## 4 Discussion  
The null hypothesis was that there would be no difference in the posterior cavities restored with the application of shrinking and no shrinking material's combination, in a bulk or in a multilayer technique. The results showed that different models exhibited higher stresses along the dentine-restoration interfaces with different magnitude according to the restorative material combination. Thus, the hypothesis was rejected. It has been exposed that teeth have complex behavior during mastication in reason of anatomical arrangements based on the different enamel and dentine combination. Chewing is similarly influenced by jaw muscles response for differently rigid foods [30; 31]. In addition, the present study showed that when different restorative materials were applied, the chewing load dissipation can also be affected regardless class I or class II designs. Stress distributions within posterior teeth are a function of 3D shape, stiffness and loading, even though the E modulus of most of the components are known [32]. Dental human enamel has a higher elastic modulus than dentine which is a more compliant tissue. This mechanical combination in posterior teeth permits a higher fracture resistance under chewing and a more uniform stress distribution [33; 34]. Therefore, the restorative procedure should be performed in order to recover the natural tooth mechanical behavior, by means of resistant and compliance biomimetic materials in different layers placed [35]. Premolars and molars adhesively restored using different shrinking resin-based composites has been mechanically investigated under occlusal loading under laboratory conditions [35; 36; 37] or by means of FEA of restored teeth [13; 26; 27; 28; 31; 34]. However, the combination of chewing load application and polymerization shrinkage effect should be applied as resultant of mechanical behavior in restored tooth structures [10]. The major concept is that adhesive materials are aimed to rebuild a durable adhesive bridge between the contrasting walls of the restored cavity [29] targeting to replicate properties and function of the dentine and enamel lost as closely as possible and reducing debonding, leakage at the margins and fracture risk [10; 22; 38; 39]. Morphology, function and aesthetics must also be replicated. For that reason, dentin and enamel should be considered as individual tissue with unique characteristics that the biomimetic restoration should aim to replace. Numerous analyses on adhesive posterior resin composite restorations were carried out using in vitro methods [40; 41; 42] or using in silico simulations [10; 32; 43] and have verified the influence of polymerization shrinkage, cusps deflection occlusal loading, enamel crack propagation and cavities design in the stress distribution. The information on how stresses redistribute in posterior restored teeth assists to prevent post restorative problems [9]. FEA presents several advantages than in vitro tests because of it permits the management of complex settings and because it delivers a superior understanding of detailed results about the internal stress of tooth, restorations and materials [16; 29]. Finite Elements Analysis needs a detailed modelling and a multifaceted scheming with correct boundary conditions [10; 43]. To minimize the stresses arising from composite polymerization during restoration of teeth there is a proposed approach in composite layering of class I composite restoration from bulk placement [44]. The objective was obtained by covering the cavity surfaces with a thin resin composite layer, vertically and horizontally placed. This layer was named the \"prelayer\" and it was followed, in a second step, by further composite horizontal layering. The FEA of this modified class I technique showed a 75% reduction in the shrinkage stresses. The \"prelayer\" assured a strong linking of the remaining layers with the tooth tissue due to appropriate shrinkage vectors. After the \"prelayer\" setting, the cavity becomes smaller.