Irreversible hydrocolloids (IR) is a dental impression material commonly used in Brazilian and European dental practice because it is inexpensive, easy to handle, has good reproductive detail and is comfortable for the patient. This research aimed to analyze the chemical composition of eight different IRs for dental use. A sample of 0.2 g was weighed and transferred to a Teflon beaker moistened with drops of distilled or deionized water; 5 mL of nitric acid was added until total solubility of the sample; the solution was transferred to a 100 mL volumetric flask, the volume was filled with distilled or deionized water and homogenized. Thirty-five chemical elements were found: Lithium, Beryllium, Boron, Sodium, Magnesium, Aluminum, Silicon, Phosphorus, Potassium, Titanium, Manganese, Cobalt, Nickel, Vanadium, Zinc, Rubidium, Arsenic, Iron, Copper, Strontium, Yttrium, Zirconium, Niobium, Molybdenum, Ruthenium, Cadmium, Tin, Antimony, Barium, Lanthanum, Cerium, Mercury, Lead, Thorium and Uranium. Only one of the samples contained no Nickel, Antimony and Lead; and Arsenic and Uranium were found in 2 samples. This study provided evidence of high toxicity of the IR brands, pointing out the need for better quality control of this product, in order to prevent health damage in dentists, prosthesis technicians and patients.