## 4 Discussion
The 3D mapping technique provided a user-friendly tool that converted the obtained data into a quantitative color-coded map. For example, [PERSON] et al. used 3D computer tomography to describe acute and subacute scaphoid fracture morphology [40]. To the best of our knowledge, our present work was the first study to evaluate the association between unilateral premolar scissors bite and mandibular symmetry via the 3D distance mapping technique. The distance mapping algorithm computed the distance distribution between any two opposing surfaces by sampling the surface of the original mandible. Then, it identified the corresponding minimum distance to the mirrored mandible. The color-coded distance maps can be read similarly to topographic maps. Each color represented a different distance. So, the morphological differences can be quickly located. Moreover, different from [PERSON] et al. [12], who only evaluated the entire mandible, this study also assessed mandibular functional units, respectively. Therefore, more detailed information can be identified and compared. Different from the previous measurements, this methodology will enable researchers to effectively interpret the imaging, save measuring time, reduce human error, and facilitate further medical research. In this retrospective study, all the images were not taken specifically for this experiment. Subjects were selected from the image database of the Hospital of Stomatology, Guanghua School of Stomatology, Sun Yat-sen University, from 2014 to 2021. As a digital tool, the 3D distance mapping method itself is not risky when calculating and visualizing the data. Consideration of the risks of CBCT is still meaningful, even if the radiation dose is lower than before. Future research needs to follow and respect ALARA (As Low As Reasonably Achievable) principles [41] and other statements such as the guideline of the European Academy of DentoMaxilloFacial Radiology (EADMFR) [42]. To minimize the risk, improvements in hardware and software components can reduce the radiation dose to the patients, including changes in sensor technology and a smaller field of view depending upon the application [43]. Various exposure protocols can be chosen according to different groups, such as child mode, adult mode, high-resolution mode, high-definition mode, and endodontic mode [44]. Moreover, shielding devices are necessary to reduce doses for the patients [42]. The present study is limited to the control group. Because in practice, it was not realistic to find the ideal normal individuals in a dental hospital. However, to avoid affecting the results, the control samples used in this retrospective study were carefully selected from hospital imaging databases. Their occlusions were relatively normal, without scissors bite. Images with severe dental pathology were avoided in this experiment. Moreover, a longitudinal study would require if the study wants to evaluate the effects of growth and development in mandibular asymmetry. However, for ethical reasons, it is unrealistic to follow a malocclusion without treatment. This study suggested that this technology may have potential applicability in various fields. The evaluation of bone structure with this method will be helpful for orthodontic treatment planning and clinical curative effect evaluation after treatment. Moreover, this technology also showed its potential and advantages in computer-aided design in orthognathic surgery, prosthodontics, airway analysis, etc. [45; 46; 47]. Of course, the clinical applications are not limited to mandible or dentistry, and they can also be applied in orthopedics.