Dry Mouth: The Effects of Diseases and Radiation on Salivary Glands

Other Conditions Affecting Salivary Glands

Systemic Diseases

Many systemic diseases are reported to cause or be associated with salivary gland hypofunction as mentioned in Table 1 [29], [64].

Of these systemic diseases, Sjogren’s syndrome (SS) is the most common disease that causes both xerostomia and salivary gland hypofunction with the incidence of xerostomia in the SS patient reaching nearly 100% [29], [65].

Dr. Roseanne Mulligan, DDS, MS, Geriatric Dentistry Online Postgraduate Dental Degree Program, USC Dentistry
Dr. Roseanne Mulligan, DDS, MS, Geriatric Dentistry Online Postgraduate Dental Degree Program, USC Dentistry

SS is a chronic, autoimmune disease that is characterized by progressive injury to the exocrine glands, mainly the lacrimal glands and the salivary glands. Although the exact mechanism of SS is not known, it is associated with B lymphocyte hyper-reactivity, autoantibody production and T-cell lymphocytic infiltration to exocrine glands and other organs [65].

SS may present as a primary disease or a secondary disease that is associated with other autoimmune diseases such as rheumatoid arthritis, systemic lupus erythematosus and systemic sclerosis [64], [65].

All ages can be affected by SS but it generally becomes overt during the fourth and fifth decade of life [65] and elderly patients account for up to 20% of Sjogren’s cases [29].

As the HIV infected population ages, more salivary conditions are being noted as a result of the HIV virus or the anti-retrovirals used for its treatment. Mulligan et al. also found that women who are HIV positive presented salivary gland disease manifested by glandular enlargement, tenderness, and absence of saliva on palpation [66].

Table 1: Etiology or Causes of Salivary Gland Hypofunction and Xerostomia [25], [29], [44], [46], [58], [64], [65].

General• Old age
• Female sex
• Dehydration
• Disability (cognitive and physical)
• Institutionalization
• Habits (mouth breathing, smoking, alcohol and drug abuse)
• Compromised masticatory function
Iatrogenic• Medications*
• Therapeutic irradiation*
• Chemotherapy/immunotherapy
• Chronic graft vs host disease
• Salivary duct ligation
• Liquid diet feeding
Salivary Gland Diseases and Disorders• Agenesis of the salivary glands (with or without ectodermal dysplasia)
• Sialoadenitis
• Sialolithiasis
Chronic Inflammatory
Autoimmune Diseases
• Sjogren’s syndrome*
• Other rheumatologic diseases; Rheumatoidarthritis, SLE, scleroderma, mixed connective tissue disease
• Sarcoidosis Amyloidosis
• Crohn’s disease, ulcerative colitis
Endocrine Diseases• Diabetes mellitus
• Hyper-and hypothyroidism
• Cushing’s syndrome
• Addison’s disease
Neurologic Diseases and Disorders• Stroke
• Parkinson’s disease
• Bell’s palsy
• Alzheimer’sdisease
Psychogenic Diseases and Conditions• Stress
• Anxiety and nervousness
• Depression
• Eating disorders (anorexia nervosa, bulimia)
Infections• HIV/AIDS
• HCV
• Tuberculosis
• Human T lymphotropicvirus (HTLV-1)
Other Diseases• Cysticfibrosis
• Hypertension
• Fibromyalgia
• Chronic fatigue syndrome
• Burning mouth syndrome
• Primary biliary cirrhosis
• Liver transplant candidates
• Renal diseases and Renal dialysis
• Anemia
• Atrophicgastritis
*Major causes of dry mouth

Radiation Therapy Effects

Another major cause of dry mouth is head and neck radiation with or without chemotherapy for cancer treatment near salivary glands.

Radiotherapy in the head and/or neck region can cause temporary or permanent damage to the salivary glands [25], [29], [58], [65], [67]. Salivary flow rates were the most severely reduced in patients with a history of radiation therapy when compared with patients with SS patients or patients on xerogenic medications [68].

Once head and neck radiation therapy is begun, salivary gland flow decreases as does oral health related quality of life; these reductions often continue on a chronic basis and may result in a lifelong condition [68], [69].

The prevalence and the severity of xerostomia and salivary gland hypofunction in head and neck cancer patients depends on the tumor site, stage, type of radiation therapy, the cumulative dose of irradiation, and the volume of salivary gland tissue included in the treatment portals [69].

The highest prevalence and severity of salivary gland hypofunction and xerostomia has been reported in nasopharyngeal [29], [69] and oropharyngeal carcinoma where all salivary glands bilaterally are included in the radiation treatment.

In contrast, the least prevalence of these conditions are when the cancer is located in the laryngeal/epilaryngeal area, which is more remote from the salivary glands [69].

Conventional radiotherapy doses of ∼60 Gy to the glandular tissue results in high rates of tissue destruction and the described sequelae [69]. The treatment of head and neck cancer with radiation usually is extended over 5–7 weeks and includes a total dose of 50–70 Gy delivered in daily allotments of 1.8–2.0 Gy [70].

Salivary flow begins to be impacted fairly quickly after initiation of therapy, falling to 50–70% of baseline once 10–16 Gy is delivered. Flow becomes nearly undetectable after the cumulative doses of 40–42 Gy [68], [70].

Radiation induced salivary hypofunction is accompanied by changes in the composition of saliva, including the lowering of salivary pH and therefore buffering capacity; and decreases in amylase activity, while at the same time it demonstrates increasing osmolality and viscosity, and higher concentrations of lactoferrin, protein, sodium, chloride, alterations in mucin and calcium concentration [29], [70].

Using 3D conformal radiation therapy can reduce the radiation dosage to the contralateral parotid gland and Intensity-Modulated Radiation Therapy (IMRT) allows more accurate delivery of specific radiation dosage and distribution to the tumor mass, while sparing the salivary glands. By doing so, both 3D conformal radiation therapy and IMRT can decrease the prevalence and severity of radiation induced salivary hypofunction [69].

In addition to salivary hypofunction, there are other head and neck radiation induced outcomes that can occur including taste loss, mucositis, radiation caries and susceptibility to osteonecrosis of the jaw bone, all of which can negatively impact oral health related quality of life (Fig. 1) [64], [69], [71].

Other treatments for cancer such as radioactive iodine therapy, total body irradiation/chemotherapy and hematopoietic stem cell transplantation, chemotherapy, and immunotherapy have also been reported to have the potential of causing dry mouth but there is not sufficient data to report on the severity and grading of the resulting dry mouth outcomes [69].

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About the Authors

The article, “Dry mouth: A critical topic for older adult patients,” was authored by Phuu Han, Piedad Suarez-Durall, and Roseann Mulligan, Director Geriatric Dentistry Master and Certificate programs at the Herman Ostrow School of Dentistry of USC, and was originally published by Elsevier in the Journal of Prosthodontic Research.

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