Orthodontic study cast analysis--reproducibility of recordings and agreement between conventional and 3D virtual measurements.

Digital imaging of dental casts has become an alternative to conventional cast analysis in orthodontic treatment planning. The reproducibility of angular measurements made on virtual digital models has not as yet been evaluated. In order to study reproducibility for and agreement between a conventional analysis technique and virtual 3D imaging, 20 dental casts from subjects in the early mixed dentition, were measured twice with each technique by two orthodontists. Variables of interest were incisor rotation, angulation and irregularity, arch width, arch circumference, overjet, and overbite. Standard deviation (Dahlberg 1940) and coefficient of variation were used for evaluation of reproducibility. Mean differences between methods and examiners, correlation between mean differences and mean levels and 95% limits of agreement were used for describing systematic errors. The conventional technique showed less intraexaminer variation for angular variables than the 3D imaging method. Linear variables, with the exception of overbite, showed no clear trend as regards differences in reproducibility between the two methods. In general, examiner 1 showed less intraexaminer variation than examiner 2. The mean differences between the two methods expressed higher values for assessment of rotations with the O3DM method. Both angular and linear variables exhibited poor 95% limits of agreement. The conventional technique showed better overall reproducibility and thus appears to be more suitable for scientific work. However, the reproducibility attained by O3DM is clearly acceptable for clinical use. The two methods should not be used interchangeably.

Evaluation of the validity of tooth size and arch width measurements using conventional and three-dimensional virtual orthodontic models.

Measurements and different analyses of dental casts are essential for precise diagnosis of an orthodontic case. At present, virtual computerized models, such as OrthoCAD, are available for clinicians, supplemented by dedicated software for performing needed measurements on them. The purpose of this study was to test the accuracy of measuring casts with the aid of calipers or OrthoCAD and compare these two techniques. Twenty setups using artificial teeth corresponding to various malocclusions were created. Impressions were taken of them, providing 20 plaster and 20 virtual orthodontic models. Measurements of mesiodistal tooth dimension as well as intercanine and intermolar width were made on both. Additionally, values of tooth size were calculated from the isolated artificial teeth removed from the setups and of arch width from the existing setups. The resulting values were compared by the use of nonparametric statistics, and methods' errors were also calculated. Results showed the methods being highly valid and reproducible for both tooth size and arch width. For the tested clinically applicable methods, measurement with digital calipers on plaster models showed the highest accuracy and reproducibility, closely followed by OrthoCAD. Digital calipers seem to be a more suitable instrument for scientific work. However, OrthoCAD's accuracy is clinically acceptable, and most likely, considering its present advantages and future possibilities, the examined or an equivalent 3D virtual models' procedure would become the standard for orthodontic clinical use.