effect of smear layer on the push-out bond strength of two different compositions of white mineral trioxide aggregate

introduction : the aim of this in vitro study was to evaluate the effect of smear layer on the push-out bond strength of white mineral trioxide aggregate (wmta) with and without disodium hydrogen phosphate (na 2 hpo 4 ). materials and methods: dentin discs with standard cavities were obtained from extracted human single-rooted teeth and divided to 4 groups ( n =15) according to the irrigation regimen and the canal filling material. in groups 1 and 3, canals were irrigated with normal saline; in groups 2 and 4, irrigation method included sodium hypochlorite (naocl) and then ethylenediaminetetra-acetic acid (edta). the canals were filled with wmta in first and second groups and with wmta+na 2 hpo 4 ; in groups 3 and 4. the samples were wrapped in wet gauze and incubated in 37 ° c for 3 days. the push-out bond strength was then measured by means of the universal testing machine and the failure modes were examined under stereomicroscope at 40× magnification. tow-way anova was used to evaluate the effect of material type and smear layer removal. post hoc tukey test was used for the two-by-two comparison of the groups. results: the greatest and lowest mean±standard deviation for push-out bond strength were observed in groups 4 (4.54±1.14 mpa) and 1 (1.44±0.96 mpa), respectively. the effect of removing the smear layer on the push-out bond strength of wmta+na 2 hpo 4 was significant ( p =0.01), but not for wmta ( p =0.52). interestingly, there was significant difference between groups 1, 3 and 2, 4 ( p <0.05). the failure mode for all experimental groups was of mixed type. conclusion: under circumstances of this in vitro study, removal of smear layer increases push-out bond strength when na 2 hpo 4 is added to wmta.