Comparison of marginal and internal discrepancies of zirconia crowns fabricated by various digital scan methods / 대한치과재료학회지

In this study, marginal and internal discrepancies of zirconia crowns fabricated with the CAD/CAM (computer aided design

U-net based metal segmentation on projection domain for metal artifact reduction in dental CT

Unlike medical computed tomography (CT), dental CT often suffers from severe metal artifacts stemming from high-density materials employed for dental prostheses. Despite the many metal artifact reduction (MAR) methods available for medical CT, those methods do not sufficiently reduce metal artifacts in dental CT images because MAR performance is often compromised by the enamel layer of teeth, whose X-ray attenuation coefficient is not so different from that of prosthetic materials. We propose a deep learning-based metal segmentation method on the projection domain to improve MAR performance in dental CT. We adopted a simplified U-net for metal segmentation on the projection domain without using any information from the metal-artifacts-corrupted CT images. After training the network with the projection data of five patients, we segmented the metal objects on the projection data of other patients using the trained network parameters. With the segmentation results, we corrected the projection data by applying region filling inside the segmented region. We fused two CT images, one from the corrected projection data and the other from the original raw projection data, and then we forward-projected the fused CT image to get the fused projection data. To get the final corrected projection data, we replaced the metal regions in the original projection data with the ones in the fused projection data. To evaluate the efficacy of the proposed segmentation method on MAR, we compared the MAR performance of the proposed segmentation method with a conventional MAR method based on metal segmentation on the CT image domain. For the MAR performance evaluation, we considered the three primary MAR performance metrics: the relative error (REL), the sum of square difference (SSD), and the normalized absolute difference (NAD). The proposed segmentation method improved MAR performances by around 5.7% for REL, 6.8% for SSD, and 8.2% for NAD. The proposed metal segmentation method on the projection domain showed better MAR performance than the conventional segmentation on the CT image domain. We expect that the proposed segmentation method can improve the performance of the existing MAR methods that are based on metal segmentation on the CT image domain.

A bench-top micro-CT capable of simulating head motions

Computational three-dimensional (3D) models of a dental structure generated from 3D dental computed tomography (CT) images are now widely used in digital dentistry. To generate precise 3D models, high-resolution imaging of the dental structure with a dental CT is required. However, a small head motion of the patient during the dental CT scan could degrade the spatial resolution of CT images to the extent that digital dentistry is no longer possible. A bench-top micro-CT has been built to evaluate the head motion effects on the dental CT images. A micro-CT has been built on an optic table with a micro-focus x-ray source and a flat-panel detector. A rotation stage, placed in between the x-ray source and the detector, is mounted on two-directional goniometers that can rotate the rotation stage in two orthogonal directions while the rotation stage is performing the CT scan. The goniometers can make object motions of an arbitrary waveform to simulate head tilting or head nodding. CT images of a phantom have been taken with and without introducing the motions, and the motion effects on the CT images have been evaluated. Object motions parallel to the detector plane have greater effects on the CT images than those against the detector plane. With the bench-top micro-CT, the motion effects have been visually seen at a tiny rotational motion as small as 0.3°. The bench-top micro-CT can be used to evaluate head motion effects on the dental CT images. The projection data, taken with the motion effects, would be used to develop motion artifact correction methods for a high-resolution dental-CT.

Needs and Deeds of CBCT-An Advanced Imaging in Dentistry.

CBCT is an advanced imaging technique that has proved to be a significant adjuvant in the diagnosis of oral and maxillofacial diseases and disorders and also in treatment planning. Since it’s commercial availability from the year 1999(the NEWTON DUT 9000 QR snl, verena, Italy) has been a boon in the field of dentistry for the dental practitioners. Ever since the advent of intraoral periapical radiograph in 1896,dental practitioners had relied on 2-D images for diagnosis and treatment planning. Panoromic radiographs in large has provided detailed information but with the disadvantage of magnification and distortion. CBCT imaging is an advancement in dental imaging providing a 3-D image which gives the external replica of the structures imaged without any magnification or distortion.

Lingual vascular canal assessment by dental computed tomography: A retrospective study.

Background: Lingual vascular canal (LVC) is an important anatomical structure in mandibular anterior region. Trauma to this structure during implant placement has been reported in this study. Dental computed tomography (DCT) provides a three-dimensional visualization of lingual vascular canal. Aim: To assess the frequency, location, and size of LVC using dental CT. Materials and Methods: A retrospective analysis of 75 mandibular DCT was done. Evaluation was done to detect the frequency, size, and number of lingual vascular canal using Seimens Somatom Sensation 64. Results: About 73.3% patients (male=34, female=21) demonstrated presence of LVC with only one patient showing two canals. The mean distance from the inferior border of mandible was 0.5 mm, S.D.±0.70. The mean diameter of the canal was 0.31 mm, S.D.±0.70. Conclusion:Dental CT provides adequate information regarding frequency, number, and size of lingual vascular canal, which is an important anatomical structure in mandibular anterior region.