Diagnostic Accuracy Study of Near-Infrared Transillumination for Interproximal Dentinal Caries Detection in Primary Teeth

Background/Objectives: Near-infrared light transillumination (NIRI) has emerged as a radiation-free adjunctive method for proximal caries detection in pediatric dentistry. However, evidence regarding its diagnostic performance in primary dentition remains limited. The aim of this prospective diagnostic accuracy study was to evaluate the diagnostic performance of NIRI for detecting interproximal dentinal caries lesions in primary molars, using bitewing radiography as a pragmatic clinical reference standard. Methods: Thirty-one pediatric patients aged 5–12 years were included, contributing 273 interproximal surfaces of primary molars. Clinical examination was performed using ICDAS criteria, while proximal lesions were assessed using bitewing radiography and NIRI integrated into the iTero Element 5D intraoral scanner. For diagnostic accuracy analysis, only dentinal lesions classified as D1–D3 according to the Mejàre classification were considered positive cases, whereas E0–E2 surfaces were classified as negative. Sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and overall diagnostic accuracy were calculated. Results: The overall prevalence of caries lesions was 37.4%; however, only 11 surfaces showed dentinal involvement (D1–D3) and were included as positive cases in the diagnostic accuracy analysis. NIRI demonstrated a sensitivity of 81.8% and a specificity of 74.8%. The PPV was 12.0%, whereas the NPV was 99.0%. Overall diagnostic accuracy was 75.1%. A total of 66 false-positive findings and 2 false-negative findings were identified. Conclusions: NIRI demonstrated high sensitivity and excellent negative predictive value for detecting interproximal dentinal caries lesions in primary molars, suggesting potential usefulness as an adjunctive screening tool. However, the low positive predictive value and high number of false-positive findings indicate that positive NIRI findings should be interpreted cautiously and should not be used as a standalone basis for treatment decisions. Further studies using more robust reference standards are required to clarify the clinical significance of NIRI-positive findings.