# Cytotoxicity and Antimicrobial Activity of BioAktTM and Phytic Acid: A Laboratory-Based Study
## 1 Introduction  
Bacteria infect more than 70% of dentinal tubules in the presence of endodontic infections, and about 65% of these tubules remain infected even after root canal instrumentation and disinfection [1]. Although root canal irrigation procedures are needed for bacterial load reduction [2], an optimal irrigation with robust antibacterial features and marginal cytotoxic effects on the host tissue has not been identified. Sodium hypochlorite (NaOCl), used at various concentrations (0.5 to 6%), combined with ethylenediaminetetraacetic acid (EDTA) remains the gold standard for irrigation procedures thanks to their combined capability in exerting antimicrobial and antifungal activity, dissolving necrotic tissue, acting on endodontic biofilm, and eradicating smear layers [3]. The use of NaOCl is broadly accepted and recommended by the American Association of Endodontists (AAE) (1.5% concentration) and the European Society of Endodontology (ESE) (1.5 to 3% concentration) [4]. Nevertheless, it remains controversial given some drawbacks due to a high risk of weakening of instruments' structure [5], allergic reaction [6, 7], sodium hypochlorite accident [8], pertubular or intertubular erosion via proteolytic degradation, this last enhanced if NaOCl is used with EDTA [9], and finally, damage to clothing [10] or eyes [11]. Similar issues have been reported about EDTA, which is used as a chelating agent in conventional root canal treatment for smear layer removal. EDTA shows some cytotoxic effects at various concentrations [12, 13] and, when combined with NaOCl, can reduce the pH of NaOCl in a time-dependent manner thus affecting free chlorine in solution and resulting in increase in chlorine gas and hypochlorous acid. In this way, EDTA reduces the hypochlorite ion [14], reducing NaOCl effectiveness in removing the necrotic tissue and exerting its antibacterial activity [15]. Moreover, given the high surface tension of NaOCl and EDTA, these solutions do not deeply penetrate dental tubules or other anatomical irregularities [16]. According to a recent study, the evaluation of biocompatible materials should consider as decisive the adequacy of the host reaction, i.e., the extent of the different biological responses from cytotoxicity and adverse reaction to the biostimulatory effects on tissues, and not the complete non-toxicity of the tested material [17]. In research on the balance between irrigant therapeutic effects against their potential cytotoxicity effects [18], some new irrigants have been introduced, such as BioAktTM and phytic acid. BioAktTM is a water solution composed mainly of silver ion (0.003%) and citric acid (4.846%), whose active ingredient is silver citrate dihydrate. This substrate is weakly bound with silver ions and has the function of reversibly combining with another molecule. As a result, bacteria, which identify citric acid as a metabolic nutrient, are first attracted to the compound and then blocked by the compound itself, causing the microorganism's death. For this reason, BioAktTM is also defined as a metabolic antimicrobial substrate. Previous studies showed that acidic solutions such as BioAktTM can more efficiently reduce the smear layer [19] and improve antimicrobial activity in the root canal system [20] compared to EDTA-based solutions. However, some doubts have recently arisen about its cytotoxicity when used at higher than 0.5% concentration [21], which can limit its safe clinical use [22]. Although there are no direct comparisons between BioAktTM and NaOCl tissue response, studies conducted so far have compared silver nanoparticles, whose action is broadly similar to that of silver ions, and NaOCl showed a mild-to-moderate inflammation reaction in the case of silver nanoparticles and a higher inflammatory response in the case of NaOCl [23]. Phytic acid, i.e., inositol hexakisphosphate (IP6), is a six-fold dihydrogen phosphate ester of inositol, which is a part of human beings' daily diet and is also present in mammalian cells [24] with a shallow or null cytotoxic profile.