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MTT versus other cell assays to evaluate the biocompatibility of root canal filling materials. A systematic review.

OBJECTIVES
This systematic review aimed to compare the cytotoxicity of root canal filling materials (RCFM) obtained using tetrazolium salt-based tests (TSBT), including the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay, with those obtained using other cell viability assays.


METHODS
A search was performed on PubMed, Scopus, Web of Science and OpenGrey up to March 2019, followed by a manual search. According to the Participants, Exposure, Comparator, and Outcomes (PECO) criteria, in vitro studies that evaluated the cytotoxic effect of RCFM on animal and/or human cells through TSBT and at least one other viability assay were compared. The methodological quality of selected papers was assessed using ToxRTool® and SciRAP® . Data were analysed using the Wilcoxon's signed rank test for paired samples and Linear Weighting Kappa.


RESULTS
A total of 230 non-duplicated records were identified. After applying the eligibility criteria, 55 studies were selected for methodological evaluation, seven were selected by manual searching, 22 were excluded for methodological reasons and 40 were included. A total of 410 comparisons were performed between TSBT and distinct cell viability tests (DCVT). MTT had moderate concordance with DCVT using human cells (n=138 samples) (p=0.507; k=0.4225) and animal cells (n=122 samples) (p=0.124; k=0.5775). XTT had good concordance using human (n=110 samples) (p=0.507; k=0.6336) and animal cells (n=12 samples) (p=0.564 k=0.6604). MTT, XTT, WST and MTS assays showed moderate concordance with DCVT (n=410 samples) (p=0.375; k=0.5138), and complete agreement in 226 samples.


DISCUSSION
The included studies had methodological heterogeneity that was minimized by the systematic review methodology.


CONCLUSIONS
MTT and XTT do not cause over- or underestimation of cell viability during cytotoxicity screening of root canal filling materials, implying that these assays can be considered reliable for this purpose. Nonetheless, the development of protocols for the cytotoxic screening of these materials on 3D-tissue-like cultures aiming to improve their predictability in the clinical scenario is suggested.