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 Table of Contents  
ORIGINAL ARTICLE
Year : 2016  |  Volume : 28  |  Issue : 3  |  Page : 246-251

Effectiveness of transcutaneous electrical nerve stimulation on saliva production in post-radiated oral cancer patients


Department of Oral Medicine and Radiology, Rishiraj College of Dental Sciences and Research Centre, Bhopal, Madhya Pradesh, India

Date of Submission10-Dec-2015
Date of Acceptance30-Nov-2016
Date of Web Publication13-Dec-2016

Correspondence Address:
Dr. Sakshi Ojha
Department of Oral Medicine and Radiology, Rishiraj College of Dental Sciences and Research Centre, Bhopal - 462 036, Madhya Pradesh
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0972-1363.195664

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   Abstract 

Aims and Objectives: To determine the effectiveness of transcutaneous electrical nerve stimulation (TENS) in stimulating salivary flow in post-radiated oral cancer patients, and to compare the salivary flow rate between unstimulated saliva and saliva stimulated with TENS in post-radiated oral cancer patients. Materials and Methods: In 30 patients who underwent radiotherapy for oral cancer, unstimulated saliva was collected every minute for 5 min in a graduated test tube. The TENS unit was activated and stimulated saliva was collected for 5 min in a separate graduated test tube, and the flow rate was compared with the unstimulated salivary flow rate. Results: A statistically significant improvement was seen in saliva production during stimulation (P < 0.001). In addition, statistically significant increase in TENS stimulated saliva was observed in patients aged ≥50 years compared to that in patients aged <50 years (P < 0.05). There was no significant difference in salivary flow rate between the two genders in both stimulated and unstimulated conditions, however, statistically significant increase in salivary flow rate was observed in males under stimulated condition (P < 0.01). Conclusion: TENS was highly effective in stimulating the whole salivary flow rate in post-radiated oral cancer patients. It is an effective supportive treatment modality in xerostomia patients caused by radiotherapy in oral cancer patients.

Keywords: Oral cancer, saliva flow rate, TENS, whole saliva


How to cite this article:
Ojha S, Bhovi TV, Jaju PP, Gupta M, Singh N, Shrivastava K. Effectiveness of transcutaneous electrical nerve stimulation on saliva production in post-radiated oral cancer patients. J Indian Acad Oral Med Radiol 2016;28:246-51

How to cite this URL:
Ojha S, Bhovi TV, Jaju PP, Gupta M, Singh N, Shrivastava K. Effectiveness of transcutaneous electrical nerve stimulation on saliva production in post-radiated oral cancer patients. J Indian Acad Oral Med Radiol [serial online] 2016 [cited 2019 Nov 23];28:246-51. Available from: http://www.jiaomr.in/text.asp?2016/28/3/246/195664


   Introduction Top


Saliva is a critical fluid necessary for oral health. There is an old axiom which states “You will never miss water till the well runs dry.” This is very true especially when it comes to saliva, the fact is, a world without saliva is a world without pleasure, like living in a drought.[1],[2] Saliva has many important physiologic functions as it maintains neutral pH and contains calcium and phosphate that are essential for maintaining enamel mineralization. As a lubricant, it aids in speech, swallowing, clearing of debris and reduces friction.[3] In edentulous individuals, it is required for the retention of complete dentures and the protection of the denture bearing tissues.[4]

The functional disturbances of the salivary glands can cause a reduction in salivary flow, resulting in dryness.[5] Saliva is composed of approximately 99% water and 1% proteins and salts.[6] Parotid glands consist entirely of serous acini, submandibular and sublingual glands contain mucous and serous acini, and minor salivary glands contain predominantly mucous acini.[7] The normal daily production of saliva is between 0.5 and 1.5 litres. The submandibular glands are the major contributors to resting (unstimulated) saliva, and the parotid glands are the major contributors to stimulated saliva. The contribution of sublingual glands to unstimulated and stimulated whole saliva is low.[6]

Xerostomia is the conventional term used to describe the subjective sensation of oral dryness resulting from severe reduction of salivary flow rate.[8] However, it does not equate consistently with hyposalivation.[9] It is a common clinical phenomenon present in approximately 40% of adults over the age of 50 years.[10] It can be caused by several medications without an actual reduction in the salivary flow. The major cause of xerostomia, however, is objectively assessed salivary gland hypofunction, which can be attributed to various systemic diseases such as Sjogren's syndrome, rheumatoid arthritis, and systemic lupus erythematosus.[6] Other causes include radiotherapy and chemotherapy of head and neck cancers, medications, psychogenic disorders, dehydration, decreased mastication, etc.[1],[11],[12]

Palliative management of xerostomia includes wetting agents such as ice chips and saliva substitutes. Other measures can include increase in water intake, applying lip balm, chewing sugar free gum, or sucking sour sugar-free lemon drops, paraffin, and citric acid containing lozenges and rinses. The addition of a humidifier to the room may be beneficial. Patients need to be counselled to avoid mouth breathing, caffeine, smoking, carbonated beverages, alcohol-based drinks and mouthwashes, and changing or discontinuing drugs causing dry mouth.[2],[3]

Systemic sialogogues such as pilocarpine, anethole trithione, bromhexine, and cevimeline are used to stimulate the salivary flow. Acupuncture has brought about improvement in xerostomic and healthy patients.[2],[10] A mucin spray and herbal agent with vitamin supplements have also been found to be useful against xerostomia.[12] Among the disadvantages of these therapies, however, are that the effects are short lived and application needs to be frequent. Adverse effects have also been reported such as profuse sweating, urinary frequency, rhinitis, and dyspepsia.[10] All the above mentioned treatment modalities have met with a limited success.

Electrostimulation is also a technique to increase the salivary output in patients with xerostomia. The procedure uses an electrostimulation device to increase saliva production from existing glandular tissue.[13] Transcutaneous electrical nerve stimulation (TENS) is a well-known physical, noninvasive and nonpharmacological method for the electrical stimulation of the nerves through electrodes applied to the skin.[14]

Electrostimulation to produce saliva has been studied in the past and showed moderate improvement; however, it never became a main stream therapy. Results of recent preliminary investigations of noninvasive electronic stimulation of reflex salivation in xerostomic patients have been encouraging.[15],[16] Research in this area is sparse, and hence this study was undertaken to evaluate the effect of TENS on whole salivary flow rate in post-radiated oral cancer patients with xerostomia.


   Materials and Methods Top


This prospective study was conducted in the Department of Oral Medicine and Radiology, Rishiraj College of Dental Science and Research Centre and Jawaharlal Nehru Cancer Hospital, Bhopal, Madhya Pradesh, after obtaining institutional ethical committee clearance and informed written consent from the participants. A total of 30 patients who underwent radiotherapy for oral cancer were enrolled for the study. Extreme care was taken to selectively exclude patients mentioned below:

  • Patients with pacemakers, defibrillator, hearing aid and cochlear implants
  • Pregnant females
  • Patients with skin lesions or abrasions on the face
  • Patients with history of any systemic diseases
  • Patients who were on medications that are known to cause xerostomia
  • Patients who underwent any head and neck surgery involving salivary glands.


All the 30 patients who underwent radiotherapy for oral cancer were explained the need and the design of the study and were asked to refrain from eating, drinking, chewing gum, and smoking. The TENS unit employed for this study was VMD TENS (Vishal Medical Devices Pvt. Ltd., Hyderabad) with four channels [Figure 1]. The surface electrode pads were placed externally on the skin overlying the parotid, submandibular, and sublingual glands with the TENS unit in the “off” position. The patients were made to sit in an upright position with the head inclined forward and with minimal body and orofacial movements [Figure 2]. 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 collected every minute for 5 min in a graduated test tube fitted with a funnel. The TENS unit was then activated with a pulse rate of 50 Hz and stimulated saliva was collected for 5 min in a separate graduated test tube [Figure 3]. The salivary flow rate was calculated by dividing the amount of collected saliva (volume in ml) by the duration of the collection period (5 min) and compared.
Figure 1: Transcutaneous electrical nerve stimulation machine (VMD) with four channels

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Figure 2: Patient positioning with electrode pads placed overlying the salivary glands

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Figure 3: Unstimulated and stimulated saliva collected in test tubes

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   Results Top


The statistical analysis was done using the Statistical Package for Social Sciences (SPSS) version 21 for windows (IBM Corporation, New York, U.S.). The values were represented in number (%) and mean ± standard deviation (SD). Wilcoxon signed ranks test (nonparametric equivalent of paired t-test) and Mann–Whitney U test (nonparametric equivalent of unpaired t-test) were applied for comparison between different groups. For age and gender-wise comparison of net change in salivary flow rate, Pearson's Chi-square test was applied.

Out of 30 patients, 23 (26.67%) were males and 7 (23.33%) were females. A total of 13 (43.33%) patients were aged <50 years and 17 (56.67%) were ≥50 years of age [Table 1]. The mean salivary flow rate in unstimulated patients was found to be 0.21 ± 0.13 ml/min, whereas in stimulated patients it was found to be 0.25 ± 0.13 ml/min. Statistically, the increase was found to be significant (P < 0.001) [Graph 1]. In addition, statistically significant increase in TENS stimulated saliva was observed in patients aged ≥ 50 years compared to those aged <50 years (P < 0.05). The mean salivary flow rate among old age group was significantly higher compared to the young age group under stimulated conditions [Graph 2]. No significant difference in salivary flow rate between the two genders in both stimulated and unstimulated conditions, however, statistically significant increase in salivary flow rate was seen in males under stimulated condition (P < 0.01) [Graph 3].
Table 1: Age and gender-wise distribution of patients

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   Discussion Top


Saliva plays an important role in oral health monitoring, regulating, and maintaining the integrity of the oral hard and soft tissues.[1] It has many important physiologic functions as it maintains neutral pH, aids in oral immunology, speech, swallowing, clearing of debris, and reduces the friction, however, medications, radiation therapy, systemic conditions and functional disturbances of salivary glands can decrease the salivary flow leading to xerostomia.[3],[5]

Xerostomia is the conventional term used to describe the subjective sensation of oral dryness resulting from severe reduction of salivary flow rate.[8] Various etiologic factors for xerostomia include iatrogenic causes (drugs, chemotherapy, radiotherapy, graft versus host disease), diseases of salivary glands, and autoimmune disorders. It is a serious and almost ubiquitous complication after radiotherapy for head and neck malignancies. At minimally 6 months after completion of treatment, 93% of all patients complain of dry mouth and 65% experience moderate to severe xerostomia.[17]

The palliative management for xerostomia of any cause includes providing relief of its symptoms with the help of wetting agents and saliva substitutes.[3] However, this provides only temporary relief. Only natural saliva contains all the enzymes and other components essential for normal function and protection. For this reason, salivary stimulation was developed to stimulate the production of whole saliva.[18]

The salivary secretion is normally controlled by reflex stimulation with effector nerve impulses traveling along the sympathetic and parasympathetic nerves to the glands.[2] 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.[12]

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.[2],[19] The use of TENS in dentistry was described in 1967 by Shane and Kessler.[20] Although the concept is not new, it has gained widespread acceptance in dentistry. Several studies have been carried out in the past with electrostimulation as a treatment modality for xerostomia and have showed moderate promise, however, they never became part of mainstream therapy. As a result, research in this area has been sparse. Several studies have been conducted to assess the efficacy of electrostimulation in improving salivary flow in xerostomia patients, however, only few studies have been conducted so far to assess extra oral transcutaneous electric nerve stimulation as a means for stimulating saliva in xerostomic patients.[19],[21] In this study, an extraoral TENS device has been used to evaluate its effectiveness as a therapeutic modality in post-radiated oral cancer patients having xerostomia.

The method of saliva collection was based on Aagard et al.,[22] except that a graduated tube was used instead of a preweighed cylinder. The adjustment of pulse rate at 50 Hz and placement of electropads on the skin overlying the salivary glands was similar to the method of Hargitai et al.[3] 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. They also provide meaningful information concerning the quantitative aspects of gland function and can be obtained easily in a dental office.[23]

A wide range of unstimulated and stimulated salivary flow was observed in our study. This variation of salivary flow rate was similar to the observations made by Yeh et al.[1] and Vilas et al.[2] The mean salivary flow rate under unstimulated conditions was found to be 0.21 ± 0.13 ml/min whereas under stimulated conditions it was found to be 0.25 ± 0.13 ml/min. Statistically, the increase was found to be significant (P < 0.001) [Graph 1]. Twenty four (80%) out of 30 patients responded positively to TENS therapy [Graph 4]. This result was in agreement with the studies conducted by Hargitai et al.,[3] in which 15 (68.18%) out of 22 healthy individuals demonstrated significant increase in the parotid salivary flow, and in Vilas et al.[2] where 85 (85%) out of 100 healthy individuals demonstrated significant increase in the whole salivary flow rate. Similarly, in a study by Domingo,[21] 6 (33.33%) out of 18 post-radiation head and neck cancer patients demonstrated significant increase in the salivary flow during the application of TENS.



The mechanism by which the TENS unit worked on the salivary glands is not clear. It is possible that it directly stimulated 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. The early investigators of electrostimulation postulated that normal physiologic salivary reflexes are augmented. Salivation is controlled by both sympathetic and parasympathetic efferent nerves. Sympathetic stimulation produces sparse, viscous saliva. 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 at lower frequencies, and it is this voluminous serous saliva of the parotid gland that would be clinically most useful in the management of xerostomia.[3]

In 4 patients (13.33%), the salivary flow decreased with the application of TENS. This finding was similar to the studies conducted by Vilas et al.,[2] in which 4 patients demonstrated a decreased salivary flow and in Hargitai et al.[3] in which 2 patients demonstrated a decreased salivary flow. TENS, by itself, is less likely to be effective in cases where there is no baseline saliva flow, such as in long-standing Sjogren's syndrome or high-dose radiation therapy where complete destruction of the salivary gland unit has occurred. Therefore, it is likely to be more effective in cases of decreased salivary gland function rather than absolute absence of function.[3]

As mentioned in different studies done by Gheezi et al.,[11] Percival et al.,[5] Tylenda et al.,[24] the 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 the aging process. However, in one study, Narhi et al.[25] reported that over a 5 year period, an elderly individual's stimulated salivary flow had significantly decreased. Contrary to this, in our study, it was found that statistically significant increase in TENS stimulated saliva in patient aged ≥50 years compared to that aged <50 years (P < 0.05). The mean salivary flow rate among old age group was significantly higher as compared to younger age group under stimulated conditions [Graph 2].

Further, the study was carried out to compare the salivary flow rates between males and females. It was found that no significant difference in salivary flow rate between two genders in both stimulated and unstimulated conditions. However, there is statistically significant increase in salivary flow rate in males under stimulated condition (P < 0.01) [Graph 3]. In one study conducted by Gheezi et al.[11] who showed that there was no significant age and gender differences in the salivary flow rates. On the other hand, studies conducted by Vilas et al.[2] and Hargitai et al.[3] showed higher salivary flow rate in males as compared to females. The reason for the lower salivary flow rate in women can be attributed to smaller salivary glands, and it may be associated with postmenopausal changes.[4]

The only side effect of the TENS therapy seen in 2 patients in our study was mild twitching of the facial musculature, which was also described by Hargitai et al.[3] and Vilas et al.[2] 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 glands more effective.

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.[2],[3] Chewing gum bases may need to be avoided in those with temporomandibular disorders; it has had favorable but mixed results in reported studies.[3],[26]


   Conclusion Top


There are very few studies published in the literature to show the potential of TENS in increasing salivary flow rate in post-radiated oral cancer patients. The 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 when other therapies have failed or are contraindicated. It can also be used as a supportive treatment modality with other sialagogues for the management of xerostomia following radiation therapy for oral cancer.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Acknowledgement

The authors acknowledge Jawaharlal Nehru Cancer Hospital, Bhopal for assisting to carry out the procedure at the radiotherapy department.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

 
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2.
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Kararmaz A, Kaya S, Karaman H, Turhanoglu S. Effect of the frequency of transcutaneous electrical nerve stimulation on analgesia during extracorporeal shock wave lithotripsy. Urol Res 2004;32:411-5.  Back to cited text no. 14
    
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Talal N, Quinn JH, Daniels TE. The clinical effects of electrostimulation on salivary fuction of Sjogren's syndrome patients. Rheumatol Int 1992;12:43-5.  Back to cited text no. 18
    
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Shane SM, Kessler S. Electricity for sedation in dentistry. J Am Dent Assoc 1967;75:1369-75.  Back to cited text no. 20
    
21.
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22.
Aagard A, Godiksen S, Teglers PT, Schiodt M, Glenert U. Comparison between new saliva stimulants in patients with dry mouth: A placebo controlled double blind crossover study. J Oral Pathol Med 1992;21:376-80.  Back to cited text no. 22
    
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24.
Tylenda CA, Ship JA, Fox PC, Baum BJ. Evaluation of submandibular salivary flow rate in different age groups. J Dent Res 1988;67:1225-8.  Back to cited text no. 24
    
25.
Narhi TO, Kurki N, Ainamo A. Saliva, salivary micro-organisms and oral health in the home dwelling old elderly– A five year logitudinal study. J Dent Res 1999;78:1640-6.  Back to cited text no. 25
    
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Jenkins GN, Edgar WM. The effect of daily gum-chewing on salivary flow rates in man. J Dent Res 1989;68:786-90.  Back to cited text no. 26
    


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