Radiation induced xerostomia would cause dental caries in:

This type of caries is known as radiation caries. Regardless of the patient's previous caries history, the development of xerostomia is inevitably followed by rampant dental decay unless stringent protective steps are taken. Cariogenesis is so greatly accelerated that frank lesions may appear within 3 months after radiotherapy. However, the ravages of dental decay in the radiated patient can be almost completely prevented with one daily application of a 1 % sodium fluoride gel containing a red, plaque-disclosing dye. This protocol was developed by Daly and Drane in 1972. The gel is applied for at least 5 minutes by means of custom fabricated flexible plastic carriers. To be maximally effective, the programme must be instituted at the beginning of radiotherapy and continued every day. Such a regimen can also arrest caries caused by xerostomia in previously unprotected patients. Because of the ever present risk of caries in xerostomic patients, only diligent, lifelong cooperation will assure prevention. Reference: Shafer’s Textbook of ORAL PATHOLOGY Eighth Edition page no 686