Effects of bone graft materials on the microhardness of mineral trioxide aggregate

Introduction: Large through-and-through lesions have been reported to heal faster and better when filled with bone graft material at the time of an apicoectomy. It is unknown what effect these have on retrograde filling materials such as white mineral trioxide aggregate (WMTA). In this study, the null hypothesis was tested that the presence of bone graft materials does not affect the microhardness of WMTA. Methods: Freshly mixed WMTA was condensed into acrylic cylinders and preincubated aerobically at 37°C for 1 hour. Cylinders were immersed in simulated body fluid in close proximity to graft materials: xenograft (Bio-Oss, n = 60), freeze-dried bone allograft (MinerOss, n = 60), demineralized freeze-dried bone allograft (OraGraft, n = 40), and allograft (Puros, n = 60). Knoop microhardness of half the samples in each group was evaluated after 2 weeks of incubation and the remainder at 4 weeks. The values for each group were then compared with 2-way analysis of variance and Bonferroni post hoc tests. Results: WMTA microhardness values for Bio-Oss, MinerOss, and Puros groups were lower than those for OraGraft and control groups regardless of incubation period (P < .001); values for the OraGraft group were higher than those for the control group at 2 weeks (P < .001), with no difference at 4 weeks. Microhardness values were higher at 4 weeks compared with 2 weeks for MinerOss (P <.05), OraGraft (P <.01), and control (P <.001), with no differences for Bio-Oss and Puros groups. The null hypothesis was rejected. Conclusions: Demineralized and mineralized graft materials appear to have a differential effect on the microhardness of WMTA.