**3. Pathogenic mechanism**

In general, the pathogenic mechanism for metal allergy has been classified as a type IV allergic reaction, which is the same as that for ordinal contact dermatitis (Fisher, 1973). In some cases it has been reported that removal of intraoral dental material containing allergypositive metal elements relieves atopic dermatitis and asthma symptoms. Thus, this indicates that metal allergies may contain an aspect of the pathogenic mechanism for type I allergic reactions (Hosoki et al., 2002, Nakayama, 2002).

Under normal conditions, chemically stable metallic material rarely causes allergic symptoms. In the human body, the metallic ion itself cannot act as an allergen. However, if an electron from the external shell of a metallic item is removed, then the ionized metal element can be released within the human body. In such cases, these metal elements can bind to protein and form a hapten, which is then recognized by T-cells, and thus, ultimately leads to an allergic reaction (Davies et al., 1977, Ishii et al., 1990). Therefore, the tendency for ionization can be very influential with regard to the creation of an allergic reaction. If this potential ionization of a metal element can be prevented, the risk of metal allergy can be decreased. Unfortunately, intraoral circumstances, such as large amounts of electrolytic solutions, i.e. saliva, always surround metallic restorations and thus, the pH of a solution can rapidly fluctuate in line with the type of diet followed. Overall, this increases the difficulty in preventing changes of the dental metal material that can initiate allergies.

Dental Metal Allergy 93

In these patients, erythema, blisters with pustules, scale and crust typically appear on the palm and plantar (Fig. 3). In addition, sterile pustules are sometimes accompanied by itch, heat and painful sensations, and on occasion, osteoarthritis may also be found. Osteoarthritis symptoms involve the trunk, peripheral nerves, and the extra-articular region, and frequently there is local swelling, tenderness, heat sensation, and flare noted in these patients. During the early stages, histological findings show there is lymphocyte infiltration into the epidermis along with spongy degeneration. After formation of blisters and at the point where the blister reaches the horny cell layer, neutrophils appear and pustule development begins. At the present time, detailed pathoetiology of these symptoms has yet to be reported. Focal infection of the chronic inflammation from the palatine tonsil, marginal and periapical periodontitis, and metal allergy are all suspected as being predisposing

(a) Pustulosis Palmaris (b) Pustulosis Palmaris

(c) Pustulosis Palmaris (crooked nails) (d) Pustulosis Plantaris

Chronic inflammatory disease can include dyskeratosis of the skin, oral and external genitalia mucosa. When it appears on the oral mucosa, lace or stitch pattern keratinizations

Fig. 3. Pustulosis palmaris et plantaris and dyshidrotic eczema.

**4.3 Lichen planus** 

**4.2 Pustulosis palmaris et plantaris, and dyshidrotic eczema** 

factors.
