Comment: Generally correct.

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In reply to comment: Why? (see in situ)

Generally correct.

"I have wondered... and I am guessing that the bond between sodium and fluorine is much weaker than the bond between calcium and fluorine. When the bond is broken, then the highly reactive fluorine is free to cause havoc by reacting with our cells..." - Henry, DailyPaul member

This point is key to allow folks to fit the rest of this puzzling matter to suit themselves. Me restating what you wrote well enough could confuse more that help.
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Much more difficult to understand is why?:

Medical Journal Article. Excerpt of 2 pages.

How did something that is so rare in nature – fluorine – become so common in medicines? A fundamental strategy for medicinal chemists when inventing new drugs is to take a molecule, frequently from nature, and make modifications to its structure to alter its activity. Replacing hydrogen and other functional groups with fluorine can
have a dramatic effect on biological activity.

This explains why fluorine is used in medicine. It completely ignores the Hippocratic Oath: Do no harm. After the medicine is absorbed in our bodies, what becomes of the free fluorine? It latches onto something else... Most anything. The free fluorine element does perhaps more harm than the medicine's benefit.

        Do no harm. - Hippocratic Oath

Disclaimer: Mark Twain (1835-1910-To be continued) is unlicensed. His river pilot's license went delinquent in 1862. Caution advised. Daily Paul