Introduction

Radiotherapy for head and neck cancer is commonly associated with acute and late complications in healthy tissues located in the irradiated area. Common acute oral complications include mucositis, dysphagia, xerostomia, tender or painful soft tissues, and fungal infections.^1,2 Other late complications include trismus, hyposalivation, osteoradionecrosis, changes in dental structures, and radiation-related caries.^2-4

Radiation-related caries affect approximately 37% of irradiated head and neck cancer patients: it appears between 3 and 12 months after treatment is complete and is considered a late complication.⁵

Radiation-related caries is caused by a combination of the indirect effects of radiotherapy, such as damage to the salivary glands that modify the oral flora and reduce remineralization, damage to the temporomandibular joint and masticatory muscles causing trismus, and damage to the mucous membranes, which causes mucositis and limits adequate oral hygiene. There are also direct consequences on tooth structure,^3,5 such as changes in microhardness, chemical composition, and micromorphology of enamel and dentin,^6,7 predisposing patients to an increased risk of caries. It differs from conventional caries because it develops rapidly, is highly destructive, and is mostly painless.^3,8-10 It mainly affects the root area near the cementoenamel junction⁴ and includes root-dentin caries.¹¹

Restorative treatments for this type of caries are compromised by the harmful effect of radiotherapy on the bonding strength of the materials to enamel and dentin.^12,13 This entails ineffective adhesion between the restoration and the dental substrate, mainly after high doses of radiotherapy.

Methods

An advanced search was conducted in PubMed, LILACS, and Web of Science databases using the following keywords in English, Spanish, and Portuguese: “radiation-related caries,” “radiotherapy,” “ionizing radiation,” “permanent dental restoration,” “composite resins,” “glass-ionomer cements,” “modified glass-ionomer cement,” “conventional glass-ionomer cement,” and “direct restoration.” The literature search was conducted from April to June 2021. The studies included fulfilled the following inclusion criteria: patients with head cancer treated with radiotherapy and treated for caries lesions, patients with any direct restoration with or without fluoride, clinical studies, randomized clinical trials, case-control, cohort, reviews without follow-up period restrictions. Exclusion criteria: reviews, letters, opinions, editorials, books, book chapters, in vitro or in situ studies, and other design studies different from those described in the inclusion criteria, and studies written in non-Latin script.

Development

We found the following studies on managing radiation-related caries: seven clinical studies, one case report, two systematic reviews, and one narrative review. One case report was excluded because it referred to indirect restorations, and one clinical study was excluded because it was written in non-Latin script. The studies included were in English, all available in full text and mainly in PubMed (Table 1).

Table 1: Main methodological data obtained from the studies on treating radiation-related caries 

NRS: non-randomized study; SR: systematic review; NR: narrative review; GIC: glass-ionomer cement; AG: amalgam; RMGIC: resin-modified glass-ionomer cement, ART: atraumatic restorative treatment.

The oldest study was conducted in 1993 by Wood et al.¹⁴ They clinically compared VIC and AG restorations in the treatment of Class V caries in xerostomic patients with head and neck cancer. They divided the patients into fluoride users and non-fluoride users. They found that GIC failed, and AG restorations did not in patients using a slightly acidic sodium fluoride gel (pH 5.8) daily. In patients who stopped using topical fluoride as indicated, GIC restorations did not fail, but AG restorations did. The mean time to loss of restoration for both materials was 8.5 months.

In a 2002 study, Mc Comb et al.¹⁵ clinically compared GIC, RMGIC, and CR + conventional two-step adhesive system restorations to treat root caries in patients treated with radiotherapy for head and neck cancer. Each patient underwent a restoration with each of these materials. In addition, the daily use of a pH-neutral sodium fluoride gel in customized trays was indicated. Follow-up appointments were made after 6, 12, 18, and 24 months, and the restorations were examined for loss of material, marginal integrity, and recurrent caries at the restoration margin. No statistical differences were found between GIC and RMGIC, but statistical differences were found between these materials and CR in each recovery period. Reductions in recurrent caries in GIC and RMGIC restorations compared to CR were greater than 80% in patients using topical fluoride supplementation. The authors concluded that this clinical comparison provided evidence of the therapeutic efficacy of fluoride materials in reducing recurrent caries regardless of the material. They also concluded that fluoride-releasing restorative materials may offer a different clinical approach to the overall disease management of high-caries-risk patients.

In 2002, Hu et al. conducted a clinical study on 15 adult patients with radiation-related caries. They used two high-viscosity GICs in each patient to restore 146 caries lesions in exposed dentin and 93 in cementum areas. The restorations were monitored directly for two years to detect retention, secondary caries, anatomical shape, marginal integrity, marginal discoloration, and surface texture, and all patients received oral hygiene education. The authors found that placing highly viscous GIC in highcariesrisk patients seemed to prevent secondary caries, even when the restorations were subsequently lost.¹⁶

In 2003, Haveman et al. conducted a clinical study comparing RMGIC and AG restorations. They showed that fluoride-releasing materials could reduce caries around restorations in patients who do not use topical fluoride regularly.¹⁷

In 2005, Hu et al. conducted a clinical study restoring radiation-related caries at the root surface: GIC was placed in 72 conventional and 74 atraumatic restorative treatment (ART) preparations. Two professionals evaluated the restorations after 6, 12, and 24 months for retention, marginal defects and surface wear, and recurrent caries. They concluded that using hand instruments and the ART method was an equally effective alternative to conventional rotary instrumentation for cavity preparation. More extensive restorations had greater failure rates, usually due to loosening.¹⁸

In 2011, De Moor et al. evaluated the clinical performance of adhesive materials in Class V cavities in patients with head and neck cancer in terms of marginal adaptation, anatomical shape, and recurrent caries. Thirty-five adult patients with radiation-related caries with three or more root caries lesions in the same arch were selected. Each patient was treated with a restoration with GIC, RMGIC, CR + conventional 3-step adhesive system. Patients were instructed to use 1% neutral sodium fluoride gel in custom trays daily. After 6, 12, 18, and 24 months, the restorations were examined for loss of material, marginal integrity, and recurrent caries. The authors concluded that GIC is an optimal option to treat radiation-related root caries since its use is associated with protection against secondary caries (even after the loss of filling material). However, adaptation and disintegration are more marked in glass-ionomer cements than in composite resins. If glass ionomer cements fail, the defective restorative materials can be replaced, preferably preserving the remains of the glass-ionomer filling and restoring the tooth with a sandwich technique (with a composite covering the remains of the glass-ionomer cement).¹⁹

In 2015, a systematic review was published by Gupta et al. on the treatment and prevention of radiation-related caries. They state that, although this type of caries occurs for several reasons, hyposalivation remains the primary cause. Therefore, radiation-related caries can be prevented by preserving the salivary glands, or through prevention, by providing comprehensive dental care before, during, and after radiotherapy.²⁰

In 2020, Palmier et al. wrote a narrative review on current diagnostic, prognostic, and management paradigms with clinical relevance. They found that several factors, such as xerostomia and dietary changes, may influence the development of radiation-related caries. CR with fluoride application appears to be the ideal option to manage radiation-related caries.²¹The most recent study found in the literature is a systematic review and meta-analysis conducted by Palmier et al. in 2021 on the impact of head and neck radiotherapy on the longevity of adhesive restorations, which includes the studies above.^14-16,19 They concluded that head and neck radiotherapy affects the longevity of dental adhesive, and better survival rates were observed for CR restorations compared to GIC and RMGIC restorations. They also found that fluoride application showed a positive result in CR restorations and that CR restorations associated with fluoride gel applications appear to be the best method to restore Class V lesions in patients treated with head and neck radiotherapy.²²⁾

Discussion

Studies show that the direct materials used to restore radiation-related caries are AG, CR, GIC, and RMGIC.^{14-16,19,21,22} GIC has the lowest success rate. Regarding the cavity restoration technique, only one study compared the conventional technique and ART and found no differences.¹⁸

Radiotherapy may induce a reduction in enamel crystallinity and enlarged crystals, contributing to reduced enamel wear resistance.⁷ Chemical alterations in dentin can occur during radiotherapy since its chemical components reorganize, thus altering the structures. This leads to a change in the structural organization of collagen.¹³ This causes the decarboxylation of the carboxylate side bonds in collagen, and this bond is responsible for the interaction of the mineral matrix and hydroxyapatite crystals.²³ Morphologically, a disorganized dentin structure can be observed after radiotherapy using a scanning electron microscope. This can be associated with the reorganization of the collagen structure and compromises the dentin’s mechanical and adhesive properties.¹³ Performing direct restorations on patients undergoing radiotherapy is important since the literature shows that restorations can be compromised by the harmful effect of ionizing radiation on the bond strength to enamel and dentin, affecting the formation of the hybrid layer.^12,13

CR restorations with fluoride gel applications seem to be a suitable alternative to restore Class V lesions in patients who have undergone radiotherapy.²² As irradiated patients present a high risk of caries, fluoride is recommended as it can reduce recurrent caries^16,17 at defined specific concentrations and use instructions. The number of clinical studies is too small to determine the best management and protocol to follow to obtain better long-term results. Studies including CR as a restorative material did not analyze several adhesive systems.

The most analyzed failures in the studies were loss of material, marginal integrity, and recurrent caries at the restoration margin. Patient motivation, adequate plaque control, stimulation of salivary flow, and fluoride are essential to reduce the incidence of radiation-related caries.²⁰ The follow-up period of the studies was two years, so long-term clinical studies are needed. These lesions most typically appear on roots. As the lesion progresses rapidly and salivary fluid decreases, the condition can advance and affect the root.¹¹ In 2018, Velo et al. demonstrated that irradiated root dentin was less mineralized in vitro study. This could have decreased the substrate’s permeability and solubility¹¹ and consequently affected the adhesion of restorative materials.

Conclusions

Based on the literature, it is concluded that radiation-related caries is commonly restored with conventional glass-ionomer cement, resin-modified glass-ionomer cement, and composite resin with fluoride applications. More studies are needed to determine the best treatment, including cavity preparation technique and restorative material with better results. We suggest conducting studies comparing various adhesive systems, fluoride concentrations, and root dentin restorations.