目的:评价锥形束CT(cone beam computed tomography,CBCT)在不同分辨率设置下检测牙根外吸收的可靠性,为临床选择恰当的CBCT扫描参数设置提供依据。方法:收集51颗离体单根前磨牙,分别在其舌面的根颈、根中和根尖部随机制备洞型,直径为1 mm,深度分别为0.1、0.2和0.3 mm,共153个位点(其中随机选择51个位点未制备洞型)用以模拟牙根外吸收的微小缺损。将离体牙置于人干下颌骨内,采用ProMax 3D和 DCT PRO型CBCT机分别对样本进行容积扫描;两名观察者评估图像,进行受试者工作特征(receiver operating characteristics,ROC)曲线分析,得到曲线下面积(Az值),用于评估不同分辨率设置下该设备检测牙根外吸收的可靠性。结果:ProMax 3D CBCT可提供高(high)、正常(normal)和低(low)3种分辨率模式扫描,其Az值分别为0.867、0.703和0.665(P<0.05)。DCT PRO CBCT提供了两种分辨率参数设置,组合可得到4种曝光模式,分别为正常质量+正常分辨率(normal quality + normal resolution)、正常质量+高分辨率(normal quality + high resolution)、高质量+正常分辨率(high quality + normal resolution)和高质量+高分辨率(high quality + high resolution), 其Az值分别为0.527、0.725、0.743和0.794(P<0.05)。结论:分辨率设置可显著影响锥形束CT检测牙根外吸收的可靠性,在不增加患者辐射剂量的前提下,采用计算机辅助后处理的方法可显著提高锥形束CT的诊断能力。

Objective: To evaluate the diagnostic accuracy of cone beam computed tomography (CBCT) with different resolution settings in detecting the simulated external root resorption defects. Methods: External root resorption defects were simulated in 51 human single rooted premolar teeth. Ca-vities simulating root resorption defects of 1 mm in diameter and 0.1 mm, 0.2 mm, and 0.3 mm in depth were drilled in the cervical, middle and apical thirds of lingual surfaces of the teeth. In addition to the 51 locations as controls, a total of 102 cavities were obtained in the present study. Specimens were placed in a human dry mandible and scanned by ProMax 3D and DCT PRO CBCT with different resolution settings, respectively. The three-dimensional CBCT images were evaluated by two experienced observers. The data were analyzed with receiver operating characteristics (ROC) analysis. ROC curves were generated and the area under ROC curve (Az) was employed to express the diagnostic accuracy. Results: The diagnostic accuracy (Az value) of ProMax 3D CBCT with high, normal and low resolution settings were 0.867, 0.703 and 0.665 (P < 0.05), respectively. Defects with depths of 0.2 mm and 0.3 mm were easier to be detected than those with depths of 0.1 mm (P < 0.05). The images obtained by high resolution mode scanning had obvious advantages in detecting smaller defects (depth 0.1 mm and 0.2 mm). The DCT PRO CBCT provided 4 resolution settings including normal quality + normal resolution, normal quality + high resolution, high quality + normal resolution and high quality + high resolution. The Az values for those 4 resolution settings were 0.527, 0.725, 0.743, and 0.794 (P < 0.05), respectively. Similar to ProMax 3D CBCT, the scanning mode with high resolution played a better role in detecting the defects with depth of 0.1 mm. Except for the scanning setting mode with normal quality + normal resolution, the other three modes could well be evaluated for the defects with depth of 0.2 mm and 0.3 mm. Conclusion: It is concluded that the diagnostic ability for external root resorption of CBCT could be affected by resolution settings. Computer-aid imaging method can improve the CBCT diagnostic accuracy for external root resorption without increasing the radiation dose level during CBCT scanning.