Influence of Image Size and Display on Radiographic Caries Detection

Objectives: This study investigated the validity of approximal caries detection on digital bitewing radiographs displayed at different sizes either on a cathode-ray-tube (CRT) and a thin-film transistor (TFT) monitor. Materials and Methods: 5 observers assessed digital bitewing radiographs (SidexisÒ, Sirona) of 160 unrestored premolars and molars embedded in 10 pairs of models using a 5-category caries rating scale. Images were displayed at magnification ratios of 1:1, 1: 2 and 1:7 on a CRT monitor (Nokia 446 XS) and a TFT display (Panasonic LC 50 S). Evaluation of histological serial sections were used as gold standard. Diagnostic accuracy was expressed as areas under ROC curves and calculated at two levels of caries penetration: presence of caries (I) and presence of a lesion in dentin (II). Influence of the factors “monitor type” and “magnification level” were analyzed with repeated measures ANOVA (unstructured covariance matrix). Results: Validity of approximal caries detection at both penetration levels was not influenced by the type of monitor display whereas the image size had a significant impact (p<0.01). ROC areas for magnification level 1:7 (I: 0.62; II: 0.65) were smaller compared to ratios of 1:1 and 1:2 (p<0.01). No differences were observed between the ratios 1:1 (I: 0.69; II: 0.74) and 1:2 (I: 0.68; II: 0.73). Conclusions: Based upon data from this study the type of monitor did not influence accuracy of approximal caries diagnosis on digital radiographs, whereas larger display of bitewing images resulted in higher validity.