**2. Epidemiology**

The prevalence of dental metal allergy has gradually increased over the last decade (Fig. 1). The demography of the dental metal allergy patients who visited Tokushima University Hospital is seen in Table 1. During July 2000 to June 2005, a total of 148 out of 212 patients (69.8%) exhibited a positive allergic reaction to at least one kind of the patch-test reagents. Since more than 80% of these patients were referred from dentists and dermatologists at other medical institutions, we expected to find a higher positive reaction rate as compared

Dental Metal Allergy 91

There have only been a few studies that examined healthy volunteers and the prevalence of metal allergies. Inoue used 18 types of metal reagents (Patch test allergens metal series, Tori Pharmaceutical Co., Ltd., Japan) to investigate allergic reactions in 1035 adult volunteers. Based on the International Contact Dermatitis Research Group (ICDRG) criteria, Inoue determined that 3.9% of the volunteers (male, 2.7%; female, 4.0%) exhibited positive reactions, regardless of the reagent used. Higher reaction rates were observed for metal reagents that contained HgCl2 (11.1%), SnCl2 (6.3%), CoCl2 (5.4%), and K2Cr2O7 (5.1%) (Inoue, 1993). However, since this study was reported in 1993, the estimation of the

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

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.

prevalence rate of metal allergy at present time would be expected to be higher.

Fig. 2. Positive reaction rates for all patch-test reagents.

allergic reactions (Hosoki et al., 2002, Nakayama, 2002).

**3. Pathogenic mechanism** 

to that of the other studies. Over a five-year surveillance period, nickel, palladium, chromium, cobalt and stannum exhibited the highest positive reaction rates to the patch tests in these patients. During this time period, the increases in the positive reaction rates for nickel, palladium, chromium and molybdenum were greater than those seen in our previous study (Fig. 2). (Hosoki et al., 2009)

Fig. 1. Number of patients with dental metal allergy.


Table 1. Positive patch-test rates.

Akyol et al. have reported on the results of a European standard series of patch tests performed on 1038 contacts dermatitis patients. A total of 32.3% appeared to have a positive reaction with more than one reagent, and nickel exhibited the highest positive reaction rate (17.6%) (Akyol et al., 2005). Lam et al. investigated 2585 contact dermatitis patients and found that 54.7% exhibited a positive reaction rate, with the highest result seen for nickel (24.4%). In 2008, Lam et al. confirmed these results (Lam et al., 2008). On the other hand, Khamaysi et al. reported patch-test results for 121 patients and showed there was a higher positive reaction rate for gold-sodium-thiosulphate (14.0%), nickel sulfate (13.2%), mercury (9.9%), palladium chloride (7.4%), and cobalt chloride (5.0%) (Khamaysi et al., 2006).

to that of the other studies. Over a five-year surveillance period, nickel, palladium, chromium, cobalt and stannum exhibited the highest positive reaction rates to the patch tests in these patients. During this time period, the increases in the positive reaction rates for nickel, palladium, chromium and molybdenum were greater than those seen in our

Period July 2000 to June 2005 July 1995 to June 2000 July 1987 to June 1995

148 60 41 (+2.4) (–3.2) (+0.7)

> 54 (+3.2)

19 (–0.7)

Patient number 212 114 60

Positive rate (%) 69.80 52.60 68.90

(9.9%), palladium chloride (7.4%), and cobalt chloride (5.0%) (Khamaysi et al., 2006).

Akyol et al. have reported on the results of a European standard series of patch tests performed on 1038 contacts dermatitis patients. A total of 32.3% appeared to have a positive reaction with more than one reagent, and nickel exhibited the highest positive reaction rate (17.6%) (Akyol et al., 2005). Lam et al. investigated 2585 contact dermatitis patients and found that 54.7% exhibited a positive reaction rate, with the highest result seen for nickel (24.4%). In 2008, Lam et al. confirmed these results (Lam et al., 2008). On the other hand, Khamaysi et al. reported patch-test results for 121 patients and showed there was a higher positive reaction rate for gold-sodium-thiosulphate (14.0%), nickel sulfate (13.2%), mercury

64 (–2.4)

previous study (Fig. 2). (Hosoki et al., 2009)

Fig. 1. Number of patients with dental metal allergy.

Positive

Negative

(adjusted residual)

(adjusted residual)

Table 1. Positive patch-test rates.

Fig. 2. Positive reaction rates for all patch-test reagents.

There have only been a few studies that examined healthy volunteers and the prevalence of metal allergies. Inoue used 18 types of metal reagents (Patch test allergens metal series, Tori Pharmaceutical Co., Ltd., Japan) to investigate allergic reactions in 1035 adult volunteers. Based on the International Contact Dermatitis Research Group (ICDRG) criteria, Inoue determined that 3.9% of the volunteers (male, 2.7%; female, 4.0%) exhibited positive reactions, regardless of the reagent used. Higher reaction rates were observed for metal reagents that contained HgCl2 (11.1%), SnCl2 (6.3%), CoCl2 (5.4%), and K2Cr2O7 (5.1%) (Inoue, 1993). However, since this study was reported in 1993, the estimation of the prevalence rate of metal allergy at present time would be expected to be higher.
