Good bacteria vs. bad breath: probiotics show promise for brace wearers

Copied word for word from the study's registry entry, so the wording is the study team's rather than ours.

Inclusion Criteria: * Patients eligible for the trial must comply with all of the following at randomization: * Age between 12 and 18 years for the group with conventional orthodontic appliances This age group represents the majority of patients seeking orthodontic treatment and is homogeneous regarding occupational status (high-school and lyceum students in Greece). Younger patients might present with cooperation problems. Age ≥18 for the Invisalign™ group This age group represents the majority of patients seeking orthodontic with aligners (Invisalign™) regarding social status and other factors. * Good general health * Fixed orthodontic appliances Patients should have fixed labial appliances (brackets) on all teeth from central incisor to first molar, in both the maxillary and the mandibular arch. Fixed appliances should have been placed at least two months before the patient is accepted into the study and remaining treatment should be at least 3 months. All brackets will be the same (metallic, conventional/not self-ligating, same size). Molars should be banded (same bands on all molars) and all other teeth bonded. * At least 20 natural teeth (in case of extraction orthodontic treatment patients can be enrolled two months after extractions) The outcomes will be evaluated at all teeth from first molar to first molar. Exclusion Criteria: * Patients will be excluded for any of the following reasons: * Active caries * Periodontitis * Syndromes, mental disabilities and craniofacial deformities * Smoking or use of other tobacco products * Dental fluorosis/tooth malformation * Antibiotics during the last 2 months * chlorhexidine in the previous 3 week * Suffering from any disease within 2 months before measurements * Allergy to dairy products * Participation in other trials Consent / assent Parents/guardians and patients will provide written informed consent and patients will provide written assent before randomization and before any procedures are applied.