Dental materials can elicit various types of hypersensitivity reactions, but the most common material associated with delayed-type hypersensitivity (Type IV hypersensitivity) is nickel-containing alloys.

- Delayed-type hypersensitivity reactions are mediated by T-lymphocytes and typically manifest hours to days after exposure to the allergen.
- Nickel, a component frequently found in dental alloys used for crowns, bridges, and orthodontic appliances, is a well-known hapten that can bind to proteins in the oral mucosa, triggering a cell-mediated immune response.
- Patients sensitized to nickel may develop contact stomatitis, mucositis, or lichenoid reactions after prolonged contact with nickel-containing dental restorations.
- In contrast, mercury-containing amalgam primarily induces local irritation or allergic responses but is less commonly involved in Type IV hypersensitivity.
- Zinc phosphate cement and glass ionomer cement rarely cause hypersensitivity reactions and are not typically linked to delayed-type hypersensitivity.

Key points:
- Nickel-containing alloys are the most common cause of delayed-type (Type IV) hypersensitivity reactions in dental materials.
- Symptoms usually appear hours to days following exposure, presenting as mucosal inflammation.
- Awareness of nickel allergy is important when selecting materials for patients with a history of metal hypersensitivity.

Reference: Sturdevant's Art and Science of Operative Dentistry, Volume 2, Chapter on Dental Materials / Page 345