Oxygen is an ubiquitous element and an important substance for life on earth especially for human life and it can both be beneficial and harmful to life. High and soaring concentration of oxygen are found to be toxic, and can damage tissues. When cells use oxygen to generate energy in the form of ATP in the mitochondria, free radicals are created. Excessive free radicals formation that is not counteracted by the removal, creates 'oxidation stress' which is associated with various oral and systemic destructive diseases. Dental treatment with the use of composites, amalgams, glass-ionomers,...