PreOrtho is a functional device for pre-orthodontic treatment. Orthodontic treatment consists of 2 stages for orthodontics depending on the age group. This device can be used for preventive treatment on mixed dentition, and it is available to improve occlusion, chewing, nasal breathing, open mouth habit, speech impediment, and swallowing. In order to complete the effectiveness of orthodontic treatment, we recommend following the proper procedure from phase I orthodontic treatment with PreOrtho to phase II orthodontic treatment with a fixed appliance like braces.