The "furcation arrow". A reliable radiographic image?

When radiographs of maxillary molars are observed, a small, triangular radiographic shadow is sometimes noted over either the mesial or distal roots in the proximal furcation area. This study was undertaken to determine the reliability of using this radiographic image as an aid in diagnosing proximal furcation involvement. Sixty-six Degree 1, 53 Degree 2 and 43 Degree 3 proximal furcation involvements in maxillary molars in dry skulls were assessed visually with the Nyman and Lindhe classification. An additional 120 uninvolved furcations were included as controls. The involved maxillary molars were radiographed with standard periapical radiographic techniques. Projected radiographs were evaluated independently by six dentists who determined whether there was a triangular radiographic shadow ("furcation arrow") over the mesial and distal proximal areas. The association of the furcation arrow image with Degree 2 or 3 furcation involvement was significant when compared with uninvolved furcations. The image was equally apparent over mesial or distal furcations and was not affected by the existence of a buccal furcation involvement. The incidence of the image over both uninvolved proximal furcations and proximal furcations with Degree 1 involvement was low and did not differ significantly. Because the furcation arrow seldom appears over uninvolved furcations, the appearance of the image indicates that there is proximal bony furcation involvement. However, absence of the furcation arrow image does not necessarily mean absence of a bony furcation involvement because the arrow was not seen in a large number of furcations with Degree 2 or 3 involvement.