Characterisation of resin-dentine interfaces by compressive cyclic loading

The aims of this in vitro study were to evaluate the ultra-morphological changes in resin-dentine interfaces after different amounts of thermomechanical load (TML), and to determine the corresponding microtensile bond strengths (muTBS). Enamel/dentine discs with a thickness of 2mm were cut from 24 human third molars and bonded with four adhesives involving different adhesion approaches: Syntac (Ivoclar Vivadent, used as multi-step etch-and-rinse adhesive), Clearfil SE Bond (Kuraray: two-step self-etch adhesive), Xeno III (Dentsply DeTrey; mixed all-in-one self-etch printer adhesive system), and iBond (Heraeus Kutzer: non-mixed all-in-one self-etch adhesive). The resin-dentine discs were cut into beams (width 2mm; 2mm dentine, 2 mm resin composite) and subsequently subjected to cyclic TML using ascending amounts of mechanically hernial cycles, (20N at 0.5 Hz of mechanical load and 5-55degreesC of thermal cycles: for 0/0, 100/3, 1000/25, 10,000/250: 100,000/2,500 cycles). Loaded specimens were either cut perpendicularly in order to measure muTBS (n = 20; crosshead speed: 1 mm/mm) or were immersed in an aqueous tracer solution consisting of 50wt% ammoniacal silver nitrate and processed for ultra-morpholopeal nanoleakage examination using transmission electron microscopy (TEM). muTBS were significantly decreased by increasing amounts of TML for all adhesives (p<0.05). Bond strengths after 0 vs. 100,000 thermornechanical cycles were: Symac: 41.3/30.1 MPa; Clearfil SE Bond 44.8/32.5 MPa; Xeno III 27.5/13.7 MPa; iBond 27.0/6.2MPa. Relatively early, a certain amount of nanoleakage was observed in all goups by TEM, which was more pronounced for Xeno III and iBond. The incidence of nanoleakage remained stable or was even reduced with increasing load cycles for all adhesives except iBond, where exact failure origins were detected within the adhesive and at the top ol the hybrid layer. (C) 2004 Elsevier Ltd. All rights reserved.