光学相干断层扫描技术诊断牙根裂的实验研究

目的：以组织学切盘检查作为金标准，评价光学相干断层扫描技术（optical coherence tomography, OCT）诊断根管预备后牙根裂的准确性。方法：收集20颗完整的离体下颌切牙，使用自凝树脂和藻酸盐印模材料进行包埋，暴露根尖区3 mm，使用旋转镍钛器械预备根管至 #30/0.09，每次更换器械，使用1%（质量分数）的次氯酸钠溶液冲洗根管。应用扫频OCT（swept source OCT，SS-OCT）系统及驱动装置，对牙根根尖部进行360°均匀环扫，对距根尖孔1、2和3 mm处的牙根横断面进行图像重建，由两名观察者诊断扫描图像中的牙根裂。OCT扫描后，对牙根进行组织学观察，在距根尖孔1、2和3 mm处制作横切盘，利用立体显微镜观察并记录牙根不同横截面根裂的发生情况，并作为金标准评价OCT诊断根管预备后牙根裂的准确性。结果： 20个离体下颌切牙样本进行根管预备后，组织学检查60个（20牙×3 截面/牙）根尖区牙根截面上，有9颗牙共13个截面存在牙根裂；应用OCT扫描成像，正确诊断了其中12个截面牙根裂，即OCT扫描阳性预测值为1.000；对于组织学切盘检查未发现根裂的47个牙根截面，OCT 无误诊发生，OCT发现根裂的阴性预测值为0.979。OCT诊断牙根裂的准确性为0.983，灵敏度为0.923，特异度为1.000。结论：OCT系统可以准确诊断根管预备后根尖部管壁牙根裂。

Detection of root cracks after root canal preparation using rotary NiTi systems by optical coherence tomography (OCT) scan

Objective： To evaluate the accuracy of optical coherence tomography (OCT) in detecting root cracks after root canal instrumentation using histological gold standard. Methods： Twenty complete extracted human mandibular incisors that were free of caries, calculus, and root treatment were chosen and accessed coronally with a diamond bur, then mounted in resin blocks with alginate impression material using simulated periodontal ligaments, and the apex was exposed 3 mm. The teeth were stored in water at room temperature. Then the teeth were then instrumented to the major apical foramen (AF) at #30/0.09 using ProTaper Universal rotary nickel titanium system(Dentsply Maillefer, Ballaigues, Switzerland), irrigation with 1% sodium hypochlorite (NaOCl) by using a 26 gauge needle followed after each instrument. The apical root was scanned with 360° of rotation by Swept-Source Optical Coherence Tomography （SS-OCT） (wavelength: 1 310 nm, scan rate: 20 kHz, axial resolution: 16 μm) with driving device（stepper motor and lifting platform）. The reconstruction images of axial planes 1, 2 and 3 mm from the apex were examined and the root cracks were blindly diagnosed by two observers. The horizontal section was performed at 1, 2 and 3 mm from the apex using low speed disc saw (Leica SP1600, Wetzlar, Germany). The presence of cracks was noted under an optical stereomicroscope (ZOOM-630E) with a cold light source using as gold standard to evaluate the accuracy of OCT in detecting root cracks after root canal instrumentation. Results： After canals instrumentation with ProTaper Universal rotary nickel titanium system to #30/0.09, root cracks were detected in 9 of 20 teeth by histological examination. Crack lines were observed on 13 of 60 horizontal sections and cracks on 12 of the 13 sections were detected by OCT. No cracks were observed in the other 47 of the 60 horizontal sections，none of which was misdiagnosed by OCT. The overall accuracy rate for detection of root cracks with OCT was 0.983, the sensitivity was 0.923, the specificity was 1.000, the positive predictive value (PPV) was 1.000 and the negative predictive value (NPV) was 0.979. Conclusion： OCT may be a promising nondestructive imaging method for diagnosing root canal cracks after canal instrumentation.