The technology underlying AI applications was machine learning, which iteratively learned the inherent statistical patterns from specific datasets and algorithms5. However, as the most effective number of characteristic annotators was unclear, the data used to train the machine was small, and the result generation process was invisible, there were doubts about the accuracy and replicability8, 27.
This study developed a SSD and V2V-PoseNet based system for image recognition and characteristic points capture, then implant position design. Based on the deep learning frame, the datasets were trained using the designed SSD algorithm to generate image identification and location models. Besides that, V2V-PoseNet method was used to detect the feature of the ROI. After training the image set, 12 independent test images were used to evaluate the trained model. Our AI system showed good performance for the implant position design and the accuracy is similar with the recently reported statistic guide28.
Moreover, we found that the number of characteristic annotators influenced the performance of our AI system. A trend of more characteristic annotators induced more accuracy was observed. In brief, Group C performed better than Group A and B, for global (apical and coronal), angular, depth, lateral, bucco-lingual and mesia-distal deviations. In another word, Group C was the most accurate, and it was used to further improve the AI system. This phenomenon reminded us that our AI system was full of learning ability, and more information contributed to the accuracy.
In Group C, the average deviations were 0.6638±0.2651 (range: 0.2060 to 1.109 mm) for the coronal deviation, 1.157±0.3350 (range: 0.5840 to 1.654 mm) for the apical deviation, and 5.307 ±2.891° (range: 2.049 to 10.90°) for the angular deviation (Table 2, Fig. 6A-B), and the results are similar with the traditional statistic guide28. For instance, Zhaozhao et al.26 recently reported 0.85mm (range:0.42 to 1.51 mm) global deviation at the coronal level, 0.93 mm (range: 0.64 to 1.72 mm) global deviation at the apical level, and 3.11° (range:0.66 to 4.95°)for the angular deviation. Vinci et al.6 reported 0.43 mm (range: 0.30–1.77 mm) global deviation at the apical level and 0.28 mm (range: 0.08–1.18 mm) at the coronal level.
For the depth deviation, the average deviation was -0.1886±0.4639 for Group C, smaller than Group A (-0.2085±0.5605) and Group B (-0.2742±0.5060) (Table 2, Fig. 6C). And for all the three groups, the implants were in a more coronal direction compared to the virtual position. This phenomenon also has been reported by Vercruyssen et al29 and Zhaozhao et al26. However, as more characteristic annotators been calculated, the deviation decreased.
Regarding the bucco-lingual deviation, the implants tended to move buccally both at coronal and apical level, and a greater deviation was found at the apical level. The coronal/apical deviation may occur during the processes of either drilling or implant placement26.However, the bucco-lingual deviation was small in Group C (Table 3, Fig. 6E). As to the mesia-distal deviation, for Group C, there were nearly no tendency neither toward mesial nor distal, both at the coronal and apical level (Table 3, Fig. 6F). For Group C, tiny bucco-lingual and mesia-distal deviations would bring mechanical equilibrium, which be beneficial to the long-term success of dental implant.
The high accuracy of our AI system mostly depended on SSD, a deep learning technology based superior convolutional neural network (CNN) algorithm30. SSD is one of the best AI models in image identification and location, which consist of at least 16 layers31,32. It is an effective object detector for multiple targets recognition within just one stage10. Yao-Kuang et al.31 used a SSD system for diagnosing esophageal cancer, which showed good diagnostic performance and the accuracy can achieve 90%. Orhan et al.33 also reported that the volume calculation with CNN algorithm were compatible with the clinicians.
The high accuracy of our AI system also attributes to the V2V-PoseNet algorithm. It’s a 3D CNN put forward by Gyeongsik Moon et al34, which provided accurate estimates. V2V-PoseNet took voxelized grids as inputs and estimated the per-voxel likelihood for the key parameters. This 3D CNN can detect the actual contour of the objects without perspective distortion and estimate the per-voxel likelihood of each parameter, so it can learn the designed task easily34.
To sum up, SSD and V2V-PoseNet were used to train the datasets32, 35, and the deep learning neural network, especially the 10 characteristic annotators based algorithm group, was fairly accurate and clinically reliable. The core of SSD model is to explore objects and corresponding locations in given bounding boxes, realizing object location prediction36. It relatively simplified the processing, while increasing the identification.
However, due to the limited test size, the results in this study should be interpreted with caution, and more training images were needed to improve the performance of our system. Besides that, there are some real clinical elements, such as limited view and inter-occlusal distance37 that the present in vitro study cannot reflect. Moreover, based on the pronounced learning abilities of the AI system, in the future more key parameters would be incorporated into the algorithm to figure out the best implant plan.