Caries, the world’s most common chronic disease, remains a major cause of invasive restorative dental treatment. To take advantage of the diagnostic potential of optical coherence tomography (OCT) in contemporary dental prevention and treatment, an intraorally applicable spectral-domain OCT probe has been developed based on an OCT hand-held scanner equipped with a rigid 90°-optics endoscope. The probe was verified in vitro. In vivo, all tooth surfaces could be imaged with the OCT probe, except the vestibular surfaces of third molars and the proximal surface sections of molars within a "blind spot" at a distance greater than 2.5 mm from the tooth surface. Proximal surfaces of 64 posterior teeth of four volunteers were assessed by intraoral OCT, visual-tactile inspection, bitewing radiography and fiber-optic transillumination. The agreement in detecting healthy and carious surfaces varied greatly between OCT and established methods (18.2–94.7%), whereby the established methods could always be supplemented by OCT. Direct and indirect composite and ceramic restorations with inherent imperfections and failures of the tooth-restoration bond were imaged and qualitatively evaluated. The intraoral OCT probe proved to be a powerful technological approach for the non-invasive imaging of healthy and carious hard tooth tissues and gingiva as well as tooth-colored restorations.

Objectives: This in vitro study evaluated the validity and reliability of spectral domain optical coherence tomography (SD-OCT) to detect approximal carious lesions compared to bitewing radiography. Methods: Forty extracted human premolars and molars with fifty-four unrestored approximal surfaces (ICDAS ll score 0 – 3) were mounted in a patient-equivalent simulator and imaged by digital radiography (DR) and the prototype of an intraoral OCT probe. The lesion status of the tooth surfaces was validated histologically and by microtomography (µCT). Five calibrated raters with low to high level of clinical expertise analyzed the DR and OCT images at intervals of 2 to 4 weeks each. Intra- and interrater agreement (weighted Cohen's kappa κ, Fleiss' kappa), sensitivity, and specificity were calculated. Results: The sensitivity of OCT (0.66 - 0.91) was higher than that of DR (0.46 - 0.82), as was the specificity (OCT: 0.67 - 0.92; DR: 0.33 - 0.58). Intra-rater agreement with OCT was moderate to substantial (κ: 0.53 - 0.77; p < 0.001) and fair to substantial for DR (κ: 0.36 - 0.78; p < 0.05). The DR interpersonal agreement ranged from slight to substantial (κ: 0.1 - 0.74, Fleiss’-κ: 0.23/0.24; p < 0.001), towards fair to substantial with OCT (κ: 0.27 - 0.62; Fleiss’­κ: 0.23/0.18; p < 0.001). Agreement between histology and µCT was almost perfect (κ: 0.82; p < 0.001). Conclusions: In a clinically oriented simulation, OCT was more sensitive in detecting early approximal carious lesions than DR without impairing specificity or reproducibility. Clinical studies will have to show whether OCT can confirm these promising results. Clinical significance: Non-invasive real-time OCT imaging of the approximal spaces may validly and reproducibly supplement established diagnostic procedures for detecting and monitoring early approximal lesions. Training of examiners might further improve the interpretation of OCT images.