Root Canal Obturation by Electrochemical Precipitation of Calcium Phosphates

At a Glance

Metadata	Details
Publication Date	2022-03-14
Journal	Applied Sciences
Authors	Maximilian Koch, Victor Palarie, Maximilian Göltz, Marvin Kurzer, Manuel Zulla
Institutions	Friedrich-Alexander-Universität Erlangen-Nürnberg, Nicolae Testemițanu State University of Medicine and Pharmacy
Citations	2
Analysis	Full AI Review Included

Executive Summary

This research investigates a novel electrochemical approach for in situ root canal obturation using Boron-Doped Diamond (BDD) electrodes to precipitate a biocompatible calcium phosphate material.

Core Innovation: BDD electrodes are used to trigger the rapid precipitation of Brushite (CaHPO₄ · 2 H₂O) directly inside the root canal, overcoming issues associated with conventional sealing materials (biocompatibility and sealing ability).
Mechanism: Maleic acid acts as a chelating retardant, stabilizing a highly supersaturated calcium phosphate precursor solution (Ca/P ratio 1:1, pH 6.5). BDD application oxidizes the maleic acid, releasing Ca²⁺ ions and initiating precipitation within minutes.
Material Confirmation: The precipitated material was unequivocally identified as Brushite via X-ray Diffraction (XRD) and Raman Spectroscopy (RAMAN).
Microstructure: Scanning Electron Microscopy (SEM) revealed flower-like crystal structures that adhered closely to the root canal walls, demonstrating sealing of dentin tubules.
Efficiency and Control: The precipitation amount is directly correlated with the charge quantity applied, showing a purported efficiency maximum of approximately 30% at charge quantities less than 15 As.
Sealing Performance: Micro-computed tomography (µCT) showed the filling material had an overall porosity of 11.27% ± 7.47%. Dye penetration tests confirmed apical leakage, suggesting that while the material is biocompatible, it does not yet provide a tight seal.

Technical Specifications

Parameter	Value	Unit	Context
Precipitate Material	Brushite (CaHPO₄ · 2 H₂O)	N/A	Confirmed by XRD and RAMAN.
BDD Electrode Substrate	Niobium wire	N/A	Wire diameter 200 µm, length 2.5 cm.
Applied Potential Range	6 to 16	V	Constant potential applied during precipitation.
Precipitation Duration	2	min	Time applied per precipitation cycle in reaction tubes.
Precursor Solution pH	6.5	N/A	Initial pH of the Ca-phosphate precursor.
Ca/P Molar Ratio (Precursor)	1:1	N/A	Stoichiometric ratio in the initial solution.
Maleic Acid Concentration	0.89	M	Used as chelating agent/retardant.
CaCO₃ Concentration	0.445	M	Calcium source concentration.
Precipitation Efficiency (Max)	~30	%	Observed at charge quantities < 15 As.
Precipitate Porosity (Overall)	11.27 ± 7.47	%	Measured via µCT analysis over a 3 mm range.
µCT Resolution (Inveon)	13.1	µm	Total scan duration 39.0 min.
X-ray Tube Voltage (µCT)	80.0	kV	Applied for both Siemens Inveon and ZEISS Xradia.
Effective µCT Pixel Size (ZEISS)	4	µm	Achieved using 4× objective and 2-fold binning.
Max Gap (Precipitate to Wall)	less than 100	µm	Measured in µCT scans of obturated roots.
Drying Temperature (Precipitate)	65	°C	Used for drying precipitate under vacuum.

Key Methodologies

Precursor Solution Formulation: A stable, supersaturated Ca-phosphate precursor solution (Ca/P 1:1, pH 6.5) was created by mixing calcium carbonate (0.445 M) and maleic acid (0.89 M) with ammonium phosphates. Maleic acid served as a chelating agent to retard spontaneous precipitation.
BDD Electrode Application: BDD-coated niobium wires (200 µm diameter) were used as electrodes. A constant potential (6-16 V) was applied to induce electrochemical oxidation of the maleic acid.
Precipitation Triggering: Oxidation of maleic acid by the BDD electrode releases free Ca²⁺ ions, triggering the rapid precipitation of solid calcium phosphate (Brushite) within minutes.
In Situ Obturation Protocol: Root canals (in training blocks and extracted teeth) were filled via repeated cycles: precursor solution addition, BDD application, drying of excess liquid (using paper points), and mechanical condensation (plugging) of the precipitate.
Chemical Monitoring: Ion Chromatography Mass Spectrometry (IC-MS) was employed to quantitatively track the degradation of maleic acid in the supernatant, confirming the correlation between maleate degradation and CaP precipitation.
Phase and Morphology Analysis: Precipitates were characterized using X-ray Diffraction (XRD) and Raman Spectroscopy (RAMAN) for phase identification (confirming Brushite), and Scanning Electron Microscopy/Energy Dispersive X-ray Spectroscopy (SEM/EDX) for morphology (flower-like crystals) and elemental ratio (Ca/P ~1.11).
Sealing and Porosity Assessment: Micro-computed tomography (µCT) was utilized to analyze the internal structure, density, and porosity (11.27% ± 7.47%) of the filling. Dye penetration tests were used to evaluate apical leakage.

Commercial Applications

Advanced Endodontic Therapy: Development of a complete root canal treatment system combining BDD-mediated disinfection (as previously demonstrated) and in situ obturation using biocompatible calcium phosphates.
Biocompatible Cement Manufacturing: Controlled electrochemical synthesis of Brushite and other calcium phosphate salts for use as bone substitutes, dental restorative materials, and implant coatings.
Targeted Drug/Ion Release Systems: Utilizing the BDD-mediated decomposition of chelators to achieve localized, controlled release of ions (Ca²⁺, PO₄^3-) or other active agents in medical settings.
Advanced Oxidation Processes (AOPs): Leveraging the high oxidative power and stability of BDD electrodes for efficient degradation of organic contaminants (like maleic acid and other chelators) in industrial or municipal wastewater streams.
Dental Remineralization Products: Utilizing the ability of maleic acid to act as a self-etching primer, combined with Brushite precipitation, to enhance the bonding and remineralization capabilities of dental sealers and adhesives.

View Original 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 (µCT) 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.

Tech Support

Original Source

DOI: https://doi.org/10.3390/app12062956

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