Background: The aim of this in vitro study was to evaluate and compare the effect of preheating microleakage among three different filler size composites which include Filtektm Z250 micro hybrid, Z250xt Nano hybrid and nanocomposite Z350xt. in Class II cavity preparation .
Materials and methods: sixty maxillary first premolars were prepared with class II cavities. Samples were divided into three groups according to material used group A (FiltekZ250 micro hybrid). Group B(Z250xt Nano hybrid). Group C (nanocomposite Z350xt)and each group divided into two subgroups of ten teeth according to temperature of composite: Group A1 Teeth are restored by composite at room temperature(24±1˚C), A2 Teeth are restored by same composite at preheated temperature(54±1˚C). After 24 hrs. immersion in 2% in methylene blue, samples were sectioned and micro leakage was estimated.
Results: The greater scores of micro leakage mentioned in Group A( Z250 micro hybrid) in cervical margin while in Group B( Z250xt Nano hybrid) and Group C (Z350xt nanocomposite) have least score of micro leakage especially in occlusal margin.
Conclusions: The scores of micro leakage for all groups varied with different material, margin and temperature. Generally, preheating decreased micro leakage in all groups of composites ,but Preheating decreased micro leakage effectively in Z250 micro hybrid more than Z250xt Nano hybrid and Z350xt nanocomposite micro leakage .
