Abstract
Objectives
Impedance spectroscopy is a non-destructive, quantitative method, commonly used nowadays for industrial research on cement and concrete.
The aim of this study is to investigate the interest of impedance spectroscopy in the characterization of setting process of dental cements.
Methods
Two types of dental cements are used in this experiment: a new Calcium Silicate cement Biodentine™ (Septodont, Saint Maur-des Fossés, France) and a glass ionomer cement resin modified or not (Fuji II ® LC Improved Capsules and Fuji IX ® GP Fast set Capsules, GC Corp., Tokyo, Japan). The conductivity of the dental cements was determined by impedance spectroscopy measurements carried out on dental cement samples immersed in a 0.1 M potassium chloride solution (KCl) in a “like-permeation” cell connected to a potentiostat and a Frequency Response Analyzer. The temperature of the solution is 37 °C. From the moment of mixing of powder and liquid, the experiments lasted 2 weeks.
Results
The results obtained for each material are relevant of the setting process. For GIC, impedance values are stabilized after 5 days while at least 14 days are necessary for the calcium silicate based cement.
Significance
In accordance with the literature regarding studies of cements and concrete, impedance spectroscopy can characterize ion mobility, porosity and hardening process of dental hydrogel materials.
1
Introduction
A better understanding of the setting process can be achieved by using a non-destructive electrochemical method: the impedance spectroscopy. A small amplitude sinusoidal electrical signal is applied to a cement sample in order to measure its complex impedance. The value of this impedance is a complex number with a real and an imaginary part. From the imaginary part, the dielectric properties of the cement, related to the insulating properties of the solid phase, can be characterized. From the real part value, the electrical resistance of the material can be deduced. This resistance depends on:
- –
the open porosity of the cement,
- –
the nature, concentrations, and mobility of the ionic species dissolved in the interstitial liquid filling the pores.
The change in porosity occurring during the hardening of the cement results in a change of its resistivity that can be characterized by impedance measurements, as shown by numerous studies on materials like concrete, mortars and Portland cement pastes .
Furthermore, impedance spectroscopy is a non-destructive method allowing to follow the evolution of the material for a long time .
In this study, the setting and hardening processes of two types of cements used in dentistry (GICs and new tricalcium silicate cement) are investigated through impedance measurements.
Glass ionomer cements (GIC) have been described more than 30 years ago by Wilson and Kent . These calcium fluoroaluminosilicate cements present a wide field of clinical application in dentistry (pediatric dentistry, base and liner in restorative dentistry, luting cement…) and orthopedics. The main properties of these bioactive materials lie in fluoride release and spontaneous adhesion to dental tissue. Their setting process is based on a single acid–base complex reaction. Resin-modified GIC (RM-GIC) are an evolution of conventional GIC (C-GIC) developed for an improved esthetic result. Their setting process is based on a single acid–base complex reaction coupled to a light cure reaction of a hydroxyethylmethacrylate (HEMA) monomer resin, into a polyHEMA polymer network . The setting reaction leads to a hydrogel layer surrounding glass fillers after the acid–base reaction .
Tricalcium silicate materials as Mineral Trioxide Aggregate (MTA) could also be called bioactive material. A new Ca 3 SiO 5 -based restorative cement (Ca Si cement) Biodentine™ has been developed (Septodont, Saint-Maur des Fosses, France). The main component of the powder is a tricalcium silicate, with the addition of CaCO 3 and ZrO 2. The liquid is water with addition of CaCl 2 . The setting process follows the reaction:
This reaction leads to a gel structure, allowing ionic exchanges.
Both materials exhibit a porous gel structure, a setting reaction lasting for several days and a non-linear kinetics of setting process (maturation process).
2
Materials and methods
2.1
Materials
Two commercially available materials were tested:
conventional GIC (Fuji IX ® GP Fast set Capsules, Fuji, Tokyo, Japan),
- –
resin-modified GIC (Fuji II ® LC Improved Capsules, Fuji, Tokyo, Japan),
- –
and new Calcium Silicate cement Biodentine™ (Septodont, Saint Maur-des-Fossées, France).
Their compositions, their batch numbers and manufacturers are shown in Table 1 . The samples were mixed according to the manufacturer instructions.
| Material | Batch | Powder | Liquid |
|---|---|---|---|
| Fuji IX GP Fast Set (GC, Tokyo, Japan) | 0408093 | Glass fluoroaluminosilicate: 95% Polyacrylic acid: 5% Pigments: traces |
Polyacrylic acid: 40% Polycarboxylic acid: 10% Distilled water: 50% |
| Fuji II LC Improved (GC, Tokyo, Japan) | 041118 | Glass fluoroaluminosilicate: 100% Medium particle size: 4.8 μm Maximal particle size: 25 μm |
HEMA: 38% Polyacrylic acid: 43% Resins: 12% Tartric acid: 5% Distilled water: 1% Camphorquinone: 0.1% |
| Biodentine™ (Septodont, Saint Maur des Fossés, France) | 803035 | Tricalcium silicate (3CaO·SiO 2 ) Calcium carbonate (CaCO3) Zirconium dioxide (ZrO 2 ) |
Water Calcium chloride (CaCl 2 ·2H 2 O) Water reducing agents |
2.2
Methods
2.2.1
Sample preparation
Five samples of each material were performed using a mould (diameter 16 mm, thickness 2 mm). The mould was mounted on a glass plate. The cements were inserted into the mould in excess and covered by a second glass plate. Slight pressure was applied. The samples were maintained during 5 min for Fuji IX, 10 for Biodentine™ between glass plates. The Fuji II LC samples were photopolymerized during 60 s on each side with a quartz-tungsten-halogen light curing unit: Astralis 7 (Ivoclar-Vivadent, Schaan, Liechtenstein) mode High Power Density, 750 mW/cm 2 . The irradiance of the light source was measured with a radiometer (Demetron ® ).
2
Materials and methods
2.1
Materials
Two commercially available materials were tested:
conventional GIC (Fuji IX ® GP Fast set Capsules, Fuji, Tokyo, Japan),
- –
resin-modified GIC (Fuji II ® LC Improved Capsules, Fuji, Tokyo, Japan),
- –
and new Calcium Silicate cement Biodentine™ (Septodont, Saint Maur-des-Fossées, France).
Their compositions, their batch numbers and manufacturers are shown in Table 1 . The samples were mixed according to the manufacturer instructions.
| Material | Batch | Powder | Liquid |
|---|---|---|---|
| Fuji IX GP Fast Set (GC, Tokyo, Japan) | 0408093 | Glass fluoroaluminosilicate: 95% Polyacrylic acid: 5% Pigments: traces |
Polyacrylic acid: 40% Polycarboxylic acid: 10% Distilled water: 50% |
| Fuji II LC Improved (GC, Tokyo, Japan) | 041118 | Glass fluoroaluminosilicate: 100% Medium particle size: 4.8 μm Maximal particle size: 25 μm |
HEMA: 38% Polyacrylic acid: 43% Resins: 12% Tartric acid: 5% Distilled water: 1% Camphorquinone: 0.1% |
| Biodentine™ (Septodont, Saint Maur des Fossés, France) | 803035 | Tricalcium silicate (3CaO·SiO 2 ) Calcium carbonate (CaCO3) Zirconium dioxide (ZrO 2 ) |
Water Calcium chloride (CaCl 2 ·2H 2 O) Water reducing agents |
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