The influence of experimental silane primers on dentin bond strength and morphology: A laboratory and finite element analysis study Ammar A. Mustafa, MSc, PhD, a Jukka P. Matinlinna, MSc, PhD, b Syafiqah Saidin, PhD, c and M. R. Abdul Kadir, MEng, PhD d International Islamic University Malaysia, Kuantan Campus, Pahang, Malaysia; Faculty of Dentistry, University of Hong Kong, Hong Kong SAR, China; Faculty of Biosciences & Medical Engineering, Universiti Teknologi, Malaysia, Johor Bahru, Malaysia Statement of problem. The inconsistency of dentin bonding affects retention and microleakage. Purpose. The purpose of this laboratory and finite element analysis study was to investigate the effects on the formation of a hybrid layer of an experimental silane coupling agent containing primer solutions composed of different percentages of hydroxyethyl methacrylate. Material and methods. A total of 125 sound human premolars were restored in vitro. Simple class I cavities were formed on each tooth, followed by the application of different compositions of experimental silane primers (0%, 5%, 25%, and 50% of hydroxyethyl methacrylate), bonding agents, and dental composite resins. Bond strength tests and scanning electron mi- croscopy analyses were performed. The laboratory experimental results were validated with finite element analysis to deter- mine the pattern of stress distribution. Simulations were conducted by placing the restorative composite resin in a premolar tooth by imitating simple class I cavities. The laboratory and finite element analysis data were significantly different from each other, as determined by 1-way ANOVA. A post hoc analysis was conducted on the bond strength data to further clarify the effects of silane primers. Results. The strongest bond of hybrid layer (16.96 MPa) was found in the primer with 25% hydroxyethyl methacrylate, suggesting a barely visible hybrid layer barrier. The control specimens without the application of the primer and the primer specimens with no hydroxyethyl methacrylate exhibited the lowest strength values (8.30 MPa and 11.78 MPa) with inter- mittent and low visibility of the hybrid layer. These results were supported by finite element analysis that suggested an evenly distributed stress on the model with 25% hydroxyethyl methacrylate. Conclusions. Different compositions of experimental silane primers affected the formation of the hybrid layer and its resulting bond strength. (J Prosthet Dent 2014;-:---) Clinical Implications The use of a novel formula of silane primers may enhance the bond strength between the tooth substrate and the composite resin restoration. The bond between composite resin and dentin is essential to the biome- chanical and biologic properties of a bonded restoration. Important factors influencing a bonded system are the mechanical interlock between both bodies and the infiltration of resin into the demineralized intertubular dentin, both widely understood to be the a Assistant Professor, Dental Materials Science Department, Faculty of Dentistry, International Islamic University Malaysia, Kuantan Campus. b Associate Professor, Dental Materials Science Department, Faculty of Dentistry, University of Hong Kong. c Doctor, Clinical Sciences Department, Faculty of Biosciences & Medical Engineering, Universiti Teknologi, Malaysia. d Professor, Medical Devices Technology Group (MEDITEG), Faculty of Biosciences & Medical Engineering, Universiti Teknologi, Malaysia. Mustafa et al