Ability of BlueCheck Liquid for Detection of Initial Lesions on Occlusal Surfaces In Vitro

Background/Objectives: Visual examination remains the standard for caries detection, but its subjectivity limits reproducibility. Adjunctive methods may support objectivity, yet many require costly equipment or extensive training. BlueCheck (BC) liquid is a hemoglobin-based dye that binds reversibly to porous hydroxyapatite, producing a visible blue discoloration in demineralized enamel. This study aimed to evaluate the ability of BC liquid to detect initial occlusal caries lesions and assess lesion activity. Methods: An in vitro study was performed on 54 extracted permanent posterior teeth. Caries detection and lesion activity assessment were performed visually (International Caries Classification and Management System) and with BC liquid. Histology, including methyl red staining, served as the reference standard for lesion depth and activity. Agreement, sensitivity, specificity, and ROC analyses were calculated. Results: BC liquid showed almost perfect intra- and inter-examiner reproducibility (κ = 0.86). Overall agreement with visual examination was 92.6%, and agreement with histological activity assessment was 79.6%. For detection of initial lesions, BC liquid achieved sensitivity of 81.8% and specificity of 100%, with an AUC of 0.909. For activity assessment, BC liquid showed higher sensitivity than visual examination (89.5% vs. 60.5%), but lower specificity (75% vs. 100%), yielding an AUC of 0.822. Conclusions: Within the limitations of this in vitro study, BC liquid demonstrated good diagnostic accuracy and agreement with visual criteria for both detection and activity assessment of occlusal caries lesions. BC liquid may serve as an adjunctive tool for caries diagnosis, but further in vivo and longitudinal studies are required to validate its clinical applicability.