There has been no lab test that everyone could agree upon as a being a reliable test of the effect of fluoridation on human health. From the viewpoint of a lawyer, epidemiology is used as a next best kind of evidence when laboratory tests or expert medical testimony is unavailable or is unable to answer the exact question.
Epidemiological statistics can show how a population is affected by fluoridation.
They do not prove that any one individual was harmed, benefitted or impervious to any effect at all. Chronic low level exposure to fluorides can cause a variety of symptoms which are not the same in all people. Causation can be shown, but only for each individual tested. Double blind testing for chronic fluoride intolerance has been reported by Grimbergen and others. Grimbergen's group began with 300 patients who had already self-tested and were convinced that they could tell the difference between fluoridated and unfluoridated food and water.