Effect of artificial aging on optical properties of ultra-translucent zirconia ceramics of different brands.

OBJECTIVES: This work aimed to evaluate the effect of artificial aging on the translucency and color difference (ΔE) of ultra-translucent zirconia and provide a reference for clinical application. METHODS: The discs of ultra-translucent zirconia from six brands (Wieland, 3M ESPE, Amann Girrbach, Kuraray Noritake, Upcera, and Besmile) were cut and sintered according to each manufacturer's product instructions; the experimental groups were named ZNT, LVP, AG, KAT, UPC, and BSM, respectively. IPS e.max Press was used as the control group (PLT). The specimens (n=6) were prepared with a diameter of 14 mm and a thickness of 1 mm. The specimens were subjected to artificial aging treatment according to the following conditions: in an autoclave at 134 ℃ at 0.2 MPa for 4, 8, and 12 h. According to the CIE1976Lab system, the CIE L*, a*, and b* values of the specimens before and after aging were measured by a co-lorimeter. The translucency parameter (TP) and ΔE were calculated. RESULTS: The mean TP values of each group before aging inorder were PLT>KAT>AG>ZNT>BSM>UPC>LVP. We found no significant difference in translucency in all experimental groups after aging for 4 and 8 h compared with those before aging. After 12 h of aging, the TP values of the KAT and ZNT groups were not significantly different from those before aging, but the TP values of the AG, BSM, LVP, and UPC groups were significantly lower than those before aging (P<0.05). The TP value of the control group was significantly higher than that of the other experimental groups at different stages (P<0.05). ΔE=3.3 was considered the visible color difference, and ΔE was less than 3.3 in all groups after 4 h of aging. After aging for 8 h, ΔE of the UPC group was slightly higher than 3.3. ΔE of the BSM and UPC groups was greater than 3.3 after 12 h of aging. CONCLUSIONS: The TP and ΔE of different brands of ultra-translucent zirconia may change after various aging times. The translucency of some zirconia showed a decreasing trend and the color difference showed an increasing trend with the aging time.

Evaluation of an integrated teaching model of oral preclinical practice based on endodontic-restorative sequential treatment / 口腔疾病防治

Objective@#Evaluate the effect of an integrated teaching model of oral preclinical practice based on endodontic-restorative sequential treatment to provide a reference for the exploration of the teaching mode of the stomatology specialty. @* Methods @#This retrospective study was reviewed and approved by the Ethics Committee. The study was divided into 2 groups. There were 450 2018-grade and 2019-grade students in the discipline integration teaching method (DIT) group, and a preclinical practice course (root canal therapy and fixed prosthetic treatments were integrated into an endodontic-restorative sequential treatment) using the DIT method was applied. There were 443 2016-grade and 2017-grade students in the traditional teaching method (TT) group, and a TT preclinical practice course (root canal therapy and fixed prosthetic treatments training courses were taught separately) was applied. Both groups were taught by the same two teachers. The scores of clinical skills examination and treatment planning were compared between the two groups. In addition, students in the two groups were asked to complete the questionnaires about the teaching methods, and students in Group DIT and their teachers were asked to complete the questionnaires on their degree of satisfaction with the DIT method in the preclinical course. @*Results @# Students in the DIT group had an average score of 90.2 ± 4.16 in the practical skill evaluation, which was higher than that of the TT group (86.3±3.57) (P = 0.001). In the case analysis, 91.8% (413/450) of the students in the DIT group successfully planned the treatment, compared to a significantly lower rate in the TT group of 74.7% (331/443) (P = 0.001). The questionnaire results showed that recognition degrees of cultivated clinical thinking, improved indication analysis ability, improved operational skills, stimulated enthusiasm for learning, and improved autonomous learning were higher in the DIT group than in the TT group, and both teachers (2/2) and 98.4% (443/450) of students recognized the DIT method. @*Conclusions@#The DIT method significantly improved students’ learning quality and ability, proved effective in the endodontic-restorative sequential treatment practice course and was more acceptable to teachers and students. The DIT method is more effective than the TT method in improving students’ clinical thinking and operation ability.

Research Status of High-Purity Metals Prepared by Zone Refining.

The zone refining method is a physical method for effectively purifying metals. Increasing yield and reducing impurity content have always been the focus of its research. This article systematically summarizes the relevant research on the production of high-purity metals by zone refining, including mechanisms, parameter optimization, zone refining types, analysis methods, limitations, and future development directions, and it provides relevant theoretical foundations for the production of high-purity metals as well.