# Effect of Endodontic Irrigation on the Bond Strength of Composite Restoration Repair
## 4 Discussion
On the contrary, in a study by [PERSON] and [PERSON] [35], it was shown that the bond was significantly reduced when irrigation with CHX was used with a total-etch system. The reasons for this were reported to be that after dentin was etched with phosphoric acid, dentin fluid could flow out due to increased permeability, chemical irrigants remaining in the fluid would come out onto the dentin surface, and the penetration of adhesives into dentin could be negatively affected [35]. CHX was applied in the current study following the application of NaOCl and NaOCl + EDTA, while in these previous studies investigating bonding, CHX was generally applied alone. Unlike previous studies, a study carried out by [PERSON] et al. [36] showed that CHX application after NaOCl may have a slight positive effect on the decrease in bond strength caused by NaOCl. When the results of our study were examined, although CHX application after NaOCl did not bring the bond strength to the level of the control group, it significantly increased the bond strength that was reduced by NaOCl. In the present study, the samples (composite discs) were abraded using a diamond fissure bur tip with the help of an aerator under water cooling to simulate clinical conditions [37]. When an endodontic access cavity is opened according to the principles of a Class I cavity without completely removing a previously made composite restoration, a bur-abraded composite cavity surface is formed. Failed capping or root canal-treated teeth can be provided as examples for such cases. In order to simulate this situation, all groups in our study were abraded with a bur before applying endodontic irrigation solutions. According to the literature, it has been reported that by applying mechanical surface treatments such as bur abrasion or sandblasting, a surface providing a micro-retentive retention effect is obtained, and the composite-composite bond is increased [38,39]. Although there is no definitive method for aging teeth, thermal cycling is one of the most common techniques among the methods used. In this process, teeth are exposed to temperature changes to simulate hot/cold fluctuations that they may encounter in the oral environment. Repeated expansion and contraction cycles are performed for a certain period of time, usually at temperatures ranging between 5 \({}^{\circ}\)C and 55 \({}^{\circ}\)C. In addition, other aging methods, such as exposure to acidic solutions and boiling water, have been used. It has been reported that these methods used for aging cause less aging compared to thermal cycling. It is generally accepted in the literature that thermal cycling weakens the physical properties of dental materials by causing wear or a certain level of damage to their structure, and this causes a decrease in bond strength [14]. However, there are a few studies in the literature that indicate that thermal cycling increases bond strength. It has been suggested that this is due to the high-temperature (55 \({}^{\circ}\)C) thermal cycling that improves the polymerization rate and physical properties at the repair interface [40,41]. In our study, no significant positive or negative effect of thermal cycling (applied as 5000 cycles) on the bond strength was observed. The reason for this may be that the outer surface most affected by the thermal cycle was removed by abrading the thermally cycled disks (substrate) with a bur, and the negative effects of the thermal cycle were neutralized by increasing the bond surface. Considering that the previous restoration could have been carried out recently or a long time ago, the discs were divided into two groups, and half of them were aged. After the aging process, abrasion with a bur and irrigation solutions were applied. Thus, the effect of endodontic irrigation solutions on both new and aged composite restorations was investigated. One of the limitations of our study is that the repaired samples were not re-aged, which limited our ability to obtain information about long-term results.