# A Comparison of Dental Arch Width and Length on 3D Digital and Plaster Models
## 1 Introduction  
Accurate diagnostics in orthodontic treatment planning are essential for correct identification of the orthodontic problem and the underlying causes. This allows orthodontists to create a personalized treatment plan and increases the likelihood of achieving optimal results for each patient. Among the standard components of orthodontic diagnostic records, conventional plaster casts play a significant role in diagnostic procedures and consequent treatment planning, evaluation of the treatment progress and outcomes, and record keeping [1]. However, the impression and pouring process of plaster casts presents certain drawbacks that can lead to errors, such as the distortion of impression material and volumetric deformation of the plaster casts [2, 3]. Furthermore, plaster casts require a physical storage space, and there is the risk of damage or breakage [2, 3, 4, 5, 6].  
In recent years, the digitization of orthodontic dental models has made significant changes in orthodontics, providing numerous benefits. Digital models have significantly improved efficiency and accessibility, allowing quick access to patient records and seamless exchange of patient data for communication with other specialists [2]. Furthermore, digital dental models offer significant advantages in treatment planning, as they enable the creationof virtual setups and the fabrication of customized aligners and brackets [7]. Additionally, digital models eliminate the need for physical storage space and the risk of damage or breakage [2].  
Digital three-dimensional (3D) models can be obtained by scanning a plaster model or impression with a 3D model scanner, directly scanning dental arches with an intraoral scanner, or generating from CBCT scans [8].  
Previous studies have demonstrated the high accuracy, reproducibility, and reliability of orthodontic measurements made on digitized models obtained from plaster casts or impressions compared to conventional plaster models [9; 10; 11; 12; 13; 14]. It is important to note that digitized models share certain drawbacks with plaster models, including impression and pouring process errors, as well as patient discomfort. The disadvantages associated with plaster models can be avoided by using direct intraoral scanning [15]. However, several factors can impact the precision of digital impression, such as the examiner's experience, the scanning strategy, and software algorithms [16; 17; 18; 19; 20; 21].  
Most studies have reported that intraoral scanners have higher accuracy compared to digitized models or conventional plaster models, especially when the scan length is shorter. When comparing the accuracy of the full arch impression, it appears to be lower than that of conventional plaster models [22; 23; 24; 25; 26]. Moreover, the presence of dedentulous areas, restorative materials, saliva, or blood can also affect the accuracy of digital impressions [27; 28; 29].  
The objective of this study was to determine potential deviation in measurements of commonly used orthodontic variables--intermal width (IMW), intercanine width (ICW), and arch perimeter (AP)--when measured on three-dimensional images compared to measurements performed on plaster models obtained from alginate impressions using a hand-held digital vernier caliper.