PurposeThe aim of the present study was to compare the malocclusion indices KIG (Kieferorthopadische Indikationsgruppen, Orthodontic Indication Groups), ICON (Index of Complexity, Outcome and Need), and mIOTN (modified Index of Orthodontic Treatment Need) regarding differences in malocclusion prevalence and their assessment of orthodontic treatment need in German 8- to 9-year-old children of the Sixth German Oral Health Study (Deutsche Mundgesundheitsstudie, DMS 6).MethodsThe necessary data for the calculation of the KIG, mIOTN, and ICON were collected by a dentist as part of a clinical orthodontic examination during the field phase of the DMS 6 and by a subsequent digital orthodontic model-analytical evaluation of intraoral scans of the dental arches and the occlusal situation in habitual occlusion.ResultsPrevalence, severity, and treatment need of tooth and jaw misalignments differed in part considerably depending on the index used for assessment. On the other hand, there were several outcomes which yielded quite similar results for the different indices used, such as orthodontic treatment need, which ranged from 40.4% (KIG) over 41.6% (ICON) to 44.2% (mIOTN). Interestingly, orthodontic treatment need for the individual subject could differ considerably, when assessed using different indices.ConclusionsIn general, the results show that the mIOTN is much more conservative in assessing malocclusion prevalences often being smaller than those derived by KIG or ICON. In contrast, KIG and ICON often yield similar prevalences with certain distinct differences due to discrepancies in the respective definitions and also clearly differentiate between treatment possibility and arbitrarily determined treatment need.