Introduction: Anxiety and fear are feelings routinely associated with the dental experience, especially in childhood and adolescence. These have been prominent in the world for many years and are currently considered a public health issue. Since the young population is an assiduous user of virtual inputs, it was sought to develop a mobile application (app) with the function of reducing the levels of dental anxiety in children before dental treatment and evaluate its effectiveness. Materials and Methods: An app, entitled "Hello, Dentist!", containing dental anticipation videos, was developed by a multidisciplinary team and evaluated. This app was tested in two children groups (dental and school settings), aged 6-10 years. Children and caregivers answered sociodemographic questions. In addition, to measure children's dental anxiety, they completed the Children's Fear Survey Schedule before and after app utilization. Control groups were utilized. A total of 100 children were included in this study. Results: Anxiety levels were statistically lower in the groups using the app when compared with their control groups (p < 0.05). The effectiveness in reducing anxiety was greater when the initial anxiety values were higher, as seen in the dental environment group (p = 0.029). Dental procedures previously experienced, as well as the environment (dental or school) in which children were inserted, were factors that influenced their initial anxiety levels. Conclusions: The creation and utilization of an app to reduce dental anxiety are feasible and effective. The app developed decreased children's anxiety, especially in the dental setting, by anticipating dental situation.