Introduction: Study models are an essential part of an orthodontic record. Digital models are now available. One option for generating a digital model is cone-beam computed tomography (CBCT) scanning of orthodon- tic impressions and bite registrations. However, the accuracy of digital measurements from models generated by this method has yet to be thoroughly evaluated. Methods: A plastic typodont was modiﬁed with reference points for standardized intra-arch and interarch measurements, and 16 sets of maxillary and mandibular vinyl- polysiloxane and alginate impressions were made. A copper wax-bite registration was madewith the typodont in maximum intercuspal position to accompany each set of impressions. The impressions were shipped to Or- thoProofUSA (Albuquerque, NM), where digital orthodontic models were generated via CBCT. Intra-arch and interarch measurements were made directly on the typodont with electronic digital calipers and on the digital models by using OrthoProofUSA’s proprietary DigiModel software. Results: Percentage differences from the typodont of all intra-arch measurements in the alginate and vinylpolysiloxane groups were low, from 0.1% to 0.7%. Statistical analysis of the intra-arch percentage differences from the typodont of the alginate and vinyl- polysiloxane groups had a statistically signiﬁcant difference between the groups only for maxillary intermolar width. However, because of the small percentage differences, this was not considered clinically signiﬁcant for orthodontic measurements. Percentage differences from the typodont of all interarch measurements in the al- ginate and vinylpolysiloxane groups were much higher, from 3.3% to 10.7%. Statistical analysis of the inter- arch percentage differences from the typodont of the alginate and vinylpolysiloxane groups showed statistically signiﬁcant differences between the groups in both the maxillary right canine to mandibular right canine (alginate with a lower percentage difference than vinylpolysiloxane) and the maxillary left second molar to mandibular left second molar (alginate with a greater percentage difference than vinylpolysiloxane) seg- ments. This difference, ranging from 0.24 to0.72 mm,is clinically signiﬁcant. Conclusions: In this study, digital orthodontic models from CBCT scans of alginate and vinylpolysiloxane impressions provided a dimensionally accurate representation of intra-arch relationships for orthodontic evaluation. However, the use of copper wax-bite registrations in this CBCT-based process did not result in an accurate digital representation of inter- arch relationships. (Am J Orthod Dentofacial Orthop 2010;137:456.e1-456.e9)
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White AJ, Fallis DW, Vandewalle KS. Analysis of intra-arch and interarch measurements from digital models with 2 impression materials and a modeling process based on cone-beam computed tomography. Am J Orthod Dentofacial Orthop 137:456 e1-9, 2010.