The basic treatment of oncological patients is administered by using radiotherapy, chemotherapy, surgery and a combination of these methods. All patients should undergo a dental examination at least three weeks prior to oncological treatment. It is necessary to treat oral diseases that may be exacerbated during therapy and prevent oral complications and discomfort so as not to interrupt oncological treatment. Poor oral mucositis control is one of the leading causes of unplanned termination of malignant process treatment. To reduce the risk of complications the hard supragingival and subgingival dental plaque is removed and the teeth are protected by fluoridation. If needed, tooth extractions should be performed with antibiotic protection and minimal trauma. It is necessary to smooth the bone on the edges of the wound to avoid irritation and ensure the primary healing. Acute complications of head and neck radiotherapy include: oral mucositis, xerostomia, secondary infections, dysgeusia, insufficient nutrition. Chronic complications of radiotherapy occur several weeks to several years after radiation. These include: xerostomia, radiation-related caries, teleangiectasia, muscle fibrosis with trizmus, reduction of vascularization, soft tissue necrosis, osteoradionecrosis, dentofacial malformation, insufficient nutrition, tooth sensitivity, pulp pain and necrosis. Chemotherapy complications include: mucositis, electrolyte imbalance, nausea, vomiting, bleeding, oral infections, photosensitivity, central nervous system dysfunction, alopecia, insufficient nutrition. Xerostomia is one of the factors that causes accelerated development of radiation-related caries and increases the risk of mucosal infection. Osteonecrosis is an aseptic ischemic necrosis of the bones which occurs in patients receiving head and neck radiation therapy and in patients taking bisphosphonates. Radiated patients are permanently endangered by osteoradionecrosis.