Does Sodium Fluoride prevent cavities?

The same mechanisms that supposedly protect teeth also cause tooth mottling.

It is quite the double-edged sword.

Reference: "The Fluoride Question, Panacea or Poison?" Page 21 ~ By Anne-Lise Gotzsche

FLUORIDATION TRIAL CONTROLS: ERRORS, OMISSIONS AND MIS-STATEMENTS

Superior dental care in Brantford: The United Kingdom Mission (1953) said:
“Brantford, however, over a period of 15 years, has provided more free dental services for children than most Canadian cities, and this has resulted in the ratio of corrected to total defects being higher than in either Sarnia or Stratford.”

It considered that in Brantford “dental care was outstandingly good.” Also, Brown, in 1952, said:

“The recordings so far obtained indicate both a higher treatment and an apparently better oral hygiene status of the Brantford children when compared with the controls, and it is therefore suggested that caution should be exercised in the interpretation of the rates shown. The lack of a pre-fluoridation survey on a comparable basis is a further limiting factor in interpreting the results.” 

Reference: http://www.fluoridationfacts.com/science/papers/sutton/sutton_1c.htm