The lost control and other mysteries: Further revelations on New Zealand's fluoridation trial

The Hastings fluoridation trial in the 1950s is listed in textbooks as an important study confirming the effectiveness of fluoridation. A paper to the 56th (1987) Congress of the Australian and New Zealand Association for the Advancement of Science co‐authored by one of us (JC) showed, from government archives obtained under the Official Information Act, that the claimed tooth decay reductions were mainly the result of local changes in diagnostic procedure in school dental clinics, which were not mentioned in published versions of the study. The experimental control town, at first described as ‘ideal’, was abandoned following the discovery that after fluoridation commenced younger children had less tooth decay in the unfluoridated control town. Proponents claimed in explanation that a previously unknown soil factor had resulted in the control town having below average tooth decay. Opponents claimed that fluoride had worsened the teeth in the fluoridated town. This paper comments on reactions to the earlier published findings, and reports some further discoveries which help to answer questions concerning the old debate over the lost control, the behavior of those concerned and some other mysteries.