 Thermoplastic devices are used in orthodontic treatment and consists of a series of nearly invisible, removable aligners. However, every device used in the mouth can change the buccal flora and increase the number of bacterias. This is a risk factor for enamel demineralization. The treatment can vary in time of use per day. The patient under orthodontic treatment has to use the device for 22 hour each day. When the period of retention comes, it is reduced to 8 hours. The investigators want to know if the concentration of bacterias in saliva and dental plaque will increase, and if the material can cause damage on gingiva. 