Saliva: The Mouth's "Bloodstream"
Saliva is a fluid that flows throughout the mouth, playing an important role in bolstering and maintaining the health of oral soft and hard tissues. Among the body's defense mechanisms, saliva works to lubricate, digest and protect.
Saliva is produced and secreted by major and minor salivary glands lining the inner lip and soft palate. Chewing is the most efficient way to stimulate salivary flow. It causes muscles to compress the salivary glands, releasing saliva. The "mouth-watering" taste and consistency of foods also affect saliva production.
Saliva, Oral Health and Disease Protection
Saliva coats and lubricates tissues in the mouth, making it easier to speak, chew and swallow. Saliva helps remove oral waste and cavity-causing bacteria, protects teeth from decay by neutralizing harmful acids, and helps re-mineralize tooth enamel. Saliva also keeps oral tissues healthy by preventing infection by controlling bacteria and fungi in the mouth.
The primary roles and benefits of saliva include:
Waste Removal: The physical flow of saliva helps remove disease-causing viruses, bacteria and yeast from teeth and soft oral surfaces. Saliva also can cause microbes to clump together so they can be swallowed before they become attached to the surfaces of teeth and soft oral tissues.
Barrier and Buffering Agent: Saliva provides an effective barrier against drying and helps limit the penetration of physical irritants, toxins and carcinogens in foods, beverages and tobacco. Saliva contains buffering systems that help neutralize acidic foods and drinks to protect teeth and soft oral tissues from acid attacks. When swallowed, salivary buffers protect the esophagus, helping to neutralize the reflux acids associated with conditions such as heartburn.
Caries Protection: Saliva is the mouth's primary defense against tooth decay. Caries result from bacteria that generate acids, which attack tooth minerals. Saliva's buffering systems help counter acid formation. Saliva flow helps wash away the sugars and food particles that, when broken down, also produce tooth-damaging acids.
For instance, when you eat high-starch foods such as bread, the carbohydrates they contain block natural saliva flow and aren't easily dissolved. To ensure its free flow throughout the mouth, saliva contains amylase, an enzyme that breaks down starch into sugars that clear the mouth and facilitate salivary flow.
Mineral salts in saliva calcium and phosphate ions slow demineralization of tooth structure and encourage ongoing re-mineralization of tooth enamel, thus reversing the decay process.
Fostering Healthy Plaque Biofilm: Immune proteins in saliva regulate the growth, maintenance and movement of healthy plaque biofilm. Microbes and the immune system work together to eliminate and prevent visiting microorganisms from living in the mouth. After a tooth is cleaned, its enamel surfaces become coated with a salivary protein film called the pellicle. The pellicle supports the attachment of free-floating bacteria. The more bacteria attach to one another, the more they "attract" other bacteria, creating large clumps that are easier to swallow and eliminate. In this way, mature plaque biofilm depends on salivary flow for waste removal and nutrients. The pellicle, which is insoluble, limits acid flow to the teeth and the destruction of tooth minerals. If salivary flow is reduced, the organisms within the biofilm undergo changes, which frequently cause inflammation of supporting tissues and can lead to gingivitis.
Wound Healing: Saliva contains molecules, such as epidermal growth factor (EGF) and vascular endothelial growth factor (VEGF), which help repair and regenerate oral tissues.
Consequences of Low Salivary Flow: Dry Mouth
Dry mouth (xerostomia) is a chronic reduction in salivary flow. Dry mouth can irritate and inflame the mouth's soft tissues, making them more susceptible to infection and growth of harmful organisms. Without sufficient saliva flow, the mouth is less able to clean and shield itself from tooth decay, gum disease and tooth erosion. Dry mouth also can lead to altered taste; bad breath; mouth ulcerations or sores; difficulty in chewing, swallowing and speaking; oral tissue infections and dental attrition and wear.
Causes of Low Salivary Flow
While dry mouth may be a sign of a serious health condition, it also can be caused by stress, radiation therapy and chemotherapy, prescription and non-prescription medications (such as antidepressants, diuretics, analgesics, antihistamines, anti-hypertensives, anti-anxiety, appetite suppressants, excessive alcohol consumption, etc.). People suffering from xerostomia include patients with autoimmune diseases, HIV/AIDS, diabetes, Alzheimer's disease, as well as people who have received radiotherapy for head and neck cancer, suffered a stroke or those who do not drink enough water. Additionally, head or neck injuries can damage nerves that tell salivary glands to produce saliva.
Certain systemic conditions, such as Sjögren's syndrome an autoimmune disease in which a person's white blood cells attack moisture-producing glands also may diminish salivary flow. Most often afflicting women in their 40s, Sjögren's syndrome is difficult to diagnose. Symptoms which vary greatly and can mimic those of menopause; drug side effects, allergies or medical conditions such as rheumatoid arthritis; fibromyalgia; and chronic fatigue syndrome may include dryness in the mouth and eyes, fatigue, and joint pain. Rheumatologists have primary responsibility for managing Sjögren's syndrome, but dentists and eye care providers also offer treatment.
Dry Mouth Treatments
In addition to chewing sugar-free gum with xylitol, commercial over-the-counter products such as artificial saliva and tissue lubricants also relieve dry mouth symptoms by increasing salivary flow. To ease the symptoms of dry mouth, your dentist also may recommend the following:
- Brush and floss twice daily
- Avoid alcohol, caffeine and smoking
- Avoid acidic juices, such as grapefruit or orange
- Avoid dry foods, such as toast or crackers
- Avoid overly salty foods
- Drink plenty of water
- Schedule regular dental visits
- Suck on ice chips or sugar-free hard candy
- Use a humidifier at night
Too Much Saliva: Hypersalivation
Hypersalivation, also known as sialorrhea or ptyalism, refers to too much saliva production or the presence of too much saliva in the mouth caused by decreased salivary clearance. Hypersalivation may occur in association with pregnancy, excessive starch intake, gastroesophageal reflux disease, pancreatitis, liver disease, serotonin syndrome, and oral ulcers.
Use of certain medications like clozapine, pilocarpine and potassium chlorate, and toxins such as mercury, copper and arsenic also may be associated with hypersalivation.
Hypersalivation resulting from decreased saliva clearance may be related to an inability to properly close the mouth (drooling) or to swallow the saliva. Conditions which may affect salivary clearance include tonsillitis and mumps, jaw problems such as fractures or dislocation, radiation therapy, and neurologic disorders such as Parkinson's disease, rabies and facial nerve palsy.
Treatments for hypersalivation focus on treating or avoiding the underlying causes. Tooth brushing and rinsing with alcohol-containing products also will produce drying effects.
Saliva as a Diagnostic Tool
Dentists, physicians and scientists are looking to salivary diagnostics as a significant and promising area with many potential uses. Sampling saliva instead of blood or urine provides an effective way to detect a range of biomarkers, such as proteins, electrolytes, hormones, antibodies and DNA/RNA, that can identify or predict disease.
Advantages of using saliva as a diagnostic tool include easy access, noninvasive sample collection, better patient acceptance (most patients prefer giving saliva samples over blood or urine ones), fast results and cost-effectiveness. Compared to blood, collecting saliva provides reduced risk of infectious disease transmission. Saliva collection is simple, painless and can be completed repeatedly without patient discomfort. Not requiring special training or onsite equipment, salivary diagnostics lends itself to testing at home and dental clinics, so it can be used to reach patients with limited access to preventive care due to personal, logistical or economic reasons.
The potential for salivary diagnostics includes:
- Detecting viral diseases, such as HIV and viral hepatitis
- Measuring salivary protein levels to help in the diagnosis, treatment and follow-up care of breast cancer (For example, periodic salivary tests could be prescribed for women recovering from breast cancer to ensure that their cancer remains in remission.)
- Portable salivary testing for abusive drugs such as cocaine, ethanol and opiates, as well as therapeutic monitoring of drugs such as methadone and certain anticonvulsants
- Monitoring responses to anxiety and depression treatment
- Chairside diagnostic testing using "lab-on-a-chip" technologies to identify oral fluid biomarkers associated with good health and oral and/or systemic diseases such as Sjögren's syndrome
- Self-contained saliva test kit for use at the point of care that will target markers for periodontal diseases, caries, infectious diseases, pancreatic cancer, diabetes, salivary gland diseases, renal diseases, steroids and inflammatory markers for cardiovascular and pulmonary diseases
- Determining hormone levels, including estrogen (estradiol), progesterone, testosterone and cortisol (This is especially important in the case of estradiol, an indicator of premature birth and low birth-weight babies.)
What's Ahead for Saliva?
In the future, with coordinated collaboration between dentists, physicians and other healthcare professionals, salivary tests may be combined with traditional approaches and methods for verification, resulting in rapid and reliable diagnosis of numerous dental/medical conditions and diseases, as well as the ability to monitor and evaluate a person's response to, and the effectiveness of, treatment.