LAUSR

AIM To compare the fracture strength of extracted human roots with apical plugs of Mineral Trioxide Aggregate (MTA) mixed with either Ca- and Mg-free phosphate-buffered saline (PBS) or water, with and without calcium hydroxide (CH) premedication. METHODOLOGY A total of 180 single-rooted human teeth were prepared to resemble immature roots and divided into groups (n = 20). The negative control received canal irrigation only, the positive control received treatment with CH for either two or twelve weeks. MTA mixed with water was used in Group 1: (i) without CH premedication - MTA(W); (ii) after 2-weeks CH premedication - 2/52CH + MTA(W); (iii) after 12-week CH premedication - 12/52 CH + MTA(W). MTA mixed with PBS was used in Group 2: (i) without CH premedication - MTA(PBS); (ii) after 2-week CH premedication - 2/52CH + MTA(PBS); (iii) after 12-week CH premedication - 12/52 CH + MTA(PBS). A compressive force was applied to each root until the point of fracture. The results were analysed by the Kruskal-Wallis and Dunn's multiple comparisons tests (P < 0.05). RESULTS There was no significant difference between groups MTA(W), MTA(PBS) and 2/52CH + MTA(PBS), and all three groups were significantly (P < 0.01, P < 0.05, P < 0.05, respectively) more resistant to fracture than the negative control. Within Group 1, the samples that received two- (P < 0.01) and twelve- week (P < 0.001) CH pre-treatment were more prone to fracture than those which did not. No difference was found among the control groups. The roots of the MTA(PBS) group had a higher dependability (P < 0.05) than the MTA(W) group when compared by the Weibull modulus. The difference was also present when a 2-week CH premedication was used. CONCLUSIONS MTA mixed with Ca- and Mg-free phosphate-buffered saline had a significant strengthening effect on the fracture resistance of structurally weak roots, even when short-term calcium hydroxide pre-medication had been used. MTA mixed with water lost its strengthening effect on human roots when 2- or 12-week CH pre-treatment had been used. Use of CH dressing for up to 12 weeks had no negative effect on fracture resistance of human roots.