Marginal leakage of bulk fill composites in Class II restorations: A microCT and digital microscope analysis Carlo Rengo a,n , Gianrico Spagnuolo b , Gianluca Ametrano b , Cecilia Goracci a , Antonio Nappo a , Sandro Rengo b , Marco Ferrari a a Department of Dental Materials and Fixed Prosthodontics of the University of Siena, Tuscan School of Dental Medicine, University of Florence and Siena, Policlinico Le Scotte, Viale Bracci, Siena 53100, Italy b Department of Oral and Maxillofacial Sciences, University of Napoli "Federico II", Napoli, Italy article info Article history: Accepted 8 April 2015 Available online 23 April 2015 Keywords: Adhesion Bulk fill Microleakage Resin based composites Restorative material Shrinkage stress abstract Purpose: To assess the marginal leakage of experimental resin composites for bulk filling in direct comparison with their precursors for conventional layering technique. Methods: Class II cavities were prepared on 36 sound human molars. Teeth were randomly assigned to 6 equal groups based on the type of resin composite to be used for the restoration. Three resin com- posites for conventional layering technique, G-aenial Flo, G-aenial Universal Flo, Kalore (GC), and their experimental counterparts for bulk application, G-aenial Flo bulk fill, G-aenial Universal Flo bulk fill, Kalore bulk fill (GC), were tested. The marginal leakage of the materials was separately evaluated at enamel and dentin margins by assessing interfacial infiltration of silver-nitrate through micro-compu- terized tomography (microCT) and digital microscope analysis. A score system was defined to quantify the extent of the infiltration. Between-group differences in leakage scores were statistically analyzed using Kruskal–Wallis Analysis of Variance. The Cohen's Kappa coefficient was calculated to measure the inter-rater agreement between microCT and digital microscope observations. In all the statistical tests the level of significance was set at α ¼0.05. Results: With any of the tested materials, at the interproximal margin silver nitrate infiltration never progressed beyond the cervical wall into the axial walls of the box. At the occlusal margin and in the majority of the specimens, the infiltration did not extend over the enamel–dentin junction. No statisti- cally significant difference in microleakage scores emerged among the tested materials either at the occlusal or the cervical margin, both on microCT and digital microscope images (p 40.05). The calculated Kappa coefficients indicated that the agreement between microCT and digital microscope observations was very good both at the occlusal (k ¼0.915) and at the cervical margin (k ¼0.810). Conclusion: The marginal leakage demonstrated in Class II restorations by new bulk fill resin composites was similar to that of their precursors for conventional layering technique. Similar findings were obtained when assessing interfacial leakage either with microCT imaging or digital microscopy. & 2015 Elsevier Ltd. All rights reserved. 1. Introduction The long-term clinical success of composite resin restorations depends substantially on material's adaptation to the cavity walls and integrity of the adhesive bond between composite resin and dental tissues [1]. Managing the contraction stress of dental com- posites is crucial to ensure adequate marginal integrity and therefore durability of the restoration [2–4]. Known clinical implications of polymerization shrinkage are cuspal deflection, debonding, enamel microcracks, post-operative sensitivity, secondary caries, and micro- leakage [5–8]. The factors involved in the development of shrinkage stress have been widely investigated in the literature. A relevant role has been ascribed to polymerization kinetics, filler content, and matrix composition [9–12], which determine viscoelastic properties and degree of conversion of the material. Besides, cavity geometry is a primary factor for interfacial stress development. A high C-factor [13], is known to adversely affect material's adaptation and bonding. Several clinical strategies have been suggested to minimize shrinkage stress. Promising results have been achieved adopting soft-cure methods [14], using of a low-modulus liner material as a flowable composite to absorb part of the contraction stress [15,16], or with the incremental technique, aimed at reducing the C-factor and ensuring adequate penetration of the curing light [13,17]. Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/ijadhadh International Journal of Adhesion & Adhesives http://dx.doi.org/10.1016/j.ijadhadh.2015.04.007 0143-7496/& 2015 Elsevier Ltd. All rights reserved. n Corresponding author. Tel.: þ39 0577233131; fax: þ39 0577233117; mobile: þ39 3335309229. E-mail address: carlorengo@alice.it (C. Rengo). International Journal of Adhesion & Adhesives 60 (2015) 123–129