimulation to produce saliva has been studied in the past and the results were encouraging. However, it never became a part of the mainstream therapy. Research in this area has been sparse, and hence, this study was undertaken to evaluate the effect of TENS on whole salivary flow rate in healthy adult subjects and to compare the flow rate between unstimulated saliva and saliva stimulated with TENS.
| Materials and Methods|| |
Fifty healthy adults who visited the Department of Oral Medicine and Radiology with no history of salivary gland disorder were enrolled in the protocol. Written informed consent was obtained from all participants. All the relevant data were entered in the proforma. Ethical clearance was obtained for the study from the institutional ethical committee.
Exclusion criteria included: Age under 18 years, those with pacemakers, those having autoimmune disease, pregnancy, history of salivary gland pathology, and current use of any medications which cause xerostomia. All the participants were explained the need and design of the study and asked to refrain from eating, drinking, chewing gum, and smoking for at least 1 h prior to the appointment. They were told about the importance of oral hygiene procedures like brushing and mouth rinsing, at least 1 h prior to the appointment.
The TENS unit used for this study was Duke's TENS (four channel). The electrode pads were placed externally on the skin overlying the parotid glands with the TENS unit in the "off" position. The subjects were made to sit in an upright position, with the head inclined forward and with minimal body and orofacial movements. They were asked to swallow saliva first and then instructed to stay motionless, so that the saliva would collect passively in the anterior region of the floor of the mouth. With "low forced spitting," unstimulated saliva was then collected every minute for 5 min in a graduated test tube fitted with a funnel. The TENS unit was then activated. The intensity was increased up to 1 increment at a time at 5-s intervals until the subject indicated by raising their hand that an optimal intensity level had been reached. Stimulated saliva was then collected for 5 min into a separate graduated tube and the flow rate was compared with the unstimulated salivary flow rate.
Any increase in salivary flow of each subject with electrostimulation was considered a positive finding. A paired "t" test was applied to look for statistically significant differences as a group between the amount of unstimulated and TENS-stimulated samples of saliva.
| Results|| |
Fifty subjects were included in the study, of which 23 were male and 27 were female. The mean age was 25.92 years (age range 19-53 years). Forty-three out of 50 subjects showed increase in salivary flow when stimulated via TENS. The mean unstimulated salivary flow rate was 0.354 ml/min (range 0.1-0.6 ml/min). There was 37% increase in the salivary flow, i.e. 0.494 ml/min (range 0.1-1.3 ml/min), during TENS application and the difference was highly significant (P < 0.001).
Statistical analysis of flow rates for inter-group analysis demonstrated that the difference between unstimulated and stimulated salivary flow was statistically significant [Table 1] and [Graph 1 [Additional file 1] ]. The mean difference in salivary flow rate between males and females [Table 2] and [Graph 2 [Additional file 2] ] and the difference in salivary flow rate between different age groups [Table 3] and [Graph 3 [Additional file 3] ] were statistically not significant. There were no side effects of using TENS, except mild twitching of the facial musculature. This effect was transient and ceased immediately once the TENS unit was turned off.
|Table 1: Comparison between unstimulated and stimulated salivary flow rate (ml/min)|
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|Table 2: Comparison between salivary flow rate of males and females (ml/min)|
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| Discussion|| |
Saliva is produced by the parotid, submandibular, and sublingual glands, as well as by hundreds of minor salivary glands that are distributed throughout the mouth. Daily salivary output is estimated to be approximately 1 l/day and the flow rates can fluctuate by as much as 50% with diurnal rhythms. Salivary flow is categorized as unstimulated, or resting, and stimulated, when an exogenous factor acts on the secretary mechanisms. Both the parasympathetic and sympathetic nervous systems innervate the salivary glands. Parasympathetic stimulation induces more watery secretions, whereas the sympathetic system produces a sparser and more viscous flow. Therefore, a sensation of dryness may occur, for example, during episodes of acute anxiety or stress, which cause changes in salivary composition owing to predominant sympathetic stimulation during such periods. 
Transcutaneous electrical nerve stimulation has been evaluated in stimulating salivary flow and it was found to be effective in patients with xerostomia secondary to radiation therapy for head and neck cancer. However, there are only a few studies on stimulating the salivary flow using transcutaneous electric nerve stimulator.  Therefore, the present study was conducted to evaluate the efficacy of TENS therapy in healthy adults subjects. In our study, we collected the whole saliva. Forty-three of 50 subjects showed significant increase in salivary flow. The result was in agreement with the study by Hargitai et al., in which 15 (out of 22) healthy subjects demonstrated significant increase in the parotid salivary flow.  Similar result was obtained in the study by Vilas et al. in which 85 of 100 subjects demonstrated increase in whole salivary flow.  Also, in the study done by Damingo, 6 of 18 postradiation head and neck cancer patients demonstrated significant increase in saliva flow during the application of TENS.  The stimulated salivary flow rate was higher for males than for females, but was not statistically significant. Similar observation was made by Ghezzi et al.  Thorselius et al. stated that the reason for the lower salivary flow rate in women was that they had smaller salivary glands and it may be associated with postmenopausal changes. 
The mechanism by which the TENS unit worked may be that it directly stimulates the auriculotemporal nerve that supplies secretomotor drive to the parotid gland. It is less clear if peripheral stimulation of the gland results in a reflex facilitation of central output from the salivatory nucleus of the medulla. Salivation is controlled by both sympathetic and parasympathetic efferent nerves. Sympathetic stimulation produces sparse, viscous saliva. In order to electrically stimulate sympathetic salivation, higher frequencies and longer pulse duration are required. Electrical stimulation of parasympathetic nerves of the salivary glands produces copious amounts of watery saliva at lower frequencies, and it is this voluminous, serous saliva of the parotid gland that would be clinically most useful for managing xerostomia. In this dual autonomic system, it is clear that salivation is primarily under parasympathetic control.
The main advantages offered by TENS over other nonpharmacologic measures are as follows. TENS unit is an extraoral device. Thus, the potential for salivary production while eating would be beneficial. The TENS unit used in this study was a less expensive model. TENS is a nonpharmacologic measure. A side effect of TENS therapy noted in the study included twitching of the facial musculature. This effect was minimal and transient. These effects could be minimized by adjusting the electrode placement and ceased once the TENS unit was turned off. Perhaps modifications can be made in future in TENS units, such as smaller electrodes, to minimize the side effects and make electrostimulation more effective.
| Conclusion|| |
TENS therapy was highly effective in significantly stimulating whole salivary flow in healthy adult subjects with minimal side effects, which were transient. Further research of this modality in the stimulation of salivary flow is required to determine its role in the treatment of xerostomic patients secondary to various local and systemic causes.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Table 1], [Table 2], [Table 3]