One of the long-term side effects of head and neck radiotherapy (RT) is radiation-induced tooth decay. Hyposalivation, associated with radiation therapy, further increases caries susceptibility and caries progression, due to the lack of salivary protective effects and of tooth minerals useful for remineralization processes, especially calcium phosphate (CaP). Dental extractions that could be required in case of severe tooth decay expose the patient to the risk of osteoradionecrosis of the jaws (i.e. the necrosis of the bone tissue following a local trauma, including surgical trauma). This protocol aims at verifying the effectiveness of CaP mousse in the prevention of carious lesions, added to topical fluoride. A randomized controlled clinical trial will be performed comparing CaP + fluoride treatment versus no treatment in head and neck cancer patients, who received radiotherapy. The hypothesis is that CaP, which is lacking in the mouth of these patients due to hyposalivation, can combine with fluoride to promote remineralization, reducing the risk of carious lesions.