Purpose: Bulk-fill resin composite (bulk-fill resin) permits better light transmittance than conventional light-cured resin composite and can be polymerized even in deep dental cavities that are difficult to reach using light irradiation. Resin composite loses its mechanical properties due to water sorption and becomes discolored over time. However, there are few reports on the water sorption and discoloration of bulk-fill resins. In this study, the effect of water sorption on the discoloration of commercially available bulk-fill resins of different compositions was evaluated.

 Methods: Four bulk-fill resins were tested: GRACEFIL Bulk Flo (GC), Sonic Fill 2 (Kerr, USA), Tetric N-Ceram Bulk Fill (Ivoclar Vivadent, Liechtenstein), and BEAUTIFIL Bulk Flow (Shofu). Each was filled into stainless steel molds (diameter, 15.0 mm; thickness, 1.0 mm), polymerized using light irradiation from opposite sides for 90 s each, then polished with waterproof sandpaper (#1000 grit) and kept in water at 37℃ for 24 h. Water sorption of each specimen was measured following the standard JIS6514: 2013, dried using a desiccator, immersed in distilled water for 7 days, then weighed (n=5). The specimens were dried again, weighed, then the water sorption was calculated. The specimens were immersed in red wine for 7 days at 37℃, and their color tones before and after immersion were measured using a spectrophotometer (CM-3610d; Konica Minolta). The color changes due to discoloration of the bulk-fill resins were quantified using CIELab (ΔE^＊ab) and CIEDE2000 (ΔE₀₀) values (n=5) and compared using one-way ANOVA. Tukey’s multiple comparison test was used to determine significant differences between groups (α=0.05). Pearson’s product-moment correlation coefficient was used to analyze the correlation between water sorption and color difference of the bulk-fill resins.

 Results: GRACEFIL Bulk Flo had significantly lower water sorption and color difference (ΔE^＊ab, ΔE₀₀) in comparison with the other bulk-fill resins, while the corresponding values for BEAUTIFIL Bulk Flow were significantly higher than the others. All bulk-fill resins had color differences that exceeded the value considered to be visually discernable (ΔE^＊ab＞3.3, ΔE₀₀＞2.3). Furthermore, a positive correlation was observed between water sorption and color difference (p＜0.001).

 Conclusion: Water sorption and discoloration differ markedly among various bulk-fill resins. A strong positive correlation was measured between water sorption and discoloration. Water sorption of bulk-fill resin is an important factor affecting discoloration.

 Purpose: We conducted a questionnaire survey of students who undertook CAD/CAM inlay restoration practice using an intraoral scanner as part of basic restorative training at the Showa University School of Dentistry for third and fourth year students, and examined the educational effects of this training and future issues.

 Methods: Questionnaires were collected and evaluated for students who attended the practical training from 2019 to 2022. The questions were as follows.

 1. Are you interested in digital dentistry?

 2. Do you think this practice is effective for learning?

 3. Did you gain a better understanding of CAD/CAM inlay restoration using an intraoral scanner?

 4. How difficult was the content of this practice?

 5. Which step was the most interesting for you?

 6. Which step was the most difficult?

 7. How would you rate the use of the intraoral scanner for impression-taking compared with conventional impression-taking using impression materials?

 8. As a dentist, do you want to practice using a CAD/CAM system in the future?

 9. Do you want to continue taking practical practice using the CAD/CAM system in the future?

 10. Please freely write your opinions and impressions about this training.

 Results: The results of the survey were as follows.

 1. About 60% of the students answered “very interested” or “interested.”

 2. The proportion of students who answered “very interested” and “somewhat interested” was approximately 90% in 2021 and 2022.

 3. Approximately 70% of the students answered “considerably deepened” or “deepened” in 2020, and more than 90% in the other years.

 4. Approximately 80% answered “very difficult” or “difficult” in 2021 and 2022.

 5. There was substantial variation from year to year.

 6. In all years, cavity preparation was considered to be the most difficult step.

 7. More than 50% of students answered “easy.”

 8. More than 80% of students answered “very much” or “quite a lot.”

 9. More than 80% of students answered “agree.”

 Conclusion: A questionnaire survey on CAD/CAM inlay restoration practice using an intraoral scanner revealed that approximately 90% of students felt that this practice was effective for education in FY2022. However, various issues, such as the lack of digital equipment and the quality and number of instructors, were also identified. Additionally, the results suggested that students wanted to practice using the CAD/CAM system as dentists in the future, and wanted to learn more.

 Purpose: Rubber dams are widely used to isolate diseased teeth from the oral cavity to perform antiseptic procedures. Though rubber dams are thought to be good at isolating diseased teeth, there is a risk of leakage from areas of poor fit between the rubber dam sheet and the surface of the affected tooth. Various rubber dam sheets have appeared in recent years, but few studies have compared their performance in isolating the treatment field based on the characteristics of each type of sheet. In this study, differences in the amount of leakage from the treatment field with each type of sheet used in rubber dams and methods to decrease the impact when leakage does occur were investigated.

 Methods: To detect the amount of leakage from areas of poor fit in the rubber dam sheet, a rubber dam was used on a jaw model with artificial teeth using four types of rubber dam sheets of different materials and thicknesses. After injecting water with an air turbine toward the tooth to which the rubber dam sheet was attached, the weight of cotton rolls fixed under the clamp was measured with a precision scale, and the weights before and after the experimental manipulation were compared. To investigate methods of reducing leakage, edge caulking was applied around the entire periphery of the affected tooth cervix after the rubber dam was affixed, and, as in the abovementioned method, the change in weight of the cotton rolls was measured.

 Results: The results of the comparison of the amount of leakage with the different types of rubber dam sheet revealed a significant increase in the weights of the cotton rolls from leakage only in the thin non-latex sheet group as the NLB group, whereas the LB and LG groups, which were latex sheet groups, showed dehiscence from the hole. In an experiment with edge caulking added to the rubber dam, no significant increases in weight were seen in any group.

 Conclusion: Leakage when using a rubber dam occurred regardless of the state of dehiscence of the hole in the rubber dam sheet, suggesting that this leakage could be decreased by using edge caulking.

 Purpose: Light-cured flowable resin composites (FRCs) have a wide range of clinical applications owing to their superior mechanical strength while resin composites have inferior mechanical strength owing to water absorption. Therefore, deterioration of the physical properties of resin matrices can cause significant degradation of FRCs. Few studies have examined the effects of long-term water immersion on FRCs. In this study, we evaluated the flexural strength and flexural modulus of six commercially available FRCs that had different resin matrix compositions after immersion in distilled water for one day or one year.

 Methods: Specimens of Filtek Supreme Ultra Flow (FSU), ESTELITE UNIVERSAL FLOW Super Low (EUF), Clearfil Majesty ES Flow Super Low (CME), Beautifil Flow Plus X F00 (BFP), mainly comprising the resin matrices Bis-GMA, Bis-MEPP GRACEFIL ZeroFlo (GZF), and UDMA MI FIL (MIF), were subjected to the three-point bending test after being immersed in water for one day or one year, to determine their flexural strength and flexural modulus values. The results were analyzed using the two-way analysis of variance (ANOVA) and Tukey’s test. The surfaces of the specimens were observed using scanning electron microscopy (SEM).

 Results: GZF and MIF had significantly higher values of flexural strength than the other FRCs after one day of water immersion (p＜0.05). By contrast, BFP had a significantly lower flexural strength (p＜0.05). Compared with the other FRCs, after one year of water immersion, GZF exhibited a significantly higher flexural strength and BFP exhibited a significantly lower flexural strength (p＜0.05). The deterioration rates of GZF and BFP after one day or one year of water immersion were −5.0% and ＋28.4%, respectively. MIF, EUF, and BFP demonstrated a significant difference in their deterioration levels after water immersion in contrast to the other FRCs (p＞0.05). The analysis revealed no significant differences in flexural modulus for the FRC and water immersion conditions and no significant interactions between the two factors (p＞0.05). SEM conducted on specimens immersed in water for one day or one year revealed no significant change in the surface of GZF before and after its immersion in water.

 Conclusion: Among the FRCs tested, the FRC that had Bis-MEPP as its primary component had the highest flexural strength after one year of water immersion. The resin matrix composition of FRCs may be one of the factors which influence their mechanical strength after one year of water immersion.