The accuracy and reliability of measurements made on computer-based digital models.

For reasons of convenience and economy, orthodontists who routinely use and maintain pre- and posttreatment plaster casts are beginning to use computer-based digital models. The purpose of this study was to determine the accuracy (validity), reproducibility (reliability), efficacy, and effectiveness of measurements made on computer-based models. A plastic model occlusion ie, dentoform, served as a gold standard to evaluate the systematic errors associated with producing either plaster or computer-based models. Accuracy, reproducibility, efficacy, and effectiveness were tested by comparing the measurements of the computer-based models with the measurements of the plaster models--(1) accuracy: one examiner measuring 10 models made from a dentoform, twice; (2) reproducibility and efficacy: two examiners measuring 50 models made from patients, twice; and (3) effectiveness: 10 examiners measuring 10 models made from patients, twice. Reproducibility (reliability) was tested by using the intraclass correlation coefficient. Repeated measures of analysis of variance for multiple repeated measurements and Student's t-test were used to test for validity. Only measurements of maxillary and mandibular space available made on computer-based models differed from the measurements made on the dentoform gold standard. There was significantly greater variance for measurements made from computer-based models. Reproducibility was high for measurements made on both computer-based and plaster models. In conclusion, measurements made from computer-based models appear to be generally as accurate and reliable as measurements made from plaster models. Efficacy and effectiveness were similar to those of plaster models. Therefore, computer-based models appear to be a clinically acceptable alternative to conventional plaster models.