Oral Cancer and Complications of Cancer Therapies _ _____________________________________________
dependent on food particles dissolved in a salivary medium, taste perception is altered. Patients often attempt to compen- sate for this by selecting foods that are very spicy or very sweet, which further compromises their medical and dental health. Swallowing food becomes more difficult as the bolus of food is less lubricated. Patients may need frequent sips of water during meals to alleviate this problem. The oral tissues can become subject to frequent irritation, tissue trauma, and opportunistic infection. The cleansing action that saliva provides for the teeth can be severely compromised. This can lead to a form of multiple caries that occurs after radiotherapy has damaged the salivary glands. RADIATION CARIES The changes that occur in the oral environment after radio- therapy portals have damaged the salivary glands may cause rapid and widespread destruction of teeth that previously had no dental pathology [65]. It is postulated that radiation alters the organic and inorganic matrix of enamel and the remaining tooth structure [47]. Decalcification may be favored over remineralization as an initiator of the carious process. The decrease in pH levels, which is commensurate with the amount of damage to the salivary glands, begins the creation of a caries-prone oral environment. When the serous component of saliva decreases and the viscosity increases, adherence of cariogenic bacteria to tooth structure increases. These organ- isms thrive in the more acidic oral environment that develops after radiotherapy. These factors, coupled with the difficulty patients have with their oral hygiene maintenance amidst sensitive teeth and soft tissues, create a problem known as “radiation caries.” This is an aggressive and rapid form of dental decay, targeting parts of the tooth that are usually not prone to decay. The smooth buccal (outer) and lingual (inner) walls of the tooth become involved with rapidly advancing carious lesions. The area of the tooth that is closest to the gingival tissues, the cervical area, is a frequent point of origin. The process can also affect the incisal edges of anterior teeth and the cusp tips of posterior teeth. Within weeks or months, the process renders teeth that were previously devoid of any dental pathology completely destroyed. Extractions of the teeth should only be done after a consulta- tion with the patient’s primary care physician. Oral surgery procedures can produce extensive postsurgical complications, with significant morbidity and even death in patients who have undergone a full course of radiotherapy. OSTEORADIONECROSIS The most serious of the complications postradiotherapy is osteoradionecrosis (ORN), occurring in 3% to 10% of patients [66]. This is defined as necrosis of the bone in areas that have received radiotherapy. Patients who have received doses of radiation for head and neck malignancies in excess of 6,000 cGy have the highest risk of this pathologic entity [66; 67]. The blood vessels that supply the bones with oxygen
and nutrients become hyalinized, with a subsequent decrease in the ability to perfuse the tissue with enough oxygen-rich blood. Areas of bone supplied by these damaged vessels lack the oxygen and nutrients necessary to sustain the appropriate levels of metabolism. These areas of bone become ischemic and ultimately necrotic. The mandible is affected more frequently because it has less of a blood supply than the maxillary arch [66]. Necrotic pieces of bone may be small fragments or large sections whose loss undermines support for either arch. A pathologic fracture of the affected arch is a possible complica- tion. Three grades of ORN have been categorized [67; 68]. Grade I occurs in close proximity to the completion of surgery and radiotherapy. Exposed alveolar bone is observed [67]. Grade II designates ORN that does not respond to hyperbaric oxygen therapy and requires sequestrectomy/saucerization [67]. Grade III is demonstrated by full-thickness involvement and/ or pathologic fracture. Patients may demonstrate grade I or III ORN at initial presentation [67]. Given the tumoricidal doses of radiation used, the 6,000 cGy threshold is easily reached for most patients with head and neck malignancies. Changes within the bone marrow include fibrous and fatty degeneration. The cells responsible for the production of bone, the osteocytes, are greatly diminished in number secondary to radiotherapy. The cells whose function is the resorption of bone, the osteoclasts, have fewer losses after radiotherapy. Thus, the dynamics of bone metabolism now favor bone resorption rather than bone apposition [60]. When this is combined with the damage to the blood vessels, the risk of ORN will be present for the remainder of the patient’s life. Unfortunately, the passage of time does little to reverse the damage and the subsequent risk of ORN. Treatment for ORN is variable. Small pieces of necrotic bone may migrate through the tissue and can be removed under local anesthesia. Larger segments of bone may require hospitaliza- tion for their removal. The risk of osteomyelitis, an infection of the bone, is increased in the patient who has undergone radiotherapy. The bony segments that perforate the mucosal tissues create a portal of entry for microbial organisms of the oral flora. Aggressive surgical and antibiotic treatment is needed to debride the area and resolve the infection. Hyper- baric oxygen treatments may help in the regeneration of new blood vessels with a resultant increase in the oxygen supply to the affected bone [69]. There is also evidence to suggest that hyperbaric oxygen treatments may be helpful as a therapy for soft tissue injury caused by radiation, as well as restoring tissues and cells damaged by chemotherapy and radiation treatments [66]. However, routine use is not recommended, and clinicians should assess any potential benefit to the patient on a case-by- case basis [67; 70]. Any oral surgery procedure increases the risk of the development of spontaneous ORN, even if it is performed years after the last radiotherapy treatment. Trauma to the soft tissue by any means also causes a localized area of inflammation and infection that can extend to the bone and cause ORN. Bone that has been irradiated can undergo dire consequences from seemingly minor events.
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