Tang Peijun, Le Nhan, Lu Jie, Chung Kwok-Hung, Subhash Hrebesh, Kilpatrick-Liverman LaTonya, Wang Ruikang K
Department of Bioengineering, University of Washington, 3720 15th Ave NE, Seattle, WA 98195, USA.
Department of Restorative Dentistry, University of Washington, Seattle, WA,98195, USA.
Biomed Opt Express. 2022 Jul 19;13(8):4247-4260. doi: 10.1364/BOE.464707. eCollection 2022 Aug 1.
Due to rod-like hydroxyapatite crystal organizations, dental enamel is optically anisotropic, i.e., birefringent. Healthy enamel is known to be intrinsically negatively birefringent. However, when demineralization of enamel occurs, a considerable number of inter-crystallite spaces would be created between the crystallites in the enamel, which could lead to a sign reversion in birefringence of the enamel structure. We propose that this sign reversion can be leveraged in polarization sensitive OCT (PSOCT) imaging to differentiate early caries lesions from healthy enamel. In this study using PSOCT, we first confirm that the change in birefringence sign (negative to positive) can lead to a 90-degree alteration in the local axis orientation because of the switch between the fast and slow optic axes. We then demonstrate, for the first time, that the local axis orientation can be utilized to map and visualize the WSLs from the healthy enamel with a unique contrast. Moreover, the sharp alteration in local axis orientation gives a clear boundary between the WSLs and the healthy enamel, providing an opportunity to automatically segment the three-dimensional WSLs from the healthy enamel, enabling the characterization of their size and depth information in an intuitive way, which may aid clinical decision making and treatment planning.
由于牙釉质呈棒状羟基磷灰石晶体结构，因此具有光学各向异性，即双折射性。已知健康牙釉质本质上是负双折射的。然而，当牙釉质发生脱矿时，牙釉质中的微晶之间会形成大量微晶间间隙，这可能导致牙釉质结构双折射的符号反转。我们提出，这种符号反转可用于偏振敏感光学相干断层扫描（PSOCT）成像，以区分早期龋损与健康牙釉质。在这项使用PSOCT的研究中，我们首先证实双折射符号的变化（从负到正）会由于快轴和慢轴的切换而导致局部轴方向发生90度的改变。然后，我们首次证明，局部轴方向可用于以独特的对比度映射和可视化健康牙釉质中的白色不透明条纹（WSLs）。此外，局部轴方向的急剧变化在WSLs和健康牙釉质之间形成了清晰的边界，为从健康牙釉质中自动分割三维WSLs提供了机会，从而能够直观地表征其大小和深度信息，这可能有助于临床决策和治疗计划。
