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Management of the Patient Undergoing Radiotherapy or Chemotherapy
Dental Management of Patients Undergoing Radiotherapy to the Head and Neck
Radiotherapy (i.e., radiation therapy and x-ray treatment) is a common modality for treating malignancies of the head and neck. Approximately 30,000 cases of head and neck cancer occur each year in the United States. The use of therapeutic irradiation to treat this cancer is ideally predicated on the ability of radiation to destroy neoplastic cells while sparing normal cells. In practice, however, this is never achieved, and normal tissues experience some undesirable effects. Any neoplasm can be destroyed by radiation if the dose delivered to the neoplastic cells is sufficient. The limiting factor is the amount of radiation that the surrounding tissues can tolerate.
Radiotherapy destroys neoplastic (and normal) cells by interfering with nuclear material necessary for reproduction, cell maintenance, or both. The faster the cellular turnover, the more susceptible the tissue is to the damaging effects of radiation. Thus neoplastic cells, which usually reproduce at higher rates than normal tissue, are selectively destroyed (relatively). In practice, normal tissues with rapid turnover rates are also affected to some degree. Therefore hematopoietic cells, epithelial cells, and endothelial cells are affected soon after radiotherapy begins.
Early in the course of radiotherapy the oral mucosa shows the effects of treatment. Most notable to dentistry are the changes in and around the oral cavity as a result of destruction of the fine vasculature. Salivary glands and bone are relatively radioresistant, but because of the intense vascular compromise resulting from radiotherapy, these tissues are subject to considerable hardship in the long run.
Radiation Effects on Oral Mucosa
The initial effect of radiotherapy on the oral mucosa, which is seen in the first 1 or 2 weeks, is erythema that may progress to severe mucositis with or without ulceration. Pain and dysphagia may be severe and make adequate nutritional intake difficult. These mucosal reactions begin to subside after the completion of radiotherapy. The taste buds, also composed of epithelial cells, show similar reactions. Loss of the sense of taste is a prominent complaint early in treatment, but it gradually returns, depending on the quantity and quality of saliva that remains after treatment.
Relief from mucositis is not predictable. Antibiotic lozenges containing amphotericin, tobramycin, and neomycin may be of some benefit. When symptoms are severe, viscous lidocaine may be useful.
The long-term effects of radiotherapy to the oral mucosa are characterized by a predisposition to breakdown and delayed healing, even after minor insult. The epithelium is thin and less keratinized, and the submucosa is less vascular, giving a pale appearance to the tissue. Radiotherapy induces submucosal fibrosis, which makes the mucosal lining of the oral cavity less pliable and less resilient. Minor trauma may create ulcerations that take weeks or months to heal. These ulcerations are often difficult to differentiate from recurrent malignant disease.
Radiation Effects on Mandibular Mobility
When irradiated, the pterygomasseteric sling and periarticular connective tissues become inflamed. Irradiated muscle becomes fibrotic and tends to contract, and the articular surfaces degenerate. These factors herald the onset of trismus. Decreased ability to open the mouth may be insidious in onset, usually occurring over the first year after radiation therapy, and is painless. When the interincisal opening decreases to 20 mm, food intake becomes difficult. Additionally, inability to open the mouth wide makes it difficult to perform dental work and to provide a general anesthetic.
Radiation Effects on Salivary Glands
The salivary gland epithelium has a slow turnover rate; therefore, the salivary glands might be expected to be radioresistant. However, because of the destruction of fine vasculature by radiation, the salivary glands show considerable damage with resultant atrophy, fibrosis, and degeneration. This damage manifests clinically as xerostomia (decreased production of saliva) and causes dry mouth. The severity of xerostomia depends on which salivary glands were within the field of radiation. Dry mouth may be the patient's most significant complaint.
Loss of salivary function leads to a plethora of adverse sequelae, including difficulty tasting, chewing, and swallowing; difficulty sleeping; esophageal dysfunction, including chronic esophagitis; nutritional compromises; greater intolerance to medications; and increased incidence of glossitis, candidiasis, angular cheilitis, halitosis, and bacterial sialadenitis. In addition, there may be decreased resistance to loss of tooth structure from attrition, abrasion, and erosion; loss of buffering capacity; increased susceptibility to mucosal injury; inability to wear dental prostheses; and rampant caries.
The effects of xerostomia on the oral cavity are devastating. Because saliva is the principal protector of oral tissues, its absence results in serious complications. Salivary proteins such as peroxidase, lysozyme, and lactoferrin are antibacterial and limit the growth of cariogenic bacteria. The film of salivary mucins on teeth and mucosal surfaces is believed to protect these oral structures from wear. Histatins, a family of salivary proteins, have potent antifungal properties that limit the growth of oral yeast. These salivary components, in conjunction with mucosal tissues, form part of the innate immune system that continually protects the human body from infection. The oral cavity is also protected by secretory immunoglobulins A and M, which are produced locally by B cells within the salivary glands. These antibodies include those with specificity against oral cariogenic bacteria. When salivary volume is significantly reduced, patients are at risk for serious oral complications.
The xerostomia makes it difficult for patients to eat a normal diet because of dysphagia. Therefore patients may adopt a more cariogenic diet. Rampant radiation caries can swiftly destroy the remaining dentition and predispose the patient to severe infection of the jaws ( Fig. 19.1 ). Teeth thus affected exhibit decay around the entire circumference of the cervical portion ( Fig. 19.2 ). Periodontitis is accelerated in the absence of saliva. Dysgeusia, dysphonia, and dysphagia are also caused by xerostomia. Another sequela of low salivary flow is an increase in oral infections such as candidiasis.
Treatment of Xerostomia
After radiotherapy, patients often complain of chronic dry mouth. At present, there is no general agreement on how to prevent these changes. Unfortunately, in many cases, xerostomia never improves substantially, and exogenous replacement of saliva is necessary. For the simplest form of replacement, water can be sipped throughout the day. Sipping water during meals aids in chewing, swallowing, and taste perception. In addition, several saliva substitutes can be obtained without a prescription. These substitutes contain several of the ions in saliva and other ingredients (e.g., glycerin) to mimic the lubricating action of saliva. Patients should be advised not to use products containing alcohol or strong flavors, which may irritate the mucosa. Sugar-containing products should be avoided by these patients who have an increased susceptibility to dental caries. They should also avoid caffeine and over-the-counter antihistamines and decongestants because these agents can further decrease the production of saliva and worsen the symptoms. Many of the salivary substitutes available in the United States contain carboxymethylcellulose, but studies have shown that the animal-derived mucin-based products that are available in other countries are better able to reduce the severity of symptoms associated with xerostomia.
Unfortunately the different types of artificial saliva available on the market do not possess the protective proteins present in the salivary secretions. Patients are therefore still prone to the problems induced by xerostomia. For comfort, however, many patients seem to find plain water just as satisfying as artificial saliva and keep small quantities available at all times to sip.
Efforts to stimulate patients’ residual saliva have met with some success. Sugar-free chewing gum stimulates saliva production as long as some saliva is being produced. The U.S. Food and Drug Administration has approved the use of two medications to stimulate the flow of saliva: (1) pilocarpine hydrochloride and (2) cevimeline hydrochloride; both have been shown to relieve symptoms of xerostomia. Both drugs are parasympathomimetic agents that function primarily as muscarinic agonists, causing stimulation of exocrine gland secretion. This stimulation can increase the production of saliva even in patients whose salivary glands have been exposed to radiation. An oral dose of 5 mg of pilocarpine four times a day or 30 mg of cevimeline three times a day has been shown to improve many symptoms of xerostomia without significant drug-related side effects. The administration of these medications may prove to be beneficial for some patients with postradiation xerostomia.
Radiation Effects on Bone
One of the most severe and complicating sequelae of radiotherapy for patients with head and neck cancer is osteoradionecrosis ( Fig. 19.3 ). This involves the devitalization of bone by cancericidal doses of radiation. The bone within the radiation beam becomes virtually nonvital from endarteritis, which results in elimination of the fine vasculature within bone. The turnover rate of any remaining viable bone is slowed to the point of being ineffective in self-repair. The continual process of remodeling normally found in bone does not occur, and sharp areas on the alveolar ridge will not smooth themselves, even over considerable time ( Fig. 19.4 ). The bone of the mandible is denser and has a poorer blood supply than that of the maxilla. Thus the mandible is the part of the jaw most commonly affected by nonhealing ulcerations and osteoradionecrosis.
Other Effects of Radiation
Patients undergoing radiotherapy may have an alteration in the normal oral flora with overgrowth of anaerobic species and fungi. Most researchers feel that oral flora colonizing the mucous membranes play an important role in the severity of mucositis and subsequent healing process. Candida albicans commonly thrives in the oral cavities of patients who have been irradiated. It is not known whether the alteration in the flora is caused by the radiation itself or the resultant xerostomia. Patients frequently require the application of topical antifungal agents such as nystatin to help control the number of Candida organisms present. Another oral rinse frequently prescribed is 0.12% chlorhexidine (e.g., Peridex, Periogard). This agent has been shown to have potent in vitro antibacterial and antifungal effects. When used throughout the course of radiation treatment, it has been shown in at least one study to greatly reduce the prevalence and symptoms associated with radiation-induced mucositis. Findings from other studies regarding the use of chlorhexidine have been equivocal.
Evaluation of the Dentition Before Radiotherapy
The most feared side effect of radiotherapy is osteoradionecrosis. Most patients who have this complication have residual teeth throughout the course of radiotherapy. Thus the clinician may wonder what to do with such teeth before irradiation. Should they be extracted? This question has no definitive answer; however, several factors must be considered.
Condition of the Residual Dentition
All teeth with a questionable or poor prognosis should be extracted before radiotherapy. The more advanced the periodontal condition, the more likely the patient is to have caries and continued periodontitis. Although this may not be in keeping with usual dental principles, the recommendation is “If in doubt, extract.” Extraction in these cases may spare the patient months or years of suffering from osteoradionecrosis.
Patient's Dental Awareness
The present state of the dentition and periodontium is a good clue to the past care they have received. In patients with excellent oral hygiene and oral health, as many of the teeth as possible should be retained. However, if patients have neglected their oral health for years, chances are that they will continue to do so, especially in the face of severe xerostomia and oral pain, which will make oral hygiene even more difficult. Patient preparation prior to radiotherapy is similar to patient preparation prior to orthodontic procedures. If an individual cannot or will not care for his or her mouth before the application of the braces, it will be impossible for him or her to do so when faced with future obstacles.
Immediacy of Radiotherapy
If the radiotherapist feels that therapy must be instituted urgently, sufficient time may not be available to perform the necessary extractions and allow for initial healing of the extraction sites. In this instance, the dentist may elect to maintain the dentition; but he or she must work closely with the patient throughout the course of radiotherapy and thereafter in an attempt to maintain the patient's oral health as optimally as possible.
Radiation Location
The more the salivary glands and bone are involved in the field of radiation, the more severe are the resultant xerostomia and vascular compromise of the jaws. Thus the dentist should discuss with the radiotherapist the locations of irradiation and should estimate the severity of the probable xerostomia and bone changes. Xerostomia of itself may not result in severe problems if the dentition can be maintained because bone is still healthy. The combination of xerostomia and irradiated bone usually causes the problem. In individuals who will have radiation to the major salivary glands and a portion of the mandible, preirradiation extractions should be considered. Often the radiotherapist agrees to delay the institution of irradiation for 1 to 2 weeks if the dentist feels that such time is necessary to allow the extraction sites to begin to heal.
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