# Effect of Endodontic Irrigation on the Bond Strength of Composite Restoration Repair
## 1 Introduction  
Endodontic treatment aims to preserve the integrity of the tooth structure and prevent or treat apical periodontitis. A critical aspect of this treatment is the effective sealing of the root canal system, a process that often involves the use of various irrigation solutions to enhance the preparation and disinfection of the dentin surface. Irrigation solutions alter the surface properties of dentin, thus affecting the bond strength of dental composites [1]. Sodium hypochlorite (NaOCI) is one of the most widely used endodontic irrigants due to its strong antimicrobial properties and ability to dissolve organic tissue. Studies have shown that long-term exposure to NaOCI can denature the collagen structure on dentin and lead to changes in mineral content, which weakens bond strength [2, 3, 4].  
To reduce the adverse effects of NaOCI, the use of chelating agents such as ethylene-diamine tetraacetic acid (EDTA) has been suggested [5]. EDTA effectively removes the inorganic components of dentin, exposing collagen fibers that increase the bonding potential of composite materials [6]. Contrary to this view, there are also studies indicating that EDTA does not provide adequate improvement [7, 8]. Additionally, the application of chlorhexiidine (CHX) has been suggested to provide sustained antimicrobial effects and improve bonding results [9, 10, 11]. CHX has a near-neutral pH and a strong affinity for dental hard tissues, allowing it to remain on the surface for extended periods, which maycontribute to its prolonged efficacy [12]. However, the interactions between these solutions and their overall effects on the bond strength of composites are not fully understood [13].  
Aging procedures are critical for simulating the natural degradation processes of dental materials over time and essential for assessing the longevity of bond strength between composites and dentin. Various methods, such as thermal cycling, can simulate aging under conditions experienced in the oral environment. Understanding how aging affects the bond strength of composites exposed to various irrigation solutions is critical for predicting clinical outcomes [14].  
In this study, a microhybrid resin composite (Filtek Z250, 3M ESPE, St. Paul, MN, USA) was used as both the substrate and repair material. This composite is commonly preferred in repair studies due to its high filler content, favorable mechanical properties, and wide clinical use. Microhybrid composites have demonstrated consistent bonding behavior with adhesive systems, making them suitable for standardizing repair protocols. Filtek Z250 contains a resin matrix of UDMA, Bis-GMA, Bis-EMA, and TEGDMA, and is filled with silane-treated ceramic and aluminum oxide particles, which contribute to its reliable bonding performance [15; 16]. Therefore, the use of a single, well-established material allowed for a more controlled evaluation of the effects of irrigation solutions on repair bond strength.  
Although numerous studies have investigated the effects of endodontic irrigation solutions on dentin structure--and, consequently, on the bond strength of composite resins to dentin--no research to date has examined their impact on composite-to-composite bond strength when these solutions are applied directly to the composite surface. The present study aims to evaluate the effect of commonly used irrigation solutions on the bond strength between aged or non-aged composite restorations and newly applied composite material. To achieve this, shear bond strength (SBS) testing was employed to quantitatively assess adhesive performance following various irrigation protocols. Focusing on a previously unexamined area of post-endodontic restorative care, this study may help to enhance the longevity of composite restoration repairs.