# Effect of Endodontic Irrigation on the Bond Strength of Composite Restoration Repair
## 4 Discussion
To date, no published study has investigated the effect of endodontic irrigation solutions on the bond strength between aged and freshly added composite resins--that is, composite-to-composite bonding following exposure to irrigation agents. Therefore, due to the lack of relevant literature on this specific topic, the current discussion refers to previous studies that have evaluated the impacts of irrigation solutions on dentin-to-composite bonding. Different results are seen in these studies. The most probable reasons for this may be methodological differences. These differences may be due to the rate and duration of the applied solution, the adhesive technique used, the adhesive and restorative material, the solution in which the extracted teeth are kept, whether the samples are subjected to aging or not, and the test method [1]. NaOCl is used as the gold standard for disinfection in root canal treatment, and, in most of the previous studies, it has been reported that it negatively affects the bonding of adhesive systems [1]. Various possible mechanisms have been proposed as the reason for this, including the oxidation of the dentin matrix by NaOCl and the formation of reactive free radicals, making it less susceptible to bonding [2; 24; 25; 26]. Previous studies have reported that the use of some reducing agents can reverse this oxidation caused by NaOCl [3; 24; 27]. In studies where EDTA was applied after NaOCl, it was reported that the bond strength to dentin decreased [28; 29]. On the other hand, in their study investigating the bond strength of various adhesive materials to dentin, [PERSON] and [PERSON] [5] reported that the effects of EDTA application following NaOCl treatment varied depending on the adhesive approach. In the majority of groups where the self-etch technique was used, the bond strength--which had been reduced by NaOCl--was restored to control group levels after EDTA application. Conversely, in most groups utilizing the total-etch technique, EDTA did not result in a significant change in bond strength. Although our study only investigated the total-etch technique and observed an increase in bond strength after EDTA application, our findings are partially consistent with this previous study. Sodium hypochlorite is known for its strong oxidative effect, and it is possible that NaOCl infiltrated micro-retentive areas on the composite surface and left residual oxidative by-products, which may have interfered with adhesive penetration or disrupted proper polymerization. However, in our study, subsequent rinsing with other irrigants (e.g., EDTA or CHX) appeared to mitigate this negative effect, as bond strength values approached those of the control group. These findings suggest that the adverse impact of NaOCl on composite repair bonding may be reversible under certain conditions. Although no studies were found that directly examined the effect of sodium hypochlorite (NaOCl) on composite-to-composite bonding interfaces, similar chemical interactions have been investigated in other dental materials. For instance, in a study evaluating the surface roughness of acrylic resins used in removable dentures, immersion in NaOCl--albeit at lower concentrations but for longer durations--led to measurable increases in surface roughness due to matrix degradation and surface erosion [30]. While acrylic resins differ from composite materials in terms of their composition, such findings support the notion that NaOCl can adversely alter surface topography and potentially compromise interfacial adhesion in restorative procedures. When bonding studies using CHX are examined, the predominant view is that it has no effect on the dentin-composite bond due to the lack of an oxidizing agent [31; 32; 33]. However, there are different views, albeit fewer. [PERSON] et al. [34] claimed that CHX can increase bond strength by inhibiting metalloproteinases (MMPs) on the dentin surface.