Comparison of orthodontic measurements on dental plaster casts and 3D scans

Over recent years, we have witnessed a growing trend in orthodontics toward the use of three-dimensional (3D) techniques for diagnostic purposes, treatment planning, and fabricating appliances. This study was undertaken to compare the traditional manual technique of using vernier calipers to take orthodontic measurements on plaster dental casts versus an all-digital measuring technique based on virtual 3D scans of casts. In this study, we focused on the quantitative agreement between and time requirements of both methods.

Plaster casts obtained from the jaws of 55 fully dentate patients who had not previously undergone orthodontic treatment underwent 3D scanning using a white-light scanner (d-Station (3D); Breuckmann, Meersburg, Germany). Once the casts had been blinded by an independent individual, three examiners with different degrees of expertise in dentistry and orthodontics measured the mesiodistal widths of teeth 6-6 in each jaw. A randomized sequence was used when taking the measurements three times using OnyxCeph(3TM) analysis software (Image Instruments, Chemnitz, Germany) and a dental vernier caliper. Bland-Altman plots were used to illustrate the level of agreement between the two methods, standard deviations of repeated measurements were calculated to assess their reproducibility, and the Wilcoxon's signed-rank test was employed to compare their time requirements.

The Bland-Altman analysis of all single values revealed no statistically significant difference between the software-based and caliper-based measurements of mesiodistal tooth width. Assuming the presence of normal distribution, the limits of agreement disclosed a 95% probability for the software values to range between +0.499 and -0.545 mm of the same value measured with the caliper. The standard deviations of repeated measurements were 0.33 mm with the software and 0.21 mm with the caliper. The digital method required significantly less time (p<0.01); however, differences were observed to be associated with operator experience.

Inexperienced examiners, in particular, take measurements of mesiodistal tooth dimensions faster using a software-based method than when using a dental vernier caliper. Similar values were obtained with both methods.