Tooth decay from radiation therapy, known as radiation caries, is a rampant form dental decay that may occur in individuals undergoing radiation therapy for cancer in the head and neck region. It is one of the many side effects associated with radiation therapy. The elderly who are at a greater risk of many different types of cancer are more likely to have to deal with these consequences of undergoing radiation therapy. However, it should not detract from the fact that the benefits of radiation therapy in the treatment of cancer often outweighs these side effects.
The radiation therapy reduces the flow of saliva as it causes damage to major and minor salivary glands. The altered salivary flow makes the teeth susceptible to develop new points of decay or worsens pre-existing decay. The lesions defer from normal dental decay as they are rapidly progressing and follow unusual patterns.
Clinically radiation caries can be categorized in three types :
The first type is the widespread superficial lesions that attack all surfaces of the teeth. Unlike carious lesions in non-irradiated individuals the radiation caries tend to involve the incisal edges of the crowns and cusp tips of canines and molars.
The second type is the encircling type of caries that occur over the root surface (cementum caries) and dentin. The destruction generally begins at the cervical third of the teeth. The lesion may aggressively encircle the tooth causing the entire crown to be lost with only root stumps remaining within the tooth sockets.
The third type is associated with pigmented lesion over the entire crown of the teeth. Generally dark spots are seen on the crown at the surfaces adjacent to the gums
Combination of all three types may also be seen in some individuals. Lesions associated with radiation caries progress rapidly involving dental pulp and may lead to complications during the course of radiotherapy.
Radiation caries is a side effect of ionizing radiation. During radiation therapy the salivary gland tissue damaged due to free radicals generated by radiation. The damage to the salivary glands not only reduces the amount of saliva produced but also alters the pH and composition of saliva. Normally saliva has an antimirobial action but the altered saliva is not as effective as normal saliva against the bacteria causing dental decay. Therefore patients undergoing radiation therapy have increase amounts of cariogenic bacteria such as Streptococcus mutans and Lactobacilli.
The altered saliva composition also reduces the ability of the saliva to re-mineralize the initial carious lesions. The reduced re-mineralization activity makes the carious lesion rapidly progressive. The lack of saliva also causes food and debris accumulation leading to an increase in cavities.
The best way to treat radiation caries is by minimizing the risk factors before initiation of radiation therapy. The possibility of decay arising should not stop a person from undergoing radiation therapy. Existing decay lesions, deep pits, fissures, abnormal grooves on the tooth surface or sites more prone to develop decay should be restored before the radiation therapy. All additional dental work should also be ideally completed before the onset of therapeutic radiation dosage.
Radiation therapy patients are advised to maintain strict oral hygiene practices to reduce the incidence of tooth decay. Using mouthwashes, fluoride-containing gels and toothpastes and flossing is highly beneficial. Dietary changes to avoid carbonated drinks, sugary food and fermentable carbohydrates are also recommended. The patient is advised to refrain from alcohol and smoking.
The lack of saliva can be managed by artificial salivary supplements (carboxymethyl cellulose saliva substitute) or drugs inducing saliva secretions (pilocarpine). The patient is also advised to sip non-carbonated sugarless fluids and xylitol-containing chewing gums.