Abstract
Objective
Root canal filling sealers based on polymethyl hydrogensiloxane or polymethyl hydrogensiloxane-guttapercha – introduced to improve the quality of conventional guttapercha-based and resin-based systems – showed advantages in handiness and clinical application.
The aim of the study was to evaluate the chemical–physical properties of a novel polysiloxane-guttapercha calcium silicate-containing root canal sealer (GuttaFlow bioseal).
Methods
GuttaFlow bioseal was examined and compared with GuttaFlow2, RoekoSeal and MTA Fillapex sealers. Setting times, open and impervious porosity and apparent porosity, water sorption, weight loss, calcium release, and alkalinizing activity were evaluated. ESEM-EDX-Raman analyses of fresh materials and after soaking in simulated body fluid were also performed.
Results
Marked differences were obtained among the materials.
GuttaFlow bioseal showed low solubility and porosity, high water sorption, moderate calcium release and good alkalinizing activity. MTA Fillapex showed the highest calcium release, alkalinizing activity and solubility, RoekoSeal the lowest calcium release, no alkalinizing activity, very low solubility and water sorption. Only GuttaFlow bioseal showed apatite forming ability.
Significance
GuttaFlow bioseal showed alkalinizing activity together with negligible solubility and slight calcium release. Therefore, the notable nucleation of apatite and apatite precursors can be related to the co-operation of CaSi particles (Si OH groups) with polysiloxane (Si O Si groups).
The incorporation of a calcium silicate component into polydimethyl polymethylhydrogensiloxane guttapercha sealers may represent an attractive strategy to obtain a bioactive biointeractive flowable guttapercha sealer for moist/bleeding apices with bone defects in endodontic therapy.
1
Introduction
Root canal treatment aims to remove the infected tissues – i.e. pulp, root apex and periapical bone – and to seal/cut off the communication between oral environment and periapical tissue occurring through the root canal using guttapercha points and root canal sealers.
An ideal root canal filling material should be able to create an accurate 3 dimensional obturation of all the length of the endodontic space. Failures are related to the coronal-to-apical leakage due to unsatisfactory physical–chemical properties and to the presence of gaps, microchannels and porosities.
A successful root canal treatment depends critically on the physical blockage of the root canal – from invading bacteria originating in the oral cavity – the primary function of the root canal filling. Therefore, the root canal fillings must ensure impervious sealing and should be volumetrically stable (or expand slightly), low soluble, low porous, biocompatible and able to positively interact with the periapical bone tissue.
Materials such as elastomers i.e. gummy polymers having both viscosity and elasticity may offer advantages to accommodate root flexures when subjected to masticatory or other stresses .
In the past, conventional root canal sealers were zinc oxide-eugenol-based cements. Since then, new root canal sealers have been developed in the attempt of improving physical, chemical and biological properties as silicone-based sealers (RoekoSeal, GuttaFlow), epoxy resin-based sealers (AH Plus, TopSeal), MTA-based Sealers (MTA Fillapex), calcium silicate phosphate-based (iRoot, Bio aggregate) and methacrylate resin-based (EndoREZ, Realseal) sealers.
RoekoSeal introduced in 1999 is a silicone-based material mainly containing polydimethyl siloxane and silicone oil. It was strongly innovative for that time in relationship to its siloxane-based composition. Poly(dimethylsiloxane) are dimensionally stable materials with reduced hydrophobicity . The silicone-based sealer Roekoseal Automix had better wettability than epoxy-resin (2Seal, AH Plus) and methacrylate-based sealers (EndoRez, RealSeal, Real-Seal SE, Seal 3D) .
GuttaFlow is a flowable sealer introduced in the market in 2003 – as a modified version of RoekoSeal mainly containing powered gutta-percha, polydimethyl siloxane and silicone oil. Manufacturer states virtually no solubility in tests according to ISO 6876. It resulted insoluble in tissue fluids and showed good adaptation to the root canal walls , slight expansion during setting and tight seal although small areas of porosity after setting have been described .
GuttaFlow 2 introduced in 2012 as an advancement of GuttaFlow, based on a slightly different composition and containing gutta-percha powder with a particle size less than 30 μm. GuttaFlow 2 showed higher porosity – measured using a micro-CT scanner – than EndoRez and RealSeal and poor wettability because of the presence of silicone, which possibly produces high surface tension forces, making spreading difficult on the root dentin surface .
Silicone-based root canal filling systems showed advantages in handiness and clinical application. However, an ideal root canal sealer should be able to exert positive effects/interactions with the adjacent hydrated dentinal tissue when sealing open wide canals with copious moisture.
GuttaFlow bioseal , a novel formulation of polydimethylsiloxane-guttapercha doped with calcium silicate particles has been launched in late 2015. No information on its properties are available in the current scientific literature.
Calcium silicate cements , conventionally known in dentistry as mineral trioxide aggregate (MTA) cements, showed remarkable clinical outcomes when used as filling-sealing materials in root-resection and root-perforation repair in relationship to their chemical–physical and biological properties . Calcium silicate materials are biointeractive materials – setting and sealing in fluid-contaminated environments – able to release biologically relevant ions available for the nucleation in situ of apatite deposits and for dentin remineralization . They exhibited higher push-out strength after soaking in simulated body fluids for the formation of a physical bond with the moist dentin surface via the apatitic interface deposits .
Experimental calcium silicate-based sealers showed good sealing throughout long periods and the ability to seal the interface gaps in relationship to the hydrophilicity and water sorption, to the slight setting expansion and to the marked apatite-forming ability .
MTA Fillapex is a calcium silicate-based sealer marketed in 2011. It is a salicylate resin-based sealer containing calcium silicate particles (mineral trioxide aggregate, MTA) and silicon dioxide. It showed suitable flow, good sealing and low solubility .
The aim of the study was to evaluate the chemical–physical properties of GuttaFlow bioseal, a novel polysiloxane-guttapercha calcium silicate-containing root canal sealer.
2
Materials and methods
2.1
Materials
GuttaFlow bioseal prototype was examined in comparison with GuttaFlow2, RoekoSeal, MTA Fillapex root canal sealers. Table 1 shows the specifications (manufacturer, lot number and composition) of the tested materials. Due to recurrent changes in the composition made by the manufacturers, the lot number has been reported to identify an approximate period of production, thereby allowing a comparison of results with studies on materials with same formulations.
| Materials | Manufacturer | Lot number and expiration date (year-month) | Composition |
|---|---|---|---|
| GuttaFlow bioseal | Coltène/Whaledent AG, Altstatten, Switzerland | 140814P3EZB | Gutta-percha powder, polydimethylsiloxane, platinum catalyst, zirconium dioxide, silver (preservative), coloring, bioactive glass ceramic |
| GuttaFlow2 | Coltène/Whaledent AG, Altstatten, Switzerland | G07095 (2016-12) | Gutta-percha powder, polydimethylsiloxane, platinum catalyst, zirconium dioxide, microsilver (preservative), coloring |
| RoekoSeal Automix | Coltène/Whaledent GmbH, Langenau, Germany | 640512 (2017-06) | Polydimethylsiloxane, silicone oil, paraffin-base oil, zirconium dioxide, platinum catalyst |
| MTA Fillapex | Angelus, Londrina, Parana, Brazil | 32645 (2016-09) | Salicylate resin 20–25%, diluent resin 20–25%, mineral trioxide aggregate (MTA) 20–25%, bismuth trioxide 20–25%, silicon dioxide 1–5%, titanium dioxide 1–10% * |
* Percentages obtained from the Materials Safety Data Sheet from Angelus.
The materials were prepared according to the manufacturer’s instructions. Fresh materials were placed into PVC molds.
2.2
Radiopacity
Freshly prepared samples (10 ± 0.1 mm diameter; 1.0 ± 0.1 mm height, n = 3 per group) were radiographed – in accordance with ISO 6876 clause 7.8 for Dental root canal sealing materials – using a radiographic unit (Myray Cefla, Imola, Italy) with a reference aluminum step wedge (60 mm long, 10 mm wide).
Operative conditions were as follows: 3 cm distance, 0.13 s exposure at 70 kVp and 8 mA. The film (Kodak dental film, Eastman Kodak Company, Carestream Health Inc., Rochester, New York, NY, USA) was processed (automatic developer, 4 min at 30 °C) and scanned. The radiographic density (color intensity) data were converted (software Image J, National Institute of Health, USA; rsb.info.nih.gov/ij/) into aluminum step-wedge equivalent thickness (mm Al).
A radiopacity ≥3 mm Al is recommended by ISO 6876.
2.3
Setting times
The freshly mixed cement pastes ( n = 4 per group) were placed in a mold measuring 10 mm in diameter and 2 mm thick and then stored at 37 °C and 95 ± 5% relative humidity.
In accordance with ASTM standard C266-07, the initial setting time was determined using a Gilmore needle weighing 113.4 g with a tip diameter of 2.12 mm and the final setting time was determined using a Gilmore needle weighing 453.6 g with a tip diameter of 1.06 mm. The setting time was recorded when no indentation was caused by the needle.
2.4
Porosity, water sorption and solubility
Material disks ( n = 10 for each material group) were prepared using molds (8.0 ± 0.1 mm diameter × 1.6 ± 0.1 mm thickness) and allowed to set (at 37 °C and 99% relative humidity) for a period equal to 70% of the final setting time (i.e. a period 50% longer than the time stated by the manufacturer, according to ISO 6876) and then removed from the molds.
Each sample was weighed to determine the initial mass ( I ) and immediately immersed vertically in 20 mL of distilled water and placed at 37 °C. After 24 h immersion the specimens were removed from the water and the mass while suspended in water ( S ) was determined. The excess water from the surface from each sample was removed using a moistened filter paper (20 mL of distilled water dropped on a 9 wide 12.5 long glass plate covered by a filter paper) and the saturated mass ( M ) was recorded. Finally, the samples were dried at 37 °C until the weight was stable and the final dry mass ( D ) was recorded. Each weight measurement was repeated three times using an analytical balance (Bel Engineering series M, Monza, Italy) and determined to the nearest 0.001 g.
The exterior volume V ( V = M − S ), the volume of open pores V OP ( V OP = M − D ), the volume of the impervious portion V IP ( V IP = D − S ) and the apparent porosity P ( P = [( M − D )/ V ] × 100) were calculated in cm 3 or in percentage, following Archimedes’ principle (and according to ASTM C373-88). The water sorption A ( A = [( M − D )/ D ] × 100) and the solubility S ( S = [( I − D )/ D ] × 100) were calculated as percentage of the original weight.
2.5
Calcium release and alkalinizing activity (pH)
Material disks ( n = 10 for each material) were prepared using molds (8.0 ± 0.1 mm diameter × 1.6 ± 0.1 mm thickness) and immediately immersed in 10 mL of deionized water (pH 6.8) in polypropylene sealed containers and stored at 37 °C. The soaking water was collected and replaced at six endpoints (3 and 24 h and 3, 7, 14 and 28 days). The collected water was analyzed for pH and Ca using a potentiometric method under magnetic stirring at room temperature (24 °C).
The pH was measured using a selective temperature-compensated electrode (Sen Tix Sur WTW, Weilheim, Germany) connected to a multi-parameter laboratory meter (inoLab 750 WTW, Weilheim, Germany) previously calibrated with standard solutions. The amount of calcium ions was measured using a calcium probe (Calcium ion electrode, Eutech instruments Pte Ltd, Singapore) after addition of 0.200 mL (2%) of ionic strength adjuster (ISA, 4 mol/L KCl, WTW, Weilheim, Germany).
2.6
Statistical analysis
The results were analyzed using two-way ANOVA followed by RM Student–Newman–Keuls test ( p < 0.05). Different letters represent statistically significant differences ( p < 0.05) in the same line (capital letters) or in the same column (small letters).
2.7
ESEM-EDX-Raman surface analysis
Material disks were immediately immersed vertically in 20 mL of HBSS (Hank’s Balanced Salt Solution, Lonza Walkersville, Inc, Walkersville, MD, USA) used as a simulated body fluid and stored at 37 °C for 28 days. The medium was renewed weekly with fresh HBSS. The surface of each damp sample was examined using an environmental scanning electron microscope (ESEM, Zeiss EVO 50; Carl Zeiss, Oberkochen, Germany) connected to a secondary electron detector for energy dispersive X-ray analysis (EDX; Oxford INCA 350 EDS, Abingdon, UK) using computer-controlled software (Inca Energy Version 18). The discs were placed directly onto the ESEM stub and examined in wet conditions without any previous preparation (the samples were not coated for this analysis) at low vacuum (100 Pascal) in both Variable Pressure Secondary Electron (VPSE) and Quadrant Back-Scattering Detector (QBSD) modes, using an accelerating voltage of 20 kV, working distance 8.5 mm, 0.5 wt% detection level, 133 eV resolution, amplification time 100 μs, measuring time: 600 s for element mapping and 60 s for spectra.
EDX microchemical analysis (elemental X-ray microanalysis) was carried out at random in areas of ∼50 μm × 50 μm to evaluate the relative element content. Elemental microanalysis (weight % and atomic %) with ZAF correction method was performed in full frame to analyze entire areas.
The Ca/P atomic ratio calculated from the outer surface of the sealers after soaking in HBSS was assigned to apatitic (Ca/P 1.5–1.67) or nonapatitic (Ca/P < 1.47) calcium phosphates and then the sealers were defined – following Gandolfi classification – materials acting as substrates for the chemical bonding/adsorption of environmental ions and chemi/physisorption-related nonapatitic calcium phosphates deposition and sealers having intrinsic biointeractivity-related apatite precursors-forming ability .
EDX element mapping was performed on the surface to detect the element distribution using a 512 × 384 pixel matrix, 30–40 frames, 100 μs dwelling time, and 600–700 μs total reading time.
A system (Renishaw plc, Gloucestershire, UK) composed by a micro-Raman spectrometer with a SCA (Structural and Chemical Analyser for SEM) laser probe into ESEM chamber was used. The probe was connected by optical fiber to the spectrometer, equipped with edge filter to cut Rayleigh scattering, monochromators (1800 lines/mm for Ar + laser) and a Charge-Coupled Device (CCD) thermoelectrically cooled (203 K) detector. Operative conditions for Raman analysis inside SEM chamber were: variable pressure 90 Pa, EHT 20 KeV; operative conditions for SCA were: green Ar + beam laser (514.5 nm), Laser Power inside ESEM chamber = 2.5 mW, laser spot size < 2 μm FWHM, Mag = 2000×, time for scan = 30 s, number of scan = 4, spectral resolution = 1.5–2 cm −1 , spectroscopy software WIRE 2.0.
2
Materials and methods
2.1
Materials
GuttaFlow bioseal prototype was examined in comparison with GuttaFlow2, RoekoSeal, MTA Fillapex root canal sealers. Table 1 shows the specifications (manufacturer, lot number and composition) of the tested materials. Due to recurrent changes in the composition made by the manufacturers, the lot number has been reported to identify an approximate period of production, thereby allowing a comparison of results with studies on materials with same formulations.
| Materials | Manufacturer | Lot number and expiration date (year-month) | Composition |
|---|---|---|---|
| GuttaFlow bioseal | Coltène/Whaledent AG, Altstatten, Switzerland | 140814P3EZB | Gutta-percha powder, polydimethylsiloxane, platinum catalyst, zirconium dioxide, silver (preservative), coloring, bioactive glass ceramic |
| GuttaFlow2 | Coltène/Whaledent AG, Altstatten, Switzerland | G07095 (2016-12) | Gutta-percha powder, polydimethylsiloxane, platinum catalyst, zirconium dioxide, microsilver (preservative), coloring |
| RoekoSeal Automix | Coltène/Whaledent GmbH, Langenau, Germany | 640512 (2017-06) | Polydimethylsiloxane, silicone oil, paraffin-base oil, zirconium dioxide, platinum catalyst |
| MTA Fillapex | Angelus, Londrina, Parana, Brazil | 32645 (2016-09) | Salicylate resin 20–25%, diluent resin 20–25%, mineral trioxide aggregate (MTA) 20–25%, bismuth trioxide 20–25%, silicon dioxide 1–5%, titanium dioxide 1–10% * |
* Percentages obtained from the Materials Safety Data Sheet from Angelus.
The materials were prepared according to the manufacturer’s instructions. Fresh materials were placed into PVC molds.
2.2
Radiopacity
Freshly prepared samples (10 ± 0.1 mm diameter; 1.0 ± 0.1 mm height, n = 3 per group) were radiographed – in accordance with ISO 6876 clause 7.8 for Dental root canal sealing materials – using a radiographic unit (Myray Cefla, Imola, Italy) with a reference aluminum step wedge (60 mm long, 10 mm wide).
Operative conditions were as follows: 3 cm distance, 0.13 s exposure at 70 kVp and 8 mA. The film (Kodak dental film, Eastman Kodak Company, Carestream Health Inc., Rochester, New York, NY, USA) was processed (automatic developer, 4 min at 30 °C) and scanned. The radiographic density (color intensity) data were converted (software Image J, National Institute of Health, USA; rsb.info.nih.gov/ij/) into aluminum step-wedge equivalent thickness (mm Al).
A radiopacity ≥3 mm Al is recommended by ISO 6876.
2.3
Setting times
The freshly mixed cement pastes ( n = 4 per group) were placed in a mold measuring 10 mm in diameter and 2 mm thick and then stored at 37 °C and 95 ± 5% relative humidity.
In accordance with ASTM standard C266-07, the initial setting time was determined using a Gilmore needle weighing 113.4 g with a tip diameter of 2.12 mm and the final setting time was determined using a Gilmore needle weighing 453.6 g with a tip diameter of 1.06 mm. The setting time was recorded when no indentation was caused by the needle.
2.4
Porosity, water sorption and solubility
Material disks ( n = 10 for each material group) were prepared using molds (8.0 ± 0.1 mm diameter × 1.6 ± 0.1 mm thickness) and allowed to set (at 37 °C and 99% relative humidity) for a period equal to 70% of the final setting time (i.e. a period 50% longer than the time stated by the manufacturer, according to ISO 6876) and then removed from the molds.
Each sample was weighed to determine the initial mass ( I ) and immediately immersed vertically in 20 mL of distilled water and placed at 37 °C. After 24 h immersion the specimens were removed from the water and the mass while suspended in water ( S ) was determined. The excess water from the surface from each sample was removed using a moistened filter paper (20 mL of distilled water dropped on a 9 wide 12.5 long glass plate covered by a filter paper) and the saturated mass ( M ) was recorded. Finally, the samples were dried at 37 °C until the weight was stable and the final dry mass ( D ) was recorded. Each weight measurement was repeated three times using an analytical balance (Bel Engineering series M, Monza, Italy) and determined to the nearest 0.001 g.
The exterior volume V ( V = M − S ), the volume of open pores V OP ( V OP = M − D ), the volume of the impervious portion V IP ( V IP = D − S ) and the apparent porosity P ( P = [( M − D )/ V ] × 100) were calculated in cm 3 or in percentage, following Archimedes’ principle (and according to ASTM C373-88). The water sorption A ( A = [( M − D )/ D ] × 100) and the solubility S ( S = [( I − D )/ D ] × 100) were calculated as percentage of the original weight.
2.5
Calcium release and alkalinizing activity (pH)
Material disks ( n = 10 for each material) were prepared using molds (8.0 ± 0.1 mm diameter × 1.6 ± 0.1 mm thickness) and immediately immersed in 10 mL of deionized water (pH 6.8) in polypropylene sealed containers and stored at 37 °C. The soaking water was collected and replaced at six endpoints (3 and 24 h and 3, 7, 14 and 28 days). The collected water was analyzed for pH and Ca using a potentiometric method under magnetic stirring at room temperature (24 °C).
The pH was measured using a selective temperature-compensated electrode (Sen Tix Sur WTW, Weilheim, Germany) connected to a multi-parameter laboratory meter (inoLab 750 WTW, Weilheim, Germany) previously calibrated with standard solutions. The amount of calcium ions was measured using a calcium probe (Calcium ion electrode, Eutech instruments Pte Ltd, Singapore) after addition of 0.200 mL (2%) of ionic strength adjuster (ISA, 4 mol/L KCl, WTW, Weilheim, Germany).
2.6
Statistical analysis
The results were analyzed using two-way ANOVA followed by RM Student–Newman–Keuls test ( p < 0.05). Different letters represent statistically significant differences ( p < 0.05) in the same line (capital letters) or in the same column (small letters).
2.7
ESEM-EDX-Raman surface analysis
Material disks were immediately immersed vertically in 20 mL of HBSS (Hank’s Balanced Salt Solution, Lonza Walkersville, Inc, Walkersville, MD, USA) used as a simulated body fluid and stored at 37 °C for 28 days. The medium was renewed weekly with fresh HBSS. The surface of each damp sample was examined using an environmental scanning electron microscope (ESEM, Zeiss EVO 50; Carl Zeiss, Oberkochen, Germany) connected to a secondary electron detector for energy dispersive X-ray analysis (EDX; Oxford INCA 350 EDS, Abingdon, UK) using computer-controlled software (Inca Energy Version 18). The discs were placed directly onto the ESEM stub and examined in wet conditions without any previous preparation (the samples were not coated for this analysis) at low vacuum (100 Pascal) in both Variable Pressure Secondary Electron (VPSE) and Quadrant Back-Scattering Detector (QBSD) modes, using an accelerating voltage of 20 kV, working distance 8.5 mm, 0.5 wt% detection level, 133 eV resolution, amplification time 100 μs, measuring time: 600 s for element mapping and 60 s for spectra.
EDX microchemical analysis (elemental X-ray microanalysis) was carried out at random in areas of ∼50 μm × 50 μm to evaluate the relative element content. Elemental microanalysis (weight % and atomic %) with ZAF correction method was performed in full frame to analyze entire areas.
The Ca/P atomic ratio calculated from the outer surface of the sealers after soaking in HBSS was assigned to apatitic (Ca/P 1.5–1.67) or nonapatitic (Ca/P < 1.47) calcium phosphates and then the sealers were defined – following Gandolfi classification – materials acting as substrates for the chemical bonding/adsorption of environmental ions and chemi/physisorption-related nonapatitic calcium phosphates deposition and sealers having intrinsic biointeractivity-related apatite precursors-forming ability .
EDX element mapping was performed on the surface to detect the element distribution using a 512 × 384 pixel matrix, 30–40 frames, 100 μs dwelling time, and 600–700 μs total reading time.
A system (Renishaw plc, Gloucestershire, UK) composed by a micro-Raman spectrometer with a SCA (Structural and Chemical Analyser for SEM) laser probe into ESEM chamber was used. The probe was connected by optical fiber to the spectrometer, equipped with edge filter to cut Rayleigh scattering, monochromators (1800 lines/mm for Ar + laser) and a Charge-Coupled Device (CCD) thermoelectrically cooled (203 K) detector. Operative conditions for Raman analysis inside SEM chamber were: variable pressure 90 Pa, EHT 20 KeV; operative conditions for SCA were: green Ar + beam laser (514.5 nm), Laser Power inside ESEM chamber = 2.5 mW, laser spot size < 2 μm FWHM, Mag = 2000×, time for scan = 30 s, number of scan = 4, spectral resolution = 1.5–2 cm −1 , spectroscopy software WIRE 2.0.
3
Results
3.1
Radiopacity
All the sealers showed high radiopacity ( Table 2 ) with homogeneous values fitting with ISO 6876 recommendation. In particular GuttaFlow2 and MTA Fillapex displayed marked radiopacity (8.16 and 7.17 mm Al, respectively) with values more than twice than that recommended by ISO. GuttaFlow bioseal and RoekoSeal had good radiopacity showing 5.62 and 5.60 mm Al, respectively.
| Radiopacity | Setting times | ||
|---|---|---|---|
| Initial | Final | ||
| GuttaFlow bioseal | 5.62 ± 0.61 a | 25 ± 5 c | 45 ± 5 c |
| GuttaFlow2 | 8.16 ± 0.65 b | 35 ± 5 b | 65 ± 5 b |
| RoekoSeal | 5.60 ± 0.28 a | 65 ± 5 a | 125 ± 5 a |
| MTA Fillapex | 7.17 ± 0.65 b | 130 ± 5 d | 270 ± 5 d |
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