The effect of different surface treatments and adhesive systems on shear bond strength in universal nanohybrid composite resin repair

Background The aim of this study is to evaluate the effect of different surface treatments and adhesives on shear bond strength (SBS) in the repair of composite resin restorations. Methods In this study, 60 discs (2 mm x 10 mm) were prepared using a universal nanohybrid composite resin (GrandioSo, Voco, Germany). The discs were aged by exposure to 5000 thermal cycles between 5 and 55 degrees C for 30 s with an immersion procedure. Then samples were divided into 3 groups (n:20) according to the surface treatments (Group 1: no surface treatment, Group 2: roughening by bur, Group 3: roughening by Er, Cr: YSGG laser). Subsequently, the specimens were classified into two groups (n:10) according to the adhesive systems; a two-step self-etch adhesive (Clearfil SE bond (SE)), or a universal adhesive (Scotchbond Universal Plus (SB)). After surface treatments and adhesive applications, the same universal nanohybrid composite resin with a height of 2 mm and a diameter of 3 mm was placed in the center of the samples. The samples were then submitted to the SBS test using universal testing equipment (Autograph AGS-X; Shimadzu, Kyoto, Japan) with a crosshead speed of 1 mm/min. The failure modes were examined using a stereomicroscope. The surface topography of the roughened and fractured surfaces resin composite (n = 1) was assessed using scanning electron microscopy (SEM). Analyses were performed using IBM SPSS 25 programme (p < 0.05). Results The highest bond strength was observed in the laser + SE group (22.69 +/- 4.49), while the lowest was recorded in the control + SE group (14.12 +/- 3.00). In the SE adhesive group, no significant difference was found between the laser + SE and bur + SE groups (p > 0.05). Similarly, in the SB adhesive group, there were no significant differences among the surface roughening procedures (p = 0.078). Additionally, no significant differences were observed between the adhesives according to various surface roughening procedures. The failure mode was predominantly cohesive in old composites. Conclusion The bond strength can be improved by surface treatments such as diamond burs, Er, Cr: YSGG laser application for better bonding strategies in the repair of nanohybrid resin composite restorations. There was no statistically significant difference in bond strength between the adhesives tested in this study.