Effect of high-speed sintering on the marginal and internal fit of CAD/CAM-fabricated monolithic zirconia crowns.

This study compared the marginal and internal fit of zirconia crowns fabricated using conventional and high-speed induction sintering. A typodont mandibular right first molar was prepared and 60 zirconia crowns were fabricated: 30 crowns using conventional sintering and 30 crowns using high-speed sintering. We presented a new evaluation methodology to measure the marginal and internal fit of restorations through digital scanning, aligning the two datasets, and measuring the distance between two arbitrary point sets of the datasets. For the marginal fit, we calculated the maximum values of the shortest distances between the marginal line of the prepared tooth and that of the crown. The calculated values ranged from 359 to 444 µm, with smaller values for the high-speed sintered crowns (P < 0.05). For the internal fit, we employed mesh sampling and computed the geodesic distances between the prepared tooth surface and the crown intaglio surface. The measured values ranged from 177 to 229 µm with smaller values for the high-speed sintered crowns, but no significant difference was found (P > 0.05). Based on our results, the high-speed sintering method can be considered a promising option for single-visit zirconia treatment in dental practice.

A digital workflow for pair matching of maxillary anterior teeth using a 3D segmentation technique for esthetic implant restorations.

We investigated a state-of-the-art algorithm for 3D reconstruction with a pair-matching technique, which enabled the fabrication of individualized implant restorations in the esthetic zone. This method compared 3D mirror images of crowns and emergence profiles between symmetric tooth pairs in the anterior maxilla using digital slicewise DICOM segmentation and the superimposition of STL data. With the outline extraction of each segment provided by 100 patients, the Hausdorff distance (HD) between two point sets was calculated to identify the similarity of the sets. By using HD thresholds as a pair matching criterion, the true positive rates of crowns were 100, 98, and 98%, while the false negative rates were 0, 2, and 2% for central incisors, lateral incisors, and canines, respectively, indicating high pair matching accuracy (> 99%) and sensitivity (> 98%). The true positive rates of emergence profiles were 99, 100, and 98%, while the false negative rates were 1, 0, and 2% for central incisors, lateral incisors, and canines, respectively, indicating high pair matching accuracy (> 99%) and sensitivity (> 98%). Therefore, digitally flipped contours of crown and emergence profiles can be successfully transferred for implant reconstruction in the maxillary anterior region to optimize esthetics and function.

ZnS Quantum Dot Based Acetone Sensor for Monitoring Health-Hazardous Gases in Indoor/Outdoor Environment.

This study reports the ZnS quantum dots (QDs) synthesis by a hot-injection method for acetone gas sensing applications. The prepared ZnS QDs were characterized by X-ray diffraction (XRD) and transmission electron microscopy analysis. The XRD result confirms the successful formation of the wurtzite phase of ZnS, with a size of ~5 nm. Transmission electron microscopy (TEM), high-resolution TEM (HRTEM), and fast Fourier transform (FFT) images reveal the synthesis of agglomerated ZnS QDs with different sizes, with lattice spacing (0.31 nm) corresponding to (111) lattice plane. The ZnS QDs sensor reveals a high sensitivity (92.4%) and fast response and recovery time (5.5 s and 6.7 s, respectively) for 100 ppm acetone at 175 °C. In addition, the ZnS QDs sensor elucidates high acetone selectivity of 91.1% as compared with other intrusive gases such as ammonia (16.0%), toluene (21.1%), ethanol (26.3%), butanol (11.2%), formaldehyde (9.6%), isopropanol (22.3%), and benzene (18.7%) for 100 ppm acetone concentration at 175 °C. Furthermore, it depicts outstanding stability (89.1%) during thirty days, with five day intervals, for 100 ppm at an operating temperature of 175 °C. In addition, the ZnS QDs acetone sensor elucidates a theoretical detection limit of ~1.2 ppm at 175 °C. Therefore, ZnS QDs can be a promising and quick traceable sensor nanomaterial for acetone sensing applications.