## 4 Discussion  
It is a continuous quest for the perfect restorative material and restoration technique that ensure the ideal adherence to the tooth surface for eliminating the microleakage. It is, also, very important to maintain the marginal seal in time and to minimize the clinical issues due to microleakage, like marginal discolorations or recurrent caries [15]. The ability of restorative material to reduce the microleakage along the restauration/dental wall interface is crucial in its clinical success. There are several methods that have been proposed in order to assess the correctness of a restoration and the degree of microleakage alongside the margins. One of the most used methods is the dye diffusion. This method involves the use of different dyes like methylene blue, eosin, aniline blue, Indian ink or fluorescein [16]. It is important to mention that the diameter of the dye particles should be smaller than the diameter of dental tubules (1-4 \(\upmu\)m), otherwise they might be retained by the dental structures or the restorative material, representing a source of errors. According to other dye penetration studies, it is recommended to use a dye with a particle diameter equal to the bacterial size or smaller (-2 \(\upmu\)m) [17]. For this reason, in this study methylene blue solution was used as a dye, since its particle size is smaller than bacteria (1.2 nm\({}^{2}\)) [18]. Microleakage that occurs along the restorative material/dental tissue interface is the most important issue when composite resins are used for restorations. In order to reduce the shrinkage associated with resins polymerization, different methods of restoration placement were imagined in trying to reduce the bonded to unbonded restoration surface ratio [19]. One of this methods is represented by the oblique layering technique which reduces the contraction forces that occur between opposing walls, and, by that, the cuspal fissures or gap formation [20]. In order to simulate the degradation of composite bond in this study, the aging by thermocycling was used. Different authors suggested different dwell times. These ranged from 4 to 180 s, without any justification. After a careful analysis of more studies, [PERSON] and [PERSON] [21] noticed wide variations in the thermocycling regimens and concluded that there no rule must be respected when choosing a regimen by the contrary, [PERSON] et al. [22] concluded that the dwell time should be of maximum 10 s in order to be clinically relevant. One more issue that needs to be mentioned in microleakage studies is related to the scoring systems. The evaluation in these studies, usually uses the observer's interpretation, so the leakage scoring can be considered a semi-measurable method [23,24]. In addition, various studies mention that dye leakage in different sections of the restoration may show significant differences [25,26]. For this reason, it is mandatory to assess the leakage on more just one section from a tooth, in order to increase the accuracy of the study. For the moment, there are no quantitative methods that can be applicate for the microleakage determination. The microleakage was measured through quantification in the present study. The method within stereomicroscopic studies is based on the interpretation of the dye leakage on the cavity walls and is defined as a semi-quantitative approach where the leakage is calculated solely at the surface where the section is made [27]. The present study showed that the marginal microleakage was present in both groups, but in different proportions. Even if the differences were not statistically validated, the teeth restored by oblique layering technique showed lower scores compared to those restored by horizontal layering technique. Therefore, this difference can be due to the different layering technique that was used. The results are in agreement with [PERSON] et al. [14] and [PERSON] et al. [28] who concluded that, regarding the microleakage, there are not any differences between different layering techniques.