Date Published: April 12, 2019
Publisher: Public Library of Science
Author(s): Izabela Świetlicka, Ewa Tomaszewska, Siemowit Muszyński, Jose Luis Valverde Piedra, Michał Świetlicki, Adam Prószyński, Krystian Cieślak, Dariusz Wiącek, Sylwia Szymańczyk, Daniel Kamiński, Kornelius Kupczik.
Alterations in the structure and mechanical properties of teeth in adult Wistar rats exposed to cadmium were investigated. Analyses were conducted on two sets of incisors from female and male specimens, that were intoxicated with cadmium (n = 12) or belonged to the control (n = 12). The cadmium group was administered with CdCl2 dissolved in drinking water with a dose of 4mg/kgbw for 10 weeks. The oral intake of cadmium by adult rats led to the range of structural changes in enamel morphology and its mechanical features. A significant increase of cadmium levels in the teeth in comparison to the control, a slight shift in the colour and reduction of pigmented enamel length, higher surface irregularity, a decrease of hydroxyapatite crystals size in the c-axis and simultaneous increase in pigmented enamel hardness were observed. The extent of these changes was sex-dependent and was more pronounced in males.
Enamel, the hardest material in the body consists on average of 95% hydroxyapatite (HA) crystals (Ca10(PO4)6(OH)2), 4% water and 1% organic matter . The organic phase is composed of proteins (amelogenins, ameloblastin, enamelin, and tuftelin) and minor concentrations of proteoglycans and lipids [2–4]. Enamel is characterised by strict hierarchical organization. Hydroxyapatite (HA) crystals, tightly packed into groups and bound together, form prisms, that along with the protein-rich interprism matter are assembled into prism bands [1, 5]. Enamel formation process (amelogenesis) is highly ordered and runs through three functional phases: pre-secretory, secretory and maturation stage [2, 3]. At each stage amelogenesis may be disturbed by environmental or developmental factors and each disturbance may translate into changes in the final structure of the tissue.
The experiment was approved by the Bioethics Commission at the University of Life Sciences in Lublin, Poland (reference number 83/2015) and was conducted in accordance with EU Directive 2010/63/EU for animal experiments. The animals were purchased from the certified Animal Husbandry in Brwinów, Warsaw, Poland.
Cadmium is a toxic metal with a biological half-life of 10–30 years. It is not degradable, and does not decay and accumulates in the organisms, where it gives rise to a number of adverse health effects, such as nephrotoxicity and bone damage [49, 50]. Long-term exposure to Cd causes toxic effects, especially in the liver and kidneys, and can change the structure of intestinal mucosa . In rats exposed to Cd reduction of bone geometrical parameters, mechanical endurance, densitometry, trabecular bone histomorphometry, as well alteration of the structure of articular and growth plate cartilages were observed [10, 13, 52]. Exposure to cadmium also impacts teeth enamel. Its action covers, among others, inhibition of proteinolysis process  and triggering crystal defects such as perforations in developing tooth enamel . Cadmium also decreases alkaline phosphatase activity and mineralization process  and causes perturbation of the vitamin D metabolic pathway, which leads to a higher caries prevalence . Such actions may cause variations in the arrangement and size of hydroxyapatite crystals and thereby alter enamel colour, structure and mechanical features [23, 26, 54, 55].