2026 年 6 巻 1 号 p. 38-44
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.
