Oral health is an underestimated factor affecting overall human health and quality of life. Long-term enteral or parenteral nutritional treatment requires not only regular assessment of access routes, the patient’s nutritional status, and tolerance to the selected method of nutrition but also of oral health. This article discusses the connections between the influence of chewing function, salivation, and xerostomia on the health of the oral cavity of patients on long-term enteral and parenteral nutrition. In addition, the role of nurses in assessing oral health is presented as well as crucial elements of a comprehensive oral assessment in a nursing care plan. Patients receiving long-term enteral and parenteral nutrition have an increased risk of developing oral diseases. Increasing knowledge about the factors affecting oral health among nurses is crucial to provide appropriate care for patients requiring long-term nutritional treatment with omission of the natural route of food intake. Regular assessment of oral health by nurses should be an important aspect in long-term nutritional treatment recommendations.