# Root Canal Obturation by Electrochemical Precipitation of Calcium Phosphates
###### Abstract  
Achieving adequate disinfection and preventing reinfection is the major goal in endodontic treatment. Variation in canal morphology and open porosity of dentine prevents achieving complete disinfection. Questionable biocompatibility of materials as well as a lack of sealing ability questions the usefulness of current obturation methods. With a novel disinfection approach based on the use of boron-doped diamond (BDD) electrodes having shown promising results it was the goal of this series of experiments to investigate the possibility of BDD-mediated in situ forming of a biocompatible obturation material. A combination of calcium phosphate and maleic acid was used as precursor solution while Ion Chromatography Mass Spectrometry (IC-MS), Raman spectroscopy (RAMAN), X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDX), scanning electron microscopy (SEM), dye penetration and micro-computed tomography (uCT) were applied for characterizing the precipitate. It was possible to achieve a BDD-mediated precipitation of brushite in a clinically applicable timeframe. However, tight sealing of the canal system based on brushite could not be achieved. boron-doped diamond; brushite; hydroxyapatite; obturation; reactive oxygen species of calcium Phosphates +
Footnote †: journal: selected Topics in Applied Sciences  
As a novel experimental approach to root canal disinfection, boron-doped diamond (BDD) electrodes have recently been introduced [14]. The major advantage of this method consists in the controlled generation of highly reactive oxygen species directly in the canal system. In order to overcome the two major issues with conventional sealing materials i.e., biocompatibility [15; 16] and a lack of sealing ability in non-uniformly shaped root canals [17; 18], it was the goal of this experiment to investigate the possibility of in situ forming of a biocompatible obturation. The basic requirements for a BDD-based obturation protocol were identified as follows (i) high precipitation rate of biomaterial, (ii) biocompatibility of the product, (iii) absence of toxic byproducts and (iv) tight and complete seal of the root canal. Calcium phosphates such as hydroxyapatite constituting the main inorganic component of enamel and bone [19] were identified as ideal candidates to meet these requirements. This group of substances is well known for biocompatibility and has been investigated for a variety of medical applications [20] including toothpastes for triggering remineralization, bone substitutes and coatings of dental implants for optimizing osseointegration [21; 22; 23; 24]. In this context, calcium phosphate nanoparticles have been shown to be osteoconductive [25]. Especially brushite, CaHPO\({}_{4}\)\(\times\) 2 H\({}_{2}\)O, can act as a connecting layer binding to enamel, mediating remineralization and undergoing transformation to hydroxyapatite [26; 27; 28]. Low solubility of calcium phosphates was identified as the major issue for establishing an in situ formed obturation material. To obtain a higher saturated solution of calcium phosphate, maleic acid was added to act as chelating agent and thereby retarding the precipitation [29; 30]. Maleic acid can easily be oxidized by BDD electrodes [31; 32; 33; 34; 35], which then triggers the obturation process. With maleic acid being able to dissolve calcium ions from tooth substance and constituting an important component of self-etching dental adhesives [36], sealing of the root canal surface may also benefit from this approach. This study consisted of several experiments aimed at evaluating the feasibility of BDD-mediated root canal obturation using a calcium phosphate/maleic acid solution. Following formation of the obturation precursor solution, degradation of maleic acid was monitored using Ion Chromatography Mass Spectrometry (IC-MS). The precipitation product was characterized using Raman spectroscopy (RAMAN), X-ray diffraction (XRD) and energy dispersive X-ray spectroscopy (EDX).