الفهرس 
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Abstract
The purpose of this study was to evaluate the effect of Maleic acid and Lactic acid versus Ethylene diamene tetra-acetic acid (EDTA) as root canal irrigants on root dentine microhardness of instrumented human root canal.
Methodology: Seventy eight straight, single rooted human teeth were standardized at 15 mm. Each canal was enlarged with rotary Nickel Titanium K3 0.06 taper up to file size # 40. The roots were divided into a control group (n=12) and three experimental groups (n=22 each) according to the final irrigant used; saline, 17% EDTA, 7% Maleic acid and 10% Lactic acid. A total of 1 ml of each solution was used for 3 and 15 min. After irrigation, coronal section of 3 mm thickness was cut from each specimen. The microhardness of root dentine was determined with a Vickers Microhardness Tester at two levels 0.5 mm and 1 mm from the canal wall. Data was statistically analyzed. A specimen was randomly taken from each subgroup, split after the irrigation regimens longitudinally for scanning electron microscope (SEM) examination.
Results: Saline group had the highest microhardness values followed by EDTA and least was Maleic and Lactic acid. Microhardness values decreased with statistical significant difference after 15 min when compared to 3 min for test solutions. Lower microhardness values were obtained at 0.5 mm compared to 1 mm from the canal wall. EDTA and Maleic acid removed smear layer similar to each other while the least was Lactic acid.
Conclusion: Maleic acid and Lactic acid effectively reduced microhardness more than EDTA. Microhardness is time dependent and decrease with increasing time of application of test solutions. Dentine microhardness was not dependent on depth from canal wall. Smear layer removal and changes in structure of root dentine was dependent on type of test solution and its time of application.