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Influence of white mineral trioxide aggregate on inflammatory cells before and after expiry date.

INTRODUCTION
The aim of this study was to compare the effect of subcutaneously implanted white mineral trioxide aggregate (WMTA) on inflammatory reactions before and after expiry date.


METHODS
Fifty Wistar rats were used in this study. Polyethylene tubes were filled with WMTA with expiry dates of 2008, 2009, and 2011, and empty ones serving as the controls were implanted into the subcutaneous tissue. The rats were sacrificed at 7-, 14-, 28-, and 60-day intervals. 5-μm sections were stained with hematoxylin and eosin and observed under a light microscope. Inflammatory reactions were categorized as 0, none (without inflammatory cells); 1, mild (inflammatory cells < 25); 2, moderate (25-125 inflammatory cells); and 3, severe (more than 125 inflammatory cells). Statistical analysis was performed with Kruskal-Wallis test.


RESULTS
All the experimental materials provoked moderate to severe inflammatory reactions after 7 days, which significantly differed from the control group (P < 0.05). At 14-day interval, WMTA with expiry date of 2008 and the control group elicited mild to moderate infiltration of inflammatory cells. However, WMTA with expiry dates of 2009 and 2011 provoked moderate to severe inflammatory reactions, which were significantly different from WMTA with expiry date of 2008 and the control group (P < 0.05). At 28- and 60-day intervals, the overall inflammation subsided in all the groups to mild to moderate infiltration of inflammatory cells without any significant differences (P < 0.05).


CONCLUSION
It seems that the expiry date has less negative effects on the response of inflammatory cells. WMTA keeps its biocompatibility even after expiry date.