In vitro Comparative Study of Compressive Strength of DifferentTypes of Composite Resins in Different Periods of Time

To evaluate the ultimate compressive strength of five composite resins after 1 hour,24 hours, 7 days and 1 month . twenty four cylindrical 4 nunx8mm specimens ofeach commonly used composite resins in posterior region (nulite-f , z250 , p60,biscore, tetric ceram hb) were prepared. each group of composite resins weredivided into four time groups of 1 h, 24 h, 7 days and 1 month. all of specimensstored in an incubator with 37°c. after each period of time all of the specimenswere tested by zwickiroell z020 (germany) for ultimate compressive strength atcross head speed of 0.5 em/min. results were analyzed by anoya and scheffe test.p60 and z250 had the highest and nulite-f and tetric ceram hb had the lowestcompressive strength at all the times. the difference between these two groups wasstatistically significant (p<0.05). the results of the biscore was steady among theother groups. it is suggested to use z250 or p60 in posterior restorations instead ofthe other composite resins tested.