# Effect of Endodontic Irrigation on the Bond Strength of Composite Restoration Repair
## 2 Materials and Methods  
This in vitro study was approved by the Clinical Research Ethics Committee of Afyonokarahisar Health Sciences University (13 December 2024--No: 2024/485). The sample size was calculated using GPower 3.1 (Heinrich Heine University, Dusseldorf, Germany), revealing that a minimum of 18 specimens was required to obtain 80% statistical power with an effect size of 0.262 and a significance level (\(\alpha\)) of 0.05. Based on a previous study [17], a group size of at least 15 specimens was considered adequate. Composite discs were fabricated using a light-curing microhybrid composite resin (Filtek Z250, A2, 3M ESPE, St. Paul, MN, USA) and a mica mold with a diameter of 1 cm and a thickness of 1.4 mm. The prepared samples were polymerized for 20 s with a light-emitting diode (LED) light device (Elipar FreeLight, 3 M ESPE, St. Paul, MN, USA) at an output power of 1000 mW/cm\({}^{2}\). The samples were divided into 2 groups, and no aging process was applied to the first group. However, the second group was subjected to thermal cycling (5000 cycles, between 5 and 55 \({}^{\circ}\)C, waiting time: 30 s), and an aging process was applied. Then, all discs were roughened with a green belt fissure bur under water cooling. After this stage, the discs were divided into 5 subgroups (\(n=18\)) and exposed to endodontic irrigation solutions according to different protocols. In Group 1, no endodontic solution was applied (control group). In all other groups (Groups 2, 3, 4, and 5), the discs were kept in a completely submerged position in 5% NaOCI solution for 20 min. The solution was renewed at 5 min intervals. These procedures were carried out in an oven at 37 \({}^{\circ}\)C and 100% humidity. No procedure was performed after exposure to NaOCI in Group2. In Group 3, 5 mL of 17% EDTA (2 min) was applied; in Group 4, 5 mL of 17% EDTA (2 min) + 5 mL of 2% CHX (2 min) were applied; and in Group 5, 5 mL of CHX (2 min) was applied. After all solution changes and the last irrigation, the samples were irrigated with 5 mL of distilled water. Subsequently, all the discs were fixed on the pipe pieces with a cyanoacrylate adhesive. The total-etch method was preferred, and after the surface of the composite samples was roughened with 37% phosphoric acid (Etching Gel, Kerr Corporation, Orange, CA, USA) for 30 s, the sample surfaces were rinsed with water for 20 s and dried with light air for 15 s. Then, Bond Force II (Tokuyama Dental Co., Tokyo, Japan) was applied according to the manufacturer's instructions and dried with light air for 5 s. The bonded surfaces were polymerized with the LED light device for 10 s. Composite samples (Filtek Z250, A2, 3M ESPE, St. Paul, MN, USA) were created using 1 mm diameter and 2 mm high tygon tubes (3 or 4 on a composite disc) and polymerized by applying light with the LED light device for 20 s. Details of the materials used in this study are presented in Table 1.  
The specimens were fixed to a universal testing machine for SBS testing. A wedge-shaped stainless steel metal tip was positioned closest to the specimens' attachment point and did not impede their movement. Then, a compressive load was applied parallel to the bonding surface at a speed of 1 mm/min. The value at which fracture occurred was recorded in Newton. Then, the \(\upmu\)SBS value for each specimen was calculated by dividing the force by the surface area and recorded in MPa. Statistical analysis of the data was conducted using the two-way ANOVA test. Multiple comparisons were performed using the Tukey post hoc test (SPSS 23.0, IBM, Armonk, NY, USA). A dental microscope (OMS 2380; Zumax, Suzhou, China) at 20\(\times\) magnification was used to analyze the failure modes of all specimens. The observed failure patterns were classified into five distinct categories (Figure 1). For scanning electron microscopy analysis (LEO 1430 VP, Zeiss, Oberkochen, Germany), a total of 20 composite discs with a diameter of 8 mm were prepared, with two specimens from each group.