_applied_  
_sciences_  
_Article_  
**Assessment of Mineral Trioxide Aggregate Setting in Simulated Root Canal with Different Root Canal Wall Thickness:**  
**In Vitro Study**  
**[PERSON] 1,2,*, [PERSON] 3, [PERSON] 4, [PERSON] 5, [PERSON] 5, [PERSON] 1**  
**and [PERSON] 1**  
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Although various powder-to-water ratios of MTA do not influence expansion of the material [4] or dimensional stability [5], adding excessive amount of water over the suggested powder-to-water ratio during mixing increases porosity, solubility [6], setting time, calcium release [7], decreases bond strength [8], and diminishes compressive strength [9]. On the other hand, this undesirable scenario can occur if the wet curing of MTA is used, and the cotton pellet is too wet and placed on the material too early [10]. Several studies have assessed the effect of presence of intracanal moisture, the influence of intrinsic moisture source [11] or different thickness of applied MTA on its quality and properties [12]. There are indices that moist cotton pellet placement may not be crucial for MTA setting in apexification procedures [11] or in cases where thickness of the material does not exceed 4 mm in total [13]. But there is reported only marginal interest on the influence of the physiological moisture in dentin or dental permeability on setting of MTA. This could be more noticeable in immature teeth and teeth with extensive retrograde cavity where limited amount of dentin or wide dental tubules are present and could lead to improper setting of MTA and failure of treatment. There are studies which describe setting of dry MTA by moisture absorbed through the root [14], through the apical foramen [15], or in the presence of interstitial fluid alone [11]. However, the limitations of these studies are the use of Vickers indentation (four-sided pyramid) and measurement on horizontal sections which has only limited information about setting in different parts of material. Only a few studies have studied mechanical properties of MTA on longitudinal sections [16]. Another limitation is standardization of root canal wall thickness. The information about sizes of roots and their shape is usually missing, and usually only apical preparation is standardized; the inter-study comparison of results, thus, remains almost impossible. The last limitation is that, in many studies, the size of used specimen is out of clinical relevance. Besides, investigation of the mechanical properties of contemporary dental materials at relevant scale and environment is necessary for understanding their performance, application limits and of course, for optimization of their application protocols. It should be noted that mechanical properties of dental restorative materials may exhibit an important size-dependent character [17] as was proved in the case of calcium silicate cements [16]. One of the most commonly mentioned mechanical properties of MTA related to setting is microhardness.