Comparison of bond strength of white Mineral Trioxide Aggregate with and without adding Na2HPO4 in different water to powder ratios

Abstract

MTA is used in vital pulp therapy and root canal perforation repairs . This material is also used as an apical plug in open apex nonvital teeth and root-end filling material in apical surgery, but primary reaction of inflammatory cells to this material and its setting time are not ideal. Studies have showed that disodium hydrogen phosphate solution as an accelerator decreases setting time of MTA and preserves its pH at the same level . An ideal root-end filling material should resist to forces such as mechanical stresses during tooth function or filling procedure and doesEnt dislodge but MTA cement may displace in some clinical cases such as furcal perforation repair or pulp capping ;due to coronal forces applicated during filling procedure. One of the methods to study the resistance of different materials to dislodgement is push-out test. The aim of this in vitro study is to investigate the effect of adding disodium hydrogen phosphate to MTA powder and using different water to powder ratios on its push-out bond strength . Methods: 120 specimens were made from the middle third of the teeth with single root canals to study the push-out bond strength of MTA. After preparation thickness of all specimens were 2mm and their canal diameter was 1.3 mm . The sections were immersed in 17% ethylene-diamin etetraacetic acid for 3 minutes, followed by immersion in 1% sodium hypochlorite for another 3 minutes. In sixty specimens the prepraid cavities were filled with pure white MTA and in another sixty specimens they were filled with the mixture of disodium hydrogen phosphate and white MTA. The pushout bond strength values of both groups with water to powder ratios of 0/33 to 1, 0/5 to 1 and 0/6 to 1 were measured after 72 hours. Factorial ANOVA test and Mann-Whitney U test were used to compare the means between independent groups. P<0/05 was considered significant. Results: Push-out bond strength values of cement in pure MTA group and disodium hydrogen phosphate with MTA group were 10.96 5.78 and 13.32 5.03 and Mann-Whitney U test showed statistically significant differences between the two groups. Also push-out bond strength values of cement in groups with water to powder ratios of 0/33 to 1 , 0/5 to 1 and 0/6 to 1 were 16.77 5.41 , 10.92 4.47 and 8.84 3.28 and Factorial ANOVA test showed significant differences between the groups. Conclusion: Adding disodium hydrogen phosphate into MTA increases its pushout bond strength and increasing the water-to-powder ratio decreases its bond strength