Objective: To observe the effect of hypoxia on changes of proliferation ability of cultured human periodontal ligament fibroblasts (HPLFS) in vitro. Methods: HPLFS were randomly divided into two groups (experimental group and control group) by different oxygen concentrations. The oxygen concentration of control group was 21%. The oxygen concentrations of experiment group were 10%, 5% and 2%. The proliferation ability of HPLFS was detected by MTT colorimetric assay. The cell ultrastructure was observed by transmission electron microscope (TEM). Results: MTT assay results showed that compared with the control group, at the 12 h and 24 h, cell proliferation was enhanced with the hypoxia degree. At 24 h, cell proliferation showed significant differences. At 48 h and 72 h, proliferation of the cultured HPLFS in severe hypoxia group reduced significantly. Observed by TEM, at 24 h, not only the number of mitochondria, rough endoplasmic reticulum but also cell process increased in the cultured HPLFS in severe hypoxia group. At 72 h, the number of lysosome increased and the cell structure degenerated. Conclusion: Long-time severe hypoxia may lower the repair and remodeling abilities of periodontium, which might be one of the important etiological factors of periodontal disease under condition of high altitude.

Objective:To investigate the application of digital teaching system in the teaching of onlay abutment teeth preparation for trainees receiving standardized residency training of stomatology (abbreviated as "resident trainees").Methods:The digital simulation teaching system unit was established by using the tissue morphology memory characteristics of 3Shape Trios oral scanner and Geomagic Control X 3D imaging design software. Eighteen resident trainees from the Daping Hospital were randomly divided into two groups, nine in the control group, preparing the onlay resin tooth model independently after taking the routine PPT + demonstration operation teaching; the other nine in the test group, preparing onlay model after learning digitization teaching system unit. All resident trainees prepared on three models respectively. After the teaching, the amounts of preparation and polymerization degree were compared between the two groups, making a summary teaching evaluation. Amounts of preparation, polymerization degree and teaching satisfaction were tested by independent-samples t-test with software SPSS 21.0. Results:Compared with the resident trainees in control group, the t values of width difference of buccal shoulder, lingual shoulder, proximal middle shoulder and distal middle shoulder, height difference of functional cusp and the lowest part of the proximal middle fossa, and degree of buccal polymerization, lingual polymerization and distal polymerization were 6.21, 6.12, 3.83, 4.73, 3.73, 4.79, 8.35, 4.35, and 6.69 respectively , while P values were respectively as <0.001, <0.001, <0.001, <0.001, 0.001, <0.001, <0.001, <0.001, and <0.001, with statistical difference ( P<0.05) . The t values of height difference of non-functional cusp, the lowest part of the distal middle fossa and degree of proximal polymerization were 1.02, 1.97, and 1.43, while P values were respectively 0.312, 0.054, and 0.158, with no statistical difference ( P>0.05). All indicators of teaching satisfaction were statistically significant ( P<0.05). Conclusions:The application of digital teaching system is conducive to improving the onlay abutment teeth preparation level of residents with high teaching satisfaction, which is worth promoting in clinical practice.