# A Comparison of Dental Arch Width and Length on 3D Digital and Plaster Models
## 4 Discussion  
Precise measurements and thorough analysis of study models are essential elements for the efficacy of orthodontic treatment. The present study was performed to evaluate and compare commonly used orthodontic variables (IMW, ICW, and AP) on plaster models and 3D digital models. The canine and molar relationships have been identified as predictors of stability of orthodontic treatment results, while arch length is one of the most crucial parameters for space analysis (representing available space) [25; 30]. The measurements of the maxillary and mandibular intercanine and intermalor width significantly differed between the methods. Digital analyses gave significantly lower values. The greater difference in width measurements between manual and digital methods was 1.23 mm. In several studies, the discrepancy in measurements between manual calipers and digital analyses was found to be clinically insignificant, with variances of less than 1.5 mm [2; 31; 32]. These findings underscore that the differences in measured values are minor and do not impact therapeutic diagnosis. In our study, the agreement between methods for mandibular ICW measurements was weaker than that for the maxillary ICW, possibly due to the smaller dimensions being assessed. The differences between manual and digital measurements of mandibular and maxillary IMW were smaller than the difference observed in ICW, which confirms that longer dimensions have better agreement between measurement methods. Regarding the mandibular and maxillary arch perimeter, the obtained differences between the measurements on plaster models significantly differed from digital models in a range from 2.48 to 2.78 mm, which could be clinically significant. In contrast, no significant difference was observed between measurements obtained from digital models. The linear distances (ICW and IMW) obtained from digital models were observed to be smaller compared with the measurements taken from plaster models. In contrast, digital measurements yielded larger values when assessing the arch perimeter. Some authors have also noted that digital measurements of linear distances often result in smaller values compared to manual measurements [12; 13; 33]. The study conducted by [PERSON] et al. demonstrated certain similarities in comparison to our results. Notably, their research highlighted superior measurement repeatability in digital models, particularly those obtained from intraoral scans and silicone impressions, when compared to plaster models. Furthermore, the alignment patterns observed in the maxilla and mandible, emphasizing advantages in arch width over length and intermalor dimensions over intercanine ones, align with our findings. It is noteworthy that the differences identified were more frequently associated with random errors than with systematic discrepancies [33]. The comparison between 3D digital models and plaster models in this study highlights the advantages of digital models in terms of accuracy and reliability. The standardized nature of digital scanning techniques contributes to the enhanced consistency observed among digital models, offering potential benefits for orthodontic assessments and treatment planning [9; 12; 21]. The identification of points represents significant sources of random measurement error, with difficulties in accurately identifying and placing landmarks leading to potential inaccuracies. The reliability of model analysis is substantially influenced by the accuracy of landmark identification, which is closely related to the shape of the anatomical structure being measured and the operator's experience [32; 34]. In this study, we demonstrated that the precision of defining anatomical landmarks can lead to error reduction if the examiners have experience. However, it is important to recognize that inaccuracies in point identification may exist. Point positioning, on the other hand, relies on the measuring instrument used and the specific item being measured [3].