The Importance of Saliva

Saliva is a complex fluid containing proteins, including histine and secretory IgA, electrolytes and minerals, and organic molecules, and forms a protective pellicle on the teeth and soft tissues.¹ An adequate saliva volume is a critical component of oral health. The medical/dental importance of saliva includes lubricating and moistening food for swallowing; solubilizing material for taste; initiating digestion; preventing dental caries; maintaining the pH of the upper gastrointestinal tract; maintaining the health of the oral mucosa and dentition; preventing opportunistic infection such as candidiasis by keeping the oral microflora balance; speaking; cleaning the mouth; and clearing the esophagus.²

Saliva is so important to oral and general health that ideally a clinical assessment should be done at each appointment. If a pool of saliva is observed in the floor of the mouth, the patient very likely has a normal salivary flow rate. Exceptions include the patient with oral ulcers or infections that can constantly stimulate salivary flow. Patients with oral ulcers or infections should have the salivary flow rate measured after the oral lesions have healed. Patients with advanced destruction of salivary gland tissue, such as Sjogren’s syndrome or other immune mediated diseases, may not be able to produce saliva even when stimulated.

Salivary Hypofunction

Medications are a well-known cause of salivary gland hypofunction (SGH). Medication induced dry mouth is often in the range of a 20%-40% reduction in flow rate.³ More than 700 medications are known to cause dry mouth, including 63% of those on the top 200 list of most frequently prescribed medications in the United States.⁴ Other causes include a variety of conditions that contribute to local oral drying and systemic conditions. These include: mouth breathing, smoking, candidiasis, menopause, aging, dehydration, diabetes mellitus, radiation therapy, and SOX (sialadenitis, osteoarthritis, and xerostomia). Other medical conditions include: thyroid disease; AIDS; stress/depression/anxiety; autoimmune including Sjogren’s syndrome; Parkinson’s disease; rheumatoid arthritis; systemic lupus; erythematosus; systemic sclerosis; calcinosis cutis, Raynaud’s phenomenon, esophageal dysmotility, scleroderma, and telangiectasias (CREST); primary biliary cirrhosis; polymyositis/dermatomyositis; lymphoma; autonomic neuropathy and primary fibromyalgia; HIV-related diffuse infiltrative lymphocytosis syndrome; type V hyperlipidemia; eosinophilic myalgia syndrome; silicone breast disease; multiple sclerosis; myasthenia gravis; antiphospholipid antibody syndrome; and botulism or the use of Botox.^5,6 In approximately 30% of patients the etiology of SGH is unknown.^7,8

An important first step in the diagnosis of xerostomia or SGH is the accurate measurement of a baseline salivary flow rate. Measuring salivary flow is analogous to monitoring blood pressure and optimally should be done at each appointment. Identifying SGH early with treatment will prevent many of the adverse consequences. Patients with SGH and meticulous oral hygiene may have a normal appearance of the oral cavity, although they are lacking a pool of saliva in the floor of mouth. Additional clinical signs of SGH include lipstick adhering to the maxillary incisors; the clinician’s gloved finger sticks to mucosa during oral examination; altered texture of saliva, often white, frothy, stringy or sticky; frequent recurrences of oral candidiasis; atrophic glossitis or hairy tongue; dental caries at the gingival margin especially mandibular incisors; increased rate of carious lesion development; dental erosion or abrasion; excessive amounts of dental plaque in spite of daily brushing; chronic oral pain or burning sensation; patient awareness of normal intraoral structures; frequent cheek biting; sensation of swollen cheeks or salivary gland swelling; a sensation of a film, grit, or sand on teeth or in mouth; a sense of a bad taste or bad breath; frequent thirst; difficulty with speech; and the complaint of thick saliva. Measurement of the salivary flow rate is an important diagnostic step in any patient with complaints of oral burning, altered taste, or sensation. Patients with SGH often have non-oral symptoms due to hypofuncton of other exocrine glands such as frequent dry cough; difficulty swallowing; blurred vision or the sensation of burning, itching, gritty eyes that require eye drops; vaginal dryness, itching, burning, or frequent infections; dry skin; constipation; and nasal dryness.

Salivary flow exhibits a circadian rhythm, with the lowest flow during sleep. The lowest level of normal salivary flow rate during sleep in the majority of cases, will be within the range of normal salivary flow in patients with normal salivary gland function. Saliva is produced by the major and minor (accessory) salivary glands, although the majority of unstimulated saliva—65%—is produced by the submandibular glands.⁹ The parotid glands produce 20% of unstimulated salivary flow and 50% of stimulated saliva.⁹ The submandibular glands produce 7%-8% and the accessory salivary glands produce 7%-8% of unstimulated saliva.⁹

Patient Preparation

Measuring salivary flow can be done quickly and inexpensively in the dental office as a part of routine dental hygiene care.¹⁰ There are two basic methods to measuring salivary flow rate—the volumetric draining technique or calibrated paper

Patient preparation for either technique is identical and begins before the scheduled appointment. Ideally a patient should be fasting for 1 hour prior to measuring baseline unstimulated salivary flow and avoid eating, drinking, chewing gum, brushing teeth, and flossing. The appointment confirmation courtesy call should review these instructions.

If the patient has had something to eat, drink, or chew in the hour prior to salivary flow measurement, an unstimulated salivary flow measurement cannot be determined. If the measurement is done, this will be a stimulated salivary flow measurement. The unstimulated salivary flow rate is most important because it represents the base line amount of salivary flow. A stimulated salivary flow rate indicates the presence of functional salivary gland tissue.

Volumetric Measurement

To measure an unstimulated salivary flow rate, the patient can sit on the edge of the dental chair with his or her feet on the floor in the coachman’s position. The dental chair height should be adjusted so that the patient’s thighs are parallel to the floor. The patient sits leaning forward resting his or her body weight, elbows, and arms on the tops of the thighs and knees while bending the neck. In one hand, he or she holds a funnel resting in a calibrated tube gently on the face. The lips are opened and any saliva that is produced in 5 minutes is allowed to passively flow into the funnel and tube. The saliva is collected for 5 minutes. The use of a timer is recommended. At the end of 5 minutes, the saliva specimen is examined. Clinical observations about saliva color and consistency can be recorded in the patient record. Normal saliva is clear and thin, similar to the appearance and consistency of water. The total volume is recorded. The total volume collected in 5 minutes, divided by five, results in the volume per minute or unstimulated salivary flow rate. The normal unstimulated flow rate varies between 0.3 and 0.4 Ml/min11,12 and values < 0.1 Ml/min should be considered abnormal (see Table 1).^13,14

If the unstimulated salivary flow rate is abnormally low, the next step is measuring the stimulated salivary flow rate. The stimulated salivary flow rate measures the ability of the salivary glands to produce saliva when stimulated. Chewing unflavored paraffin for 5 minutes, applying 1% citric acid to the tongue, and prescription salivary stimulants are used to capture a stimulated salivary flow rate.

A stimulated salivary flow rate may be determined by having the patient chew a piece of unflavored paraffin for 1 minute, then repeating the measurement process. A normal stimulated salivary flow rate is 1-2 Ml/minute with less than or equal to 0.5 Ml/minute considered abnormally low. A 1% topical solution of citric acid applied to the tongue can also be used to stimulate saliva. Another method is to administer a 5 mg test dose of pilocarpine, a drug that stimulates salivary flow.15 The stimulated salivary flow rate can be measured 20-30 minutes after oral administration of 5 mg pilocarpine. Contraindications to administering pilopcarpine are known hypersensitivity to pilocarpine, narrow angle glaucoma, and uncontrolled asthma. The most common adverse effect is sweating. An advantage with using pilocarpine to stimulate salivary flow is that the patient can see if the medication works, compare the oral sensations before and after the pilocarpine challenge, and determine whether or not pilocarpine or other salivary stimulant is likely to be effective as a long term treatment for SGH. Individuals who do not respond to a test of pilocarpine are more likely to have irreversible salivary gland destruction due to immune disease such as Sjogren’s syndrome.

If a patient has a salivary flow rate less than or equal to 0.1 Ml/minute, the patient may require a prescription medication salivary stimulant to maintain an adequate salivary flow rate.

Calibrated Paper method

The modified Schirmer test (MST) measures the submandibular salivary flow rate.^16,17 This test uses a calibrated filter paper test strip developed to measure lacrimal tear flow. Schirmer test strips with a blue dye impregnated into the strip that mark the amount of flow are very easy for both the clinician and the patient to see results. The strip is held on the submandibular salivary caruncle for 3 minutes. At the end of 3 minutes, the amount of salivary flow is measured. A normal salivary flow rate using the MST method is 30 mm/3 minutes. A flow of 25 mm or less is diagnostic of SGH. For patients with a low unstimulated salivary flow rate, the test can be repeated after preparation with unflavored paraffin, topical 1% citric acid, or a test dose of pilocarpine for a stimulated salivary flow rate measurement. Patients who are able to produce saliva when stimulated are known as responders. Responders are often candidates for treatment with prescription salivary gland stimulants (secretagogues).

Salivary flow can also be assessed using the commercially available saliva-check kit. This test measures quantitative and qualitative aspects of saliva, including the salivary pH and buffering capacity.

Salivary pH

The normal salivary pH is 7.0-7.5 or neutral to slightly alkaline. With SGH, the salivary pH decreases. Erosion of dental hard tissues occurs at pH 5.5. A low salivary pH contributes to mucosal discomfort. The most common cause of a low salivary gland pH is SGH, but patients with gastroesophageal reflux disease may also have a low pH.¹⁸

Salivary flow rate can be measured annually as part of a comprehensive oral examination for diagnosis and prevention of oral disease. If an SGH diagnosis is made, the next step is to determine if a related systemic disease is present.

Salivary Gland Biopsy

Patients with SGH should be evaluated to determine if there is systemic disease contributing to the loss of salivary gland function. The most common diseases are diabetes mellitus, hypothyroidism, and Sjogren’s syndrome. Blood tests such as the fasting blood glucose; thyroid function tests such as T3, T4, and thyroid stimulating hormone; and Sjogren’s antibodies SS-A and SS-B can detect up to 65% of contributing problems with salivary gland hypofunction.¹⁹ If blood tests fail to reveal the etiology of salivary gland hypofunction, a salivary gland biopsy of minor or major glands may increase the ability to diagnose the cause. Biopsy may identify lymphocytic infiltrates, fibrosis, amyloid, or other problems not detectable by routine blood tests.

The salivary flow rate can be measured easily with minimal patient preparation in the dental hygiene appointment. The patient with salivary gland hypofunction requires treatment, including drinking 64 oz daily of noncaffeinated beverages.

References

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From Dimensions of Dental Hygiene. January 2006;4(1):26, 28-29.