dental materials 24 ( 2 0 0 8 ) 1297–1303 available at www.sciencedirect.com journal homepage: www.intl.elsevierhealth.com/journals/dema Laboratory and FEA evaluation of dentin-to-composite bonding as a function adhesive layer thickness P.G. Coelho a,* , C. Calamia b , M. Harsono b , V.P. Thompson a , N.R.F.A. Silva a,b a Department of Prosthodontics, New York University College of Dentistry, NY, USA b Department of Biomaterials and Biomimetics, New York University College of Dentistry, NY, USA article info Article history: Received 11 December 2007 Received in revised form 11 February 2008 Accepted 11 February 2008 Keywords: Finite element analysis Adhesive system Microtensile bond strength abstract Objective. The aim of this study was to test the hypothesis that microtensile bond strength values are inversely proportional to dentin-to-composite adhesive layer thickness through laboratory mechanical testing and finite element analysis. Method. Eighteen noncarious third molars were obtained, and occlusal enamel removed per- pendicular to the tooth long axis. Two different adhesive systems were utilized as follows (n = 3): (1) application of a single layer of Single Bond (3M ESPE Co.) and Clearfil SE Bond (Kuraray Co.) following the manufacturer’s directions; (2) application of one layer of both adhesive systems followed by one additional layer; (3) application of one layer of both adhe- sive systems followed by two additional layers. A 4 mm build up was fabricated in increments on each tooth sample (Z 100 composite, 3M ESPE). Section measurements were performed and specimens were separated into three adhesive thickness groups per material (40, 40–80 and 80–120 m) for microtensile testing. The bond strength data (MPa) were analyzed by one- way ANOVA and Tukey test. Maximum principal stresses (MPS) were determined through FEA for three different adhesive layer thicknesses (20, 50 and 100 m). Results. The bond strength data obtained for Single Bond at 0–40 m presented significantly higher values compared to higher adhesive layer thickness groups. There were no statistical differences among bond strength values for all Clearfil SE Bond adhesive layer thicknesses. FEA modeling indicated that MPS increased as adhesive layer increased. The hypothesis was accepted for the Single Bond only. Significance. Correspondence (not tested statistically) between microtensile laboratory test- ing and FEA model was only observed for Single Bond as increased adhesive layer thickness did not reduce Clearfil SE Bond strength. © 2008 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved. 1. Introduction There are several approaches to produce dentin hybridiza- tion and adequate dentin bonding for resin-based composite restorations. A common approach is the total etching tech- nique followed by the application of a solution containing primer and adhesive resin to moist dentin [1,2]. An alterna- ∗ Corresponding author at: Department of Biomaterials and Biomimetics, New York University, 345 East, 24th Street (Room 816), New York, NY 10010, USA. Tel.: +1 212 9989365; fax: +1 212 9954244. E-mail address: pc92@nyu.edu (P.G. Coelho). tive approach is the self-etching priming technique, using an acidic primer followed by an adhesive resin [3]. Both approaches have produced high bond strength values and well-infiltrated hybrid layers in dentin [1]. Prati et al. [4], in 2002, evaluated the morphology of the hybrid layer using several adhesive systems. Their study demonstrated that the collagen fibrils were not completely 0109-5641/$ – see front matter © 2008 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.dental.2008.02.007