Aim :The present study aims to examine the effect of pressure changes on fracture resistance and fracture patterns of endodontically treated premolarswith short fiber reinforced composite restoration during simulated dives and flight. Materials and Methods: Thirty extracted maxillary premolars were selected and divided into three groups (n=10). All the teeth had endodontic treatment and MOD cavity design with short fiber reinforced composite resins as the final restoration.Group 1 for simulating SCUBA diving pressure(2 ATA), group 2 forflightsimulating pressure (0.37 bar) andthegroup 3 as controlgroup (atsmospheric pressure). All samples were treatedfor 1 monthandfracturetestwasperformedusing a universal testing machine (UTM) with static load was applied at a speed of 0.5 mm/min until fracture occurred and the fracture patterns was observed. Data were statistically analyzed with one-way analysis of variance (ANOVA), while for fracture patterns were tested using Fisher’s Test