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Abstract
The present study was conducted to evaluate fracture resistance of premolars restored with either bulk fill resin composite restorative material or incrementally-packed resin composite after 24 hours and or after one month storage in a storage solution. A total of 40 freshly extracted, sound, human maxillary premolars, from an age of 20-35 years extracted for orthodontic purposes were used in this study. A standardized mesio-occluso-distal (MOD) cavity with parallel walls and without proximal step was prepared using a rose head bur for gaining access then a cylinderical fissure bur. The teeth were randomly divided equally into two main groups (20 teeth each) according to the type of resin composite material used. Incrementally-packed resin compositewas applied in group( A1) and bulk-fill resin composite was applied in group (A2). Each group was subdivided into subgroups (S1 and S2) according to storage period which was either 24 hours or one month respectively, making each group formed of 10 specimens (n=10). The fracture resistance values of all test groups were measured with an Instron testing machine machine. A crosshead speed of 0.5 mm/min. was used and the loads required to fracture the teeth in KG were recorded