Coronavirus disease 2019 (COVID-19) has influenced the dental education in Osaka Dental University. The purpose of this study was to summarize the impact of COVID-19 on student performance and the current more appropriate teaching methods by comparing the changes in various oral pathology exam results before and after COVID-19. The experimental and control groups consisted of second year students in the department of dentistry at our university for the years 2019 (136 people) and 2020 (125 people). The impact of different teaching methods on student performance was compared by calculating the mean scores and percentage of failures on various exams and whether or not class credits were earned between the two years. A t test was used to determine statistical significance. The mean scores on the mini-tests were lower in 2020 than in 2019, while the average score of the intermediate exam and the number of students receiving class credits were higher. The mean scores on the practical and unit exams were not statistically significant between the years, but the failure rate on both exams was higher in 2019 than in 2020. COVID-19 had impacts on student performance. A comparison of the mean scores on the exams revealed that the use of microscopy, oral questions, and online animations contributed to improved performance on different exams. Therefore, to promote students' understanding and retention of memorized knowledge of oral pathology, the use of microscopes will be resumed whenever possible, as well as continuation with oral questions and online animations.

Aim or Purpose: The purpose of this study is to obtain basic data for PDT of human squamous cell carcinoma cell line (HSC-3) using the photosensitizer (Ce6), up-conversion particle (UC) and laser with near-infrared light (long wavelength) in vitro and in vivo. Materials and Methods After using MTT Assay to determine a relatively suitable concentration combination, HSC-3 cells were treated with PDT with Ce6 and UC. Cell death by Calcein AM assay, apoptosis by FITC-Annexin V assay, intracellular singlet oxygen (Si-DMA for Mitochondrial Singlet Oxygen Imaging) and reactive oxygen species (ROS Assay Kit-Highly Sensitive DCFH-DA) were examined. HSC-3 cells were injected into the right lingual border of BALB/c nu/nu nude mice (4-weeks-old, female) and treated with PDT after 2 weeks later, then thinly sliced specimens were observed with hematoxylin-eosin staining, apoptosis staining and immunohistochemical staining using anti- cytokeratin (CK)17 antibody. Results: PDT with 0.5ng/μL Ce6 and 0.1ng/μL UC inhibits the cell proliferation of HSC-3 (P<0.05). PDT leads to an increase of intracellular singlet oxygen and ROS amount and apoptosis has occurred (P<0.05). When PDT with Ce6 and UC was performed on the lingual border of nude mice, CK17 positive carcinoma foci were observed and a part of the foci composed of HSC-3 had disappeared, apoptosis was detected in other parts. Conclusions: These results suggest that PDT with long wavelength laser can inhibit the proliferation of cancer cells and lead them to apoptosis.

Oral squamous cell carcinoma (OSCC) is a common malignancy in the oral cavity. Photodynamic therapy (PDT) is a new alternative for the treatment of diseases using photosensitizers (PS) and light. In this study, we used a photosensitizer complex (Ce6-MnNPs—Chlorin e6 combined with up-conversion nanoparticles NaYF₄:Yb/Er/Mn) to investigate the therapeutic effectiveness of this treatment against oral cancer cells. We also investigated the mechanism of action of near-infrared light PDT (NIR-PDT) combined with the Ce6-MnNPs. After determining a suitable concentration of Ce6-MnNPs using an MTT assay, human oral squamous cell carcinoma cells (HSC-3) were treated with NIR-PDT with Ce6-MnNPs. We examined the characteristics of Ce6-MnNPs by transmission electron microscopy (TEM); a zeta potential and particle size analyzer; Fourier-transform infrared spectroscopy (FTIR); cell viability by MTT assay; and apoptosis by FITC-Annexin V/PI assay. The mitochondrial membrane potential (MMP), apoptosis-related mRNA level (Bax and Bcl-2) and p53 protein were also researched. NIR-PDT with 0.5 ng/µL Ce6-MnNPs inhibited the proliferation of HSC-3 (p < 0.05). After treatment with NIR-PDT, changes in the mitochondrial membrane potential and apoptosis occurred (p < 0.01). The ratio of Bax/Bcl-2 and p53-positive cells increased (p < 0.01). These results suggest that this treatment can induce apoptosis of oral cancer cells.