Objectives: This study investigates the consequences of substituting Articulare (Ar) for Condylion (Co) in the measurement of mandibular change through time. Since the location of Co on lateral cephalograms is considered to be highly prone to error, the virtual landmark, Ar, is frequently substituted for it in studying mandibular growth and evaluating treatment outcome. Methods: The study investigated a) the relative reliability of locating Ar and Co on representative lateral cephalograms and b) the effects of substituting Ar for Co in calculating the magnitude and direction of growth at condyle. Data were available from pre and post-treatment cephalograms for 100 randomly chosen growing orthodontic patients (Dtime=3.08± 0.86 years). Ar and Co had been located independently by 3 judges on each image. Results: Standard deviations for the replicate assessments of the two landmarks (measured in mm parallel and perpendicular to occlusal plane) were: Co(x)=4.42, Co(y)=1.80; Ar(x)=0.89, Ar(y)=0.32. For mandibular length increase between timepoints measured as change in distance from Pogonion (Po), comparable statistics (mean± sd in mm) were: Co_Po=5.8± 4.2, Ar_Po=5.5± 3.67, r=0.81. The differences in magnitude of growth at condyle with respect to occlusal plane between timepoints (Ar minus Co), were Dx=0.14± 1.7, Dy=–0.26± 2.56, r=0.8+ in each direction. The direction of displacement of the mandibular condyle, measured in terms of Co, was -30.22± 56.5^o. Measured in terms of Ar, the corresponding values were –36.28± 52.14^o. Because of the very large standard deviations, the correlation between these two was only r=0.35 and the difference was -6.1± 64.4^o, was not statistically significant. Conclusions: Mean measurements for the two landmarks were quite similar but standard deviations for each were large. This implies that while the two landmarks may be fairly interchangeable for large samples, marked differences will be encountered frequently in individual cases.

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