## 1 Introduction  
Non-carotis cervical lesions (NCCLs) are defined as a loss of dental hard tissues at the cemento-enamel junction area through processes unrelated to caries [1]. Nowadays,they are a more and more common pathology in clinical practice [2]. The development of NCCLs is a consequence of changes in lifestyle such as diet and oral hygiene habits as well as of increasing life expectancy [3]. NCCLs are usually produced by a combination of abrasive, erosive, and stress-producing factors, which generate different clinical appearances varying from shallow lesions with poorly defined margins to large wedge-shaped defects [1]. NCCLs are almost exclusively situated on the facial surfaces of teeth [1]. The identification and the management of the putative etiologic factors are mandatory before initiating treatment [4]. To date, no conclusive evidence for reliable, predictable, and successful treatment strategies for NCCLs exists [1]. Depending on the clinical appearance and the localization of NCCL (i.e., coronal or radicular), the current treatment options include monitoring and prevention [4], treatment of dentin hypersensitivity [1], restorative treatment [2], or root coverage surgery associated or not with restorative treatment [5]. If ignored, NCCLs invariably enlarge [2]. Although monitoring NCCL could be a clinical approach for incipient lesions, the placement of adhesive restorations should be considered for larger crown-located defects. Composite resins combined with adhesive systems are the preferred choice to restore NCCLs in clinical practice [6; 7]. The clinical performance of NCCL restorations is highly dependent on the adhesive system used and on the quality of the clinical restorative procedure [1; 6; 8]. However, other factors have been reported to influence the performance of NCCL restorations, such as the marginal location in enamel or cement, the quality of the dentin substrate [9; 10], the restorative materials [10], and the cavity geometry [11; 12]. More recent information reported that only tooth location or the presence of wear facets play an important role in the fate of NCCL restorations [13]. The marginal degradation of composites is frequently seen during the aging of the restorations [1]. Still, primary marginal imperfection consecutive to the localized failures of the adhesion phenomenon is a current weakness reported in cervical restorations, which impacts the longevity and the fate of NCCL restorations [14]. Secondary decay, gingival inflammation due to plaque accumulation [15], and debonding and restoration loss are clinical consequences due to the primary adhesion deficiencies [14]. To protect the adhesive interface from cervical flexural stress, NCCLs with an abstraction component should be restored with a microfilled resin composite or a flowable resin that has a low modulus of elasticity, which allows a discrete flexion in concordance with tooth movement. There is evasive information on the differences between failure rates of resin composites of different stiffness when restoring NCCLs [9; 16]. The clinical applications of flowable composites have been partially restricted principally by their mechanical shortcomings [17]. On the other hand, the increased proportion of diluent monomers in flowable composites induces higher polymerization shrinkage and, consequently, an augmented stress at the adhesive interface [18]. Flowable composites have an average polymerization shrinkage rate of 5% [17], while this rate of conventional composites could be less than 1% [19]. New nanotechnology approaches have allowed the development of flowable composites with improved mechanical and esthetic properties and minimized polymerization shrinkage by almost 20% [20]. Flowable composites seem to be a rational approach to restore NCCLs due to their lower modulus of elasticity as compared to packable composites, which could absorb the polymerization shrinkage and flexural stress [7].