Objective: To compare the effects of different imaging methods on radio-opacity. Digital imaging and traditional film imaging were used to determine the radio-opacity of dental composite resin materials.
Methods: Fourteen dental composite resins commonly used in clinic were prepared for disc samples with thickness of 1 mm and diameter of 15 mm respectively. The aluminum step wedge was used as the reference and the disc samples were irradiated with X-rays by the traditional film imaging, phosphor imaging plate and charge-coupled device(CCD) intra-oral X-ray sensor respectively. Exposure was set at 65 kV and 7 mA, with 300 mm focus to film distance and the exposure time was 0.25 s. After developing and fixing the film, the optical density of the image of the sample and that of each step of the aluminum step wedge were measured using the densitometer. The digital image file was exported to grey scale analysis software of Adobe Photoshop® to measure the average grey value in the sample image and aluminum step wedge image. The curves were drawn corresponding to the optical density/gray value of each step of the aluminum step wedge and its thickness, and the equivalent thickness of the aluminum plate was calculated according to the optical density/gray value of the actual measured thickness of the sample, so as to evaluate the radio-opacity of dental composite resin material.
Results: For the same sample, the aluminum equivalent measured by traditional film imaging and two other digital imagings had significant differences among the 14 composite resins (P < 0.05), and the aluminum equivalent measured by the two digital imagings were greater than that of the traditional film. Moreover the aluminum equivalent measured by the two digital imagings was also different, and the aluminum equivalent measured by the CCD intra-oral X-ray sensor in most composite resins was larger than that measured by phosphor imaging plate. The same sample was photographed with the same imaging method, and the aluminum equivalent was different after three exposures. The standard deviation of aluminum equivalent measured by phosphor imaging plate was the largest, while that measured by CCD intra-oral X-ray sensor was the smallest. Among the 14 dental composite resin materials, the aluminum equivalent of Tetric N-Ceram and Te-Econom Plus measured by traditional film imaging and phosphor imaging plate was significantly higher than other composite resins.
Conclusion: Based on clinical significance, three kinds of sensors designed to measure the radio-opacity of dental composite resin, the value of aluminum equivalent will change according to different types of sensors. The aluminum equivalent measured by CCD intra-oral X-ray sensor was higher than that measured by phosphor imaging plate, and the aluminum equivalent measured by phosphor imaging plate was higher than that measured by traditional film imaging. Moreover, even though the same sensor was used, the aluminum equivalent measured by multiple exposures was different. The standard deviation of the aluminum equivalent measured by phosphor imaging plate was greater than that measured by traditional film imaging and CCD intra-oral X-ray sensor. The three sensors in this study could be used for evaluating the radio-opacity of dental composite resin materials. But no matter what kind of sensor was used to measure the radio-opacity of dental composite resin, it complied to ISO 4049: 2019 standard, the materials were suitable for clinical use.
目的: 分别采用传统胶片成像和数字成像测试牙科复合树脂材料的X射线阻射性，对比3种不同成像方式对X射线阻射性的影响。
方法: 将临床常用的14种牙科复合树脂，分别制备成厚度为1.0 mm，直径15 mm的圆片。对同一个圆片试样，分别采用传统胶片成像(使用E速胶片)、数字成像(荧光成像板)和电荷耦合元件(charge-coupled device, CCD)口内X射线传感器，在相同的曝光条件下(管电压65 kV, 电流7 mA, 距离300 mm, 照射时间0.25 s)，以楔状阶梯铝板作为参照物拍摄X线片。对于传统胶片成像获得的胶片，使用光密度计测量试样和楔状阶梯铝板各阶梯图像的光密度。对于数字成像获得的数字图像，输出到Adobe Photoshop®灰度分析软件，分析试样和楔状阶梯铝板各阶梯图像的平均灰度值。分别绘出楔状阶梯铝板各台阶的光密度/灰度值与其厚度相对应的曲线，并根据试样的实际测量厚度的光密度/灰度值，计算等效铝板厚度，以此评价牙科复合树脂材料的X射线阻射性。
结果: 同一个试样片，传统胶片成像和其他两种数字成像测得的等效铝板厚度，14种复合树脂相比差异均有统计学意义(P＜0.05)，且两种数字成像测得的等效铝板厚度均大于传统胶片成像测得值。两种数字成像测得的等效铝板厚度也有差异，且多数复合树脂用CCD口内X射线传感器测得的等效铝板厚度大于荧光成像板测得值。同一样品，采用同一成像方式拍照，3次曝光获得的等效铝板厚度不同，其中荧光成像板测得的等效铝板厚度标准差最大，而CCD口内X射线传感器测得的等效铝板厚度标准差最小。14种复合树脂间，Tetric N-Ceram复合树脂和Te-Econom Plus复合树脂用传统胶片成像、荧光成像板拍照获得的等效铝板厚度值显著大于其他树脂。
结论: 基于临床意义设计的3种传感器测得的等效铝板厚度值会根据传感器种类不同而改变，CCD口内X射线传感器测得值, 荧光成像板测得值＞传统胶片成像测得值，并且即使使用同一传感器，多次曝光获得的等效铝板厚度值也不同，其中荧光成像板测得的等效铝板厚度值标准差大于传统胶片成像和CCD口内X射线传感器测得值。在评价复合树脂的X射线阻射性时，3种传感器都可以检测复合树脂的X射线阻射性，但无论采用何种传感器，等效铝板厚度值均应符合ISO 4049: 2019标准的规定，该树脂才可以判定为合格产品，材料才适用于临床。
Keywords: Dental composite resin; Digital imaging; Film imaging; Radio-Opacity.