[Application of CAD in custom tray design for teaching of dental postgraduates].

PURPOSE: To evaluate the teaching effect of making custom trays via CAD in dental postgraduates. METHODS: Twenty-seven dental postgraduates from first to third grade at the School and Hospital of Stomatology, Tongji University, Shanghai were given an informed consent to explain and request participation in the study. First, a lecture about the theory and process of fabricating custom tray via traditional hand-made method and CAD technique was given, then the students fabricated custom trays via the two methods and completed an online survey. The working time, margin extension and students' preference were analyzed with SPSS 22.0 software package. RESULTS: The working time was shorter, the margin extension was superior, and students' preference was higher via CAD than traditional method, the difference was significant(P＜0.05). CONCLUSIONS: CAD is more conducive to enhance students' understanding of custom tray manufacturing process and relevant theoretical knowledge. It is recommended to integrate digital technology into dental curriculum.

Trueness of One Stationary and Two Mobile Systems for Three-Dimensional Facial Scanning.

PURPOSE: To evaluate the trueness of one stationary and two mobile systems for 3D facial scanning. MATERIALS AND METHODS: Twenty participants were included in this study. After marking facial soft tissue landmarks, their faces were scanned using three facial scanning systems: the Bellus3D Dental Pro app on an iPad Pro 2020 (Apple; IP); the ARC-7 Face Scanning System (Bellus3D; BA); and the EinScan Pro 2X Plus (Shining 3D Tech; EP) following the manufacturers' operating instructions. Three-dimensional images were reconstructed with corresponding software and saved in object (OBJ) file format. The interlandmark distances were measured and compared to direct caliper measurements, and absolute error (AE) was chosen as the measurement to determine the trueness of the three scanners. The normal distribution and variance of homogeneity were measured, and then the data were analyzed using one-way ANOVA or Kruskal-Wallis H test. The significance level was set at P = .05. RESULTS: For the measurement of interlandmark distances, no significant differences were found among the four measuring techniques, and the mean AEs of the IP, BA, and EP systems were 1.17 ± 0.80 mm, 0.76 ± 0.61 mm, and 0.69 ± 0.65 mm. CONCLUSION: The three facial scanning systems tested provided a reliable 3D facial reconstruction. The portable IP system could meet the clinical requirements for facial scanning, but it is suggested to select the EP and BA systems when a higher trueness is required.

Accuracy of digital complete dentures: A systematic review of in vitro studies.

STATEMENT OF PROBLEM: Reports on digital complete dentures (CDs) are increasing. However, systematic reviews on their accuracy and influencing factors are lacking. PURPOSE: The purpose of this systematic review was to evaluate the accuracy of digital CDs and to summarize influencing factors. MATERIAL AND METHODS: An electronic search of the English language literature from January 2009 to October 2019 was performed in the database PubMed/MEDLINE, with the results enriched by manual searches and citation mining. Factors investigated in the selected articles included the fabrication technique, type of computer-aided design and computer-aided manufacturing (CAD-CAM) system, shape of reference model, long-term service, analytical method, and statistical indicators. RESULTS: A total of 522 articles were identified, of which 14 in vitro articles met the inclusion criteria. Eight articles compared the adaptation of the denture base between digital and conventional methods, 4 studies evaluated the occlusal discrepancies, 4 compared the trueness or adaptation of the denture fabricated with CAD-CAM milling and 3D printing, 1 compared the denture adaptation with 4 different CAD-CAM systems, and 2 evaluated the adaptation of the denture base before and after incubation in artificial saliva. CONCLUSIONS: Most of the studies reported clinically acceptable values for the occlusal trueness and adaptation of digital CDs. The digital CDs showed similar or better adaptation than conventionally fabricated CDs, and the greatest misfit of the intaglio surface was reported in the posterior palatal seal area and border seal area. The fabrication technique, CAD-CAM system, and long-term service were statistically significant in relation to denture accuracy. Clarification is needed concerning the accuracy of digital CDs according to the shape of the cast, the parameters related to the CAD-CAM process, the analytical method, and the statistical indicators. No clear conclusions can be drawn about the superiority of CAD-CAM milling and 3D printing regarding denture accuracy.

Methyl 3-[(E)-furfuryl-idene]dithio-carbazate.

The mol-ecule of the title Schiff base compound, C(7)H(8)N(2)OS(2), prepared by the reaction of methyl dithio-carbazate and furfural in an ethanol solution under reflux, adopts an E configuration; the dithio-carbazate and furan units are located on opposite sides of the C=N double bond. The planar dithio-carbazate group is twisted slightly with respect to the furan ring, making a dihedral angle of 5.2 (1)°. Adjacent mol-ecules are linked by N-H⋯S hydrogen bonding to form a supra-molecular dimer across an inversion center.

2-Methyl-benzaldehyde 2-methyl-benzyl-idenehydrazone.

The mol-ecule of the title compound, C(16)H(16)N(2), is centrosymmetric and the dihedral angle between the benzene ring and the dimethyl-hydrazine mean plane is 16.11 (15)°.

3-Ethyl-4-[(E)-2-methyl-benzyl-idene-amino]-1H-1,2,4-triazole-5(4H)-thione.

Crystals of the title compound, C(12)H(14)N(4)S, were obtained from a condensation reaction of 4-amino-3-ethyl-1H-1,2,4-triazole-5(4H)-thione and 2-methyl-benzaldehyde. In the mol-ecular structure, there is a short N=C double bond [1.255 (2) Å], and the benzene and triazole rings are located on opposite sites of this double bond. The two rings are approximately parallel to each other, the dihedral angle being 1.75 (11)°. A partially overlapped arrangement is observed between the nearly parallel triazole and benzene rings of adjacent mol-ecules; the perpendicular distance of the centroid of the triazole ring from the benzene ring is 3.482 Å, indicating the existence of π-π stacking in the crystal structure.