Purpose: Oral epithelial cells have an important barrier function against bacteria and bacterial toxic substances. Porphyromonas gingivalis (P. g.), a periodontopathic bacteria, is thought to be closely related to the development and aggravation of periodontitis by destruction of the epithelial barrier function. However, the detailed mechanism of how P. g. affects epithelial cells and destroys the barrier function of the epithelium is still unknown. In this experiment we investigated the influence of P. g. on oral epithelial cells.

 Methods: A three-dimensional construct model composed of human oral epithelial cells and rat fibroblasts was established and two groups, with and without ground P. g. ATCC33277, were prepared. The epithelial cell layer was later air-lifted. Samples were collected at 4 to 8 days after incubation, then HE staining and immunohistological staining were performed for morphological observation. DNA microarray analysis and gene expression analysis using qRT-PCR were conducted on the collected epithelium. At air-lift day 6, samples were used for TER and FITC-dextran analyses to evaluate the barrier function.

 Results: A significant increase of the epithelial thickness was found in ground P. g. models at Air-Lift day 6. Microarray pathway analysis revealed that the level of genetic expression related to cell cycle and cell adhesion had changed. As for cell cycle, the expression level of Cdkn1a mRNA was significantly reduced and immunohistological staining showed the number of Ki67 positive cells was significantly increased. As for cell adhesion, a significant reduction of staining intensity and a decreased area of E-cadherin were confirmed. The electrical resistivity of tissue was significantly lowered and the permeability of tissue was significantly increased with dextran permeability assay in the ground P. g. models.

 Conclusion: The three-dimensional construct model revealed that cell proliferation increases, intracellular space increases, and cell adhesion protein reduces when human oral epithelium is exposed to P. g., resulting in lowered barrier functions and aggravated periodontal pathology.

 Purpose: We evaluated the enamel remineralizing potential of a calcium-fluoroaluminosilicate glass-based desensitizer (Nanoseal) on enamel subsurface lesions in vitro by using micro-focus X-ray computed tomography (μCT).

 Methods: Extracted human molars were sectioned mesiodistally and buccolingually into four specimens per molar. Specimens were immersed in a demineralizing solution (pH 4.3) for 10 days to create enamel subsurface lesions. The specimens were then randomly divided into the following four groups: DW (Milli-Q water) as a negative control, and NS (Nanoseal), NaF9000 (sodium fluoride [NaF] 9,000 ppm) and NaF900 (NaF 900 ppm) as positive controls. In the NS group, the two solutions that made up the NS material were mixed, and the coating was applied to the test surface for 20 s. In the other groups, the solutions were applied to the test surface for 20 s. After each treatment, the specimens were rinsed off with a mild air-water spray for 15 s and then immersed in artificial saliva (pH 7.0) for 10 days. μCT scans of all specimens were obtained before demineralization, after demineralization, and after remineralization. Mineral density (MD) and mineral loss (ΔZ) of enamel subsurface lesions were measured by μCT. The percentage of remineralization (%R) was calculated from ΔZ.

 Results: The specimens in all the test groups showed mineral recovery in the subsurface lesions after remineralization. However, in the DW and NaF900 groups, parts beneath the enamel surface were clearly still demineralized, in comparison with the NS and NaF9000 groups. From the mean MD profiles, the NS group showed the greatest remineralization within all parts of lesions. %R was highest in the NS group (p<0.05). The remineralization of the DW as a negative control, and NaF900 and NaF9000 groups as positive controls did not differ significantly (p>0.05).

 Conclusion: According to the results of this study, a calcium-fluoroaluminosilicate glass-based desensitizer increases the remineralization of artificial human enamel subsurface lesions.

 Purpose: After dental treatment is completed, mechanical tooth cleaning using prophylaxis paste is always performed as preventive maintenance. However, it is not yet known how the load during mechanical cleaning and the cleaning time per tooth surface affect the surface properties of computer-aided design/computer-aided manufacturing (CAD/CAM) crown restorative materials. In this study, we therefore examined the effects of mechanical cleaning load and time on the surface gloss and roughness of various CAD/CAM crown restorative materials.

 Materials and Methods: Four types of CAD/CAM blocks for crown restoration were used. Shofu Block HC, Estelite Block, IPS Empress CAD, and Celtra DUO. These blocks were cut to produce 3-mm-thick plate samples. After each specimen was polished, it was mechanically cleaned using a prophylaxis brush (Merssage Brush) and one-step prophylaxis paste (Prophy Paste PRO) at 2,500 rpm under the following conditions: Group Ⅰ, 100 gf, 10 s×4 cycles; Group Ⅱ, 100 gf, 30 s×4 cycles; Group Ⅲ, 300 gf, 10 s×4 cycles; and Group Ⅳ, 300 gf, 30 s×4 cycles. Surface gloss and roughness were measured before and after cleaning.

 Results: For CAD/CAM ceramic blocks (IPS Empress CAD and Celtra DUO), the changes in surface gloss and roughness were small during mechanical cleaning. In contrast, the gloss of composite-based CAD/CAM blocks (Shofu Block HC, Estelite Block) decreased when mechanical cleaning was performed with either 100 gf or 300 gf. In particular, when mechanical cleaning was performed with 100 gf, the surface gloss was significantly reduced by cleaning for 30 s rather than for 10 s.

 Conclusion: When mechanical cleaning is performed using one-step prophylaxis paste, it seems preferable to apply a slightly larger load to the composite resin-based restorative material for a shorter time rather than a smaller load for a longer time.

 Purpose: The purpose of this study was to elucidate the mechanism of preventing Streptococcus mutans from bacterial adhesion by sulfated vizantin (Viz-S). The change of surface property and transcriptions of genes related to bacterial adhesion were analyzed.

 Methods: Bacterial suspension of S. mutans in phosphate buffer saline was reacted with Viz-S at the concentration of 0, 50 and 75 μmol/l for 10 min, respectively. 200 μl of n-Hexadecane was added to 1 ml of each bacterial suspension, and the solution was stirred vigorously for 1 min. The hydrophobicity was assessed by the microbial adhesion to hydrocarbon test (MATH test). ZsGreen-tagged S. mutans was added in a brain-heart infusion broth (BHI) supplemented with 0.2, 0.4, 0.8 and 1.6% sucrose containing Viz-S at the concentration of 0, 50 and 75 μmol/l. Equal volumes of absorbance-adjusted suspensions were inoculated into a coverglass chamber coated with human saliva, followed by incubation for 1 h at 37°C statically. The number of microorganisms adhered on the surface was analyzed using a confocal laser scanning microscope. The transcriptions of genes related to bacterial adhesion in S. mutans incubated in the absence or presence of either 50 or 75 μmol/l Viz-S for 4 h were investigated using real-time polymerase chain reaction.

 Results: The hydrophobicity was 57.5±13.4 for the control group, 29.4±10.4 for the 50 μmol/l group and 14.9±7.0 for the 75 μmol/l group. Adherence of S. mutans in the experimental group was significantly decreased in comparison with that of the control group, showing a decrease ratio of 1/8 to 1/10 for the 50 μmol/l group and 1/40 to 1/55 for the 75 μmol/l group, respectively. The expression of gtfD was significantly downregulated in the presence of Viz-S, with 50 μmol/l Viz-S by 0.38 to 0.5-fold, and 75 μmol/l Viz-S by 0.33 to 0.36-fold. The expression of genes that encode bacterial surface protein was not significantly changed.

 Conclusion: 75 μmol/l Viz-S inhibits the bacterial adhesion of S. mutans by the mechanisms of altered surface property and the downregulation of gtfD gene transcription.

 Purpose: To compare the obturation ratio in curved root canals filled with a Thermafil obturator (Dentsply Sirona, Tokyo, Japan) or NT condenser (SybronEndo, Orange, CA, USA) with Obturation Gutta NT (Toyo, Tokyo, Japan) using micro-CT analysis.

 Methods: Twelve curved root canal models in a Thermafil training block were prepared using the Protaper system, from size S1 to F2. The samples were divided into two groups (n=6 each) for obturation: Thermafil obturator group (TF) and NT condenser with Obturation Gutta NT group (NT). Each canal was prepared to a size of F2 in accordance with the manufacturer’s instructions, and obturated without sealer to prevent artifacts in the micro-CT assessment. Three-dimensional and cross-sectional images along the long axis were obtained at every 1 mm from the apex, up to 8 mm, using the Rigaku microfocus computerized tomography system (Rigaku, Tokyo, Japan). All sectional images were digitally transferred, and the Image J software was used for image analysis. The cross-sectional area of the root canals at distances of 1, 3, and 5 mm from the root apex was used to compare the obturating ratios between groups. These areas were compared statistically at each level using the nonparametric Mann-Whitney U test.

 Results: In the TF group, a large amount of softened gutta-percha surrounded the plastic carrier, and the root canal space was completely filled, whereas in the NT group, filling was observed from the coronal surface to the apex, with a few air bubbles. The results of this study suggest that high obturation ratios can be obtained with both the Thermafil obturator (97.5%±1.101) and NT condenser with Obturation Gutta NT (96.4%±2.607) at a distance of 1 mm to 5 mm from the apex. On comparing the obturation ratio between the methods, no significant difference was observed at each point from the apex (p>0.05).

 Conclusion: These results indicate that both methods are effective and efficient for routine clinical use, however, using an NT condenser with Obturation Gutter NT does not seem to eliminate the possibility of re-infection due to the presence of air bubbles.

 Purpose: Surgical endodontic therapy with root end resection is now routinely performed if endodontic treatment was not sufficient in cases of persistent periapical lesion, procedural errors or unremovable posts and cores. Although modern techniques of root end resection establishe d in recent years have greatly improved treatment outcomes, education of surgical endodontic therapy is mostly carried out by lectures and videos without practical experience. In order to organize an educational training system that can teach surgical procedures including apical lesion removal to retrograde root canal filling, it is necessary to develop a training model for root end resection education that mimics the clinical situation. Therefore, in this study we developed an educational endodontic surgery training model with artificial teeth and apical lesions, and organized an education system including lectures and practical training.

 Materials and Methods: A new training model with two artificial teeth and apex lesions in one jaw was created and an education system was set up for dental residents who have no experience of root end resection. The effect was evaluated by comparing two groups, one that performed root end resection practice (implemented group) and one without practice (unimplemented group).

 Results: It was found that performing practical training after lectures was effective for understanding the surgical procedures of root end resection. A large bone cavity and higher angle of root resection were observed among dental residents. From these findings, we suggest that root end resection surgery requires a practical training system using an endodontic surgery model that can teach each process.

 Conclusion: Our study suggests that in order to learn the modern techniques of endodontic surgery with root end resection, an education system and training model that enable the surgery process to be studied repeatedly are required.

 Purpose: Dry mouth is a common complaint in older people. Oral humidity decreases in the environment of dry mouth. Although oral humidity affects restorative materials, there are few studies that evaluated the physical properties of these materials under dry mouth conditions. In this study, we aimed to evaluate the influence of dry and wet conditions on the weight change and flexural strength of restorative materials.

 Methods: We used three different filling materials: GRACEFIL Zero Flo (GFZ, composite resin, GC, Tokyo, Japan), FUJI ⅡLC Capsule (ⅡLC, resin-modified glass-ionomers, GC, Tokyo, Japan) and FUJI Ⅸ GP EXTRA CAPSULE (FⅨ, conventional glass-ionomer cements, GC, Tokyo, Japan). To investigate the influence of water sorption and drying, weight changes on immersion in water for 7 days and dry storage for 24 hours were measured over time. Moreover, the flexural strengths of restorative materials were measured by a three-point bending test under four different conditions: (1) 24 hours after curing (CL group), (2) in water for 7 days (WC group), (3) in dry storage for 7 days (DC group), and (4) in liquid paraffin for 7 days (LP group). The data were analyzed by one-way analysis of variance and Tukey’s multiple comparison test (p<0.05).

 Results: The weight increase by water sorption was in the order of ⅡLC, FⅨ and GFZ. The weight of all materials decreased until 4 hours by drying. There was no change of the weight in all materials after 6 hours. The flexural strength of GFZ showed the highest value followed by ⅡLC and FⅨ in the CL group. There was no significant difference in flexural strength of GFZ under all of the storage conditions. The flexural strength of ⅡLC in the DC group increased significantly and that of ⅡLC in the WC group decreased significantly compared with that in the CL group. The flexural strength of FⅨ in the WC, DC and LP groups showed an increasing tendency compared with that in the CL group.

 Conclusion: GFZ was the most stable against water sorption and drying. ⅡLC showed the highest water sorption. Although the flexural strength of ⅡLC decreased under water storage, that of ⅡLC increased significantly under the dry condition. Weight change of FⅨ due to water sorption and drying showed an intermediate behavior between GFZ and ⅡLC. The flexural strength of FⅨ increased in the dry condition.

 Purpose: RECIPROC blue (VDW, Germany) can now be formed in a more precise and standardized manner than a conventional Ni-Ti rotary file because of its flexibility and decreased exchange. In the present study, we examined whether root canal preparation with a RECIPROC blue differed depending on the operator.

 Methods: A transparent root canal model (END1002-30-#20, NISSIN) made of J-type epoxy resin was used in the experiment. Four groups (seven operators each) were included: dentists who had used Ni-Ti rotary files for more than three years (NTE), dentists who had little or no experience of using Ni-Ti rotary files (NTI), fifth-grade dental students who had completed clinical training in endodontics (DS5), and first-grade dental students who did not know endodontic treatment (DS1). The operators of each group prepared a root canal in the order of #25/.08 and #40/.06 tapers using a RECIPROC blue connected to a contra-angle 150°/30° handpiece with reciprocating motion (RECIPROC Direct) for the end after forming a glide path with a stainless steel hand K file #15. The time required for preparation was measured by the same person. A photograph (DP26, OLYMPUS) was taken using a stereoscopic microscope (SZX16, OLYMPUS) before root canal preparation and after root canal preparation with #25 and #40, with the root canal model filled with a caries-detecting solution. Subsequently, photographs before and after root canal preparation were superimposed using photo-editing software (Photoshop Elements13) to measure the increase in root canal width on the outer and inner curvature sides using image analysis software (ImageJ). The difference was regarded as root canal transportation. The medians at 1, 3, 5, and 8mm from the apical area were evaluated using the Mann-Whitney U test between the groups.

 Results: The preparation time and root canal transportation were not significantly different between the NTE and other groups (p>0.05).

 Conclusion: In the present study, the root canal preparation time and root canal transportation did not differ depending on the presence or absence of experience of using Ni-Ti rotary files. Thus, all operators could rapidly and accurately prepare an enlarged root canal using a RECIPROC blue.