## 1 Introduction  
Biomonitoring, as part of environmental dentistry, is defined as a set of activities to assess the state of the environment using biomonitors. The study of the toxic metal content forms the basis of environmental policy making, which affects the health of the human population living in a specific area. Biomonitors of toxic metal exposure in humans are so-called non-invasive matrices, which include teeth, saliva, hair, nails, or urine [1, 2]. Because of the ease of obtaining biological material in the form of deciduous teeth, there are many studies and research available that assess the toxic metal content of their structure [3, 4, 5, 6]. Teeth are a permanent record of an individual's lifestyle in a specific environment, reflecting the impact of environmental contaminants [7, 8]. In the process of teeth mineralization, toxic metal cations are incorporated into the crystalline structure of hydroxyapatite. They enter the tooth tissues via the bloodstream.  
Vitamin D3 is an offshoot of cholesterol and constitutes a part of secosterol compounds. Humans may obtain vitamin D3 from a wholesome diet; however, the greatest part is produced by organisms (\(\sim\)90%). In addition, vitamin D may reduce bone absorption by increasing gut Ca absorption and its reabsorption in the distal renal tubule. It can also affect the secretion of calcitonin (acceleration) and it reduces the proliferation of parathyroid cells, and then inhibits the synthesis and activity of PTH [9]. Vitamin D3 stimulates the co-absorption of toxic metals [10], which disrupt calcium-phosphate metabolism (Figure 1).  
On the other hand, it plays a key role in the development and mineralization of tooth germs and also participates in the formation and maturation of enamel and dentine [11].  
Extracting teeth for biomonitoring purposes is ethically unacceptable. However, the relatively high frequency of extraction procedures of completely retained third molars due to orthodontic or surgical reasons creates opportunities for their use for this purpose [12].  
The Legnica-Glogow Copper District is an urban-industrial area and a copper ore basin in the northern part of the lower Silesia Province (Poland), with an area of approximately 2200 km\({}^{2}\), inhabited by about half a million inhabitants. It is one of the largest in the world, and its development dates back to the 1960s, when deep copper deposits were first discovered there. Currently, the copper ore mining sector comprises three mines--\"Lubin\", \"Rudna\", and \"Polkowice-Sieroszowice\", supported by the \"Ore Enrichment Plant\" and the \"Hydrotechnical Plant\". In turn, the processing sector includes three steelworks--\"Legnica\", \"Glogow\", and \"Cedynia\". Copper ore tailings are stored in a huge engineering facility \"Zelazny Most\", covering an area of approximately 1400 ha [13].  
The exploitation of deposits is associated with the emission of sulfur, nitrogen, and carbon compounds into the environment, as well as dust and waste containing toxic metals [14]. The Legnica-Glogow Copper Area in Poland is a district where the risk of heavy metal contamination is increased due to the industrial profile and structure.  
There are many sources of toxic metals: polluted soil and atmosphere, contaminated food or drinking water, and cigarettes (Figure 2). Heavy metals may cause various diseases including the stomatognathic system disorders [15; 16]. To the best of our knowledge, our study is the first to assess the accumulation of toxic metals: Pb, Cd, Cr, Ni, Fe, Mn, Cu, and Zn in third molars from residents of the Legnica-Glogow Copper Area. The relationship between toxic metals and demographics, clinical data, diet, vitamin supplementation, and the concentration of vitamin D3 in the blood of patients was studied.  
Figure 1: The effects of toxic metals.