3D打印间接粘接托槽精度

Precision of three-dimensional printed brackets

目的:基于数字化正畸诊断设计流程进行间接粘接转移托盘模型的设计和3D打印,对关键性的托槽打印精度进行检验,以期对数字化正畸的临床应用有所帮助。方法:从2014年至2015年于北京大学口腔医院正畸科就诊的错牙合畸形患者中选取14例为研究对象,其中拔牙8例,不拔牙6例。所有患者牙周洁治后进行口内牙列扫描和锥形束CT(cone-beam computed tomography,CBCT)拍摄,所得STL数据与DICOM数据在自编软件中进行数据分割融合和配准、数字化矫治设计和计算机软件自动排牙、托槽虚拟定位、错牙合模型坐标还原,最终输出3D打印模型数据用于间接粘接转移定位托盘的制作。3D打印输出模型,经过后处理由水枪及超声震荡去除周围支撑材料,使用数字游标卡尺对所有样本牙颌模型上的左侧上下颌托槽及颊面管进行长度和宽度的测量,检验测量结果。测量值比较采用独立样本t检验,与托槽及颊面管设计尺寸进行比较。结果:在19个测量分析项目中有13个项目的测量均值与检验标准值间的差异有统计学意义,差异范围在0.04~0.17 mm,且除左下第二前磨牙的托槽长度外均大于检验值。结论:虽然托槽的宽度和颊面管的长度和宽度上大多稍大于检验值,但这不一定对临床上间接粘接转移托盘的制作造成影响,0.04~0.17 mm的差异是否会影响托槽实际的固位和定位有待进一步的研究证实。

Objective： This study was based on digital orthodontic diagnosis work flow for indirect bonding transfer tray model design and three-dimensional（3D） printing,and the aim of this paper was to inspect the dimensional accuracyof 3D printed brackets,which is the foundation of the follow up work and hoped that will illuminate the clinical application of the digital orthodontics work flow. Methods： The samples which consisted of 14 cases of patients with malocclusion from Department of Orthodontics Peking University were selected,including 8 cases with tooth extraction and 6 cases without tooth extraction. All the 14 patients were taken intra-oral scan（Trios 3Shape,Denmark） and cone-beam computed tomography（CBCT,New Tom 3G volumetric scanner,Aperio Service,Italy） shooting after periodontal treatment. STL data and DICOM data were obtained from intraoral scans and CBCT images. Data segmentation,registration,fusion,automatic tooth arrangement,virtual positioning of orthodontic appliance and conversion the coordinates of malocclusion model were all done with self-programming software. The data of 3D printing model with brackets on it were output finally and printed out with EDEN260V（Objet Geometries,Israel）to make indirect bonding transfer tray. Digital vernier caliper was used to measure the length and width of upper and lower left brackets and buccal tubes on those 3D models after removal of surrounding supporting material by ultrasonic vibration and water-spray. Intra-examiner reliability was assessed by using intra-class correlation coefficients（ICC）,and one-sample T test was used to compare the measurements with the standard dimensional data of the brackets. Results： There were significant differences which range in 0. 04-0. 17 mm between the 13 items out of the 19 measurement items. Except for the length of the lower left premolars＇ brackets,mean values of the other items were greater than the test value. Conclusion： Although the measurement results in the width of brackets and the width and length of the buccal tubes obtained experimentally were slightly larger than the test value,this may not reduce the accuracy of indirect bonding procedure in clinic necessarily. Whether the differences which range in 0. 04-0. 17 mm would actually affect the retention and positioning of brackets needs to be confirmed by further studies.