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Multicenter Study
. 2025 Jan 28;25(1):149.
doi: 10.1186/s12903-025-05454-z.

Dental and oral health assessments in the German National Cohort (NAKO)

Stefanie Samietz #  1 , Katrin Borof #  2 , Katrin Hertrampf  3 , Ghazal Aarabi  2 , Antonio Ciardo  4 , Hannah Finke  5 , Daniel Hagenfeld  6 , Jan Kühnisch  7 , Maurice Rütters  4 , Sebastian-Edgar Baumeister  8 , Stefan Lars Reckelkamm  6   8 , Ti-Sun Kim  4 , Thomas Kocher  9 , Wolfgang Ahrens  10 , Hermann Brenner  11 , Carina Emmel  12 , Beate Fischer  13 , Amand Führer  14 , Karin Halina Greiser  15 , Jasmin Grischke  16 , Kathrin Günther  10 , Volker Harth  17 , Stefanie Jaskulski  18 , André Karch  19 , Thomas Keil  20   21   22 , Yvonne Kemmling  23 , Alexander Kluttig  14 , Lilian Krist  20 , Oliver Kuss  24 , Michael Leitzmann  13 , Claudia Meinke-Franze  25 , Karin B Michels  18 , Nadia Obi  17 , Anette Peters  26   27 , Nicole Pischon  28   29   30 , Tobias Pischon  28   29   31 , Sabine Schipf  25 , Börge Schmidt  12 , Henning Teismann  19 , Stefan Rupf #  32 , Birte Holtfreter #  9
Affiliations
Multicenter Study

Dental and oral health assessments in the German National Cohort (NAKO)

Stefanie Samietz et al. BMC Oral Health. .

Abstract

Background: Despite considerable improvements in oral health in recent decades, caries and periodontitis are still widespread, ranking among the most prevalent diseases worldwide and requiring future research. The German National Cohort (NAKO Gesundheitsstudie, NAKO) is a large-scaled, multidisciplinary, nationwide, multi-centre, population-based, prospective cohort study with oral examinations that aims to provide a resource to study risk factors for major diseases. The aim of the present article is to provide the methodological background, to report on the data quality, and to present initial results of the oral examinations.

Methods: During baseline examinations (2014-2019), a total of 205,184 persons aged 19-74 years has been examined in 18 study centres, including, among others, a dental interview, stimulated saliva sampling, and recording of the numbers of present teeth and prostheses (standard Level 1 program). As part of the Level 2 program that was offered to 20% randomly selected participants, each study centre selected one of three modules, one of them being the Level 2 oral examination. This extended program was carried out in a subgroup of 20,828 participants, including collection of detailed information on the dental and prosthetic status as well as on periodontal, cariological and functional aspects. To ensure reliability and reproducibility, study nurses were trained and calibrated by dental experts. In addition, a reliability study was conducted among 794 Level 1 and 359 Level 2 participants, reporting intra class correlation and kappa coefficients.

Results: Intra class correlation and kappa coefficients for observer agreement and reliability were consistently above 0.7, indicating good to excellent reliability of all dental measurements. For example, intra class correlation was 0.937 for the number of present teeth (Level 1), 0.740 for mean probing depth (PD) and 0.797 for active mouth opening. An initial inspection of the data showed that the median number of present teeth was 27, of which on average 6.9 teeth were healthy and caries-free. Average mean PD was 1.92 mm. An orthodontic treatment was reported by 35.5% of participants.

Discussion: Overall, the dental study protocol was feasible and successfully integrated into the NAKO's overall assessment program. However, rigorous support of the study centres by dental professionals was required to ensure high quality data. In summary, high-quality data collection within the NAKO pave the way for future investigation of potential risk factors for oral diseases and links between oral and systemic diseases and conditions.

Keywords: Caries; Cohort study; Cross-sectional; Dental status; Epidemiology; Oral health; Periodontitis; Temporomandibular disorders.

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Conflict of interest statement

Declarations. Ethics approval and consent to participate: All procedures performed involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and is in accordance with national law and with the Declaration of Helsinki of 1975 (in the current, revised version). The research protocol was approved by the Ethics Committee of the Medical Faculty of the Ludwig-Maximilians-University of Munich / Bayerische Landesärztekammer; Nr. 13023) and all other local Ethics Committees of the study centres. Written informed consent was obtained from all individual participants included in the study. Consent for publication: Not applicable. Competing interests: The authors declare no competing interests.

Figures

Fig. 1
Fig. 1
Flowchart for the Level 1 dental interview and oral examination data
Fig. 2
Fig. 2
Flowchart for the Level 2 examination (dental/prosthetic status, orthodontics, palpation, and probing depths)
Fig. 3
Fig. 3
Study centre margins (blue) for A) full-mouth tooth counts (including third molars; Level 1), B) mean probing depth (PD), C) the Decayed-Filled-Teeth (DFT) Score and D) the active mouth opening distance (Level 2) after adjustment for age and sex using statistical models. Marginal distributions (using box plots combined with violin plots, or count plots) are additionally shown. Also, the overall mean (red solid line) and the deviation from the mean (± 1 standard deviation; red dashed lines) are displayed. In case of oddities the marginal mean is displayed in red
Fig. 4
Fig. 4
LOESS-smoothed curves for each study centre for full-mouth tooth counts (including third molars; Level 1) after adjustment for age and sex using statistical models
Fig. 5
Fig. 5
LOESS-smoothed curves for each study centre for A) mean probing depth (PD), B) the Decayed-Filled-Teeth (DFT) Score and C) the active mouth opening distance (Level 2) after adjustment for age and sex using statistical models. The red dashed lines represent the confidence interval of a LOESS curve for the whole data
See this image and copyright information in PMC

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