Adolescence remains a period during which tooth decay is still very active. There are few epidemiological studies in adolescents, and the majority of them were young people aged 15 and under. Early studies have characterized the interdental periodontal microbiota in healthy adults but, to our knowledge, no studies have analyzed the caries interdental microbiota in young people between 15 and 17 years of age. The main objective of this study is to describe the interdental microbiota in adolescents by a quantitative detection system using real-time PCR methodology. It will quantify 26 major interdental pathogens. The secondary objective is to analyse the distribution of these bacteria according to the level of caries risk and salivary risk.

Fifty Caucasian adolescents were recruited for this cross sectional study.

Fifty Caucasian subjects were recruited from a pool of first-time volunteers who were referred to the Department of Public Health of the Faculty of Dentistry at the University of Montpellier, France. Written informed consent was obtained from all enrolled individuals in accordance with the Declaration of Helsinki. The study protocol was reviewed and approved by the Committee for the protection of persons (CPP) and by the National Commission of Informatics and Liberties, France.

Standardized clinical monitoring was performed 3 weeks before microbiological monitoring. The subjects were submitted to a medical/dental anamnesis, and information regarding their age, gender, and smoking status was obtained. The clinical examination was performed by trained and calibrated dentist. Clinical measurements were taken at six sites per tooth (mesio-buccal, buccal, disto-buccal, disto-lingual, lingual, and mesio-lingual) on all teeth, with the exception of the third molars, as previously described. The full-mouth clinical measurements included International Caries Detection and Assessment System (ICDAS), Caries Bleeding on interdental brushing index (BOIB), Gingival Index (GI), Plaque Index (PI) and Hygiene Index (HI), which were recorded on a dental chair, using a smooth probe, plane mirror and a surgical lamp.

Clinical assessments of the interdental spaces were performed using an IAP CURAPROX© colorimetric probe and registered the diameter of all the interproximal spaces of four pairs of teeth (premolar-molar). At the end of the examination visit, the participants were instructed to brush their teeth 3 h before the sampling visit and not to drink, eat or practice oral hygiene during this period.

In a group of 10 individuals who did not participate in this study, pairs of examinations were conducted in each individual, with a 1-h interval between them. Intraclass correlation coefficients for ICDAS, GI, PI, HI and BOIB were calculated at the site level. The intra- and inter-examiner coefficients for PI and HI ranged between 0.80 and 0.85, and between 0.75 and 0.85 for ICDAS.

For all subjects, the same four interdental sites (15-16, 25-26, 35-36, and 45-46) were assessed (total 200 sites). The appropriate prime interdental brushes were selected based on the clinical assessment of the interdental spaces.

With an alpha error of 5%, a power of 80%, an intraclass correlation coefficient of 0.8, a mean difference of bacteria counts between the 2 caries risk groups of 1,300,000, a total of 200 sites (which means 50 subjects) will be necessary.

Qualitative variables will be described by frequencies or percentages and quantitative variables by means and standard deviations. A Shapiro-Wilks test will be used to test the normality of the data. The comparison between the 2 caries risk groups will be achieved by a McNemar test for the qualitative variables and a Student test or a paired Wilcoxon test for the quantitative variables, depending on the normality of these variables.

The "clinical" questionnaire data completed by the dentist will be captured on a paper form provided at the beginning of the study. The forms thus recovered will be entered using a software to form the database. Paper forms will be archived with the study documents.

The bacteriological data obtained will be returned with the T envelope to the scientific manager and registered in the software.

The database created with the answers of "clinical" questionnaires and the results of the bacteriological analysis will be identified by order number and no surname data will be recorded on the electronic file thus created. At the end of the study, a report with the statistical tables and conclusions will be published for analysis and discussion of the data by the scientific committee and the project managers. Scientific publications will be written. The data is the property of the administrative manager of the study, no personal data will be released. Apart from the report and scientific publications, no data sharing is planned.

Inclusion Criteria:

• presence of teeth 15-16-25-26-35-36-45-46
• At least of 22 teeth
• Good understanding of the French language
• One of the parents accepts the terms of the study and signs the written informed consent
• In good general health, without clinical abnormality and medical history
• Periodontal pocket greater than or equal to 3mm at interdental sites 15-16, 25-26, 35-36, 45-46

Exclusion Criteria:

• Smoking patient
• Patient with pathologies, orthodontic appliance
• Patient having taken antibiotics in the last 3 months
• Patient regularly using interdental brushes and / or dental floss and / or mouthwash
• Patient at risk for infectious endocarditis
• Patient unable to answer questions, non-cooperative