Biomaterials 26 (2005) 2043–2052 Characterisation of resin–dentine interfaces by compressive cyclic loading Roland Frankenberger a,Ã , David H. Pashley b , Sven M. Reich c , Ulrich Lohbauer a , Anselm Petschelt a , Franklin R. Tay d a Policlinic for Operative Dentistry and Periodontology, University of Erlangen-Nuremberg, Glu¨ckstraX e 11, D-91054 Erlangen, Germany b Department of Oral Biology and Maxillofacial Pathology, School of Dentistry, Medical College of Georgia, Augusta, GA 30912-1129, USA c Policlinic for Prosthetic Dentistry, University of Erlangen-Nuremberg, Glu¨ckstraX e 11, D-91054 Erlangen, Germany d Pediatric Dentistry and Orthodontics, Faculty of Dentistry, The University of Hong Kong, 34 Hospital Road, Hong Kong SAR, China Received 23 April 2004; accepted 5 July 2004 Available online 12 August 2004 Abstract 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 (mTBS). 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 primer adhesive system), and iBond (Heraeus Kulzer; non-mixed all-in-one self-etch adhesive). The resin–dentine discs were cut into beams (width 2mm; 2mm dentine, 2mm resin composite) and subsequently subjected to cyclic TML using ascending amounts of mechanical/thermal cycles (20N at 0.5Hz of mechanical load and 5–55 1C of thermal cycles: for 0/0, 100/3, 1,000/25, 10,000/250, 100,000/2,500 cycles). Loaded specimens were either cut perpendicularly in order to measure mTBS (n ¼ 20; crosshead speed: 1mm/min) or were immersed in an aqueous tracer solution consisting of 50wt% ammoniacal silver nitrate and processed for ultra-morphological nanoleakage examination using transmission electron microscopy (TEM). mTBS were significantly decreased by increasing amounts of TML for all adhesives (po0.05).Bondstrengthsafter0vs.100,000thermomechanicalcycleswere:Syntac:41.3/30.1MPa;ClearfilSEBond44.8/32.5MPa; Xeno III 27.5/13.7MPa; iBond 27.0/6.2MPa. Relatively early, a certain amount of nanoleakage was observed in all groups by TEM,whichwasmorepronouncedforXenoIIIandiBond.Theincidenceofnanoleakageremainedstableorwasevenreducedwith increasing load cycles for all adhesives except iBond, where exact failure origins were detected within the adhesive and at the top of the hybrid layer. r 2004 Elsevier Ltd. All rights reserved. Keywords: Dentine; Adhesives; Etch-and-rinse; Self-etch; Thermomechanical loading; Microtensile bond strength; Cyclic loading 1. Introduction Newly introduced dental adhesives frequently lack supportive clinical evidence of success prior to being introduced to the market [1–3]. Prospective long-term clinical trials remain the standard for evaluation of adhesives for tooth-coloured restorations such as resin composites [3–5]. However, once clinically proven to be suitable, the adhesive under investigation may not be on the market anymore. Therefore, valid pre-clinical in vitro investigations are desirable to estimate dental adhesives as well as restorative materials [6]. In this particular context it is mandatory to meticu- lously simulate the conditions in the oral cavity. Both the effects of temperature changes and mechanical ARTICLE IN PRESS www.elsevier.com/locate/biomaterials 0142-9612/$-see front matter r 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.biomaterials.2004.07.003 Ã Corresponding author. Tel.: +49-9131-8533693; fax: +49-9131- 8533603. E-mail address: frankbg@dent.uni-erlangen.de (R. Frankenberger).