光學同調斷層掃描術應用於牙科之研究：牙骨質與牙齒窩洞檢測

Abstract

背景：精準醫療有賴於準確的診斷與治療計畫，而牙科診斷更時常需仰賴於影像學檢查。傳統 X 光檢查雖能提供詳細影像，但存在輻射暴露、影像重疊和深度資訊受限的問題。光學同調斷層掃描術（Optical coherence tomography, OCT）是一種無輻射、非侵入性、高解析度且即時成像的三維影像技術。但易受到牙齒之光學性質影響，仍有成像深度受限、散射訊號疊加、陰影效應（Shadow effect）等限制，使得影像判讀仍不夠精確。希望能透過儀器之優化與參數調整、齒質定性與定量分析之驗證，使 OCT 可以在牙科的臨床應用上帶來突破。

研究目的：本研究旨在探討 OCT 對牙根與齲齒治療過程中窩洞修型之成像效果，並將其與其他成像技術（如傳統 X 光和錐狀射束電腦斷層掃描（Cone-beam computed tomography，CBCT））進行比較，以確定 OCT 在判讀上的優勢和局限性。此外，亦使用 OCT 對牙根壁寬度、剩餘牙本質厚度（Remaining dentin thickness, RDT）進行測量，並探討其準確性。期望 OCT 能夠為臨床牙科診斷提供更精確和有效的技術支持。 材料與方法：本研究分為兩部分：第一，掃描牙根切片探討牙骨質與相關組織之成像與牙根壁寬度之測量；第二，掃描窩洞樣本進行影像分析與剩餘牙本質厚度（RDT）之測量。兩組樣本分別進行牙根的切片包埋與咬合面的窩洞修磨後，以掃頻式光學同調斷層掃描系統（Swept-source OCT, SS-OCT）及牙科錐狀射束電腦斷層掃描術（CBCT）照射。將影像匯入 Amira® 3D Pro（Thermo Fisher Scientific, USA）軟體進行疊圖對位與分析，並測量牙根切片中的牙根壁寬度與窩洞樣本中的剩餘牙本質厚度，比較 OCT與 CBCT 之測量值，計算兩者誤差，並評估其相關性。

結果：研究結果顯示，OCT 可顯現牙骨質、牙骨質—牙本質交界、窩洞邊界、牙髓外型等解剖結構。然而，雖然 OCT 可映現待測物表面的細微結構或變化，但也有可能因散射訊號的疊加，不一定能完全反映真實的解剖構造。此外，亦有可能受到待測物本身的幾何結構影響與周圍組織的高光反射，導致影像缺失。在牙根壁寬度與剩餘牙本質厚度的測量結果顯示， OCT 測量值與 CBCT 測量值具有高度的線性相關性，具有臨床應用之潛力，但需注意 OCT 可能仍存有的誤差。

結論：OCT 在牙骨質、牙骨質—牙本質交界、窩洞邊界、牙髓外型的表現上展現出巨大潛力，能夠提供無輻射、高解析度的三維結構影像，亦驗證了 OCT 在剩餘齒質厚度測量的可行性。希望能使 OCT 在牙根相關的診斷與治療規劃（如矯正及牙周病科治療）及齲齒移除深度的臨床判斷上帶來幫助。未來的研究方向包括影像品質優化、演算法與影像校正、臨床應用之開發與人工智慧學習及影像判讀。

Background: Precision medicine relies on accurate diagnosis and treatment planning, and dental diagnosis often depends heavily on imaging examinations. Although conventional radiographic techniques provide valuable diagnostic information, they are associated with ionizing radiation exposure, image superimposition, and limited depth-resolved information. Optical Coherence Tomography (OCT) is a non-invasive, radiation-free, high-resolution imaging modality capable of providing real-time three-dimensional images. However, OCT image quality is influenced by the optical properties of dental tissues and remains subject to limitations such as restricted penetration depth, superimposed scattering signals, and shadowing effect, which may affect image interpretation. Through the optimization of OCT instrumentation, adjustment of imaging parameters, and validation of qualitative and quantitative analyses of dental tissues, it is anticipated that OCT will bring significant breakthroughs to clinical dental applications.

Purpose: This study aimed to evaluate the effectiveness of Optical coherence tomography (OCT) for imaging root canal structures and cavity preparations during the management of dental caries. In addition, OCT would be compared with conventional radiography and cone-beam computed tomography (CBCT) to determine its strengths and limitations in diagnostic image interpretation, thereby assessing its potential clinical value in dentistry. In addition, OCT was used to measure root wall width and remaining dentin thickness (RDT) to assess its measurement accuracy and clinical feasibility. The ultimate goal was to investigate the potential of OCT as a more precise and effective imaging tool for dental diagnosis and treatment planning.

Materials and methods: The study consisted of two parts. First, root section specimens were scanned to investigate the imaging characteristics of cementum and related dental structures and to measure root wall width. Second, cavity-prepared specimens were scanned for image analysis and measurement of remaining dentin thickness (RDT). The specimens in the two groups underwent root sectioning and embedding or occlusal cavity preparation, respectively, and were subsequently imaged using a swept-source optical coherence tomography (SS-OCT) system and cone-beam computed tomography (CBCT). The acquired images were imported into Amira® 3D Pro software (Thermo Fisher Scientific, USA) for image registration, superimposition, and analysis. Measurements of root wall width and RDT were performed, and the values obtained from OCT and CBCT were compared. Measurement errors were calculated, and the correlation between the two imaging modalities was assessed.

Results: OCT was able to visualize cementum, the cemento-dentinal junction (CDJ), cavity boundaries, and pulpal morphology. Although OCT was capable of depicting subtle surface and microstructural changes, scattering signal superimposition occasionally resulted in image features that did not fully correspond to the actual anatomical structures. Alternatively, image loss may occur due to the geometric characteristics of the dental structure and intense backscattering or specular reflections from surrounding tissues, which can lead to signal attenuation and incomplete visualization of deeper anatomical structures. Measurements of root wall width and RDT demonstrated a strong linear correlation between OCT and CBCT. These findings indicate that OCT possesses considerable potential for clinical applications, although the possibility of measurement errors should be taken into account.

Conclusion: OCT demonstrated significant potential for imaging cementum, the cemento-dentinal junction, cavity boundaries, and pulpal morphology, while providing radiation-free, high-resolution three-dimensional structural images. The results also support the feasibility of OCT for measuring remaining dental hard tissue thickness. OCT may contribute to diagnosis and treatment planning involving root-related conditions, such as orthodontic and periodontal therapies, as well as to the clinical assessment of caries excavation depth. Future studies should focus on image quality optimization, algorithm development and image correction, clinical implementation, and the integration of artificial intelligence for automated image interpretation and diagnostic support.