## 4 Discussion
Thus, the Scotchbond Universal self-etch (16.15 \(\pm\) 8.53 MPa) and Scotchbond Universal total-etch (16.34 \(\pm\) 4.90 MPa) groups showed lower BS values relative to the Adper Scotchbond 1 XT (19.22 \(\pm\) 6.34 MPa) and Adper Prompt L-Pop (20.27 \(\pm\) 5.89 MPa) groups. Moreover, the present study showed that the BS differed according to the type of adhesive used. Previous studies showed that etch and rise adhesive systems achieved higher BS values than self-etch adhesives [31; 32; 33]. Self-etching systems benefit most from chlorexidine application. Demineralized (etched) dentine is almost 80% more effective than mineralized (non-etched) dentine in terms of this application of chlorexidine. Through acid etching, the peritubular dentine is lost, the dental tubules are enlarged, and at the same time their water content increases, and this will allow the incorporation of the chlorhexidine within the dentine matrix [9, 31, 34, 35]. Currently, one of the biggest goals of adhesive dentistry is to improve the ageing resistance of the adhesive interface, making restorations more clinically durable [36]. The durability of the adhesive interface is strongly linked to the hybrid layer quality, that is, the entire exposed collagen and the quality of the resin coat created [7, 31]. The conservation of the correct state of the hybrid layer, through the incorporation of CHX to maintain its balance, is a key point in slowing down the loss of BS [31]. CHX has been researched as an important inhibitor of MMPs and shows no negative impact on the BS between resin and dentine [7]. Chlorhexidine 2% is the concentration that has been researched the most and had the strongest inhibitory impact on MMPs [12, 31], which is related to the mechanism of CHX cation chelation [7] and calcium sequestration [26]. In addition, its high substantivity thanks to the delivery of molecules with a positive charge to the target area, and the absence of side effects such as an unpleasant taste and brown spots after short-term application, as mentioned in the analysis by [PERSON] et al., 2010 [37], make it an important adjunct in bonding procedures. In previous studies, [PERSON] et al., 2019, [PERSON] et al., 2009 and [PERSON] et al., 2009 mentioned that the high substantivity of CHX allowed the demineralized dentinal collagen fibrils to bind in a very short period of 15 to 60 s, which was sufficient to provide long-term favorable bonding characteristics [31, 38, 39], with a 60 s application being effective for deciduous teeth [29, 30]. However, it should be noted that CHX only prevents collagen degradation; the polymer (resin layer formed) is still liable to absorb water and consequently swell, whereby leaching of the polymer occurs, creating gaps re-exposing the collagen fiber network susceptible to further degradation by MMPs [7], leading to the recurrence of caries and lesions. The bond strength measurement method is regarded as a robust indicator of the durability of direct adhesive restorations. In addition, different test methods can be considered for BS analysis [36]. However, other variables that may influence these results need to be considered. In clinical practice, some variables can have a significant influence on bond strength, such as saliva [40] or blood [41] contamination. These conditions should be tested in future studies. The micropush test may give more precise information on the impact of different adhesives on BS in comparison to the standard shear bond test, as it involves the elimination of the curing composite [36]. The advantages of using CHX 2% prior to conditioning have been previously proven; however, its use during the adhesive process increases the number of adhesive steps, which is in contrast to the proposed simplified clinical procedures for pediatric dentistry. All studies agree on the benefit of including the chlorhexidine pretreatment step, even though this step slightly increases the clinical time of the restoration [7].