The aim of this study is to evaluate the clinical use of the smartphone application "Ortodontika" for the compliance of orthodontic patients with Rapid Maxillary Expander (RME).

Patients and parents consenting to participate in the study will sign the informed consent for their child. At the baseline (T0), a periodontal examination will be carried out by means of a probe assessing Bleeding Index, Plaque Index and Modified Gingival Index on upper first incisors, first premolars/first primary molars and first molars. A professional oral hygiene will be performed using a piezoelectric instrument and a manual scaler. A RME will be cemented with a glass ionomer cement on the maxillary first molars and will be activated by parents on clinicians' instructions. Patients will receive an oral hygiene kit containing toothpaste, soft-bristled toothbrush, single tufted brush and interdental brushes (0.6 and 0.9 mm). Orthodontic wax and 1% chlorhexidine will be given for emergencies. At this point, patients will be divided into two groups:

• Control group: verbal instructions on the correct activation of the RME and on its cleaning will be given to parents at each visit, together with verbal instructions on the correct daily practices for oral hygiene;
• Trial group: use of "Ortodontika" smartphone application as adjunct to verbal instructions on the correct activation of the RME to be performed by one parent, through a daily notification until T1 (end of activations); parents have to supervise daily oral hygiene of RME and the correct daily practices for oral hygiene. A notification will be sent every 2 weeks until the end of the study to remind patients to watch the videos on oral hygiene maneuverers.

Patients will be visited at the end the activations (T1), after 1.5 months (T2), after 3 (T3) and 6 months (T6). At the recall, the periodontal indices will be evaluated again. At each recall, extra products will be given for home oral hygiene Patients and parents from the Control group will receive a questionnaire to evaluate awareness of orthodontic therapy (aims and phases) and knowledge of oral hygiene maneuverers. Patients and parents from the Trial group will receive an extra questionnaire about Ortodontika application. During the study, the number of emergencies will be recorded.

The aim of this study is to evaluate the clinical use of the smartphone application "Ortodontika" for the compliance of orthodontic patients with Rapid Maxillary Expander (RME).

Patients and parents consenting to participate in the study will sign the informed consent for their child. At the baseline (T0), a periodontal examination will be carried out by means of a probe (UNC probe 15; Hu-Friedy, Chicago, IL, USA) assessing Bleeding Index, Plaque Index and Modified Gingival Index on upper first incisors, first premolars/first primary molars and first molars. A professional oral hygiene will be performed using a piezoelectric instrument (Multipiezo, Mectron S.p.a, Carasco, Italy) and a manual scaler (LM23, LM-Dental, Pargas, Finland). A RME will be cemented with a glass ionomer cement (3M Multi-Cure, 3M Unitek, Monrovia, CA, USA) on the maxillary first molars and will be activated by parents on clinicians' instructions. Patients will receive an oral hygiene kit containing toothpaste (GUM Junior 7+, Sunstar Deutschland GmbH, Schonau, Germany), soft-bristled toothbrush (GUM Technique PRO toothbrush), interdental brush 0.6 and 0.8 mm of diameter (GUM TRAV-LER) and a single tufted brush (GUM End-Tuft). Orthodontic wax will be given for emergencies related to RME (GUM ORTHO wax) and 1% chlorhexidine gel (Curasept Periodontal gel, Curasept S.p.A, Saronno, VA, Italy) will be given for gingival inflammation. At this point, patients will be divided into two groups:

• Control group: verbal instructions on the correct activation of the RME and on its cleaning will be given to parents at each visit, together with verbal instructions on the correct daily practices for oral hygiene;
• Trial group: use of "Ortodontika" smartphone application as adjunct to verbal instructions on the correct activation of the RME to be performed by one parent, through a daily notification until T1 (end of activations); parents will have to supervise daily oral hygiene of RME and the correct daily practices for oral hygiene. A notification will be sent every 2 weeks until the end of the study to remind patients to watch the videos on oral hygiene maneuverers.

Patients will be visited at the end of the activations (T1), after 1.5 months (T2), after 3 (T3) and 6 months (T6). At the recall, the periodontal indices will be evaluated and a questionnaire will be given to patients. At each recall, extra products will be given for home oral hygiene. During the study, the number of emergencies will be recorded: RME decementation, patients perceiving pain related to plaque accumulation, mucosal ulcerations due to vestibular tubes, parents that do not understand how to perform RME activations, patients asking the clinician to perform RME activations chairside. A questionnaire will be given to patients and parents belonging to both groups to evaluate awareness of orthodontic therapy aims and phases, knowledge of oral hygiene maneuverers. A questionnaire about Ortodontika application usefulness will be given only to patients and parents belonging to Trial group.

Inclusion Criteria:

• patients and their parents are able or willing to give informed consent;
• patients who will begin orthopedic treatment with RME cemented on first maxillary molars and with welded vestibular tubes;
• patients undergone no previous orthopedic/orthodontic treatment;
• parents' willing to download and use Ortodontika application;
• parents possessing an Apple or Android smartphone with iOS ≥ 10.0 or Android ≥ 4.4 versions;
• smartphone provided with an internet connection.

Exclusion Criteria:

• no sectional wire appliances in the upper arches;
• no need of additional orthopedic/orthodontic appliances, also in the lower arch;
• no vestibular welded protraction hooks on RME;
• patients taking regular medications for systemic diseases that could alter periodontal conditions and pain perception (antibiotics, antibacterial mouth rinses, NSAIDS, steroids);
• siblings with previous orthopedic treatment with RME;
• parents and patients with low compliance.

Data will be available upon motivated request to the corresponding author.