In this paper we propose a new approach to determine the length of root canal in dental X-ray image semi-automatically. The approach consists of a sequence of the following procedures: preprocessing procedure using contrast stretching method, segmentation procedure using active shape model to find the area of root canal and thinning procedure to find centerline of the root canal area. The length of the extracted centerline to be the length of root canal. Active shape model able to find root canal area in the image, and the length of root canal can be determined. Hence, semi-automatic determination of root canal length in dental X-ray image is feasible.
