Post eruptive lead incorporation into the enamel of primary teeth and its correlation with saliva and plasma - a longitudinal study

Author(s)

Soraya Cheier Dib Gonçalves

• Document type: Doctoral Thesis
• Press: Ribeirão Preto.
• Institution: Universidade de São Paulo (USP). Faculdade de Odontologia de Ribeirão Preto (PCARP/BC)
• Defense date: 2012-03-20

Examining board members

Raquel Fernanda Gerlach; Eduardo Mello de Capitani; Elimar Adriana de Oliveira Feliciano; Alexandra Mussolino de Queiroz; Márcia Andreia Mesquita Silva da Veiga

• Advisor: Raquel Fernanda Gerlach

Abstract

Environmental exposure to lead is one of the most serious contamination problems that affect public health. Even in small amounts, lead can cause neurological and biochemical changes, such as mental problems and hyperactivity. In Brazil, there is no program for the detection of children contaminated by this metal. Children are more sensitive to the deleterious effects of chronic lead exposure. Studies that proved association between environmental exposure to lead and neurological developmental problems used dentine of primary teeth as a marker of lead exposure. Studies by our group suggest that superficial enamel of deciduous teeth would be a good cumulative marker of past exposure to lead, and this tissue has considerable advantages regarding access and the perspective of development of tests for environmental monitoring of children. An important question is whether the concentrations of lead found in deciduous enamel surface vary over time in children with low exposure and if there are correlations between the concentrations of lead in the enamel surface and those of the main body fluids from which the lead was accumulated in the enamel, which are whole blood, plasma and saliva. The aims of this study was to investigate in vivo, by testing lead concentration in deciduous enamel of primary teeth, if the lead accumulated in the first micrometers of enamel increases along three years and if the concentrations of lead found in enamel surface were correlated with those found in whole blood, plasma and saliva. The initial sample consisted of 50 children aged 2 to 3 years from Ribeirão Preto, who were receiving dental care at Children\'s Clinic of the Faculty of Dentistry of Ribeirão Preto - USP and students of Nursery Carochinha (USP-Ribeirão Preto). The following samples were obtained: first stage (2009): 01 sample of whole blood and 01 sample of enamel of a central upper incisor, second stage (2010): 01 sample of whole blood, 01 sample of blood plasma, 01 sample of saliva and 01 sample of enamel from the contralateral tooth; third stage (2011): 01 sample of whole blood, 01 sample of blood plasma, 01 sample of saliva and 02 enamel samples of lateral upper incisors. Phosphorus was determined by a colorimetric method, in order to calculate the depth of enamel tests. Lead concentrations in plasma, saliva and enamel were determined by inductively coupled plasma mass spectrometry (ICPMS) and whole blood by atomic absorption spectrometer with graphite furnace. Many children or their guardians did not allow the collection of blood in any of the periods, and thus, over the three years, we had the enrollment of only 20 children. In 2009, the concentration of lead in whole blood varied from 0.2 μg / dL to 7.48 μg /dL and the median was 0.26 μg/dL. Only one child had a blood lead level 5 μg/ dL. In 2010, the concentration of lead in whole blood ranged from 0.2 μg/dL to 3.8 μg/dL and the median was 0.32 μg/dL. In 2011, the concentration of lead in blood ranged from 1.15 μg/dL to 3.55 μg/dL and the median was 0.95 μg/dL. The blood lead data do not show statistically significant differences over the years (p> 0.05). In 2010, values of lead in plasma ranged from 0.29 to 3.20 μg/L and the median was 0.49 μg/L. In 2011, lead levels in plasma ranged from 0.38 to 1.60 μg/L with median 0.52 μg/L. The lead concentration in Saliva 2010 ranged from 0.02 to 3.00μ g/L, median 0.34 μg/L. In 2011, these values ranged from 0.02 to 4.27 μg/L and the median was 0.19 μg/L. For lead concentrations in plasma and saliva, there were no statistically significant differences between groups (Saliva 2010 x Saliva 2011; Plasma 2010 x Plasma 2011)(Mann-Whitney test, p> 0.05). To analyze enamel samples, the values of lead were recalculated so they would reflect the lead found in one same depth, which was 3.4 micrometers. None of the groups (enamel from 2009, enamel from 2010 and enamel from 2011) presented normal distribution. There was no statistically significant difference between these three groups (p=0.71, Kruskal-Wallis). A correlation analysis was performed after logarithmic transformation (log10) of all values. Even after this transformation, two groups still did not exhibit normal distribution, which were Plasma 2011 & Enamel 2010. The associations that involved these two groups were tested using the Spearman correlation test, while all other associations were tested using the Pearson correlation test. The significant positive correlations found were: Whole Blood 2009 and Whole Blood 2010 (rP = 0,64; p = 0,002) ; Whole Blood 2010 and Whole Blood 2011 (rP = 0,66; p = 0,002); between Enamel 2011 and Whole Blood 2009 (rP= 0.44, p = 0.05) and between Enamel 2009 and Enamel 2010 (rS= 0.45, p= 0.03). There was an inverse association between Saliva 2010 and Enamel 2011 (rP= - 0,55; p = 0,013). Conclusion: The lead values obtained in all samples over three years characterized low exposure to lead by the group studied. Lead concentrations in blood, saliva, plasma and enamel did not vary over time. Of the 28 associations tested, the ones between Whole Blood 2009 and 2011 and between Enamel 2009 and 2010 were positive and significant. The association between Saliva 2010 and Enamel 2011 was negative and significant. The results suggest that the lead found in the enamel is correlated with past exposure to lead characterized in this study by the yearly whole blood lead data. The results further suggest that the dental enamel can be a reliable marker to assess the degree of exposure to lead of populations, since the primary teeth´s enamel surface did not incorporate lead in substantial quantities between 2 and 5 years in children with low exposure to this metal and low caries activity. (AU)