Thanks for your query, i have gone through your query. The soreness of the gums and oral mucosa could be because of the radiation therapy. you can use topical anesthetics and analgesics to reduce pain, use lip lubricants like wax, lanolin. Maintain oral hygiene, you can also take systemic analgesics for the pain. Maintain nutritional and hydration by consuming lot of liquids. the teeth have got radiation caries consult a oral physician and get the teeth filled with restorative material. You might be having reduced salivary secretion secondary to radiotherapy that might cause difficulty in maintaining oral hygiene, burning sensation. use artificial salivary substitutes like wet mouth gel. i hope my answer will help you, take care.