Purpose: Eugenol, found in zinc oxide eugenol (ZOE), a commonly used root canal sealer, has antibacterial properties. However, eugenol can irritate tissues when used in high concentrations. A new ZOE sealer was developed by diluting eugenol with oleic acid to reduce the harmful effects of eugenol, which is released after filling, on periapical tissues. This study aimed to investigate the physical properties and antibacterial effects of this new ZOE sealer.

 Methods: Tests were conducted on the hardening time, flow behavior, radiopacity, solubility, and sealing ability of this new ZOE sealer in accordance with International Organization for Standard (ISO) 6876, and these values were compared with a commonly used control ZOE sealer (Canals). Further, tests related to the clinical application of this sealer were conducted, including a size change test, a test of time-dependent changes in hardness of the sealer immersed in water, a bacterial growth prevention test using three types of bacteria, and a test of sealer effects on curing for two types of composite resins.

 Results: The new ZOE sealer met the requirements of ISO 6876 for all test results except radiopacity. Setting time was shorter for the new ZOE sealer than for the control ZOE sealer, and was within 30 minutes. Viscosity was lower for the new sealer than for the control sealer. Disintegration ratios showed no significant difference between sealers. Unlike the control sealer, the new sealer did not show any dye penetration. The volume of the new sealer, unlike the control sealer, showed a tendency to continuously increase from 7 to 30 days after mixing. No significant difference in hardness was seen between the new and control sealers. Although the amount of eugenol in the new sealer was one-fifth that of the control sealer, antibacterial effects against Prevotella intermedia and Porphyromonas gingivalis were similar to those of the control sealer. The new sealer did not cause any significant change in the curing of composite resins, whereas the control sealer significantly inhibited curing.

 Conclusion: The new ZOE sealer, developed by reducing the eugenol content of the sealer to approximately 30％ using oleic acid and isostearic acid, is clinically applicable because it expands and cures gently, retains antibacterial properties, and does not inhibit the curing of composite resins.

 Purpose: The creation of a chairside system for predicting periodontal disease progression is a requirement for next-generation periodontal examination. Aspartate aminotransferase (AST), which is observed in gingival crevicular fluid (GCF), could be a marker for assessing tissue damage in clinical practice. The purpose of this study was to examine whether measurement of AST in GCF is effective as an indicator of periodontal disease progression during the supportive periodontal therapy (SPT) phase.

 Methods: GCF samples were randomly collected from 122 sites on single-rooted teeth in the upper and lower jaws of 40 patients who had transitioned to the SPT stage. GCF samples were collected at the time of SPT transition (baseline), and AST levels in the GCF were measured using an AST measurement kit along with periodontal examinations. Periodontal examination items at the GCF collection sites included plaque index, probing depth (PD), clinical attachment level (CAL), gingival index, and bleeding on probing (BOP). The study protocol included a 3-month recall and a 12-month observation period. Logistic regression analysis was performed using sites with PD ≥4 mm and BOP (＋) at 12 months as the pathological condition, with this condition as the dependent variable.

 Results: On logistic regression analysis, for the objective variable, a positive result of the AST measurement kit showed a significantly higher odds ratio compared to a negative result, and a CAL ≥5 mm at the time of transition to SPT also showed a significantly higher odds ratio compared to a CAL ＜5 mm.

 Conclusion: A positive result from the AST measurement kit indicates the possibility of the continuation and progression of periodontitis. In other words, the information obtained from the use of the AST measurement kit can be an indicator that strongly supports active periodontal treatment intervention during the SPT phase to stabilize the condition of periodontal disease.

 Purpose: Enamel, which covers the tooth crown surface, is highly susceptible to acidic components found in food and beverages. In recent years, dental erosion resulting from demineralization by dietary acids has received increasing attention. Habitual intake of acidic foods and beverages is recognized as a major contributor to the increasing prevalence of acid erosion. Previous studies have reported that the extent of enamel demineralization varies depending on the type of organic acid present in food, such as phosphoric acid, citric acid, acetic acid, and lactic acid. However, the influence of enamel surface properties, particularly variations in smoothness or roughness, on susceptibility to demineralization remains insufficiently understood. Therefore, this study aimed to determine the extent to which enamel surfaces with different surface properties are affected under acidic conditions, and to evaluate the effectiveness of smoothing treatments―specifically tooth surface polishing―in suppressing demineralization.

 Methods: Twenty-eight bovine mandibular incisors were used to prepare the specimens. After demineralization with a citric acid solution, surface roughness and Vickers hardness (Hv) were measured for each experimental group.

 Results: The results demonstrated an increase in surface roughness (Sa) across all groups following immersion in the acidic solution. This change was particularly pronounced in the rough group, where roughness increased progressively with longer immersion times. Furthermore, a significant decrease in Hv was observed in all groups, with the rough group exhibiting the largest ΔHv values.

 Conclusion: These findings indicate that maintaining a smooth enamel surface helps suppress demineralization and suggest that tooth surface polishing procedures designed to enhance surface smoothness may play an important role in preventing acid erosion.

 Purpose: The junctional epithelium (JE) serves as the primary line of host defense at the dentogingival interface. The role of Cdc42 in regulating the barrier function of the JE remains largely unknown. This study aimed to investigate the role of the small GTPase Cdc42 in regulating JE barrier function, inflammatory responses, and adhesion molecule expression using the murine JE cell line JE-1 and the selective Cdc42 inhibitor ML141.

 Methods: JE-1 cells were treated with ML141, and cell viability was assessed using a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay to determine the non-cytotoxic concentration. Epithelial barrier function was evaluated via a fluorescein isothiocyanate (FITC)-dextran permeability assay. Additionally, quantitative real-time polymerase chain reaction was performed to analyze the gene expression levels of inflammatory mediators (Il1b, Il6, Mmp12) and various cell adhesion molecules (Cldn1, Gja1, Itgb4, Dst, Col17a1, Dsp, Dsg3).

 Results: Treatment with 10μM ML141 did not significantly affect JE-1 cell viability, but resulted in a significant increase in epithelial permeability. Cdc42 inhibition led to significant upregulation of the pro-inflammatory genes Il1b, Il6, and Mmp12. Furthermore, the expression levels of key intercellular and hemidesmosomal adhesion molecules (Cldn1, Gja1, Itgb4, Dst, Col17a1, Dsp, Dsg3) were markedly decreased following ML141 treatment.

 Conclusion: These findings demonstrate that Cdc42 plays a critical role in maintaining the structural integrity and homeostasis of the JE. Pharmacological inhibition of Cdc42 compromises epithelial barrier function, induces a pro-inflammatory phenotype, and significantly reduces the expression of adhesion molecules. Consequently, Cdc42 dysfunction may contribute to the breakdown of the periodontal epithelial barrier.

 Purpose: To evaluate the effect of light-irradiation distance from the cementoenamel junction (CEJ) on the bonding performance of a dual-cure core build-up composite resin system to root canal dentin.

 Methods: Twelve extracted human mandibular premolars were prepared with standardized post spaces (1.5×8 mm). A universal one-step adhesive (Clearfil Universal Bond Quick 2, UBQ2) and a dual-cure composite resin (Clearfil DC Core Automix ONE) were applied according to the manufacturers’ instructions. Light curing was performed for 10 s at either 0 mm or 10 mm from the CEJ using an LED curing unit. The irradiance was 1,000 mW/cm² at 0 mm and 590 mW/cm² at 10 mm. After 24 h of water storage at 37℃, beam-shaped specimens (0.6×0.6 mm) were prepared and divided into coronal and apical groups. Micro-tensile bond strength (μTBS) was measured at a crosshead speed of 1 mm/min and statistically analyzed using Welch’s t-test with Bonferroni correction. Failure modes were examined using scanning electron microscopy (SEM).

 Results: The μTBS values were 29.8±8.7 MPa for coronal specimens at 0 mm and 15.1±5.1 MPa for apical specimens at 0 mm. At 10-mm irradiation distance, μTBS values were 16.3±5.8 MPa for coronal specimens and 12.1±5.5 MPa for apical specimens. A significant reduction in μTBS was observed in the coronal region when the irradiation distance increased from 0 mm to 10 mm (p＜0.05). Additionally, at 0-mm irradiation distance, coronal μTBS was significantly higher than apical μTBS (p＜0.05). SEM analysis showed less distinct adhesive interfaces and more interfacial defects in specimens cured at the longer irradiation distance.

 Conclusion: Within the limitations of this study, increasing the light-irradiation distance significantly reduced bonding performance in the coronal region of root canal dentin, whereas apical bond strength remained consistently low regardless of irradiation distance. These findings suggest that reduced light availability may adversely affect bonding to root canal dentin; however, inadequate polymerization could not be directly confirmed because the degree of conversion was not measured. Optimization of curing protocols, solvent-evaporation strategies, and adhesive systems suitable for low-irradiance conditions may be necessary to improve bonding reliability in deep post spaces.