Early childhood caries is often found under the name connected with the manner of feeding nutrition of children such as “Baby bottle Syndrome” or “Baby bottle caries”. The aim of the study was to determine ultrastructural changes in the enamel of primary teeth in starting phases of early childhood caries, with and without local fluoride therapy, because it has of great influence in the preventive aspect of the disease. The investigation was done on laboratory tests on tree groups extracted primary teeth: one of 20 healthy mandibular incisors, as control group and two more groups of primary tested teeth: 10 maxillary incisors with initial lesion and 10 maxillary incisors with superficial form. The all dental samples were observed with Scanning Electron Microscope (SEM) and we made comparative analyzes in ultrastructural changes of enamel between untreated and treated teeth, and control group teeth. After that, we have analysis with SEM photo attachments. In some dental samples with initial lesion after local treatmant we managed to get almost healthy enamel, i.e. complete remineralization process. Once again, we have confirmation of one of the many benefits of fluoride in dentistry which is long been known.