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Background and aims. Substituting chlorhexidine (CHX) for water has been shown to enhance antimicrobial activity of mineral trioxide aggregate (MTA). The purpose of this study was to compare the compressive strength of MTA mixed with distilled water, 0.12% and 0.2% chlorhexidine. Materials and methods. MTA was mixed according to manufacturer’s instructions in group I (n = 20). In groups II & III, 0.12% and 0.2% CHX liquid was substituted for water, respectively. Samples were condensed with moderate force into 20 tubes with 1.5 × 5 mm dimensions and were allowed to set for 72 hours at 37°C in 100% humidity. After being removed from the molds, their compressive strength was determined using Instron testing machine. Each group was divided into two subgroups according to the time of testing (at 72 hours, and one week). Fractured surfaces of 4 specimens in each group were then evaluated under Scanning Electron Microscope (SEM) to determine their microstructure. One-way ANOVA, Tu-key, and paired sample t-test was used for statistical analysis. P < 0.05 was set as significant. Results. There was no significant difference between three groups in terms of their compressive strength after 72 hours. However, the compressive strength of group II was significantly higher than group I (P = 0.034) and group III (P = 0.021) after one week. Crystalline microstructure was similar in all groups. Conclusion. Substitution of 0.012% chlorhexidine for water significantly increased the compressive strength of MTA at 1 week without significant change in crystalline structure.

Background and aims. Mineral trioxide aggregate and calcium hydroxide are considered the gold standard pulp-capping materials. Recently, Portland cement has been introduced with properties similar to those of mineral trioxide aggregate. His-topathological effects of direct pulp capping using mineral trioxide aggregate and Portland cements on dog dental pulp tis-sue were evaluated in the present study. Materials and methods. This histopatological study was carried out on 64 dog premolars. First, the pulp was exposedwith a sterile bur. Then, the exposed pulp was capped with white or gray mineral trioxide aggregates and white or gray Port-land cements in each quadrant and sealed with glass-ionomer. The specimens were evaluated under a light microscope after 6 months. Statistical analysis was carried out using Kruskal-Wallis test. Statistical significance was defined at α=5%. Results. There was no acute inflammation in any of the specimens. Chronic inflammation in white and gray mineral triox-ide aggregates and white and gray Portland cements was reported to be 45.5%, 27.3%, 57.1% and 34.1%, respectively. Al-though the differences were not statistically significant, severe inflammation was observed mostly adjacent to white mineral trioxide aggregate. The largest extent of increased vascularization (45%) and the least increase in fibrous tissue were ob-served adjacent to white mineral trioxide aggregate, with no significant differences. In addition, the least calcified tissue formed adjacent to white mineral trioxide aggregate, although the difference was not significant. Conclusion. The materials used in this study were equally effective as pulp protection materials following direct pulp cap-ping in dog teeth.

Background and aims. It is important to evaluate the effects of endodontic materials on tooth structures to avoid endodontic treatment failure. The aim of the present study was to investigate the effect of mineral trioxide aggregates (MTA) and Portland cement (PC) on fracture resistance of dentin. Materials and methods. Thirty-six freshly extracted human single-rooted premolar teeth were selected. The crowns were removed and the roots were randomly divided into two experimental groups and one control group. The root samples were longitudinally divided into two halves and a dentin bar (2×2×10 mm) was cut from each root section for short-term (2 weeks) and long-term (12 weeks) evaluations. The root sections in the experimental groups were exposed to MTA or PC, while keeping the control group specimens in physiologic saline. The fracture resistance of each specimen was measured using an Instron testing machine. The results were statistically analyzed using ANOVA, a post hoc Tukey test and paired ttest at 5% significance level. Results. The fracture resistance of MTA-treated specimens significantly increased between 2 and 12 weeks (P0.05). Conclusion. The results showed that MTA increased the fracture resistance of root dentin, while PC had no significant effect on dentin fracture resistance.

Background: The aim of this study was to evaluate the antimicrobial activity of Mineral Trioxide Aggregate (MTA) and Calcium Enrich Mixture) CEM (mixed with different concentrations of chlorhexidine (CHX). Materials and Methods: Cements used in this in vitro study included Gray proRoot MTA and CEM with the microorganisms being entrococcus faecalis, streptococcus muntas, Candida albicans, Actinomyces, Escherichia coli, and a mixture of these microorganisms. CHX was used in the form of liquid at 0.2%, 2%, and 0.12% concentrations. Contact dilution and colony count method was used to evaluate the antibacterial activity of these cements. After 0, 24, 48, 72, and 96-hour intervals, we cultured the samples on blood agar medium. Colonies were counted after incubation at 37°. Data were statistically analyzed by a Kruskal-Wallis test to compare the antimicrobial activity of MTA and CEM. Results: All concentrations of CHX were mixed with MTA and the CEM had antibacterial activities on all microorganisms′ strains except for the Enterococcus faecalis and the mixture group. MTA had better antibacterial activity than the CEM, but this difference was not significant (P = 0.13). The mixing of MTA and the CEM with CHX significantly increased the antibacterial properties of both cements (P < 0.03). There was no statistically significant difference between the different concentrations of CHX. The antibacterial activity of the materials increased through time. Conclusion: The mixture of MTA and CEM with different concentration of CHX significantly increased the antibacterial activity.

INTRODUCTION: The materials used for root-end filling and perforation repair are in direct contact with live tissues e.g. bone and connective tissue; their effects however, are uncertain. The aim of this ex vivo study was to evaluate the osteoblastic secretory activity adjacent to gray and white mineral trioxide aggregate (MTA) and Intermediate Restorative Material (IRM). MATERIALS & METHODS: The studied materials were prepared and placed in 24-wells plate. Human MG-63 osteoblasts were introduced to materials after their initial set. The supernatant fluid was collected after 1, 3, and 7 days and the level of interleukin-1b was measured by ELISA test. A microscopic exam was also performed to assess proliferation and viability of the cells. Kruskal-Wallis and Tukey tests were used for analysis. RESULTS: There were significant higher levels of interleukin-1b in the gray and white MTA groups compared to IRM group (P0.05). Morphologic appearance of osteoblasts adjacent to gray and white MTA was similar to normal osteoblasts in all observation periods, however cells adjacent to IRM were round, signifying cytotoxicity of the adjacent material. CONCLUSION: Human osteoblasts’ biological response to white and gray MTA is more favorable compared to IRM.

INTRODUCTION: The aim of this study was to evaluate the effects of remnant root canal medicament, calcium hydroxide on the short and long term sealing ability of mineral trioxide aggregate (MTA) apical barrier. MATERIALS & METHODS: Fifty single-rooted teeth were prepared and apical resorptions were made using sulfuric acid. The teeth were allocated into two experimental groups and two control groups. In group 1, calcium hydroxide was placed into canals for one week. In group 2, no medication was placed. In both groups, a 4-mm MTA plug was placed in the root canals. The remaining portion of the canal was filled with gutta-percha/sealer. The microleakage was evaluated after 7 days and 3 months using fluid filtration technique. Repeated measurement ANOVA was used for statistical analysis. RESULTS: There was no significant difference in sealing ability between the two groups in either time periods. In both groups, microleakage decreased after three months but this decrease was not statistically significant. CONCLUSION: Medication with calcium hydroxide had no adverse effect on the short and long-term sealing properties of MTA plug.