Abstract
This study aimed to evaluate the thermal, chemical, and physical properties of VDW.1Seal, Fill Root ST, and ADseal sealers. Thermal properties were analyzed using Thermogravimetric analysis (TGA) and Differential thermal analysis (DTA). Attenuated total reflection Fourier Transform Infrared Spectroscopy (ATR-FTIR) analysis was performed as a complementary test to confirm TGA/DTA analysis. The chemical composition of the set sealer material was identified using an X-ray powder diffraction (XRD) system. Other physical properties of each sealer were investigated; ten specimens were used to measure the solubility (at 24 h and 28 days), and another ten specimens were used to assess pH changes and calcium ion release (after 7 and 14 days). Film thickness was done according to ISO 6876 specs. The data were analyzed using the two-way ANOVA test. Results showed that for all sealers, TGA analysis revealed a direct relationship between sealer mass loss and temperature rise. In addition, the decomposition of the tested sealers started at 145 °C, 135 °C and 91 °C for VDW.1Seal, ADseal sealer, and Fill Root ST, respectively. XRD analysis revealed a higher degree of crystallinity for VDW.1Seal and ADseal. ADseal showed the least solubility; VDW.1Seal exhibited the highest alkalinity, calcium ion release, and the lowest film thickness.
Introduction
Obturation techniques using thermo-plasticized gutta-percha are expected to fill root canal systems better than cold gutta-percha points1. Nevertheless, sealers are still essential to fill the gaps and voids between the core material and the root canal walls2. Without a sealer, both warm and cold obturation techniques will have compromised treatment outcomes3,4. Hydraulic calcium silicate-based sealers (HCSBS) have been recently developed as a substitute for epoxy resin-based sealers5. According to the source of hydration required for their setting, they are either available as powder, liquid, or premixed ready-to-use syringes6. In the former, hydration is initiated before insertion into the root canal. While in the latter, the residual moisture inside the root canal, along with dentine humidity, purportedly provides the water necessary for the hydration of the material7. Clinical studies have reported successful application of premixed HCSBS in root canal obturation8,9. Besides technique simplicity, HCSBS also showed favorable properties, including bioactivity10, biocompatibility11, and antibacterial potential12. Most are founded on the solubility of their setting reaction by-products13. The main component of HCSBS is tricalcium silicate, which, when hydrated, forms a calcium silicate hydrate matrix and calcium hydroxide that leach out to interact with the surrounding environment14,15. Recently, new premixed sealers were marketed with innovative formulations to upgrade their clinical performance. In comparison to previous HCSBS, VDW.1Seal (VDW, München, Germany) contains relatively less tricalcium silicate (5–15 wt %) and more zirconium dioxide (50–70 wt %) in addition to dimethyl sulfoxide as filler. Fill Root ST (Dental World, Molfetta, Italy) is another recently introduced premixed sealer based on calcium aluminosilicate and zirconium dioxide. Currently, there is scarce data about their physico-chemical properties in terms of solubility, alkalinity, calcium ion release, and film thickness. Likewise, it is necessary to investigate their thermal stability to determine if they can tolerate the heating temperatures generated during thermal-based obturation techniques without decomposition. Such data would give clinicians insights for better selection of the sealer type to be compatible with heat application during obturation. Therefore, this in vitro study aimed to investigate the thermal stability and some physico-chemical properties (short- and long-term solubility, pH changes, calcium ions release, and film thickness) of VDW.1Seal and Fill Root ST in comparison to an epoxy resin-based sealer, ADseal Root canal sealer (Meta BioMed, Cheongju, Korea). The null hypothesis was that there were no differences between the tested materials.
Materials and methods
All methods were carried out following relevant guidelines and regulations. The research ethics committee at the Faculty of Dentistry at the British University in Egypt approved all the experimental protocols. Since the data were evaluated retrospectively, pseudonymously, and were solely obtained for treatment purposes, a requirement of informed consent was waived by the ethics committee at the Faculty of Dentistry, The British University in Egypt (approval number 22-031, date 18/12/2022).
TGA/DTA analysis
Approximately 16 mg of powder for each set of sealers was obtained by grinding using an agate mortar and pestle (Nahita, Istanbul, Turkey). Sample powders were analyzed to evaluate the thermal stability of each sealer using Thermogravimetric analysis (TGA) and Differential thermal analysis (DTA) using a TGA/DTA Thermal Analyzer (Shimadzu DTG-60H Thermal Analyzer, Kyoto, Japan). Thermal measurements were performed under the flow of nitrogen atmosphere with a flow rate of 100 ml min−1 in the temperature range from ambient to 250 °C. The heating rate was 20 °C per minute. Highly sintered α-Al2O3 was used as the reference material. Thermo-analytical TGA and DTA curves were obtained simultaneously. The data were analyzed using the TGA software (CDSS, v1.1).
ATR-FTIR test
Attenuated total reflection Fourier Transform Infrared Spectroscopy (ATR-FTIR) analysis (Nicolet 6700 FTIR instruments, Thermo Fisher Scientific, Waltham, USA) was performed on the set sealers as a complementary test to confirm thermal stability results. FTIR analysis was performed in the spectral range (4000–500 cm1) following the previously described procedure16.
XRD analysis
The chemical composition of the set sealer material was investigated using an X-ray powder diffraction (XRD) system (Bruker-AXS D8 X-ray diffractometer, Germany) to identify the existing crystalline phases and measure the degree of crystallinity. The crystalline structure of the test sealer was determined by passing an X-ray beam of a known wavelength into the specimen while rotating it at an angle. The intensity of X-rays from the sample was measured by a detector14, while the crystallinity was evaluated by careful evaluation of the baseline to peak separation in an extended scan range using DIFFRAC.EVA software (Bruker AXS GmbH). XRD data were collected in the 2θ range 0–60° under 30.0 mA, 40.0 kV, and a scan rate of 4°/min. The obtained XRD patterns were characterized using the Joint Committee on Powder Diffraction Standard (JCPDS) databases.
Analysis of the physical properties
Sample size calculation
Power calculation was performed using G*Power 3.1.9.7 (Heinrich Heine University, Dusseldorf, Germany). Based on the results of previous studies17,18,19 and using an alpha (α) level of 0.05 (5%) and a Beta (β) level of 0.20 (20%), i.e., power = 80%, the predicted minimum sample size (n) was nine specimens in each group. Thus, ten samples were prepared per group for evaluation of solubility, and another ten samples were prepared per group for evaluation of pH change and calcium ion release. Concerning film thickness testing, three tests were carried out according to ISO 6876 specs.
Specimen preparation
Root canal sealers were carefully injected into the specially designed molds for each test type.
Solubility
Solubility was determined according to the standards set by the International Standard Organization (ISO 6876:2012)20. Short- and long-term solubility were determined after 24 h and 28 days, respectively, following the previously described procedures20,21. Cylindrical polyethylene molds with dimensions of 1.5 mm height and 7.75 mm inner diameter were used and filled with each root canal sealer to acquire disc-shaped specimens (n = 10 per sealer), which were incubated at 37 °C and 95% relative humidity for 24 h to set. After setting, the specimens were removed from the molds and weighed three times to determine the mean mass of each specimen (M1) using a microbalance. Then, all set sealer specimens were stored separately in plastic flasks containing 7.5 mL of distilled water in an incubator at 37 °C and 95% relative humidity. The specimens were removed from the incubator, bench dried, and re-weighed (M2) after 24 h and 28 days of storage. Mass loss was expressed as a percentage of the original mass20,21. The percentage of root canal sealer solubility was calculated as follows: (M1-M2)/M1 X 100%20.