Purpose: To test the effectiveness of yogurt extract as an agent to protect tooth enamel from demineralisation in vitro. Materials and Methods: The crowns of 80 intact caries-free human premolars were selected, and standardised 5 x 3 mm2 enamel windows were isolated on the buccal and lingual surface of each tooth. The baseline weight of each specimen was recorded. Four demineralising solutions were prepared: S1: lactic acid (LA) at pH 4.8; S2: LA at pH 3.97; S3: LA + yogurt supernatant (YS) at pH 4.8; S4: LA + YS at pH 3.97. The calcium content of each solution was determined using compleximetric titration with Eriochrome black-T. The 80 teeth were randomly divided into 4 groups. Each group was incubated in its corresponding solution at 37°C for 96 h. The specimens were weighed again and the calcium content of the four solutions determined. Five samples from each group were randomly chosen, sectioned through the treatment windows, stained with rhodamine-B and viewed under a confocal laser scanning microscope (CLSM). Lesion area (LeA) and average fluorescence (AF) were calculated using Image J software. Total fluorescence (TF) values were obtained by LeA x AF. Results: There was a statistically significant difference between groups in terms of LeA and TF. No statistically significant difference was found between groups in terms of difference in weight. Conclusion: Probiotic yogurt extract is effective in reducing demineralisation of enamel under experimental conditions. Parole chiave: confocal laser scanning microscopy, demineralisation, probiotic yogurt, remineralisation