Nouri Mahtab, Massudi Reza, Bagheban Alireza Akbarzadeh, Azimi Somayyeh, Fereidooni Farzad
School of Dentistry, Shahid Beheshti Medical University, Evin, Theran, Iran.
Aust Orthod J. 2009 May;25(1):41-7.
Virtual dental casts have been recently introduced to orthodontics. The problem of capturing the shapes of teeth on study casts may be complicated by the presence of undercut areas and deep grooves.
This study aimed to develop a 3-D laser scanner and associated software, and to evaluate the reproducibility and validity of mesiodistal crown width measurements based on slice distinction.
To evaluate reproducibility: a cube was scanned with readily available equipment and the digital measurements compared to caliper measurements of the cube; and the mesiodistal widths of artificial upper teeth were measured, set-up in a dental model, scanned, measured on the virtual study models and compared with the reference measurements. Custom software was used to capture and process the resulting images. To determine validity artificial teeth were measured with calipers, set-up in 20 different malocclusions, duplicated and scanned. The caliper measurements of groups of teeth (incisors, canines, premolars, molars) were compared with digital measurements of the same teeth. In the second method to determine validity, 10 dental casts were scanned and measured by two examiners and the mesio-distal widths compared with the reference values, and with each other.
The digital measurements of the cube fell within 0.1 mm of the reference value. The absolute error in repeated measures of the dental model was 0.32 +/- 0.25 mm. The overall correlation between 3-D images of the teeth and the reference values, using the intraclass correlation coefficient (ICC), was 0.84. The most and least valid results for groups of teeth were the premolars and canines, respectively. The inter-observer ICC was 0.60, and each examiner's ICC versus the reference values were 0.833 and 0.855.
The mesiodistal widths of teeth and groups of teeth can be reliably and validly measured on virtual study models using the scanner and software developed for this purpose. Inaccuracy in the canine region may be overcome by using a smaller rotational angle during scanning.
虚拟牙模最近已被引入正畸学领域。由于存在倒凹区域和深沟，在研究模型上获取牙齿形状的问题可能会变得复杂。
本研究旨在开发一种三维激光扫描仪及相关软件，并基于切片区分评估近远中牙冠宽度测量的可重复性和有效性。
为评估可重复性：用现有设备扫描一个立方体，并将数字测量结果与用卡尺测量该立方体的结果进行比较；测量人工上颌牙齿的近远中宽度，将其排列在牙模中，进行扫描，在虚拟研究模型上测量，并与参考测量值进行比较。使用定制软件捕获和处理所得图像。为确定有效性，用卡尺测量人工牙齿，将其排列在20种不同的错颌畸形中，复制并扫描。将几组牙齿（切牙、尖牙、前磨牙、磨牙）的卡尺测量结果与同一牙齿的数字测量结果进行比较。在确定有效性的第二种方法中，扫描10个牙模并由两名检查者进行测量，将近远中宽度与参考值进行比较，并相互比较。
立方体的数字测量值与参考值相差在0.1毫米以内。牙模重复测量的绝对误差为0.32±0.25毫米。使用组内相关系数（ICC），牙齿的三维图像与参考值之间的总体相关性为0.84。几组牙齿中有效性最高和最低的结果分别是前磨牙和尖牙。检查者间的ICC为0.60，每位检查者与参考值的ICC分别为0.833和0.855。
使用为此目的开发的扫描仪和软件，可以在虚拟研究模型上可靠且有效地测量牙齿及几组牙齿的近远中宽度。在扫描过程中使用较小的旋转角度可能会克服尖牙区域的测量不准确问题。
