A Simple Etching Technique for Improving the Retention of Fiber Posts to Resin Composites Francesca Monticelli, DDS, MSc,* Manuel Toledano, MD, DDS, PhD, † Franklin R. Tay, DDS, MSc, PhD, ‡ Fernanda T. Sadek, BDSc (Hons), PhD,* § Cecilia Goracci, DDS, MSc, PhD,* and Marco Ferrari, MD, DDS, PhD* Abstract Coupling of fiber posts to composites is hampered by absence of chemical union between epoxy resins and methacrylate-based resins. This study examined a clin- ically feasible protocol for creating micromechanical retention on the surface of fiber posts, using hydrogen peroxide etching to remove the surface layer of epoxy resin. This was followed by silanization of the exposed quartz fibers to enhance their chemical bonding to composites. Etching with 24% H 2 O 2 for 10 min or 10% H 2 O 2 for 20 min produced a 50 m thick surface zone that is depleted of epoxy resin, leaving intact, undam- aged quartz fibers for silanization. Low viscosity flow- able composites were employed to infiltrate this zone, to simulate the creation of hybrid layers in acid-etched dentin by dentin adhesives. Interfacial strengths were enhanced with the adjunctive use of H 2 O 2 etching and silanization, and were probably dependent on the abil- ity of the flowable composites to completely infiltrate this interdiffusion zone. (J Endod 2006;32:44 – 47) Key Words Fiber post, flowable composite, hydrogen peroxide etching, interfacial strength, silane E tching procedures for natural and artificial substrates have been developed to en- hance adhesion (1–4). They include acid treatments of enamel (1), dentin (2, 3) or nonnoble alloys (4) that partially dissolve the substrates and generate micro-poros- ities where resin can penetrate, creating micromechanical interlocking (3). Fiber posts are extensively used in clinical practice to restore endodontically treated teeth (5–12). The clinical longevity of endodontically treated teeth restored with fiber posts and resin composite cores was recently evaluated (6, 13). Satisfactory adaptation at the post/core interface could be achieved using flowable composites as core materials (13, 14). The effect of post silanization on the interfacial strength between fiber posts and core build-up composites was recently evaluated with the microtensile test (15). Silane coupling agents can achieve chemical bonds with OH-covered inorganic substrates such as glass. A chemical bond may be achieved between the core resin matrix and the exposed glass fibers of the post at the interface level (15, 16). However, the interfacial strength is still relatively low when compared to the values normally achieved with coronal dentin or enamel (17, 18), because of the absence of chemical union between the methacrylate-based resin composites and the epoxy resin matrix of fiber posts. Hydrogen peroxide (H 2 O 2 ) is commonly employed in immunological electron microscopy to partially dissolve the resin surface of epoxy resin-embedded tissue sec- tions, and expose tissue epitopes for immunolabeling enhancement. The etching effect of H 2 O 2 depends on its capacity to partially dissolve the resin matrix, breaking epoxy resin bonds through a mechanism of substrate oxidation (19 –22). A similar H 2 O 2 etching procedure may be employed to improve the micromechanical retention be- tween the epoxy resin matrix of fiber posts and methacrylate-based resin composites. The aims of this study were to evaluate the effect of H 2 O 2 on the morphological aspects of the post surface, and the influence of different surface treatment on the interfacial strengths between fiber posts and composites. The null hypothesis tested was that different types of post surface treatment and the type of flowable core build-up composites do not affect the interfacial strength between fiber posts and resin com- posites. Materials and Methods Experimental Design Sixty DT Light-Posts (RTD, St. Egève, France), each with a 2.1 mm maximum diameter, were used in this study. These posts are made of quartz fibers (60 vol%) previously processed to a unidirectional axial tensile stress and embedded in an epoxy resin matrix (40 vol%). They were divided into five groups (n = 12) according to the experimental surface pretreatments performed. In group 1 the posts were immersed in 24% H 2 O 2 for 10 min at room temperature (RT). In group 2 they were immersed in 10% H 2 O 2 for 20 min at RT. In group 3, after immersion in 24% H 2 O 2 for 10 min at RT, the posts were silanized for 60 sec. In group 4, after immersion in 10% H 2 O 2 for 20 min at RT, the posts were silanized for 60 sec. In group 5 (control) the posts were silanized for 60 sec. After the application of H 2 O 2 , the posts were rinsed with water and air-dried. A silane coupling agent (Monobond-S, Ivoclar-Vivadent, Schaan, Liechtenstein) was ap- plied in a single layer on the post surfaces of groups 3 through 5 and gently air-dried after 60 sec, according to manufacturer’s instructions. Monobond-S is a single-com- From the *Department of Restorative Dentistry and Dental Materials, University of Siena, Siena, Italy; † Department of Dental Materials, University of Granada, Granada, Spain; ‡ Pe- diatric Dentistry and Orthodontics, Faculty of Dentistry, The University of Hong Kong, Pokfulam, Hong Kong SAR, China; and § Department of Dental Materials, University of São Paulo, São Paulo, Brazil. Address requests for reprint to Monticelli Francesca, Uni- versity of Siena, Department of Restorative Dentistry and Dental Materials, Policlinico Le Scotte, Viale Bracci, 53100 Siena, Italy. E-mail address: monticelli@unisi.it. 0099-2399/$0 - see front matter Copyright © 2006 by the American Association of Endodontists. doi:10.1016/j.joen.2005.10.005 Basic Research—Technology 44 Monticelli et al. JOE — Volume 32, Number 1, January 2006