## 4 Discussion
In the present study, each increment was light-cured for 30 s. This might explain the favorable outcome regarding the quality of the placed restorations (surface roughness, marginal adaption, marginal discoloration, and color match) in the present investigation. While the study of [PERSON] et al. with the same composite material Grandio@SO evaluated Code Bravo at 39.5% in the test group and 32.5% in the control group, [PERSON] et al. detected Code Bravo at 23.6% in the test and 32.1% in the control group. For the use of flowable composites as an intermediate stress-breaking layer, a number of in vitro studies [7; 12; 13; 52] describe a reduction in marginal microleakage and internal cavities as well as an improved adaptation of the composite to the tooth structure, while other studies did not find any positive effects on marginal adaptation [7; 53; 54]. The effect of flowable composite materials as an intermediate stress-absorbing layer in Class I and II cavities compared to the use without using this layer has been investigated in few clinical studies so far [55; 56]. Furthermore, the present study supports the findings that there is no significant influence of the flowable composite on the clinical quality of the fillings. Since, in our study, the adhesive system Futurabond(r) DC was used as a self-etch system on dentin as well as on enamel, this must be taken into account when evaluating the marginal seal. Some studies show the advantages of selective enamel etching for the bond between the tooth structure and the composite [57; 58]. Regarding the used adhesive system in the self-etch modus, the authors have shown that the bond strength values are comparable between the etch and rinse and self-etch modus when testing Futurabond(r) DC in both application modes [59]. Furthermore, this system is known to be effective in establishing a sufficient bond to tooth structures [60]. This might be an explanation for the present finding, that restorations in both groups showed no abnormalities after 24 months in the deterioration of the marginal adaptation. On average, the formation of a marginal leakage and subsequently secondary caries is more than 2 years [1; 61; 62; 63; 64], so longer assessment periods are required. Considering that biofilm is an important parameter in the etiology of caries formation around composite restorations [24], patients with an initial plaque accumulation were encouraged to improve their oral hygiene, and a thorough professional dental cleaning including oral hygiene instructions was performed. As a result, after a follow-up at 2 years, plaque accumulation was reduced from seven to five patients. In the case of study results obtained by in vivo examinations, individual differences must be taken into account. In the present study, a split-mouth design was used to avoid the impact of individual concerns. However, the different oral hygiene of the individual subjects is a parameter that can be influenced but not directly controlled. Finally, this depends on the compliance of the patient. To minimize this complication, good oral hygiene was taken into account when selecting the study participants. These findings are in accordance with the absence of secondary caries in all re-examined teeth. The improvement of oral hygiene might be the relevant factor. Unfortunately, one tooth developed an approximal lesion followed by endodontic treatment in the test group. In summary, in vitro and clinical data do not significantly support any particular method or material type in achieving an optimal performance in restoring Class I and II restorations with current composites [65; 66; 67; 68].