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. Basic design Methodological in nature, this article introduces MLM through actual and hypothetical dental examples. Setting Examples of MLM in periodontal research illustrate cross-sectional and longitudinal analyses of hierarchical dental data. Multilevel multivariate modelling is illustrated by an example in orthodontic research. The potential implications of study design in the context MLM is extensively discussed, including study sample size and accounting for examiner variability. Results The fine detail and greater insight provided by MLM enables dental researchers to review and revise old hypotheses and to generate new ones that could not be addressed by single-level methods. Conclusions MLM has the potential to increase our understanding of oral disease and health and offers the opportunity to rethink some aspects of dental research procedure.