A Deep Learning Approach to Segment and Classify C-Shaped Canal Morphologies in Mandibular Second Molars Using Cone-beam Computed Tomography

Introduction: The identification of C-shaped root canal anatomy on radiographic images affects clinical decision making and treatment. The aims of this study were to develop a deep learning (DL) model to classify C-shaped canal anatomy in mandibular second molars from cone-beam computed tomographic (CBCT) volumes and to compare the performance of 3 different architectures. Methods: U-Net, residual U-Net, and Xception U-Net architectures were used for image segmentation and classification of C-shaped anatomies. Model training and validation were performed on 100 of a total of 135 available limited field of view CBCT images containing mandibular molars with C-shaped anatomy. Thirty-five CBCT images were used for testing. Voxel-matching accuracy of the automated labeling of the C-shaped anatomy was assessed with the Dice index. The mean sensitivity of predicting the correct C-shape subcategory was calculated based on detection accuracy. One-way analysis of variance and post hoc Tukey honestly significant difference tests were used for statistical evaluation. Results: The mean Dice coefficients were 0.768 +/- 0.0349 for Xception U-Net, 0.736 +/- 0.0297 for residual U-Net, and +/- 0.660 +/- 0.0354 for U-Net on the test data set. The performance of the 3 models was significantly different overall (analysis of variance, P = .000779). Both Xception U-Net (Q = 7.23, P =.00070) and residual U-Net (Q = 5.09, P = .00951) performed significantly better than U-Net (post hoc Tukey honestly significant difference test). The mean sensitivity values were 0.786 +/- 0.0378 for Xception U-Net, 0.746 +/- 0.0391 for residual U-Net, and 0.720 +/- 0.0495 for U-Net. The mean positive predictive values were 77.6% +/- 0.1998% for U-Net, 78.2% +/- 0.0.1971% for residual U-Net, and 80.0% +/- 0.1098% for Xception U-Net. The addition of contrast-limited adaptive histogram equalization had improved overall architecture efficacy by a mean of 4.6% (P < .0001). Conclusions: DL may aid in the detection and classification of C-shaped canal anatomy.

Automated summary

This study developed a deep learning model to classify C-shaped canal anatomy in mandibular second molars and compared the performance of different architectures. The results showed that Xception U-Net and residual U-Net outperformed U-Net, and the addition of contrast-limited adaptive histogram equalization improved overall architecture efficacy.