|Year : 2009 | Volume
| Issue : 1 | Page : 7-11
Evaluation of the effects of transcutaneous electrical nerve stimulation on whole saliva flow: A clinical study
Saraf Kedar Vilas, MC Shashikant, IM Ali
Department of Oral Medicine and Radiology, College of Dental Sciences, Davangere, Karnataka, India
|Date of Web Publication||14-Nov-2009|
Saraf Kedar Vilas
Department of Oral Medicine and Radiology, College of Dental Sciences, Davangere, Karnataka
Source of Support: None, Conflict of Interest: None
| Abstract|| |
Background and Objectives : Xerostomia and salivary gland hypofunction are associated with advancing age, autoimmune diseases such as Sjφgren's syndrome, head and neck radiation, smoking and recreational drug usage. Palliative management of xerostomia includes topical agents such as ice chips, saliva substitutes, increasing water intake, paraffin and citric acid containing lozenges. Systemic agents have been used, but some drugs have been found to have unfavorable side effects. Therefore, this study was undertaken to evaluate the effect of transcutaneous electrical nerve stimulation (TENS) on whole salivary flow rate in healthy adult subjects. Study Design : One hundred healthy adult subjects (50 males and 50 females), with no history of salivary gland disorder, were enrolled in this study. TENS electrode pads were placed externally on the skin overlying the parotid glands. Unstimulated whole saliva was collected for five minutes in a graduated tube, using a standardized collection technique. The TENS unit was then activated and stimulated saliva was collected for an additional five minutes. Results : Eighty five of the 100 subjects demonstrated increased whole salivary flow when stimulated via the TENS unit. Eleven experienced no change and four experienced a decrease in the salivary flow. The mean unstimulated salivary flow rate was 0.36 ml/min (SD 0.16) and there was a 21% increase in the salivary flow following TENS application. Statistical analysis of flow rates utilizing the paired 't' test showed the difference to be statistically significant (P<0.001). Interpretation and Conclusion : The TENS unit was effective in increasing whole salivary flow in 85% of the healthy adult subjects. A further study in patients with xerostomia, secondary to various local and systemic causes, is required.
Keywords: Stimulated saliva, transcutaneous electrical nerve stimulation, whole salivary flow, xerostomia
|How to cite this article:|
Vilas SK, Shashikant M C, Ali I M. Evaluation of the effects of transcutaneous electrical nerve stimulation on whole saliva flow: A clinical study. J Indian Acad Oral Med Radiol 2009;21:7-11
|How to cite this URL:|
Vilas SK, Shashikant M C, Ali I M. Evaluation of the effects of transcutaneous electrical nerve stimulation on whole saliva flow: A clinical study. J Indian Acad Oral Med Radiol [serial online] 2009 [cited 2020 Jan 17];21:7-11. Available from: http://www.jiaomr.in/text.asp?2009/21/1/7/57771
| Introduction|| |
Saliva is a complex fluid, whose important role is to maintain the wellbeing of the oral cavity.  There are three major salivary glands (parotid, submandibular and sublingual), along with 300-500 minor salivary glands, which 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 percentage contributions from each gland, with parotid contributing more than 50% of the total salivary secretions. ,
The saliva circulating in the mouth, at any given time, is termed whole saliva and comprises secretions from the major and minor salivary glands, and gingival crevicular fluid. ,
There is an old axiom which states, 'You will never miss water till the well runs dry.' How true this is, especially for saliva. The fact is, a world without saliva is a world without pleasure… like living in a drought… there is dryness of mouth, viscous sticky saliva, altered taste, a deviant sense of smell, failed speech, lackluster singing, trouble with chewing, increased disfiguring dental caries, wedge-shaped erosion, bad breath, heart burn and esophagitis, aggravated acid reflux, changed diet, burning tongue, cracked lips; dry kisses; festering and pestering yeast infections. 
Xerostomia and salivary gland hypofunction are associated with sundry local and systemic conditions, advancing age, selected medical disorders, head and neck radiation, smoking and recreational drug usage. 
Palliative management of xerostomia includes topical agents such as ice chips and saliva substitutes, increased water intake, application of lip balm, chewing sugar-free gum, sucking sour lemon drops, paraffin and citric acid containing lozenges and rinses. Patients need to be counseled to avoid mouth breathing, smoking, carbonated beverages, alcohol based drinks and mouthwashes, and changing or discontinuing drug(s) causing dry mouth. 
Systemic agents like pilocarpine and cevimeline stimulate salivary flow, but often have unfavorable side effects such as profuse sweating, rhinitis, dyspepsia etc. Acupuncture has brought about improvement in xerostomic and healthy patients. ,
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 studies showed moderate promise. However, it never became a part of the mainstream therapy. Results of recent preliminary investigations of noninvasive electronic stimulation of reflex salivation in xerostomic patients have been encouraging. ,
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 the unstimulated saliva and saliva stimulated with TENS.
If this modality is found effective, it could be used as one of the treatment modalities for patients with xerostomia.
| Materials and Methods|| |
Patients attending the Department of Oral Medicine and Radiology, College of Dental Sciences, Davangere, Karnataka, who were apparently healthy, with no history of systemic disease or medication and no history of salivary gland disorder, were included in this study. The subjects were explained the procedure involved in the study and their consent was obtained. They comprised 100 subjects, 50 males and 50 females, between ages 18 and 75. The subjects served as their own control.
Exclusion criteria included patients wearing active pacemaker, defibrillator, hearing aid, and cochlear implants, patients suffering from any systemic disease/s, patients with history of autoimmune diseases, patients with history of head and neck radiation, patients with history of psychiatric disorders, pregnant females, and patients with a history of salivary gland pathology. All the participants were explained the need and design of the study and asked to refrain from eating, drinking, chewing gum, smoking. They were told about the importance of oral hygiene procedures like brushing and mouth rinsing, at least one hour prior to the appointment.
The TENS unit used for this study was KODYS TENS-III. The surface 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 five minutes, in a graduated test tube fitted with a funnel. The TENS unit was then activated. The pulse rate was fixed at 50 Hz and the amplitude was gradually increased to a maximum tolerable level of patient. At optimal intensity (the maximum intensity that the subject perceived to be comfortable), stimulated saliva was collected for five minutes in a separate graduated test tube and the flow rate was compared with the unstimulated salivary flow rate. A log of adverse effects was kept during and after experiment. The salivary flow rate was calculated by dividing the amount of collected saliva (volume in ml) by the duration of collection period (five minutes).
One way anova was used for multiple group comparisons and student's t-test (unpaired and paired) was used for comparisons group-wise. Correlation Analysis was performed to assess the relationship between measurements. For all the tests, P value of 0.05 or less was considered statistically significant.
| Results|| |
Eighty five of the 100 subjects showed increase in salivary flow rate. The mean unstimulated salivary flow rate was 0.36 ± 0.16 ml/min (range 0.08 ml/min-0.96 mL/min). There was a 21% increase in the salivary flow i.e. 0.42 ± 0.19 ml/min (range 0.12 ml/min-1.22 ml/min) during the TENS application and the difference was highly significant (P < 0.001 HS). Eleven subjects showed no increase in the salivation, while four of the total subjects experienced a mean decrease of 14% (i.e. 0.04 ml/min) in whole salivary flow during the stimulated session. The difference between the unstimulated and the stimulated salivary flow rate in the different age groups was statistically nonsignificant.
Statistical analysis of flow rates for inter-group analysis demonstrated that the difference between unstimulated, stimulated [Table 1] and mean difference in salivary flow rate between males and females [Table 2] was statistically significant (P < 0.01, P < 0.01 and P < 0.05 respectively) [Graphs 1 and 2]. Males had higher salivary flow rates than females.
The relation between the unstimulated salivary flow and stimulated salivary flow rate was assessed. A highly significant correlation co-efficient (r) was found between unstimulated and stimulated saliva (P < 0.001).
Mild twitching of the facial musculature was experienced by 37 patients. However, it was transient and it ceased once the TENS was turned off. No long term side effects were noted.
| Discussion|| |
It has been known that the nerves to the salivary glands control the secretion of saliva. Salivary secretion is normally controlled by reflex stimulation with effector nerve impulses traveling along the sympathetic as well as parasympathetic nerves to the glands. , Parasympathetic stimulation produces copious saliva of low protein concentration, whereas sympathetic stimulation produces little saliva but with high protein concentration, which may give a sensation of dryness. 
Neural electrostimulation of salivary gland function, through application of electric current through the oral mucosa, on afferent nerve pathway receptors, has been reported to increase the production of saliva and to reduce the symptoms of xerostomia. , Transcutaneous electrical nerve stimulation (TENS) has been evaluated in stimulating salivary flow and it was found to be effective even in patients with xerostomia secondary to radiation therapy for head and neck cancer. However, these studies are very few. ,, Therefore, the present study was conducted to evaluate the efficacy of TENS therapy in healthy, adult subjects.
In our study, we collected whole saliva instead of parotid saliva. Whole saliva measurements are simple to perform and are useful as an indicator of general salivary performance. Also, they provide meaningful information concerning the quantitative aspects of gland function and can be obtained easily in a dental office. 
A wide range of the unstimulated and stimulated salivary flow was observed in our study. This variation of salivary flow rate was similar to the observation made by Becks and Wainwright, , Anderson et al., Heintze et al.,, and Yeh et al.
In our study, there was a 21% increase in the salivary flow, which was statistically significant. The maximum increase with the TENS application was 50%. Eighty five out of the 100 responded positively to TENS therapy. This 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 and the maximum increase was 8.75 fold greater than the baseline. Also, in a study by Damingo,  six of the 18 postradiation head and neck cancer patients demonstrated significant increase in the saliva flow during the application of TENS.
In 11 subjects, there was no increase in whole saliva flow. In a previous study, Hargitai et al. had observed that TENS was unable to stimulate the parotid saliva and it was interpreted that TENS may act more efficiently as an accelerator of salivary flow rather than an initiator. Therefore, it is likely to be more effective in cases of decreased salivary gland function rather than absolute absence of function. In our study, the subjects that failed to show response to TENS had normal unstimulated baseline saliva flow, and it could be due to the patients' physical and mental condition at the time of the collection of saliva [Figure 1].
In four patients, the salivary flow was decreased with the application of TENS. This finding was also similar to a study conducted by Hargitai et al. The cause for this may involve the frequency and intensity settings. The stimulus perceived by the brain may be painful and the salivary reflex is enhanced when nociceptive input reaches the brain via trigeminal sensory nuclei. Not all preganglionic parasympathetic fibers are necessarily facilitated; some may be inhibited.  In our study, the stimulus was kept optimum, at a tolerable level.
As mentioned in different studies done by Ghezzi et al., Ikbe et al., Percival et al., and Tylenda et al. functional changes in the salivary glands have been reported to be associated with aging; however, there is no evidence to show that xerostomia is likely to result from aging process. However, in one study, Narhi et al. reported that over a 5-year period, an elderly individual's stimulated salivary flow had significantly decreased. In the present study, it was found that in all the age groups there was a statistically significant increase in TENS stimulated saliva, as compared to unstimulated saliva, except in the 66-75 age group, where the difference was not significant. The reason behind this could be the less number of subjects present in the group. The unstimulated and stimulated salivary flow rates in different age groups was not statistically significant.
In our study, the stimulated salivary flow rate was higher for males than for females. The gender difference in salivary flow rate was similar to that observed in previous studies. ,, Thorselius et al. stated that the reason for the lower salivary rate in women was that they had smaller salivary glands and it may be associated with postmenopausal changes. In one study, Ghezzi et al. had shown that there was no significant age and gender differences in the salivary flow rates.
The only side effect of the TENS therapy seen in our study was mild twitching of the facial musculature, which was also described by Hargitai et al. It was minimal and transient and ceased immediately after the TENS unit was switched off. The modifications suggested to avoid the side effects include manufacturing small electrodes to make the electrostimulation of the parotids more effective.
The mechanism by which the TENS unit worked on the parotid gland may be that it directly stimulates the auriculotemporal nerve that supplies secretomotor drive to the parotid gland. In order to electrically stimulate sympathetic salivation, higher frequencies and longer pulse duration is required. On the other hand, electric stimulation of parasympathetic nerves of the salivary glands produces copious amounts of watery saliva of the parotid gland at lower frequencies, and it is this voluminous serous saliva that would be clinically most useful in the management of xerostomia. 
The main advantage offered by TENS over other nonpharmacologic measures, such as chewing gum or citric lozenges is that it is an extraoral device, with minimal side effects. It can be used while eating food and it does not affect the normal mastication process. Thus, the salivary production while eating would be beneficial, which is not the case with the intraoral devices.  Chewing gum bases may need to be avoided in those with temporomandibular disorders; it has had favorable but mixed results in studies.  Artificial saliva preparations can be used, but they have some limitations. A majority of the commercial products available are based on carboxymethylcellulose (CMC). However, these products do not stimulate non-newtonian properties of saliva and they do not contain specific antibacterial components (including antibodies) and enzyme and other components of saliva. There are very few studies comparing currently available mouthwetting agents. 
There are very few studies published to show TENS having a potential for increasing the salivary flow and all the studies have also shown that TENS therapy is effective in parotid saliva stimulation. In our study, the effect of TENS on whole salivary flow rate was evaluated and it was found to be effective in stimulating whole saliva in normal, healthy subjects.
| Conclusion|| |
TENS therapy was highly effective in stimulating whole salivary flow. It is an effective extraoral device with minimal side effects, which are transient. The present study substantiated that TENS can be an effective therapy in increasing whole salivary flow rate in most healthy, adult subjects. 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. The encouraging results of the present study indicate that TENS has the potential to increase salivary flow and can be a viable alternative in the management of xerostomia.
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[Table 1], [Table 2]