# Study of Root Canal Length Estimations by 3D Spatial Reproduction with Stereoscopic Vision
## 4 Discussion
Tooth models identified as morphologically challenging had fewer measurement errors, suggesting that the measurement reference plane and reference point adjustments could be considered. Although there was no statistically significant difference in measurement values between the SRD and the 2D device, the consistency of measurement values in the Bland-Altman analysis suggested that the measurement environment specific to the 2D device induced psychological assumptions in the examiner and resulted in larger error ranges. Measurement time showed a significant difference between the SRD and the 2D device for the first and second measurements. The average difference in measurement time between the devices was approximately 30 s for all tooth models. Root canal length measurements using the SRD were found to be more accurate and faster than conventional 2D devices. The shortest measurement time was 6.48 s for the second measurement of the #24 tooth model when using the SRD. The #24 tooth model has two cusps and a root canal, making it moderately challenging morphologically, but the angle of the cusp apex used as the measurement reference was acute, making it easier to set the reference point. The average measurement time followed a similar pattern to the morphological difficulty, with the #44 tooth model being the fastest, followed by #24, #36, and #26, indicating that measurements using the SRD are influenced by the morphological difficulty, which affects the measurement time. The factors contributing to the longer measurement time with the 2D unit are believed to be influenced by the specific measurement method of the 2D unit. The measurement procedure with the SRD involves enlarging the image and aligning the axis plane with the occlusal surface to set the first reference point. Then, the axis plane is aligned with the anatomical apical foramen to set the second reference point, which requires approximately five mouse clicks. On the other hand, when measuring with the 2D unit, the slice planes for the first and second reference points, which represent the maximum long axis on the y axis, are first displayed on the screen using the x and y axes. Adjusting one axis causes a shift in the other axis plane, requiring the examiner to make fine adjustments one plane at a time, which increases the measurement time. In addition, the synchronized display of the slice planes during the basic adjustment process places a load on the PC, resulting in operational delays. When adjusting one axis at a time, a shift occurs on the other axis plane, causing the measurement time to be extended as the examiner repeatedly fine-tunes one screen at a time. Additionally, during the operation of basic adjustments, the synchronization of the slice plane for display puts a load on the PC, resulting in operational delays. Furthermore, the influence of factors that extend the measurement time of 2D devices was suggested to have an impact on familiarity, as a weak negative correlation with the frequency of 2D device usage was observed in the first measurement time for the #24 tooth model. In terms of subjective evaluation, feedback questionnaires were administered to assess the evaluation of tooth model measurements that were obtained by the examiners using the SRD. The Likert scale included in the feedback questionnaire referenced survey items evaluating the user experience by displaying endoscopic images on HoloLens [28]. The evaluation using the Likert scale indicated that sufficient stereoscopic vision was achievable, and technical issues such as video latency were resolved. The evaluations through using the SRD regarding the sense of depth and the image latency were obtained in skull models [21] and dental arch models [22], but evaluations specific to root canal morphology in tooth models were not identified. This study successfully obtained the evaluations of tooth models. However, the evaluation of image quality yielded lower results (average rating of 7.9/10).