ORIGINAL ARTICLE P. Stoustrup C. Verna K. D. Kristensen A. K € useler T. Herlin T. K. Pedersen Smallest detectable differences in clinical functional temporomandib- ular joint examination variables in juvenile idiopathic arthritis Authors' affiliations: P. Stoustrup, C. Verna, K. D. Kristensen, A. K€ useler, T. K. Pedersen, Section of Orthodontics, Aarhus University, Aarhus C, Denmark T. K. Pedersen, Department of Maxillofa- cial Surgery, Aarhus University Hospital, Aarhus C, Denmark T. Herlin, Department of Pediatrics, Aarhus University Hospital, Aarhus N, Denmark Correspondence to: Peter Stoustrup Section of Orthodontics, Faculty of Health Sciences, University of Aarhus, Vennelyst Boulevard 9, DK-8000 Aarhus C, Denmark E-mail: pstoustrup@odont.au.dk Stoustrup P., Verna C., Kristensen K. D., K€ useler A., Herlin T., Pedersen T. K. Smallest detectable differences in clinical functional temporomandibular joint examination variables in juvenile idiopathic arthritis Orthod Craniofac Res 2013; 16: 137–145. © 2012 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd Structured Abstract Objective – Temporomandibular joint (TMJ) arthritis in juvenile patients may interfere with optimal joint function and mouth opening patterns. Clinical assessment of maximal mouth opening capacity, laterotrusion and protrusion is critical to TMJ arthritis diagnosis, treatment choice and evaluation of a therapeutic intervention. The aim of the study was to determine the smallest minimal threshold at which differences in maximal mouth opening capacity, laterotrusion, and protrusion between two consecutive observations can be determined. Setting and Sample Population – Department of Orthodontics, Univer- sity of Aarhus, Denmark. Forty-two consecutive patients with juvenile idio- pathic arthritis. Material and Methods – Two experienced dentists used a calibrated metallic ruler to measure maximal mouth opening capacity, laterotrusion, and protrusion. Each measurement was carried out thrice by each obser- ver. Intra- and inter-observer variation and the smallest detectable differ- ence were calculated for each variable. Results – The smallest detectable differences were as follows: maximal mouth opening capacity 4.9 mm, laterotrusion 2.4 mm, and protrusion 2.8 mm (one observer and one measurement). These differences declined when measurements were repeated; maximal mouth opening capacity 3.3 mm, laterotrusion 1.4 mm, and protrusion 1.8 mm (two observers with three measurements each). We found no support for a relationship between measurement variation and patient age, measure- ment variation and TMJ pain, or between measurement variation and pre- vious/current TMJ arthritis. Date: Accepted 3 November 2012 DOI: 10.1111/ocr.12008 © 2012 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd