The aim of this study was to compare the fracture strength of two different Ribbond Fiber (Ribbond, Ribbond Inc., Seattle, WA, USA) restoration strategies in 5 mm deep standardized MOD cavities without interaxial dentin.34 extracted human molars were randomly divided into two groups and restored as follows: Group 1 restoration with Ribbond Fiber placed at the cavity floor incorporated in Estelite Bulk-Fill Flow Universal composite (Tokuyama Dental Corporation Inc., Tokyo, Japan); Group 2 restoration with RF placed at 3 mm from the occlusal plane over a 2mm layer of Estelite Bulk-Fill Flow. The occlusal plane in both groups was restored with Ceram.x Spectra ST (Dentsply Sirona, Ballantyne Corporate Pl, Charlotte, NC, USA). The restored teeth were subjected to thermal cycling by immersing them for 30 seconds in hot water (55±2°C) followed by 30 seconds in cold water (5±2°C), for 2000 cycles.Their fracture strength was then evaluated using an Instron device. Data were analyzed with Two-sample T Test statistical test to compare fracture strength among groups. Finally, a descriptive analysis of the failure location was performed.A statistically significant difference was found between groups 1 and 2 (P<0.001) in terms of fracture strength. Group 2 exhibited a higher percentage of recoverable fractures compared to group 1. Group 1 had a mean fracture load of 833N and a SD of 248 while group 2 had a mean fracture load of 1286N and SD of 447.RF placed at 3 mm depth from the occlusal plane, on a 2 mm layer Estelite Bulk-Fill Flow Universal composite (Tokuyama Dental Corporation Inc., Tokyo, Japan) contributes to improve fracture resistance in vital teeth without interaxial dentin and reduces the risk of non-recoverable fractures compared to when it is placed at a 5 mm depth. Key words:Ribbond fiber, composite restoration, fracture resistance, Instron machine.