JADA Continuing Education
Measuring salivary flow
Challenges and opportunities
Mahvash Navazesh, DMD and
Satish K.S. Kumar, MDSc
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ABSTRACT
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Background. Saliva is being studied extensively and is being used for risk assessment, diagnosis and monitoring high-risk behavior and disease progression. A variety of medical conditions and medications are associated with salivary gland hypofunction. The major disadvantage in the use of saliva for health-related purposes is the lack of standardization in saliva collection methods.
Methods. The authors provide a brief overview of different methods of saliva collection and the advantages and disadvantages associated with each method, as well as of how to assess the salivary flow rate.
Results. The authors present the complete set up and step-by-step guidelines for the collection of unstimulated and stimulated whole saliva.
Conclusions. The life expectancy of people will continue to increase with advances in medicine and therapeutic modalities, and the prevalence of salivary gland hypofunction in the elderly population will increase owing to their longevity. The assessment of salivary gland hypo-function will need to be incorporated into everyday clinical practice.
Clinical Implications. The saliva collection methods outlined in this article can be used by dentists to assess patients at risk of developing diseases and by scientists for scholarly activities.
Key Words: Saliva; saliva collection; salivary flow rate; salivary glands; salivary gland hypofunction; xerostomiaAbbreviations: SWS-Candy: Stimulated whole saliva—candy. • SWS-Gum: Stimulated whole saliva—gum. • UWS: Unstimulated whole saliva.
Promoting health by preventing disease is a goal of health care providers, and risk assessment and disease prevention are common themes in the surgeon general’s report on oral health in America.1 Clinicians commonly use health questionnaires and clinical evaluations to identify patients at risk of developing diseases. Hematologic, serologic and imaging diagnostic modalities are used to assess these patients further. In recent years, saliva-based diagnostic tests have been increasing in popularity because of their noninvasive nature.2,3
Technologies are available that use saliva to diagnose, follow and assess the risk and severity of diseases, high-risk behaviors or both. Salivary biomarkers have been used to assess the risk of developing oral, ovarian and breast cancers; HIV infection; Sjögren syndrome; and dental caries and periodontal diseases, as well as to detect exposure to alcohol and illegal drugs. Nicotine and cotinine levels also can be measured in saliva and be used by the life insurance industry to verify the smoking status of applicants. Hormone levels detected in saliva can be used to determine the presence of physiological changes (for example, pregnancy) and emotional disorders (for example, depression).2,3
Quantitative and qualitative salivary changes associated with local or systemic disorders are not always easily captured or appreciated by clinicians and scientists owing to the lack of standardization in saliva collection methods.4 Different sources (mixed versus individual glands) and methods (unstimulated versus stimulated) of collection significantly affect the desired qualitative or quantitative changes being evaluated. In this article, we focus on methods of saliva collection and the opportunities and challenges associated with each method.
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THE SALIVARY GLANDS
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The three major salivary glands (parotid, sub-mandibular and sublingual) contribute to 90 percent of the mixed fluid in the mouth that is known as whole saliva; minor salivary glands that are scattered throughout the mouth contribute to the remaining 10 percent of the mixed fluid. Food debris, microorganisms and gingival crevicular fluid are other components of whole saliva. Saliva is composed of approximately 99 percent water and 1 percent proteins and salts. The normal daily production of saliva is between 0.5 and 1.5 liters. 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 un-stimulated and stimulated whole saliva is low.5,6
Although the minor salivary glands are not major contributors to the whole-saliva volume, they play a significant role in the lubrication and protection of the oral mucosa because of their mucous secretions. Parotid gland secretion is purely serous, and submandibular and sublingual gland secretions are mixed (mucous and serous). The primary saliva, formed by the acinar cells, has an ionic composition similar to that of plasma. It is modified by the ductal cells to a hypotonic solution by reabsorption of sodium and chloride without water.
Saliva secretion can be enhanced by a variety of stimulants. The salivary flow depends on the nature of the stimulus and its duration and intensity. Strong acidic stimulus, high-frequency chewing and high bite force result in increased saliva output. Parasympathetic stimulation results in increased watery (less viscous) saliva, whereas sympathetic stimulation results in mucoid (more viscous) saliva secretions.7
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SALIVARY GLAND HYPOFUNCTION AND XEROSTOMIA
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Lack of salivary flow affects a person’s quality of life by causing difficulties in speaking, eating, swallowing and tasting.8 Xerostomia—the subjective feeling or complaint of dryness in the mouth—can be caused by several medications without actual reduction in salivary flow. The major cause of xerostomia, however, is objectively assessed salivary gland hypofunction,9–11 which could be attributed to several systemic diseases such as Sjögren syndrome, rheumatoid arthritis and systemic lupus erythematosus.8 Salivary flow rate measurement becomes essential in diagnosing salivary gland hypofunction as the cause of xerostomia.5 Accurate measurement of salivary flow rate also is essential for various other clinical and research purposes.
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ASSESSMENT OF SALIVARY FLOW RATES
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Salivary flow rates are assessed differently for different purposes. Clinicians commonly use a patient’s response to a health questionnaire and the outcome of clinical evaluation as the basis for identification and assessment of dry mouth. For example, "yes" responses to the following four questions have been significantly associated with salivary gland hypofunction:
- – Does the amount of saliva in your mouth seem too little?
- – Does your mouth feel dry when eating a meal?
- – Do you have difficulty swallowing any food?
- – Do you sip liquids to aid in swallowing dry food?12
Some clinicians and scientists use a visual analog scale, an ordinal scale based on rank-ordered categories (for example, I have no/slight/severe/ annoying feeling of dry mouth) or both to assess salivary gland function.
Objective measurements of qualitative or quantitative changes in saliva are best captured by collecting saliva from individual glands or from all that contribute to whole saliva.13 Commonly used stimulants include gum base, paraffin wax, rubber bands and citric acid. Secretagogues such as pilocarpine and cevimeline hydrochloride14 and mechanical stimuli such as a transcutaneous electrical nerve stimulator and powered toothbrushes have been used to stimulate salivary flow.15
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UNSTIMULATED AND STIMULATED WHOLE SALIVA COLLECTION
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Several methods for collecting saliva have been reported and tested for validity and reproducibility.13,16 In this article, we provide in detail the guidelines for collecting unstimulated and stimulated whole saliva (Box
, page 36S) and measuring salivary flow rate (Figure 1) as followed at the University of Southern California School of Dentistry (Figures 2–5).
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Figure 1. University of Southern California School of Dentistry Salivary Flow Rate Measurement Sheet. UWS: Unstimulated whole saliva. SWS-Gum: Stimulated whole saliva—gum. SWS-Candy: Stimulated whole saliva—candy. mL: Milliliters. Adapted with permission of Mahvash Navazesh, DMD.
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Figure 2. Three tubes with measurements, funnels, inert gum base and sugar-free candy used for the collection of unstimulated and stimulated whole saliva.
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Figure 3. To collect unstimulated whole saliva, the patient drools passively into the collection tube for five minutes.
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Figure 4. Comparison of amount of saliva collected (from left to right): unstimulated whole saliva, gum-stimulated (masticatory) whole saliva (note the heavy sediment of salivary contaminants such as food debris, microorganisms and gingival crevicular fluid) and candy-stimulated (gustatory and masticatory) whole saliva.
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Figure 5. Changes in salivary flow rates obtained by using three methods in four patients. The healthy patients (1 and 3) have increased salivary output in response to stimulation compared with that of the subjects with salivary dysfunction (2 and 4). g: Grams.
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COLLECTION OF SALIVA FROM INDIVIDUAL GLANDS
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Saliva collection from individual glands should not be contaminated with food debris and micro-organisms, so it is prudent to acquire saliva from individual major glands. The techniques, however, are tedious and require custom-made collection devices.17
Parotid gland.
The parotid gland secretion is voided in the oral cavity via the Stensen duct at the vicinity of the parotid papilla opposite the maxillary second molar. A modified Lashley cup or Carlson-Crittenden collector often is used for collecting saliva from the parotid glands (Figure 6).
Submandibular and sublingual glands.
The submandibular and sublingual gland secretions are voided in the oral cavity via the Wharton duct, which opens into the floor of the mouth. Many custom-made collectors such as the Wolff collector are used (Figure 7).17,18
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Figure 7. A custom-made Wolff saliva collector for submandibular and sublingual gland saliva collection.
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Minor salivary glands.
Minor salivary gland secretions do not have much clinical application, owing to the labor-intensive nature of collecting them. Specific methods are used to measure minor salivary gland secretions.19
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CONCLUSION
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With advances in medicine and therapeutic modalities, human life expectancy is increasing steadily. One can expect an increase in salivary gland hypofunction, along with other more prevalent medical conditions, in the elderly population. In this article, we presented saliva collection methods that can be used by dentists in their practices to assess patients at risk and by scientists for scholarly activities.
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FOOTNOTES
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Dr. Navazesh is a professor and the chair, Division of Diagnostic Sciences, University of Southern California School of Dentistry, 925 W. 34th St., DEN 4320, Los Angeles, Calif. 90089-0641. Address reprint requests to Dr. Navazesh.
Dr. Kumar is an assistant professor of clinical dentistry, Division of Diagnostic Sciences, University of Southern California School of Dentistry, Los Angeles.
Disclosure. Drs. Navazesh and Kumar did not report any disclosures.
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ABSTRACT
THE SALIVARY GLANDS
