Urinary levels of nickel and chromium associated with dental restoration by nickel-chromium based alloys

Abstract

This paper aims to investigate if the dental restoration of nickel-chromium based alloy (Ni-Cr) leads to the enhanced excretions of Ni and Cr in urine. Seven hundred and ninety-five patients in a dental hospital had single or multiple Ni-Cr alloy restoration recently and 198 controls were recruited to collect information on dental restoration by questionnaire and clinical examination. Urinary concentrations of Ni and Cr from each subject were measure by graphite furnace atomic absorption spectrometry. Compared to the control group, the urinary level of Ni was significantly higher in the patient group of <1 month of the restoration duration, among which higher Ni excretions were found in those with either a higher number of teeth replaced by dental alloys or a higher index of metal crown not covered with the porcelain. Urinary levels of Cr were significantly higher in the three patient groups of <1, 1 to <3 and 3 to <6 months, especially in those with a higher metal crown exposure index. Linear curve estimations showed better relationships between urinary Ni and Cr in patients within 6-month groups. Our data suggested significant increased excretions of urinary Ni and Cr after dental restoration. Potential short- and long-term effects of Ni-Cr alloy restoration need to be investigated.

Figure 1

Urinary levels of Ni and Cr in association with the duration of Ni–Cr alloy restoration. Data were shown as geometric mean and 25%–75% interquartile range. Cr, chromium; Ni, nickel.

Figure 2

Urinary levels of Ni and Cr in association with the number of teeth replaced by Ni–Cr alloys and the index of metal crown not covered with the porcelain. Ni excretions in urine were only analyzed in the patient group of <1 month of the restoration duration (n=205), and Cr excretions only in the pooled patient group of <6 months of restoration duration (n=463). Data were shown as geometric mean and 25%–75% interquartile range. Cr, chromium; Ni, nickel.

Figure 3

Association between ln-transformed urinary concentrations of Ni and Cr. In the subjects <1 month, which had the highest R square (R²) of 0.101 and the most significant of P value (P<0.001). The urinary Ni-Cr associations in the subjects from other duration groups had much lower values of R² (R² = 0.064, 0.065, 0.024, <0.001, for the duration group of 1 to <3, 3 to <6, 6 to <12, and ≥12, respectively). Cr, chromium; Ni, nickel.