A Comparative Study of Plaster Casts and Digital Models for Orthodontic Measurements in Different Crowding Severities

Objectives: This study aimed to evaluate the accuracy of linear measurements between the traditional gold-standard plaster model and digital models (cast scans and intraoral scans) across different severities of dental crowding. Methods: Fifteen subjects requiring orthodontic treatment were divided into two groups based on crowding severity: mild (≤3.0 mm) and moderate to severe (>3.0 mm). For each subject, three types of models were generated: plaster cast (PC), digital cast scan (CS), and intraoral scan (IOS). Linear measurements were taken using digital calipers for PC and Ortho Analyzer™ software for CS and IOS. The accuracy of measurements was determined using the deviation between the plaster casts and digital models. The accuracy was analyzed using Welch’s ANOVA and the Games–Howell multiple comparison test (p<0.05). Results: All three model types demonstrated high intra- and inter-examiner reliability (ICC>0.97). No significant differences were found in the clinical arch length or Bolton ratios between model types. Minor, non-significant underestimations in total tooth width were observed in the digital models, particularly in maxillary teeth with moderate-tosevere crowding (maximum mean difference: 1.65 mm; p=0.06). Conclusions: Both cast scans and intraoral scans are reliable alternatives to plaster casts for orthodontic measurements. While digital models slightly underestimated total tooth widths and Bolton ratios and overestimated clinical arch lengths, these variations remained within clinically acceptable limits. Operator training and scanning protocol standardization remain critical in crowded dentitions.