Fluoride is also synthesized in laboratories. Synthesized fluoride is commonly to the things we consume such as drinking water, toothpaste, mouth washes and various other chemical products.
To wrap things up fluoride can protect teeth from being demineralized by acids produced by sugar. And when it is damaged the fluoride accumulates in the demineralized area and strengthens the enamel.
Though scientists are not absolutely sure wether tin is essential to the human body, because it is not essential to many animals ,however another psychologist belief, is tin can actually decrease depression and fatigue.