Locating the periapical region in dental radiographs using digital image analysis.

An algorithm was designed to automatically obtain information on the orientation of roots in dental radiographs aimed at localizing the periapical region. A curve was approximated mathematically by a cubic polynomial to intersect the boundary of the root at its apex. The performance was judged by comparing the location of this intersection with the actual location of the apex as determined by five expert observers. In an experiment with 262 roots of the eight tooth groups, the distance between these two points was less than 1 mm in 67.9% of all cases and less than 2 mm in 88.2%. The performance of the procedure appeared to depend on the tooth group (p < 0.01). The location of the intersection was reproducible within 1 mm in 86.4% of all cases. The reproducibility was, however, not equal for all tooth groups (p < 0.01). The experts were more consistent in localizing the apex than the system was (p < 0.01), although this difference was not confirmed for four of the tooth groups (p > 0.57), and was marginal for two others (0.01 < p < 0.02). It is concluded that the algorithm is promising in its capacity to track a majority of roots down to their apex. It could therefore add important knowledge to imaging procedures aimed at the digital analysis of the periapical region.