Effects of surface treatment and joint shape on microtensile bond strength of reattached root dentin segments

Abstract

Statement of problem An effective bonding technique for reattaching vertical root fracture segments has not yet been established. Purpose The purpose of this study was to investigate the effects of surface treatment and joint shape on bond strength of reattached root dentin segments. Material and methods Microtensile dentin specimens (n=120, cross-sectional area=1.5 mm 2) were obtained from 12 bovine teeth roots, and fractured under a tensile force. The segments of each group (n=6) were reattached by a 4-META/MMA-TBB adhesive resin after different treatments (etching or polishing, a 50-μm or 500-μm gap space, butt or wedge joint). The group with a 50-μm gap space and butt joint, which was not etched or polished, served as the control. After 24 hours of storage in 0.9% normal saline solution or thermal cycling (3000 cycles, 4°C and 60°C), the specimens were fractured in a universal testing machine at a crosshead speed of 1.0 mm/min. The microtensile bond strengths (MPa) were recorded. The bonded interface and fractured surface were observed by SEM (original magnification ×1000). The results were analyzed by a 2-way analysis of variance and the Fisher protected least significant difference post-hoc test (α=.05). Results Significantly higher bond strengths ( P=.0001) were shown for the nonpolished group (9.78 ± 4.44 MPa) and the etched group (9.31 ± 1.23 MPa) than for the polished group (fractured before test). The wedge-shaped joint exhibited the highest bond strength (18.57 ± 3.40 MPa, P=.0017). SEM observations showed that the penetration of resin tags along the oblique dentinal tubules was within the wedge joint. Conclusion Etching and oblique tubule orientation contributed to significantly high bond strength of reattached segments to dentin after vertical root fracture.