## 1 Introduction  
Mineral trioxide aggregates (MTAs) are biocompatible endodontic cements that are mainly composed of calcium and silicate elements [1]. MTAs were first developed and introduced as a root-end filling and perforation repair material [2, 3], and they might also be useful for pulp capping, pulpotomy, apexification, apexogenesis, and root canal filling [4]. MTAs are a biocompatible material that are less cytotoxic than conventional endodontic materials, and they have the advantages of promoting the formation of mineralized tissue and preventing microleakage [5, 6].  
ProRoot MTA (PRM; Dentsply Sirona, Tulsa, OK, USA) is the first commercially available MTA for clinical use and is applied by mixing calcium silicate-based powder with distilled water [7]. However, PRM has several drawbacks, including a prolonged setting time, difficulty in handling, and discoloration. To overcome these disadvantages, various types of improved MTA products have been developed. Biodentine (BIO; Septodont, Saint Maur des Fausses, France) has a short setting time and improved handling properties because of the incorporation of a hydrosoluble polymer and calcium chloride in the liquid [8]. Well-Root PT (WRP; Vericom, Chuncheon, Korea) is a recently introduced MTA that is a ready-to-use, premixed, bioceramic paste that contains polyethylene glycol and polypropylene glycol. These different options for MTAs were evaluated in the present study to understand their strengths and limitations as options for clinical endodontic procedures.  
Regenerative endodontics is defined as a biologically based procedure that is designed to replace damaged structures, such as dentin, root structures, and cells of the pulp-dentin complex [9]. The development of regenerative endodontics requires research on the correct spatial assembly of stem cells, growth factors, and tissue engineering scaffolds [10]. Various dental stem cells, including stem cells from exfoliated deciduous teeth (SHEDs), stem cells from apical papilla (SCAPs), and periodontal ligament stem cells (PDLSCs), which are situated around the dental tissues, have been used for regenerative endodontics [11]. Dental pulp stem cells (DPSCs) are thought to be a superior source of multipotent mesenchymal stem cells (MSCs) [12]. DPSCs have attracted considerable interest because of their potential for use in regenerative endodontics and their easy availability in vital pulp tissues [13].  
From the perspective of tissue engineering, data on stem cells have mostly been gathered through the study of cells that have been cultured as a two-dimensional (2D) monolayer on a dish surface [14]. DPSCs have also been cultured on 2D monolayers in previous in vitro studies [15]. However, 2D cultures may not reflect the in vivo microenvironment of stem cells, and this may lead to the loss of some of their stemness properties [16]. In regenerative endodontics, DPSCs come into contact with biocompatible materials, such as MTAs, in a three-dimensional (3D) pulp space. Recently, various 3D culture methods, including the use of microspheres, have been developed to overcome the limitations of monolayer cultures. DPSCs that have been cultured in microsphere-forming plates have presented superior multilineage differentiation capacities and have demonstrated a higher expression of regeneration-related genes compared to those cultured in a conventional monolayer plate [12; 16].  
The aim of this study was to evaluate the effects of various MTAs on DPSCs that have been cultured in 3D, assessing their cell viability and tissue mineralization properties. We examined the morphology, viability, and alkaline phosphate (ALP) activity of DPSCs that reacted with various MTAs in vitro.