By fluorosis, I presume you mean staining.
There are many parts of the country -- in Oklahoma, Arkansas, Indiana, Illinois, etc. -- where natural fluoridation of water supplies is sufficient to create staining.
To my knowledge, this has never been considered a health problem -- outside of cosmetics. Consequently, I question WHO's position on this matter and wonder if it might be alarmist, in the same vein as the enviro position on natural arsenic levels.
The physical effect of fluoride on teeth is to harden them. Now, recalling dimly from over 30 years ago: This hardening effect is confined almost totally to the surface layer. Because of this, the fluoride is best applied by contact, as in brushing or in topical treatments, rather than ingestion. Accordingly, I don't know why there would be any particular application for fluoride in bone formation.
Nor do I believe that fluoridated water is a particularly effective means of transmitting caries resistance. Good diet and dental hygiene can do the trick without any help from the water supply.
No. Staining to the point of mottling (bright spots as well as darker zones). It is indication of stress raisers in the rest of the bones, not a good thing in a lamellar or laminar structure, probably not a big deal in cancellous bone.
I'm well aware of the West Texas stain and natural background levels of fluoride. There are natural background levels of all sorts of toxins in drinking water. That's why the arsenic levels in Bangladesh are such a problem. It's all a matter of dose.
I'm well aware of what fluoride does to teeth and agree that the best treatment is topical. Hardening isn't necessarily all that beneficial when fighting a chemical attack although it probably helps those who bruxate. It can also lead to cracking later in life.
It's a bad thing in water. The neurological damage is increasingly evident.