## 4 Discussion
This differs from the clinical situation of radiotherapy, where the teeth do not necessarily remain in the radiation field, depending on the location of the tumor. Today, a technique called intensity-modulated radiation therapy (IMRT) is established; in this method, the direction of radiation changes continuously, with the result that the main target keeps receiving the entire amount of radiation required for the therapy, but the surrounding tissue exposed to the radiation varies, thereby limiting the radiation dose in this area [55; 56]. As a result, it is assumed that the effects of irradiation on the bond with dentin found in this study appear to be even milder in the clinical situation, especially when treated with IMRT. In this study, we solely simulated the clinical situation in which resin fillings were applied post radiotherapy. No consideration was given to the scenario where a patient might have fillings in some teeth before radiotherapy starts. If an existing dental restoration was irradiated, this could possibly have different effects on the bond strength, as [PERSON] et al. [57] have ascertained in a previous study, or on the long-term durability of the restoration. This should therefore be investigated further, particularly in regard to the recommendation to rehabilitate patients' dentition before radiotherapy [6]. Various studies have been published in the dental literature describing direct irradiation impacts on human tissue, and dentin in particular. The results of these studies include decreased microhardness [13; 40] and micro-morphological damage, such as obliterated dentinal tubules [13; 57; 58; 59], collagen network impairment and ruptures in the dentin structure [13; 59]. These effects may explain a deterioration of the adhesive bond strength to the dentin, which was partly determined in our present study but also in a recently published study by [PERSON] et al. [57]. These findings, in combination with the observations that irradiation causes the dentin-noenamel junction (DEJ) to appear unstable [58; 59; 60; 61] and affects enamel damage [14; 59; 62; 63], are possibly some of several factors that all together promote the development of atypical radiation-related caries. Other effective aspects include hyposvalivation, poor oral hygiene and altered microbial oral flora [64; 65]. Some of the points mentioned concerning damage to the dental hard tissue caused by irradiation are still being discussed controversially, as there are also studies that refute certain aspects of them [62; 66; 67]. Still, it cannot be denied that patients have an increased risk of caries post radiotherapy [6; 68; 69] and thus there is a major necessity for dental restorations. Nevertheless, there is no consensus on which is the preferred material for conservative caries therapy in patients having undergone head and neck radiation therapy. The Oral Care Study Group of the Multinational Association of Supportive Care in Cancer and the International Society of Oral Oncology (MASCC/ISOO) published the clinical guideline 'Evidence-Based Management Strategies for Oral Complication from Cancer Treatment' in 2011 [70], recommending the use of resin-modified glass ionomer cement (GIC), composite resin or amalgam for restorations in post head and neck radiation patients, and so do [PERSON] et al. [69] for patients who use fluoride. Conventional GIC restorations are recommended for patients who do not use fluoride; although they need to be replaced more frequently due to their failure rate, they might be more effective in preventing secondary caries than composite resin restorations [21; 23; 69], due to the fluoride-releasing [71; 72] and cariostatic properties [73; 74; 75]. However, in those patients who follow the general recommendations for fluoride application after head and neck irradiation [6; 69; 76], composite resin restorations may be advantageous because they have a longer survival rate compared to GIC [77] and superior durability and erosion resistance in patients with fluoride compliance [22].