下颌骨数字曲面体层片的曲变研究

Investigation of distortion of panoramic radiographs on mandible

目的 :通过测量长方形金属标志物的垂直和水平距离以及角度变化,评估体面断层片拍摄成像后的曲变失真情况。方法:由同一医师将大小为1.0 cm×0.6 cm的金属标志物置于115例患者面部的不同位置,分为2组记录,第1组将3个相同规格的金属标志物沿下颌骨下缘置于颏部、下颌前磨牙区、下颌磨牙区,均紧贴于下颌骨下缘。第2组将3个相同规格的金属片分别置于磨牙区牙根中1/3、前磨牙区牙根中1/3以及切牙区牙根中1/3,均靠近牙槽嵴顶。拍摄数字曲面体层X线片时由同一技师选用同一台机器进行拍摄。曲面体层X线片中的金属标志物的长度、宽度、垂直距离和近中角度(曲变度α)均由2名医师独立测量,每名医师间隔1周随机测量2次并记录数据,取均值作为最终测量结果。所有数据均利用Photoshop CS6软件测量。应用SPSS 23.0软件包对数据进行统计学分析。结果:全景片中,第2组(G2)标志点垂直距离的平均放大率约为105.6%,切牙区的放大率最大,前磨牙区次之,磨牙区最小。而第1组(G1)标志点垂直距离均缩小。相比垂直距离,无论是第1组还是第2组,水平距离均缩小。2组3个区域的角度均有变化,表明存在一定曲变。结论:数字曲面体层X线片不同部位的曲变情况不同。分析特定区域的曲变情况,需要参照相应的变形系数。临床医师根据数字全景片分析种植区的骨量或拔除阻生牙时,需要考虑全景片的这一特点。

PURPOSE： To evaluate the degree of distortion in panoramic radiograph by measuring the vertical and horizontal distances of the metal markers. METHODS： Metal references, 1.0 crux0.6 cm in size, were placed on different parts of the face of 115 patients by the same dentist. They were divided into two groups. Group 1：3 metal references were placed on the region of chin, premolars and mandibular angle, respectively, all along the inferior margin of the mandible. Group 2：3 metal references were placed on 3/1 of root in the same 3 regions, all near the alveolar ridge. The panoramic radiographs were taken on the same machine. The data of the two groups were collected independently by two dentists. Each dentist will measure α, vertical and horizontal distances twice by Photoshop CS6 at one week interval, taking the mean values as the final results. The data were analyzed with SPSS 23.0 software package. RESULTS： The average magnification ratio of vertical length in group 2 was 105.6%, and the region of incisors gained the highest magnification ratio, followed by premolar and molar region, while the vertical lengths in group 1 were minimized. Compared to the vertical measurements, horizontal widths in both group 1 and group 2 were minimized. The angles in the 3 regions had tiny changes in both groups. CONCLUSIONS： Distortion of different part of panoramic radiographs is hardly identical. Related ratio was needed to analyze the distortion of specific regions. Clinicians can better evaluate bone mass of implanted regions or to analyze the resistance of impacted tooth according to the panoramic radiograghs.