17 subjects were tested epicutaneously with 22 materials, including Ni, Pd, Cr and Co. 5 subjects with a positive allergic skin reaction to Ni were tested with a pure metallic nickel plate 3 X 5 mm, which was attached to the buccal side of one lower premolar. These 5 subjects all developed local allergic contact stomatitis on the mucosa of the cheek adjacent to the metal plate. This was confirmed histologically. The same oral test with pure metallic palladium gave no reaction in subjects with a positive patch test. A control group gave no reactions to the metal plates. Allergic contact stomatitis was diagnosed with the help of both clinical and histological examinations.

An in vivo comparison was made between the contact allergic stomatitis‐inducing capacity of nickel, nickel‐containing dental alloys and a non‐corrosive precious metal. Fifteen patients with a positive allergic skin reaction to nickel were divided into 3 groups (A, B and C). The patients in Group A (n=4) were fitted with an intra‐oral corrosion‐resistant nickel‐chromium Alloy A; the patients of Group B (n=5) received a more corrosion prone nickel‐chromium Alloy B and in Group C (n=6) strongly corroding pure nickel was used. A corrosion‐resistant foil of pure palladium was placed on the contralateral side. Reactivity of pure nickel foil was also tested on the skin in Group C. Immunohistological examination of the oral mucosa on the test and reference sides was performed with monoclonal antibodies directed against T‐lymphocyte subsets and Langerhans cells (LC). The results showed that at the pure nickel site the LC did increase significantly in the connective tissue (approx. 4×) of the oral mucosa. However, statistical analysis of all 6 patients of Group C together showed no corresponding increase of LC in the epithelium at the site with the pure nickel, although a numerical increase of LC was noted in the epithelium adjacent to the pure nickel foil in 2 patients, which was remarkable. It can be concluded from statistical analysis that both the reference foils and the test foils can influence the number of suppressor/cytotoxic T‐lymphocytes in the connective tissue. The results showed also that pure nickel can cause a strong infiltration of helper/inducer T‐lymphocytes, especially in the connective tissue. This infiltration of T‐lymphocytes and LC was not observed on the reference sides or on the test sides with the nickel‐containing foils in Groups A and B. It could be concluded that neither clinically nor immunohistologically is the presence of high percentages of nickel in the nickel‐containing dental alloys necessarily associated with allergic contact stomatitis in nickel‐allergic patients.

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