Smallest detectable differences in clinical functional temporomandibular joint examination variables in juvenile idiopathic arthritis.

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, University of Aarhus, Denmark. Forty-two consecutive patients with juvenile idiopathic 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 observer. Intra- and inter-observer variation and the smallest detectable difference 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, measurement variation and TMJ pain, or between measurement variation and previous/current TMJ arthritis.
CONCLUSION: The importance of the implementation of a standardized measurement protocol is emphasized including repeated measurements to reduce the smallest detectable difference.