Xerostomia: A Drought in Disguise

INTRODUCTION

Xerostomia or dry mouth is the most underappreciated, under diagnosed and undermanaged oral health condition¹ . It is often thought that it is just a dry mouth, no big deal. Recognition and management of a xerostomia condition is important because it can significantly affect the overall quality of life and contribute to diminishing oral health in many ways. Xerostomia is defined as subjective complaint of dry mouth 2,3 that may result from a decrease in the production of saliva . The xerostomia is estimated to affect millions of people in the world. Complaints of dry mouth are generally more prevalent in women² . 

Saliva plays a critical role in the preservation of oropharyngeal health. The presence of saliva is taken for granted and it is often assumed that its presence is not required for any life sustaining functions. But, its diminution or absence can cause significant morbidity and a reduction in a patient's perceptions of quality of life^3,4 .The primary constituents of saliva are water, proteins and electrolytes⁵ .These components facilitates speech ,swallowing and transmit taste impulses. Saliva plays as first digestive enzyme, cleanses oral cavity and protection of mucous membranes in upper digestive tract³ . Additionally saliva provides antimicrobial and buffering activities that protect teeth from dental caries⁵ . Saliva aids in remineralization of teeth through its calcium ion content. Some investigators believe that saliva may mitigate the deleterious effects of some carcinogens, viruses including HIV and herpes simplex, toxins and irritants¹ . Saliva also serves as a critical luting agent in the retention of removable prosthesis.

PATHOPHYSIOLOGY

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 one liter per day⁶ .Flow rates can fluctuate by as much as 50 percent with diurnal rhythms^7-10 . Salivary flow is categorized as unstimulated or resting and stimulated as occurs when an exogenous fac tor is ac ting on the secretary mechanisms⁸. Normal values for salivary flow rate are difficult to establish because circadian rhythm and other factors that vary flow rate. 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 flow¹¹ . Therefore sensation of dryness may occur during episodes of stress or acute anxiety due to predominant sympathetic stimulation during such periods¹² .When salivary output from major or minor salivary gland decreases, the layer of saliva that covers the oral mucosa is reduced. This dehydration of the oral mucosa leads to symptoms of oral drynes^{13, 14, 15}.

AETIOLOGY:

Xerostomia is not a disease but a symptom which acts like a disease¹⁶ . Table 1 lists the temporary and permanent causes of xerostomia¹⁷ .Drugs and Medications constitute the most common cause of xerostomia. It is estimated that more than 500 prescription medications have xerostomia as a significant side effect. The risk of xerostomia increases with the number of drugs being taken^18-20 .Geriatric population is therefore more likely to be affected and this leads to avoidance of certain foods which cause difficulty in chewing and swallowing by older people²¹ .A case of a patient's inability to dissolve a sublingual nitroglycerine tablet due to xerostomia has been reported in literature²² . Although often associated with aging, evidence to support aging as cause of xerostomia is lacking. It is possible that increased use of prescription drugs are co-related with aging. For some patient's asking the physician to switch to a similar medication may give some relief. Dentist should never tell a patient to stop a prescription drug given by physician unless it is a life threatening situation. The main drugs associated with dry mouth are shown in Table 2^23-25 . Other common substances are also implicated in the process such as caffeine, alcohol, and nicotine¹ . Herbal and vitamin supplements and over the counter medications must also be considered. Radiation therapy for treatment of tumors in upper aerodigestive tract can lead to atrophy of secretory components and result in varying degrees of temporary or permanent xerostomia^{6, 26} .

CLINICAL MANIFESTATIONS

While the aetiology of xerostomia may truly be a systemic problem, the patient is likely to seek care from a dentist for a sticky, granular and dry feeling in mouth. All degrees of xerostomia exist. In some cases, the patient complains of a dry or burning sensation but the mucosa appears normal .In other cases there is a complete lack of saliva. When the deficiency of saliva is pronounced, there may be severe alterations in the mucous membrane and the patient may have extreme discomfort. The mucosa appears dry and atrophic, sometimes inflamed or more often pale and translucent¹⁷ . The patient may describe difficulty in swallowing especially dry foods such as biscuits (the cracker sign)²³ .Difficulty in speaking as the tongue tends to stick to the palate-leading of clicking speech ²³.Patient may also complain of unpleasant taste or loss of sense of taste or halitosis. Problems with denture retention and denture sores can occur if patient is denture wearer. Oral examination reveals dry, pale or red and atrophic tissue. Some areas may be shiny or ulcerated. There is an increase in amount of material alba and food debris.

COMPLICATIONS

Dental caries which tend to involve smooth surface and areas otherwise not very prone to caries such as lower incisor region and roots. Xerostomia leads to Gingivitis and Periodontitis. Lack of saliva increases susceptibility to infection of the oral cavity and oropharyngeal opportunistic fungus Candida albicans or thrush²⁷ .Candiadial infection will appear as erythema of oral mucosa; white, curd-like patches that adhere to mucosal surfaces; and inflamed fissures at the corners of the mouth known as Angular Cheilitis²⁸ .Other complications of xerostomia include halitosis ,cracking and fissuring of oral mucosa and lips, ulceration of oral mucosa, glossitis and glossodynia ,ascending (suppurative) sialadenitis. The latter presents with pain and swelling of a major salivary gland and sometimes purulent discharge from the duct and parotid gland enlargement.

DIAGNOSIS

Clinicians tend to drastically underestimate the prevalence of . dry mouth; assessment is infrequent and suboptimal. There is no widely-accepted standard for assessment. Rating scales, patient questionnaires, and measurement of saliva production and viscosity have been used, but there is poor correlation among these tools. Frequent oral examination and quarterly evaluation by a dentist are recommended. Nutritional and psychological assessment and medication review should accompany assessment of oral health .Not all people with reduced saliva production experience the sensation of a dry mouth, so careful assessment for patients at risk (including most elders) is essential. The diagnosis of xerostomia is based on the following:

• Detailed history and Examination
• Tongue blade test : Tongue blade is held 5 sec against buccal mucosa, if sticks to mucosa patient is having xerostomia.
• Lip -stick sign :Lip stick adhering to upper anterior teeth in lady patients
• Salivary flow measurements¹² : Salivary flow measurement can be done by sialometry. Collecting whole saliva is easier and more cost –effective than collecting saliva from an individual g land (parotids, submandibular/sublingual)in a private practice setup. The whole saliva can be collected under unstimulated (resting) and stimulated conditions. Patients are instructed not to drink, eat, smoke, perform oral hygiene or put anything into their mouths for 90 minutes before collection time.
• Unstimulated Saliva Collection: The patient should be seated in upright position, head tilted forward and eyes open with minimal body and orofacial movements. The patient is asked to swallow saliva first, then stay motionless and allow the saliva to drain passively for 5 minutes over the lower lip into a pre-weighed test tube fitted with a funnel. After the five minute collection period, ask the patient to void the mouth of saliva by spitting into the funnel.
• Stimulated Saliva Collection: The clinician then collects stimulated saliva by asking the patient to chew on a piece of gum at approximately 45 chews per minute. The patient will void the mouth of saliva by spitting into the collection tube every minute for a total of five minutes after one minute of pre-stimulation. 
• The clinician then calculates the salivary flow rate by dividing the amount (weight or volume) of collected saliva by the duration of the collection period (five minutes).There is no general agreement about what constitutes a normal salivary flow rate; however, researchers generally consider an Unstimulated salivary flow rate less than 0.1 to 0.2 ml/min(or grams per minute) and Stimulated salivary flow rate less than 0.7ml/min(or g/minute) are suggestive of xerostomia¹² .Currently , clinicians use a 0.1ml/minute unstimulated whole-saliva flow rate as a 12 criterion for diagnosis of Sjogren's syndrome¹² .
• Using a test dose of a sialogogues i.e. Pilocarpine 5 mg for 30 min or Cevimeline 30 mg for 90 min. may identify responders to medicinal therapy. Non responders are more likely to have irreversible salivary gland damage and should be referred to oral surgeon for diagnostic labial minor salivary gland biopsy.
• For diagnosis of underlying disorders serological tests, salivary gland imaging, salivary gland biopsy are used. Imaging modalities including sialography and scintigraphy, also have been used to examine salivary gland function²⁹ . It is important to remember in some patients complaining of dry mouth no evidence of a reduced salivary flow or a salivary disorder can be found. There may then be a psychogenic reason for the complain²³ .

MANAGEMENT

The management of xerostomia is based on the following - Relieving symptoms, preventing complications and increasing the flow of saliva if possible. The Clinician should instruct patient to practice following home care measures to relieve xerostomia and avoid certain things so as to prevent xerostomia from becoming worse. Table 3 lists the instructions to be given by the clinician to the xerostomic patient .Treatment approaches to induce salivation include various mechanical, chemical, electrical and pharmacologic stimulants listed in the following Table 4³⁰ . For systemic medications like Pilocarpine and Cevimeline to work, there must be some residual functioning salivary gland. The sialogogues stimulate saliva production, but it may take up to three months for patients to experience 1 maximum benefit .Caution must be taken in prescribing these drugs in patients with known cardiovascular disease, c ontro l l ed a sthma , ang ina pe c t o ris, chroni c bronchitis,chronic obstructive pulmonary disease, history of m y o c a r d i a l i n f a r c t i o n , n e p h r o l i t h i a s i s o r cholelithiasis.Caution should be advised when driving at night or performing hazardous activities in reduced lighting. Both Pilocarpine and Cevimeline have similar contraindications that include gall bladder disease, narrow-angle glaucoma, acute irits, uncontrolled asthmas, known sensitivity to the drug and renal colic. It is generally advisable to consult with patient's physician before prescribing these medications¹ .

PREVENTION

Secondary prevention of complications is critical. Quarterly dental exams and early intervention for dental problems is strongly recommended .Radiation oncologists continue to develop techniques to spare the salivary glands, and thus reduce the severity of both acute and chronic radiation induced xerostomia. In addition, clinical trials have demonstrated that Amifostine is effective at partially protecting healthy tissues, including the salivary glands, from the effects of radiation³¹ . . Unfortunately, patient adherence to recommended follow-up and self-care practices is generally poor.

CONCLUSION

Xerostomia is common clinical problem. If not diagnosed and managed in time can have significant impact on patient's quality of life. Awareness by dentists to this invisible oral condition may create significant enhancement to quality of life for many.