Evaluation of the Reliability, Reproducibility and Validity of Digital Orthodontic Measurements Based on Various Digital Models among Young Patients

Abstract

The advantages of intraoral model scanning have yielded recent developments. However, few studies have explored the orthodontic clinical use of this technique particularly among young patients. This study aimed to evaluate the reliability, reproducibility and validity of the orthodontic measurements: tooth width, arch length and arch length discrepancy in each digital model obtained by model scanner and intraoral scanner, relative to a plaster model. Arch length measured using two methods: curved arch length (CAL) measured automatically by digital program and sum of sectional liner arch length (SLAL) measured sum of anterior and posterior liner arch lengths. Arch length discrepancy calculated each arch length measurement methods: curved arch length discrepancy (CALD) and sum of sectional liner arch length discrepancy (SLALD). Forty young patients were eligible for the study. A plaster model (P), model-scanned digital model (MSD) and intraoral scanned digital model (ISD) were acquired from each patient. The reliability of the measurements was evaluated using Pearson's correlation coefficient, while the reproducibility was evaluated using the intraclass correlation coefficient. The validity was assessed by a paired t-test. All measurements measured in P, MSD and ISD exhibited good reliability and reproducibility. Most orthodontic measurements despite of CAL in MSD exhibited high validity. Only the SLAL and SLALD in ISD group differed significantly, despite the good validity of the tooth width, CAL and CALD. The measurements based on the digital program appeared high reliability, reproducibility and accurate than conventional measurement. However, SLAL and SLALD in ISD group appeared shorter because of distortion during intraoral scanning. However, this could be compensated by using digital programed curved arch. Although the validity of SLAL and SLALD in the ISD group differed statistically, the difference is not considered clinically significant. Although MSD and ISD are acceptable for a clinical space analysis, clinicians should be aware of digital model-induced errors.

Keywords: arch length; arch length discrepancy; digital model; digital orthodontic measurement; intraoral scanned digital model; intraoral scanner; tooth width.

Figure 1

Illustration of the flow chart of model production according to model type.

Figure 2

A representative plaster model and images scanned using a model scanner and intraoral scanner. (A) Plaster model. (B) Stereolithography language (STL) file format image scanned using the Freedom UHD^® 3D scanner(Dof Inc., Seongdong-gu, Seoul, Korea) (C) Object code (OBJ) file format image scanned using CS3600^®(Carestream Dental, Atlanta, GA, USA). The latter was converted to a STL file for measurements.

Figure 3

(A) Measurement of the mesial-distal width of the tooth and the arch length. (B) Sectional liner arch length (SLAL) measured using Maestro 3D^®. (C) Automatically designed curved arch length (CAL) using Maestro 3D^®. (D). Definition of sectional full arch length discrepancy (SLALD). (E) Definition of digital full arch length discrepancy (CALD).

Figure 4

Illustration of differences in the sectional anterior arch length measurement caused by a distortion of intraoral scanning (A) and arch shape distortion. (B). Tooth labial-lingual width distortion. Red line: actual, yellow line: difference by distortion, blue line: curved arch.