# Augmented Reality-Assisted Surgical Exposure of an Impacted Tooth: A Pilot Study
## 3 Results  
From the three-dimensional analysis of the CBCT, it was possible to ascertain that the impacted canine was in contact with the vestibular part of the root of the lateral incisor and the palatine part of the root of the central incisor. Considering the apical position of the crown and contact with the adjacent roots, accurate surgical exposure was essential to avoid iatrogenic damage to the adjacent teeth. Augmented Reality was, therefore, used to minimise the possibility of surgical error. We used AR software to perform AR-assisted surgery through the real-time superimposition of the 3D file image onto the video frame acquired by the camera positioned in front of the patient's mouth. The final 3D model was created by combining the six anterior teeth taken from the intraoral scan with the same teeth plus the included canine taken from the CBCT segmentation. Preparing the files was quick and easy; the time needed to create the uploaded file in the Augmented Reality software was around 15 min. The 3D file was uploaded into the AR software and manually positioned onto the image of the patient's teeth. Model tracking was straightforward to set up without prior registration of targets or surroundings. Software model tracking was enabled to use 3D files and their anatomical markers, as they are references for the patients. Automatic file recognition is very efficient if the uploaded object closely matches reality. The 3D object was superimposed on the image that corresponds exactly to the video image and the software was, therefore, able to recognise the edges of the object very quickly and has very accurate tracking even with moving objects. When a 3D file containing other digital information (the impacted canine and the roots of the adjacent teeth) was inserted, the software was better able to superimpose the object in video reality. Any failure to align the 3D file with the video frame was marked by the red margin (Figure 12). For this reason, the image of the impacted canine was reduced to just the vestibular portion of the crown to optimise recognition of the file by the software. One drawback found during real-time video tracking was caused by the displacement of the patient's head. This can cause the interruption of object tracking (Figure 13). Figure 12: Failed alignment attempt for the view in AR of a 3D model containing the roots of the teeth adjacent to the impacted tooth. It was, therefore, necessary to manually reposition the file image onto the patient's teeth. Furthermore, if an instrument was placed between the teeth and the camera lens, in this case, the system did not maintain the position of the 3D file and moved. This was an interference phenomenon where the object in the foreground affects the algorithm so the tracking process loses track of the object. The presence of an assistant who repositioned the file every time the software lost tracking was required, making it challenging to use Augmented Reality during surgery. The software produces the 'line model' that is equivalent to the edges of the final virtual data. The lines in different 3D directions are important for determining a good camera position. The software calculated the tracking accuracy through the inlier ratio, which depicts the ratio between found and not found parts of edges; therefore, values from 0 to 1 were allowed. A model tracking inlier ratio of 0.39:0.48 was recorded during the process. A high value inlier ratio (>0.4) means that many edges could be found in the actual camera image, making the tracking result robust. It was possible to extend model tracking with feature tracking to enhance the robustness of model tracking, achieving significantly higher inlier ratio values. The clinical advantage perceived by the surgeon is proportional to the time dedicated to creating files to upload to the software. AR using anatomical references reduces the operation time and costs compared to other surgically-assisted techniques that require surgical or extraoral templates.