Side Effects
Unavoidable toxicities/side effects are produced due to the pugnacious nature of the malignant diseases to normal cells. The oral cavity is highly susceptible to direct and indirect toxic effects of cancer chemotherapy and ionizing radiation. This risk is due to multiple factors including high cellular turnover rates for the lining mucosa, a diverse and complex microflora and trauma to oral tissues during normal oral function. Slightest change in soft tissue structures within the oral cavity presumably reflect the changes that occur throughout the gastrointestinal tract.

Oral complications may mimic selected systemic disorders. The most common oral complications related to cancer therapies are mucositis, infection, salivary gland dysfunction, taste dysfunction and pain. These complications can lead to secondary complications such as dehydration, dysgeusia and malnutrition. In myelosuppressed cancer patients, the oral cavity can also be a source of systemic infection. Radiation of the head and neck can irreversibly injure oral mucosa, vasculature, muscle and bone. This can result in xerostomia, rampant dental caries, trismus, soft tissue necrosis and osteonecrosis.

Mucositis
Mucositis is the most common type of oral complication which can be caused by radiation or chemotherapy which results from the mitotic death of the basal cells of the mucosal epithelium. Portions of the gastrointestinal tract also become inflamed and red, burn-like or ulcer-like sores appear throughout the mouth. Severity depends on the quality of dental hygiene, the treatment schedule, the irradiated area and the amount of radiation given, as well as the age of the patient.

Erythematous mucositis typically appears 7 to 10 days after initiation of high-dose cancer therapy. Late effects can be characterized by thinning of the mucosa (the soft tissues of the oral cavity), submucosal ulceration and necrosis. Mucositis is self-limited when uncomplicated by infection and typically heals within 2 to 4 weeks after cessation of cytotoxic chemotherapy.

Oral mucositis is made worse by infection. The mouth can become infected and the loss of soft tissues in the mouth can allow disease-causing organisms to enter the bloodstream. Once the mouth is affected by treatments, even the normal, good bacteria that exist as part of the natural flora of our mouth can cause infections, as well as disease-causing organisms to be picked up from other sources.

As the white blood cell count decreases, the frequency and seriousness of infection increases. Patients, who have low white blood cell counts over a long period of time are more at risk of developing serious infections.

Management of oral mucositis via topical approaches should address efficacy, patient acceptance and appropriate dosing. Antibiotics used over a long period of time can change the number of normal, beneficial bacterial organisms in the mouth. Their decreased numbers may allow an excessive growth of fungi. Steroids given at the same time as treatments can also make the problem worse. Most oral infections in patients with solid tumours are caused by yeast and other fungi, while the rest are caused by viruses (such as herpes) and bacteria.

A stepped approach is typically utilized with progression from one level to the next as follows:

  • Bland rinses (e.g. 0.9% normal saline and/or sodium bicarbonate solutions).
  • Mucosal coating agents (e.g. antacid solutions, kaolin solutions).
  • Water-soluble lubricating agents, including artificial saliva for xerostomia.
  • Topical anaesthetics (e.g. viscous lidocaine, benzocaine sprays/gels, dyclonine rinses, diphenhydramine solutions).
  • Cellulose film-forming agents for covering localized ulcerative lesions (e.g. hydroxypropyl cellulose).
Xerostomia
Xerostomia means decreased salivary flow. Saliva is needed for taste, swallowing and speech. Xerostomia is the thickening of or reduction in volume of saliva that changes the ability of the mouth to neutralize acid, clean the teeth and gums and protect the mouth from infection.

Symptoms include dryness, a sore or burning feeling (especially on the tongue), cracked lips, cuts or cracks at the corners of the mouth, changes in the surface of the tongue and difficulty wearing dentures. An extremely dry mouth will also impair proper speaking and the swallowing of foods. Saliva contains important protective enzymes which aid in the prevention of tooth decay and periodontal disease. To protect against tooth decay during and after treatments, patients with xerostomia should apply fluoride to the teeth daily to protect them.

Demineralization of the teeth and the breakdown of tooth structure can also occur as a result of xerostomia. A diminished supply of saliva or a change in the quality of saliva, particularly of the resting flow from the submandibular/sublingual glands, deprives the oral cavity of the protective components of saliva and the calcium and phosphate ions necessary to maintain the hydroxyapatite content of tooth enamel and dentin. Demineralization may contribute to dental caries or hypersensitive teeth.

Osteoradionecrosis
Perhaps the most severe side effect of radiation therapy is osteoradionecrosis (ORN) or bone death. This condition occurs in three to ten percent of patients. Osteoradionecrosis develops as irradiation diminishes the bone's ability to withstand trauma, avoid infection, poor nutrition and hygiene. This process may be spontaneous or result from trauma, leading to non-healing soft tissue and bone lesions, followed by bone necrosis. The non-healing bone may become secondarily infected. All patients who are to receive chemo-radiation therapy should have unsalvageable teeth removed, periodontal health maximized and fluoride therapy instituted prior to treatment.

Osteoradionecrosis is an extremely serious complication for patients requiring tooth extraction after radiation therapy and the risk does not appear to diminish with time (for the rest of his/her life the patient should never allow a dentist to extract a tooth after radiation therapy without consulting a radiation oncologist). The ability of the bony tissues to heal is compromised by hypovascularization.

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