The two treatment regimens were: (a) placebo treatment and (b) experimental ozone treatment. Selected subjects had to have at least two teeth with similar stages of early active fissure caries. The selection of the study teeth was determined by a review of the visual examination, including the ICDAS severity score and the caries lesion activity score, conducted at the screening visit, in conjunction with the bitewing radiographs. The decision whether a tooth was to be treated with ozone or receive placebo treatment was made randomly.