Introduction to multilevel modelling in dental research

Objective To explain the concepts and application of multilevel modelling ( MLM) and how it can be applied to the analysis of dental research data. Bas ic design Methodological in nature, this article introduces MLM through act ual and hypothetical dental examples. Setting Examples of MLM in periodonta l research illustrate cross-sectional and longitudinal analyses of hierarch ical dental data. Multilevel multivariate modelling is illustrated by an ex ample in orthodontic research. The potential implications of study design i n the context MLM is extensively discussed, including study sample size and accounting for examiner variability. Results The fine detail and greater i nsight provided by MLM enables dental researchers to review and revise old hypotheses and to generate new ones that could not be addressed by single-l evel methods. Conclusions MLM has the potential to increase our understandi ng of oral disease and health and offers the opportunity to rethink some as pects of dental research procedure.