Objectives: The aim of the present study was to evaluate the bonding effectiveness of two resin core buildup systems using conventional methods in the field of adhesive dentistry and a new non-destructive method.
Materials and methods: Twenty-four single-rooted human teeth were built up with dual-cure one-step self-etch adhesive and composite systems (SY1: Clearfil DC bond and Clearfil DC core automix, SY2: Clearfil bond SE one and Clearfil DC core automix one). The prepared samples were sectioned into approximately 1 × 1-mm-thick beams and subjected to micro-tensile bond strength (μTBS) testing (n = 24). The fractured beams after μTBS testing were analyzed by SEM and energy-dispersive X-ray (EDX) spectrometry. The three teeth filled with each resin core system were sectioned and embedded in epoxy resin to observe the dentin-bonding interface under TEM (n = 6). Moreover, three of each resin core-filled teeth without any processing were examined using μCT (n = 6).
Results: Two-way ANOVA revealed that the two factors "root region" (p < 0.001, F = 15.22) and "system" (SY1 < SY2; p < 0.001, F = 22.52) had a significant influence. The μTBS gradually decreased from the coronal side to the apical side of the root canal. Morphological evaluation revealed that SY2 was superior in terms of resin curing at the apical side. μCT non-destructive evaluation clearly revealed gap formation in SY1.
Conclusion: SY2, which included a new light-independent catalyst, showed better bonding effectiveness and adhesive interface to dentin compared to that of SY1.
Clinical relevance: The new catalyst, which is activated by contact with adhesive and resin composite, can be used for resin core buildup restorations.
Keywords: Bonding effectiveness; Direct buildup resin core; Interfacial characterization; Micro-computed tomography; Mild self-etch adhesive; Non-destructive observation.