Evaluation of tip and torque on virtual study models: a validation study

Background: The objectives of this study were to develop and validate a novel analysis protocol to measure linear and angular measurements of tip and torque of each tooth in the dental arches of virtual study models. Methods: Maxillary and mandibular dental casts of 25 subjects with a full permanent dentition were scanned using a three-dimensional model scanner. Sixty points per arch were digitized on each model, five points on each tooth. A custom analysis to measure linear distances and angles of tip and torque was developed using a new reference plane passing as a best-fit among all of the lingual gingival points, with the intermolar lingual distance set as the reference X-axis. The linear distances measured included buccal, lingual, and centroid transverse widths at the level of canines, premolars, and molars as well as arch depth and arch perimeter. Results: There was no systematic error associated with the methodology used. Intraclass correlation coefficient values were higher than 0.70 on every measure. The average random error in the maxilla was 1.5 degrees +/- 0.4 degrees for torque, 1.8 degrees +/- 0.5 degrees for tip, and 0.4 +/- 0.2 mm for linear measurements. The average random error in the mandible was 1.2 degrees +/- 0.3 degrees for torque, 2.0 degrees +/- 0.8 degrees for tip, and 0.1 +/- 0.1 mm for the linear measurements. Conclusions: A custom digital analysis protocol to measure traditional linear measurements as well as tip and torque angulation on virtual dental casts was presented. This validation study demonstrated that the digital analysis used in this study has adequate reproducibility, providing additional information and more accurate intra-arch measurements for clinical diagnosis and dentofacial research.