# Biocompatibility and Osteo/Odontogenic Potential of Various Bioactive Root-End Filling Materials
## 4 Discussion  
The biocompatibility of bioactive materials used in vital pulp therapies or repair of dentinal tissue in perforation sealing and retrograde filling is a determining factor in the success of the treatment outcome as the irritation to surrounding tissues can delay wound healing. As well as its biocompatibility, the biomaterial should have osteo/odontogenic induction properties to support differentiation of peripheral potent cells and initiate mineralization. Therefore, in the current study, MSCs were treated with different bioactive MTA-based material extracts diluted in the growth medium and were compared against osteo/odontogenic-induced and non-induced MSCs. Dental stem cells have been extensively investigated in terms of multiple lineage differentiation and demonstrated great potential in the hard tissue engineering applications of the oral region, such as the healing of bone defects or supporting cell-based pulp-dentin complex regeneration [14]. Isolated from the tooth germs of third molars, which can be considered a more primitive tissue present during young adulthood compared to more developed pulp and apical papilla tissues, tooth germ-derived MSCs are multipotent stem cells that can benefit from interactions between ectoderm and mesoderm as they are derived from epithelial cells and the underlying mesenchyme [15]. Recent studies reported a high osteo/odontogenic potential for tooth germ-derived MSCs both in vivo and in vitro, alone or in combination with scaffolds [11; 13; 16]. Hence, the present study used tooth germ-derived MSCs to demonstrate if MTA-based biomaterials can support the induction of odontogenesis and maintain viability. This investigation was able to demonstrate that tooth germ-derived MSCs can be induced with MTA-based biomaterials with comparable results to osteo/odontogenic medium-induced cells, as indicated by the elevated ALP activity and osteo/odontogenic marker genes with varying degrees. All test materials exhibited significant cell viability as indicated by comparable results in test groups with the controls via MTS and live/dead assay. Immediate exposure to extracts did not cause cytotoxicity to MSCs, but Medcem MTA demonstrated less viability initially which was compensated over the 7-day cell culture as the cells were able to proliferate. As the decrease in cell viability was not more than 30%, none of the materials were considered cytotoxic according to ISO-10993-5. Medcem MTA is composed of Pure Portland Cement with zirconium oxide added as the opacifier. Interestingly, zirconium oxide is reported to have a better biological response than bismuth oxide, which has been involved in the cytotoxicity shown by some MTA materials [17]. In the present study, Angelus MTA contains bismuth oxide as the opacifier, which demonstrated no inhibitory effects on the cell viability of MSCs. Various MTA materials were tested on bone marrow-derived MSCs and were demonstrated to be non-toxic, but they could affect tooth-derived stem cells in a concentration and time-dependent manner [18]. Studies indicate that MTA materials can promote the proliferation and survival of MSCs derived from dental tissues including apical papilla, exfoliated deciduous teeth, and dental pulp [19]. Despite minor differences, some behavioral tendencies must be acknowledged among MTA materials. MTA Angelus has been studied for a longer period and has established high biocompatibility with similar results to control medium with different types of cells including dental pulp stem cells (DPSCs), periodontal ligament fibroblasts, and osteoblasts [20; 21]. Another study reported that undiluted exposition to MTA Angelus increased cell proliferation [22], in accordance with our results which indicated higher proliferation on day 7 with the MTA Angelus group compared to that of the control group. The difference between studies can be attributed to the dilution of the MTA extract or the growth rate of the cell type, which may be comparably higher in stem cells than in fibroblasts [20].