Bonding Performance of a New Resin Core System with a Low-Polymerization-Shrinkage Monomer to Root Canal Dentin

Resin core build-ups following root canal treatment still have many issues. This study evaluated whether a new low-polymerization-shrinkage resin core system (LC2) could address these issues by assessing its bonding performance to root canal dentin using microtensile bond strength tests and gap formation using swept-source optical coherence tomography (SS-OCT). Twenty-four extracted human lower premolars were used for bonding performance tests, while forty-eight sound extracted human wisdom teeth were used for gap observation. Four systems were compared: Luminous Core LC flow (LC1), LC2, MI Core LC flow (MIC), and Filtek Fill & Core (FFC). Cylindrical cavities were prepared, bonded, and filled with resin cores, and gap formation was evaluated. The results showed significant differences in bond strength between the coronal and apical sides: LC1 (coronal: 29.9 ± 3.8 MPa; apical: 12.4 ± 2.0 MPa), LC2 (coronal: 31.2 ± 3.6 MPa; apical: 17.8 ± 3.6 MPa), MIC (coronal: 28.7 ± 3.8 MPa; apical: 8.8 ± 2.1 MPa), and FFC (coronal: 29.0 ± 4.2 MPa; apical: 9.5 ± 1.9 MPa). LC2 exhibited significantly higher bond strength at the apical side compared to the other systems (p < 0.05). Gap formation was significantly reduced in LC2 (10.9 ± 5.0%) and FFC (11.9 ± 5.0%) compared to LC1 (31.8 ± 10.5%) and MIC (32.0 ± 5.6%) (p < 0.05). These findings suggest that LC2 is advantageous for resin core build-ups, particularly in improving adhesion to root canal dentin and reducing gap formation.