Research Article Effect of Bleaching and Thermocycling on Resin-Enamel Bond Strength Horieh Moosavi, 1 Hamideh Sadat Mohammadipour, 1 Marjaneh Ghavamnasiri, 2 and Sanaz Alizadeh 1 1 Dental Materials Research Center and Department of Operative Dentistry, Faculty of Dentistry, Mashhad University of Medical Sciences, Mashhad 91735, Iran 2 Dental Research Center, Department of Operative Dentistry, Mashhad Dental School, Mashhad University of Medical Sciences, Mashhad 91735, Iran Correspondence should be addressed to Sanaz Alizadeh; alizadehs911@gmail.com Received 4 October 2015; Revised 28 November 2015; Accepted 1 December 2015 Academic Editor: Vijaya K. Rangari Copyright © 2015 Horieh Moosavi et al. Tis is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Te aim of this study was to evaluate the efect of bleaching and thermocycling on microshear bond strength of bonded resin composites to enamel. Enamel slices were prepared from ninety-six intact human premolars and resin composite cylinders were bonded by using Adper Single Bond 2 + Filtek Z350 or Filtek silorane adhesive and resin composite. Each essential group was randomly subdivided to two subgroups: control and bleaching. In bleaching group, 35% hydrogen peroxide was applied on samples. Termocycling procedure was conducted between 5 ∘ C and 55 ∘ C, for 3.000 cycles on the half of each subgroup specimen. Ten microshear bond strength was tested. Methacrylate-based resin composite had higher bond strength than silorane-based one. Te meyhacrylate-based group without bleaching along with thermocycling showed the most bond strength, while bleaching with 35% carbamide peroxide on silorane-based group without thermocycling showed the least microshear bond strength. Bleaching caused a signifcant degradation on shear bond strength of silorane-based resin composites that bonded using self-etch adhesive resin systems. 1. Introduction Bleaching popularity and introducing the new bleaching products every year lead to many studies about the efects of these products on teeth and dental restorative materials. Efects of free radicals releasing during bleaching process on physicomechanical properties of restorations such as their colour, surface roughness, strength, hardness, and ion leakage are subjects of most scientists’ discussions [1]. Con- ventional composites have marked polymerization shrinkage because of Bis-GMA monomers, but silorane-based com- posites showed less shrinkage, thus microleakage and its side efects are less. However a previous study showed that restorations of both materials were clinically acceptable afer 5 years [2]. It was shown that bleaching of fuorosed teeth reduces bracket bond strength to enamel, but the bond strength with these still exceeds the minimum [3]. It has been stated that bond strength of restorations to enamel and dentin was afected by carbamide peroxide and this defect was related by carbamide peroxide concentration [4]. Just some articles showed bleaching agents could penetrate pulp chamber through composite restorations [5, 6]. In addition, it was suggested that bleaching could adversely afect the inter- facial fracture toughness of dentin-resin composite adhesive interfaces [7]. Te other studies showed increasing marginal leakage in postoperative bleaching of class V resin composite restorations [8, 9]. However, it was found that immediate postoperative bleaching with 20% carbamide peroxide gel, 6% hydrogen peroxide, and 19% percarbonate gel for 14 days had no infuence on microleakage of Filtek composite bonded with Scotchbond 1 at the occlusal margins of the Class 1 restorations [10]. Composite materials may be failed by mechanical and thermocycling (TC) condition, interfa- cial debonding, microcracking, and fller particle fracture, Hindawi Publishing Corporation International Journal of Biomaterials Volume 2015, Article ID 921425, 6 pages http://dx.doi.org/10.1155/2015/921425