Observer performance in locating the bifurcation in mandibular molars on periapical radiographs.

The ability to identify radiographically the bifurcation in mandibular molars and the influence of morphological factors on the observers' decisions were investigated in 10 dry mandibles. Standardized periapical radiographs were obtained with and without lead markers in the bifurcation. Then 23 observers marked the bifurcation on tracing paper placed on the radiographs. The distance between the 'true' bifurcation (the lead indicators) and the observers' markings was assessed. On average, it was identified at a point 0.26 mm (s.d. 0.5) apical to its 'true' location on the first molar, and 0.65 mm (s.d. 1.15) coronal on the second molar. Interobserver variation for first and second molars was 0.5 mm and 1.06 mm respectively. Corresponding intraobserver variation was 0.47 mm and 1.14 mm. Of the four morphological characteristics analysed, the mesiodistal width of the bifurcation was found to have the strongest influence on the accuracy. It was concluded that the wide discrepancy in the ability of the observers to locate the bifurcation could be largely attributed to intraindividual variation.