There is a lack of epidemiological data on allergies to dental materials. For example, in the recently published fifth German Oral Health Study (DMS V), no information was given on any common allergies or allergies to dental materials. The aim of the present observational study was therefore to determine the frequencies and symptoms of allergies to dental materials. A public consultation hour for allergies of the oral mucosa and material incompatibilities has been integrated in the Department of Dental Prosthodontics and Materials Science in Leipzig, where clinical patient data have systematically been collected since 2012. The objective mucosal findings and the patients’ complaints are documented in detail in a specifically designed data sheet. This study included 86 subjects (83.7% women and 16.3% men) with oral symptoms of a contact allergy. The average age was 63 years (24–86). The most common allergies were to metals, of which nickel and cobalt were the most common allergens. Furthermore, many allergies were indicated to ingredients of cosmetics and composites. Allergies to components in methacrylate-containing denture resins came in at rank 5. 52.4% of the patients showed mucosal changes. Contact stomatitis (54.5%) and an oral lichenoid lesion (20.5%) were most frequently diagnosed. 86% of the patients reported subjective complaints. Pain and burning sensations in the mouth were mostly reported. Appropriate dental allergy history, clinical examination of the oral cavity for changes in the oral mucosa, analysis of specific dentures, and screening for psychogenic disorders are necessary to clarify the origin of these symptoms.