Blue-Light Transillumination Using Dental Curing Units Shows Limited Diagnostic Accuracy for Approximal Caries Detection: An Ex Vivo Comparison with Bitewing Radiography

The purpose of this ex vivo study was to evaluate the diagnostic accuracy of blue‑light transillumination using two dental curing units, in comparison with bitewing radiography, for detecting and staging approximal caries in extracted posterior teeth. Forty‑eight premolars and molars were mounted in a standardized model and assessed independently by thirteen evaluators. Lesion presence and depth were recorded against a reference standard established by an experienced cariologist (ICDAS/ICCMS criteria). Across 1,248 proximal surfaces, bitewing radiography outperformed transillumination: sensitivity and specificity were 0.584 and 0.937 for bitewings, versus 0.165 and 0.805 for the Valo unit and 0.168 and 0.758 for the X‑Cure unit, respectively. Positive predictive value was higher for radiography (0.724) than for transillumination (Valo 0.192; X‑Cure 0.163), and negative predictive values were low across methods. Agreement for depth staging was fair for radiography (κ=0.262) and non-existent for transillumination (Valo κ=−0.052; X‑Cure κ=−0.005), with a high proportion of non‑classifiable findings using curing lights. Within the tested conditions, blue‑light transillumination with curing units showed limited sensitivity and reliability and should not replace bitewing radiography for approximal caries diagnosis. Transillumination using a dental light curing unit may result in misdiagnosis of posterior proximal carious lesions, both in presence and severity, compromising adequate treatment for the patients.