Radiation Therapy Induced Dental Damage: A Review

Introduction:

Radiation therapy (RT) is a powerful technique used in the treatment of head and neck cancers (HNCs). It employs potent ionizing radiation to selectively damage the genetic material of cancer cells, ultimately leading to their destruction. Additionally, this therapy halts the production of free radicals within these cells. However, patients undergoing radiotherapy for HNCs often experience a range of dental complications. These complications include dry mouth, medically known as xerostomia, and dysfunction of the salivary glands. Dry mouth increases the vulnerability to dental caries and associated issues due to reduced saliva's protective effects. Furthermore, RT can directly impact the enamel through hard tissue demineralization. It is important to note that the adverse effects of radiation therapy on oral structures can manifest in various ways, both directly and indirectly, and may occur as either acute or chronic effects.

What Are the Radiation-Related Damages in the Oral Cavity?

• Oral Mucositis- It is characterized by painful inflammation of the oral mucous membranes and can be a challenging side effect of cancer treatment.

• Xerostomia - It is a common issue experienced by cancer patients undergoing radiation therapy, leading to discomfort and difficulty in speaking and eating.

• Chemosensory Taste Disorders - It can result in a loss of taste perception, making it difficult for patients to enjoy their food during cancer treatment.

• Radiation-Linked Dental Caries - It can weaken teeth and lead to cavities due to the effects of radiation therapy on oral health.

• Oral Infections - It can become a serious concern for immunocompromised cancer patients, necessitating vigilant oral hygiene and care.

• Trismus- It is the limited or difficulty in mouth opening, that can occur after certain cancer treatments, affecting a patient's ability to eat and speak comfortably.

• Osteoradionecrosis of the Jaw - It is a severe condition where the jawbone becomes damaged as a result of radiation therapy, requiring specialized treatment to manage and alleviate symptoms.

Of these effects, the most common and orally distressing condition is that of post-radiation caries occurring in the dental enamel and dentinal layers of the tooth.

What Factors Contribute to the Increased Risk of Post-radiation Caries in Cancer Patients?

Cancer patients undergoing radiation therapy face an elevated risk of developing post-radiation caries for several reasons. First, irradiation can lead to the rapid development of carious lesions in the demineralized tooth enamel and dentin layers, commonly referred to as rampant radiation caries. These lesions, particularly when located in the cervical or incisal teeth, can progress quickly to involve the dental pulp or root canal if left untreated. Dentists play a crucial role in managing this risk by providing timely restorative or endodontic treatment for teeth with a moderate to good prognosis before the initiation of radiotherapy. It is essential to educate patients about the importance of dental visits even after radiotherapy to monitor and address any emerging dental issues.

Furthermore, post-therapy, several factors contribute to the increased risk of caries in cancer patients. Radiation therapy can result in side effects such as reduced oral clearance and alterations in the oral microbiome. This may lead to an increase in acidogenic organisms like Streptococcus mutans, Lactobacillus, and Candida species, which are known contributors to dental caries. Irradiation can also induce a shift in the oral microflora due to increased bacterial, viral, or fungal loads, negatively impacting salivary clearance and compromising the body's ability to combat oral infections. Additionally, radiation therapy can impact salivary function by altering the composition of immunoproteins present in saliva, reducing its innate buffering action. This alteration can affect the protective pellicle formed on tooth enamel, further increasing susceptibility to caries.

In addition to caries, cancer patients undergoing radiation therapy are also at an elevated risk of developing gum infections or inflammation such as gingivitis and periodontal infections. Therefore, comprehensive oral care and regular dental check-ups are crucial for managing and minimizing the risks associated with post-radiation caries in this patient population.

What Are the Symptoms of Post-radiation Caries?

• Location of Symptoms: Post-radiation caries typically manifests on the labial tooth surface or at the cervical tooth areas.

• Prevalence in Upper Teeth: While it is more prevalent in the upper teeth, it can affect any smooth surface of the teeth, including the lower anterior teeth.

• Cervical Area Encirclement: The decay lesions progress to encircle the cervical areas of the affected tooth. This encirclement makes the tooth more susceptible to friability and breakdown, especially in an area where the enamel is naturally thin.

• Change in Tooth Translucency: Patients commonly complain of changes in tooth translucency, often noticing a brownish-black discoloration on the affected tooth crown.

• Effect on Posterior Teeth: Post-radiation caries are not limited to anterior teeth; it can also impact posterior teeth like premolars and molars. This is characterized by enamel wear on the chewing or occlusal surfaces of these teeth.

What Are the Types of Post-radiation Caries?

• Type 1 Post-radiation caries - A common dental caries pattern seen on the cervical aspect of the teeth extends up to the cementoenamel junction.

• Type 2 Post-radiation caries - These lesions are more progressive or advanced carious developments that appear as areas of demineralization that affect nearly all dental surfaces.

• Type 3 Post-radiation caries -This is the least common pattern though it can be seen as color changes or tooth translucent changes in the dentin layer.

What Are the Dental Restorative Strategies?

• Timing: Post-radiation caries is a rapidly progressing and highly destructive form of dental caries that typically occurs within or around three months following radiation therapy. Prompt dental intervention is essential to alleviate pain and discomfort. Dentists should be proactive in addressing post-radiation caries.

• Preventive Approach: Ideally, cancer patients should consult with a dentist before undergoing radiation therapy. This proactive approach allows the dentist to evaluate the patient's dental health and assess the prognosis of each tooth.

• Restorative Procedures: Restorative dental management of radiation caries is challenging due to radiation-induced changes in enamel and dentin, which interfere with bonding dental adhesive materials.

• Alternative Filling Materials: Glass ionomer cement is often preferred over composite resin fillings for patients with post-radiation caries due to its better performance in such conditions.

• Patient Counseling: Educating patients about potential dental complications before and after radiotherapy is crucial. This counseling helps them understand the importance of proactive dental care.

Conclusion:

To conclude, for all cancer patients, especially in cases of head and neck cancers, the awareness of restorative and endodontic treatment strategies after radiation therapy plays a valuable role in relieving the affected patient's dental pain, distress, and other numerous oral side effects of radiation therapy treatment (other than post-radiation caries). Restoration of carious lesions endodontic therapy as well as recontouring of teeth with a good prognosis should be initiated as early as possible by the dentist to prevent adverse complications. Likewise, the teeth with poor or hopeless prognoses should be extracted according to the patient's convenience in the pre or post-radiation phase. Though a clinical challenge to the dentist, the treatment of radiation caries is still a need in cancer patients undergoing radiotherapy.