Short communication Incremental layers bonding of silorane composite: The initial bonding properties A. Tezvergil-Mutluay *, L.V.J. Lassila, P.K. Vallittu Department of Prosthetic Dentistry and Biomaterials Science, Institute of Dentistry, University of Turku, Lemminka ¨ isenkatu 2, FIN-20520 Turku, Finland 1. Introduction The use of composite resin restorative materials has been widely accepted in dental practice. 1 Despite the continuous modifications in formulation to improve the clinical perfor- mance, they are still far from ideal because of shortcomings of composite materials. 2 One of the main shortcomings of the composite resins, polymerization shrinkage, 3 has been tried to overcome by several means. The most recent one is based on using ring- opening polymerization of the silorane molecules, instead of free radical polymerization of dimethacrylate monomers. 4,5 Silorane resin reveals lower polymerization shrinkage com- pared to the dimethacrylates. 4 The ring-opening polymeriza- journal of dentistry 36 (2008) 560–563 article info Article history: Received 11 December 2007 Received in revised form 19 March 2008 Accepted 20 March 2008 Keywords: Composite resin Silorane Adhesion Shear bond strength abstract Objectives: Lack of oxygen inhibition layer of silorane composite with cationic polymeriza- tion raises the question of the bonding of incremental layers of the composite. This study aimed to evaluate the bond strength of the silorane composite layers. Methods: Fresh, 20 s, 5 min aged silorane composite (Silorane, 3M-ESPE) was used as sub- strate to adhere new silorane composite. For a comparison, dimethacrylate-based compo- site resin (Z250, 3M-ESPE) was adhered to the silorane composite with or without intermediate adhesive resin. As a control, dimethacrylate composite with oxygen inhibition layer was attached to fresh dimethacrylate composite. The bonded specimens (n = 12/group) were water stored for 24 h. The shear bond strengths (SBS) were measured with a crosshead speed of 1.0 mm/min. Failure modes were assessed. Data were analysed by ANOVA, Tukey’s post hoc tests and Chi-square tests ( p = 0.05). Results: Dimethacrylate–dimethacrylate composite resin combination showed the highest mean SBS (33.0 MPa) values with no adhesive failures. Fresh silorane–silorane SBS was slightly lower (26.7 MPa) and was further decreased by aging the substrate for 20 s (25.4 MPa) and 5 min (22.4 MPa). The percent of adhesive failures increased from 25% to 75%, respec- tively. The failure modes were significantly different (Chi-square, p < 0.001). Silorane– dimethacrylate composite showed the lowest (4.0 MPa) SBS among the groups, which was increased significantly by use of phosphate–methacrylate-based intermediate resin ( p < 0.05). Conclusion: In order to bond dimethacrylate composite to silorane composite, a phosphate– methacrylate-based intermediate resin is required. The silorane composite showed slightly lower incremental bonding properties than conventional dimethacrylate composites. # 2008 Elsevier Ltd. All rights reserved. * Corresponding author. Tel.: +358 2 333 83 75; fax: +358 2 333 83 90. E-mail address: arztez@utu.fi (A. Tezvergil-Mutluay). available at www.sciencedirect.com journal homepage: www.intl.elsevierhealth.com/journals/jden 0300-5712/$ – see front matter # 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.jdent.2008.03.008