Effect of Shrinking and No Shrinking Dentine and Enamel Replacing Materials in Posterior Restoration: A 3D-FEA Study  
[PERSON]  
1 School of Dentistry, University of Naples Federico II, via [PERSON]. Pansini 5, 80131 Naples, Italy;  
[EMAIL_ADDRESS] (P.A. ); [EMAIL_ADDRESS] (E.E.) [PERSON]  
2 Department of Dental Materials and Prostodontics. Institute of Science and Technology, Sao Paulo State University-UNESP, Sao Jose Dos Campos 1222000, Brazil; [EMAIL_ADDRESS] (A.M.d.O.D.P. );  
[EMAIL_ADDRESS] (A.L.S.B.) Fraunhofer JL IDEAS, Department of Industrial Engineering, University of Naples Federico II, 80125 Naples, Italy; [EMAIL_ADDRESS]  
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Footnote 23: email: {[EMAIL_ADDRESS]  
Footnote 24: email: {[EMAIL_ADDRESS]  
Footnote 25: email: {fraunhofer.el.de}@unina.itDental filling direct posterior resin composites, in fact, are used to substitute lost enamel and dentine tissues. Leakage and secondary caries often represent one of the main adhesive restoration failure reason because of they normally show a volumetric polymerization shrinkage, considered as post gel shrinkage, from 1% up to 4.5% [6]. The composition of organic matrix monomers and the volume percent of inorganic filler affect the polymerization shrinkage, contributing to the prevalence of residual stresses during the composite cure [7]. But stress kinetics in posterior dental restorations is intensely linked to the polymer characteristics and to the cavity design [8]. In adhesive class I restorations, in fact, it has been showed that shrinkage depends more on high c-factor configuration and it may results in cervical dentine leakage and gap generation if the stress exceeds the resin bond strength to dentine and enamel [9]. Stresses arising from shrinkage in class II cavities adhesively restored critically react at the internal and marginal surfaces in deep cavities. They are potentially able to determine in the time clinical failure by gap creation [10]. This relationship is more complex than a simply ratio of bonded/free surfaces [11; 12]. The elastic modulus of the involved materials plays a significant role when they are associated with cavity geometry (boundary conditions) in the posterior adhesive restoration survival [13; 14]. Flowable resin composite have been introduced with this aim to replace dentine under composite restorations being more adaptable to traditional composite to break polymerization stresses [15]. In this sense, in vivo, in vitro and in silico investigations have validated this aspect, reporting that flowable composites are able to reduce polymerization shrinkage and occlusal loading stresses in combination with multi-layer composite technique [16; 17; 18; 19; 20; 21; 22]. Alternatively, various studies suggested to use no shrinking adhesive dental materials such as glass ionomers in combination with composite to reduce the critical resin based materials stress distribution in enamel and dentine replacement [19]. In the last years, bulk-fill resin composites were developed as replacing materials to overcome the multilayering clinical limitations, due to the newer chemical low shrinking monomers structure, better translucency and reduced shrinkage stress development [21; 22]. Different authors [23; 24] have already declared that bulk-fill composites can safety be used in 4 mm or deeper cavities in posterior teeth. A literature review [25] indicated that more scientific and clinical trainings are still obligatory to completely confirm the clinical benefits of bulk-fill composites, still existing divergent results on shrinkage probatematics evaluation in posterior restorations when enamel and dentine need to be replaced [26]. The aim of the present research is to clarify and to explore the effect of shrinking and no shrinking dental filling materials combination in posterior restorations, under the combined effects of polymerization shrinkage and occlusal load [27; 28] by means of 3D Finite Elements Analysis.