Mental disorders such as depression, anxiety, schizophrenia, bipolar disorder and dementia increase the risk of oral and dental diseases, leading to poor hygiene, dental caries and periodontal disease. Understanding the impact of these disorders is crucial for holistic healthcare and to guide dentists in providing effective treatments. This chapter examines the relationship between psychiatric disorders, stress, eating disorders, antipsychotic medications and communication with patients. It also discusses the potential impact of depression, anxiety and schizophrenia on oral health, stress, bruxism, eating disorders and the management of side effects such as dry mouth.