Effect of mercury (Hg) dental amalgam fillings on renal and oxidative stress biomarkers in children.

We examined the effect of mercury (Hg) associated with dental amalgam fillings on biomarkers of renal and oxidative stress in children between the ages of 5-15.5 years. Urine samples were analyzed for N-acetyl-ß-D-glucosaminidase (NAG), α(1)-microglobulin (α(1)-MG), ß(2)-microglobulin (ß(2)-MG), retinol binding protein (RBP), albumin (ALB), 8-hydroxy-2-deoxyguanosine (8-OHdG) and malondialdehyde (MDA). The level of urinary Hg (UHg-C) was calculated as µg/g creatinine. Multiple regression analyses revealed that the excretion of urinary NAG was significantly associated with the presence of dental amalgam fillings (ß=0.149, P=0.03) and the levels of UHg-C (ß=0.531, P=0), with an interaction between the two (P=0). The increase in urinary NAG in relation to UHg-C levels had a dose-effect pattern. The lowest observed effect was seen at UHg-C levels above 1.452 µg/g creatinine, which is lower than previously reported. In contrast, α(1)-MG was negatively associated with the presence of dental amalgam fillings (ß=-0.270, P=0), but positively with UHg-C levels (ß=0.393, P=0). There were 7 children without, and one child with, dental amalgam fillings with urinary α(1)-MG levels above the reference limit of >7 mg/g creatinine. Even though α(1)-MG seems to be a reliable biomarker for early changes in renal functions, it might exert its effect only at a higher level of exposure. An inverse relationship was also observed between urinary 8-OHdG levels and the presence of dental amalgam fillings. This might suggest that the dental amalgam does not increase DNA damage but reduces the capacity to repair DNA, leading to lower urinary excretion of 8-OHdG. On the other hand, we found that Hg affected the excretion of urinary 8-OHdG in a dose-related pattern that was mostly associated with long-term exposure to low Hg levels. Urinary NAG levels were positively associated with urinary MDA levels (ß=0.516, P=0) but not with 8-OHdG (ß=0.134, P=0.078) after adjustment for potential confounders. Both UHg-C and the presence of dental amalgam fillings remained predictors of the NAG model. Our data provide evidence that low exposure to Hg from dental amalgam fillings exerts an effect on kidney tubular functions in children. Oxidative stress may have played a role in this mechanism. The results of this study would also suggest that urinary NAG is the most sensitive of all the investigated renal biomarkers. These results should be confirmed with further investigation.

Mercury (Hg) burden in children: the impact of dental amalgam.

The risks and benefits of using mercury (Hg) in dental amalgam have long been debated. This study was designed to estimate Hg body burden and its association with dental amalgam fillings in 182 children (ages: 5-15 years) living in Taif City. Hg was measured in urine (UHg), hair (HHg) and toenails (NHg) by the Atomic Absorption Spectrophotometer with Vapor Generator Accessory system. Urinary Hg levels were calculated as both micrograms per gram creatinine (µg/g creatinine) and micrograms per liter (µg/L). We found that children with amalgam fillings (N=106) had significantly higher UHg-C levels than children without (N=76), with means of 3.763 µg/g creatinine versus 3.457 µg/g creatinine, respectively (P=0.019). The results were similar for UHg (P=0.01). A similar pattern was also seen for HHg, with means of 0.614 µg/g (N=97) for children with amalgam versus 0.242 µg/g (N=74) for those without amalgam fillings (P=0). Although the mean NHg was higher in children without amalgam (0.222 µg/g, N=61) versus those with (0.163 µg/g, N=101), the relationship was not significant (P=0.069). After adjusting for many confounders, the multiple logistic regression model revealed that the levels of UHg-C and HHg were 2.047 and 5.396 times higher, respectively, in children with dental amalgam compared to those without (P<0.01). In contrast, a significant inverse relationship was seen between NHg levels and dental amalgam fillings (P=0.003). Despite the controversy surrounding the health impact of dental amalgam, this study showed some evidence that amalgam-associated Hg exposure might be related with symptoms of oral health, such as aphthous ulcer, white patches, and a burning-mouth sensation. Further studies are needed to reproduce these findings. The present study showed that significant numbers of children with or without amalgam had Hg levels exceeding the acceptable reference limits. The detrimental neurobehavioral and/or nephrotoxic effects of such an increased Hg on children should be a cause of concern, and further investigation is warranted. Our results are alarming and indicate an urgent need for biomonitoring and assessment of exposure. Changes in dental practices involving amalgam, especially for children, are highly recommended in order to avoid unnecessary exposure to Hg.