Ultrathin lensed fiber-based manual scanning optical coherence tomography needle probe for the detection of the interproximal caries.

Significance: Interproximal caries detection is critical for effective dental treatment. We report an ultrathin lensed fiber-based manual scanning optical coherence tomography (OCT) needle probe to enables the direct imaging of the interproximal caries between two adjacent teeth.

Aim: We aim to design and fabricate the ultrathin lensed fiber-based manual scanning OCT needle probe, and validate the performance of the proposed probe by applying it to the imaging of the phantom sample, the human skin tissue and the interproximal caries between two adjacent teeth.

Approach: A homemade lensed fiber is packaged into a 21-gauge hypodermic needle to create a high-flexibility, ultrathin probe. A decorrelation algorithm is employed for image reconstruction based on manual scanning. The performances of the developed needle probe are experimentally measured. The probe is incorporated in a swept-source OCT system to image the phantom sample, the human skin tissue, and the interproximal caries between two adjacent teeth.

Results: The working distance and focused spot diameter of the developed probe are measured to be 1.22 mm and $18.78\mu m$ , respectively. The correctly reconstructed OCT images of the phantom, skin tissue, and the tooth tissue demonstrate the performance of the developed ultrathin lensed fiber-based manual scanning OCT needle probe. The distinct structural difference between the healthy and abnormal teeth tissue validates the efficacy of the proposed method.

Conclusion: We propose an ultrathin lensed fiber-based manual scanning OCT needle probe potentially useful for the interproximal caries detection. The design, fabrication, and performances of the developed needle probe are demonstrated. We address a critical issue in the caries diagnostics and offer a promising tool for the future clinical applications.