Effects of focal spot size on caries diagnosis with D and E speed images

Annual measurement of the x-ray unit focal spot size has been recommended by the American Academy of Oral and Maxillofacial radiology as part of the dental radiographic quality control program. This study compares the effects of focal spot size on caries diagnosis. Three x-ray units with small, medium, and large focal spot sizes were used to produce bite-wing images on extracted teeth mounted in acrylic bases. Randomized films were scored for lesion presence and depth by two general dentists. Weighted kappa statistics were used to evaluate the agreement of reviewer caries diagnosis by film speed and focal spot size. Comparisons of caries cells with small versus medium and small versus large focal spot size produced weighted kappa statistics = 0.72 and 0.70, respectively. Differences in caries calls were greater because of film speed rather than focal spot size. The results of this study suggest that the clinical significance of varied focal spot size is negligible. The value of annual measurement of focal spot size is questionable, and its recommendation should be revisited.