Minimally invasive dentistry holds an important place in the treatment of caries lesion. Introduction of laser fluorescence as a diagnostic and ozone as a therapeutic means finds more frequent usage in both preventive and curative dentistry. DIAGNOdent device (KaVo, Germany) is based on laser fluorescence which enables early diagnosis as well as monitoring the development of caries lesion while use of ozone with HealOzone device (KaVo, Germany) provides painless treatment. Even though there are number of indications for use of ozone in dentistry, most important is therapy of caries lesions. Purpose of this investigation was to observe the effect of ozone applied via HealOzone device on the total of 70 primary fissure lesions previously detected with DIAGNOdent device and to determine whether there is a decrease in lesion demineralization values between first visit, first and second recall after one and two month period. Results showed statistically significant difference in demineralization values recorded on DIAGNOdent scale between first visit and every repeated recall (p<0,001).