- Email: [email protected]
Properties of Tricalcium Silicate Sealers
Basic Research—Technology
Properties of Tricalcium Silicate Sealers Issam Khalil, DDS, MSc, PhD,* Alfred Naaman, DDS, MSc, PhD,* and Josette Camilleri, BChD, MPhil, PhD, FIMMM, FADM† Abstract Introduction: Sealers based on tricalcium silicate cement aim at an interaction of the sealer with the root canal wall, alkalinity with potential antimicrobial activity, and the ability to set in a wet field. The aim of this study was to characterize and investigate the properties of a new tricalcium silicate–based sealer and verify its compliance to ISO 6876 (2012). Methods: A new tricalcium silicate–based sealer (Bio MM; St Joseph University, Beirut, Lebanon), BioRoot RCS (Septodont, St Maure de Fosses, France), and AH Plus (Dentsply, DeTrey, Konstanz, Germany) were investigated. Characterization using scanning electron microscopy, energy-dispersive spectroscopy, and X-ray diffraction analysis was performed. Furthermore, sealer setting time, flow, film thickness, and radiopacity were performed following ISO specifications. pH and ion leaching in solution were assessed by pH analysis and inductively coupled plasma. Results: Bio MM and BioRoot RCS were both composed of tricalcium silicate and tantalum oxide in Bio MM and zirconium oxide in BioRoot RCS. In addition, the Bio MM contained calcium carbonate and a phosphate phase. The inorganic components of AH Plus were calcium tungstate and zirconium oxide. AH Plus complied with the ISO norms for both flow and film thickness. BioRoot RCS and Bio MM exhibited a lower flow and a higher film thickness than that specified for sealer cements in ISO 6876. All test sealers exhibited adequate radiopacity. Conclusions: Bio MM interacted with physiologic solution, thus showing potential for bioactivity. Sealer properties were acceptable and comparable with other sealers available clinically. (J Endod 2016;-:1–7)
Key Words BioRoot RCS, Bio MM, characterization, physical testing, sealer, tricalcium silicate-based sealers
From the *Department of Endodontics, Saint Joseph University, Beirut, Lebanon; †Department of Restorative Dentistry, Faculty of Dental Surgery, University of Malta, Msida, Malta. Address requests for reprints to Dr Issam Khalil, Department of Endodontics, Saint-Joseph University, Damascus Street, Beirut, Lebanon. E-mail address: [email protected] 0099-2399/$ - see front matter Copyright ª 2016 American Association of Endodontists. http://dx.doi.org/10.1016/j.joen.2016.06.002
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illing a root canal is Significance classically performed Single-cone obturation in combination with a biousing a gutta-percha solid ceramic sealer resulted in less porosity; rather cone in combination with than aiming for a hermetic seal of the root canal, a sealer. Initially, this was a more biological approach is being undertaken done using lateral condenin which the sealers interact with the dentin, resultsation, which was eventuing in biomineralization. ally superseded by warm vertical compaction. More recently, rather than aiming for a hermetic seal of the root canal, a more biological approach is being undertaken in which the sealers aim at interacting with the root dentin, resulting in bioactivity. Single-cone obturation in combination with a tricalcium silicate–based sealer resulted in significantly less porosity, particularly coronally compared with lateral compaction–filled teeth (1). Materials based on tricalcium silicate used in combination with a radiopacifying material are used as sealers. These sealers were developed because they induce bioactivity on the material surface when in contact with tissue fluids as a result of the interaction of calcium hydroxide produced as a reaction product of tricalcium silicate hydration (2, 3) with phosphates present in tissue fluids (4–6). The interaction of these materials with dentin has been termed the mineral infiltration zone (7). The first sealer based on tricalcium silicate was MTA Fillapex (Angelus, Londrina, Brazil). This sealer is mainly composed of a salicylate resin matrix, silica, and mineral trioxide aggregate, with the mineral trioxide aggregate being a minor component. Although the main scope of using a tricalcium silicate–based sealer is the release of calcium hydroxide from the material, hydration MTA Fillapex has been shown to be inert, and no calcium hydroxide was formed when the material set (8). However, MTA Fillapex complies with ISO 6876 (9) and is also stable when used with warm vertical compaction techniques (10). Other tricalcium silicate–based sealers have been developed. Endosequence BC Sealer (Brasseler, Savannah, GA) is a biphasic sealer because it also contains calcium phosphate monobasic together with the tricalcium silicate phase (11). It is premixed and dispensed through a syringe. It possesses comparable flow and dimensional stability to MTA Fillapex but higher film thickness and solubility than AH Plus (Dentsply, DeTrey, Konstanz, Germany) (12). BioRoot RCS (Septodont, St Maure de Fosses, France) is also based on tricalcium silicate with zirconium oxide added for radiopacity. This sealer is water based; thus, it should be used with a single-cone obturation technique rather than warm vertical compaction because the sealer properties are changed when heated (3). BioRoot RCS exhibited a significantly higher percentage of voids than AH Plus using micro–computed tomographic analysis, but there was no difference in fluid flow and microsphere penetration. A different pattern of sealer penetration and interaction with the dentin walls was observed when compared with AH Plus (13). Although a number of tricalcium silicate–based sealers are available to the clinician, none of them fulfills all the necessary criteria of stability and interaction with the dentin. The aim of this study was the development of a novel tricalcium silicate–based sealer based on tricalcium silicate that fulfills the criteria set by ISO 6876 (2012) (9) and also exhibits bioactivity potential. In the current study, the novel sealer is compared with BioRoot RCS, which is a tricalcium silicate–based sealer that does not contain any additives to the powder except for the zirconium oxide radiopacifier, and AH Plus, which is an epoxy-based sealer that has been considered the gold standard and has been used as a control material in most studies on sealers.
Tricalcium Silicate Sealers
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Basic Research—Technology Materials and Methods Three sealers were investigated: 1. Bio MM (developed at St Joseph University, Beirut, Lebanon) 2. BioRoot RCS 3. AH Plus
Sealer Characterization Bio MM was mixed at a water to powder ratio of 0.75. BioRoot RCS and AH Plus were mixed according to the manufacturers’ instructions. After preparation, the materials were allowed to set for 24 hours at 37 C and 100% humidity. Then, they were immersed in 5 mL Hank’s balanced salt solution (HBSS [H6648; Sigma-Aldrich, St Louis]) at 37 C for 1 and 28 days. The sealers were characterized by scanning electron microscopy and energy-dispersive spectroscopy (EDS) and X-ray diffraction analysis (XRD). Scanning Electron Microscopy and EDS. Disc-shaped specimens (10 mm in diameter and 2-mm high) were prepared from each sealer type. After 1 and 28 days, they were removed from HBSS and placed in acetone for 48 hours followed by desiccation in a vacuum desiccator for 24 hours. Samples were impregnated in resin (Epoxyfix; Struers GmbH, Ballerup, Denmark) under a vacuum. The resin blocks were then ground with progressively finer diamond discs and pastes using an automatic polishing machine (Tegramin 20; Struers GmbH, Ballerup, Denmark). Specimens were mounted on aluminum stubs, carbon coated, and viewed under a scanning electron microscope (SI SS40; ISI, Tokyo, Japan). Scanning electron micrographs of the different material microstructural components at different magnifications in the back-scatter electron mode were captured, and EDS of the different phases was performed. XRD Analysis. Disc-shaped specimens 15 mm in diameter and 2-mm high were prepared and allowed to set. They were immersed in HBSS for either 1 or 28 days; after which, they were retrieved, dried, and crushed to a fine powder using a mortar and pestle. Phase analysis was performed with a Bruker D8 diffractometer (Bruker Corp, Billerica, MA) with Co Ka radiation (1.78 A ). The X-ray patterns were acquired in 2q (15 –45 ) with a step of 0.02 and 0.6 seconds per step. Phase identification was accomplished using search-match software using the International Centre for Diffraction Data database (ICDD) (International Centre for Diffraction Data, Newtown Square, PA). Assessment of Setting Time The setting time of sealers was evaluated by dispensing the sealers into stainless steel molds measuring 10 mm in diameter and 2-mm high. A stopwatch was started, and the molds were placed in an incubator at 37 C and 100% humidity until the end of setting. Testing for setting was performed using an indentation technique with a weighted needle of a round cross section size of 2 0.1 mm with a total mass of 100 0.5 g. The sealers were considered to have set when the needle was lowered gently onto the material surface and did not leave a complete round indentation on it. The testing was conducted in triplicate. Assessment of Sealer Flow The materials were mixed, and, using a graduated pipette, 0.05 0.005 mL of the material was dispensed on a glass plate measuring 40 40 mm and 5 mm in thickness. The second glass plate weighing 20 g was placed centrally on top of the sealer followed by the 100-g weight. The assembly was left in place for 10 minutes from the start of mixing; after which, the maximum and minimum diameters of the compressed disc of sealer were measured using a vernier caliper 2
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to an accuracy of 0.1 mm. The mean diameter was calculated if the diameters agreed to within 1 mm. If not, the test was repeated. The testing was conducted in triplicate.
Assessment of Film Thickness For the film thickness test, the combined thickness of 2 glass plates each measuring 5 mm in thickness and having a surface area of 200 mm2 was measured by using a micrometer to an accuracy of 1 mm. The materials were mixed and placed on a glass plate, and the other plate was placed over the sealer and inserted in a loading device (Triaxial; ELE International, Leighton Buzzard, UK). A load of 150 N was applied until the sealer filled the area in between the glass plates. After 10 minutes from the start of mixing, the thickness of the combined glass plates and sealer was measured using a micrometer. Radiopacity Assessment Three specimens 10 1 mm in diameter and 1 0.1 mm thick were prepared of each sealer type. The specimens were radiographed by placing them directly on a photostimulable phosphor plate adjacent to a calibrated aluminium step wedge (Everything X-ray Ltd, High Wycombe, UK) with 3-mm increments. A standard X-ray machine (GEC Medical Equipment Ltd, Middlesex, UK) was used to irradiate X-rays onto the specimens using an exposure time of 1.60 seconds at 10 mA, a tube voltage of 65 5 kV, and a cathode target film distance of 300 10 mm. The radiographs were processed (Clarimat 300; Gendex Dental Systems, Medivance Instruments Ltd, London, UK), and a digital image of the radiograph was obtained. The gray pixel value on the radiograph of each step in the step wedge was determined using an imaging program (Photoshop; Adobe, San Jose, CA), and a graph of thickness of aluminum versus the gray pixel value on the radiograph was plotted with the best-fit logarithmic trend line. The equation of the trend line gave the gray pixel value of an object on the image as a function of the object’s thickness in millimeters of aluminum. The gray pixel values of the cement specimens were then determined, and the relevant thickness of aluminum was calculated. Assessment of pH and Mineral Ion Leaching Specimens measuring 10 mm in diameter and 1-mm high were prepared from each sealer type and were weighed to an accuracy to 0.0001 g. They were then immersed in HBSS until testing. The pH of the HBSS and HBSS after immersion of the test sealers for 1 day and 28 days was assessed. The pH meter (Hanna HI 3221; Hanna Instruments, Woonsocket, RI) and single-junction (Ag/AgCl) ceramic pH electrode (HI 1131, Hanna Instruments) using a glass probe (HI 1230, Hanna Instruments) were calibrated at 3 points (pH = 4.00, = 7.00, and = 10.00) using standard calibrating solutions (Scharlau; Scharlab, Sentimenat, Spain) with temperature compensation (HI 7662, Hanna Instruments). Calibration was performed before measurement of the pH values of the soaking solutions. The results in triplicate were recorded, and the mean and standard deviation of each were calculated. The HBSS and HBSS exposed to the test sealers for 28 days were assessed for the presence of calcium, silicon, tungsten, zirconium, tantalum, and phosphorus using inductively coupled plasma.
Results Sealer Characterization The scanning electron micrographs and EDS analysis of the test sealers showing the material microstructure and elemental analysis for the different microstructural components are presented in Figure 1A JOE — Volume -, Number -, - 2016
Basic Research—Technology
Figure 1. (A) Scanning electron micrographs and EDS plots of a particular location of test sealers after immersion for 1 day in Hank’s balanced salt solution. (B) Scanning electron micrographs and area EDS plots of test sealers after immersion for 28 days in Hank’s balanced salt solution.
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Basic Research—Technology
Figure 1. (continued).
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Basic Research—Technology BioRoot RCS
Bio MM TO
CH
15
intensity cps
intensity cps
TO
TO CC TCS
20
25
TCS
30 degrees 2 theta 1 day
CC
35
ZO
ZO
CC
TCS
ZO
40
15
45
20
25
28 days
CH ZO
30 degrees 2 theta 1 day
35
ZO
40
45
28 days
AH Plus
intensity cps
CT CT
CT ZO
15
20
25
ZO CT
ZO CT
30 35 degrees 2 theta
1 day
CT
40
45
28 days
Figure 2. X-ray diffraction plots of test sealers showing the minimum crystalline phases present after immersion in Hank’s balanced salt solution for 1 day and 28 days. CC, calcium carbonate; CH, calcium hydroxide; CT, calcium tungstate; TCS, tricalcium silicate; ZO, zirconium oxide.
for 1 day. Figure 1B portrays the material microstructure after 28 days of immersion in HBSS with area EDS analysis. The microstructure of Bio MM sealer at 1 and 28 days did not change. It was composed of a range of particles with variable sizes. The particles rich in calcium and silicon were small (labeled 1) compared with the particles rich in calcium (labeled 2). Other particles rich in calcium and phosphorus were also present (labeled 3). The matrix was also interspersed with small white particles and large particles both consisting of tantalum and oxygen (labeled 4). BioRoot RCS was composed of calcium and silicon together with white particles rich in zirconium. Areas consisting of needlelike crystals were present both at 1 day and 28 days of immersion, with more crystals being present at 28 days. AH Plus was composed of white particles composed of tungsten and calcium, which varied in size and particles composed of zirconium. The phase analysis of the sealers is shown in Figure 2. Both Bio MM and BioRoot RCS contained a tricalcium silicate phase. The peaks at 32 and 34 2q were more obvious for Bio MM according to the 1-day and 28-day analyses when compared with BioRoot RCS, indicating less reaction of the Bio MM. In addition, the faster reaction of BioRoot RCS
was evident by the calcium hydroxide peaks at 18 and 34 2q. The peak at 18 2q was more intense than that at 1 day, indicating a more advanced reaction at the later time point. Bio MM did not exhibit a presence of calcium hydroxide at both time periods. Both BioRoot RCS and Bio MM exhibited the presence of a radiopacier phase, namely, zirconium oxide (ICDD: 04-005-7378) and tantalum oxide (ICDD: 01-0818067), respectively. Bio MM had an additional phase, namely, calcium carbonate (ICDD: 04-005-6528), with the main peak at 29 2q. The crystalline phases in AH Plus were calcium tungstate (ICDD: 01-0759478) and zirconium oxide (ICDD: 04-013-4343). There was a reduction in peak intensity at 18 and 29 2q for AH Plus after 28 days. These peaks represent the calcium tungstate.
Sealer Physical Properties The test sealer physical properties are shown in Table 1. Table 1 also shows the ISO 6876 (2012) norms for sealer cements. AH Plus complied with the ISO norms for both flow and film thickness. Both BioRoot RCS and Bio MM exhibited a lower flow and a higher film thickness
TABLE 1. Physical and Chemical Properties of Test Sealers and Compliance to ISO 6876 (2012) pH Sealer type
Setting time (min)
Flow (mm)
Film thickness (mm)
Radiopacity (mm Al)
1 day
28 days
Bio MM BioRoot RCS AH Plus ISO 6876
32 4.4 27.4 2.8 1154 48.1 /
13 1.1 16 1.6 17 1.6 >17
212 32 52 17 15 5 <50
4.5 0.44 8.3 0.99 18.4 0.39 >3
10.9 0.1 12.1 0.1 8.4 0 /
11.9 0.2 12.7 0.1 8.7 0.1 /
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Basic Research—Technology TABLE 2. Concentration of Elements Leached in Hank’s Balanced Salt Solution after 1 or 28 Days* Concentration of element (mg/g) Sealer Bio MM BioRoot RCS AH Plus
Soaking time (d)
Calcium
1 28 1 28 1 28
7200 2333 19,789 28,682 40 39
Phosphorus 119 417 33 106 25 8
Silicon
Tantalum
Tungsten
Zirconium
121 168 164 0 53 0
2.1 1.6 0 0 0 0
0 0 0 0 4.6 12.3
0 0 0.2 0.2 0.5 0.4
*HBSS blank contained calcium 2.9 mg/L and phosphorus: 24 mg/L.
than that specified for sealer cements in ISO 6876 (2012). All the test sealers exhibited adequate radiopacity, with AH Plus being the most radiopaque sealer.
Sealer Chemical Properties The pH levels of all the sealers tested after 1 day and 28 days in HBSS are shown in Table 1. Both Bio MM and BioRoot RCS were alkalinizing, and the pH increased with time. The ion leaching from all sealers at 1 and 28 days is shown in Table 2. Both tricalcium silicate–based sealers leached high levels of calcium compared with AH Plus. BioRoot RCS leached more calcium at both time intervals than Bio MM, with the 28-day calcium leaching higher than the 1 day, as opposed to Bio MM in which the 28-day leaching of calcium was lower than the early-age calcium ion release. In comparison, the depletion of phosphorus from the solution was higher in Bio MM than BioRoot RCS. The tantalum and zirconium release in solution was low for both tricalcium silicate–based sealers, whereas increasing levels of tungsten were leached from AH Plus.
Discussion The materials used for this study included 2 sealers that were based on tricalcium silicate. BioRoot RCS has been launched recently by Septodont and is composed of a powder made up of tricalcium silicate and zirconium oxide and a liquid that is water based with additives of calcium chloride and a polymer. This has been shown in this study, which verifies earlier work characterizing this sealer (3, 11). The new sealer, Bio MM, was also composed of tricalcium silicate but included calcium carbonate in the formulation. Additions of calcium carbonate have also been reported for MM-MTA by Micromega (Besancon, France) (14) and Biodentine (Septodont). The calcium carbonate is added as a filler and acts as a nucleating agent. The nucleating agent’s role is to provide more reaction sites for cement hydration. In Biodentine, it has been shown to enhance the physical properties of the material (15). In formulations containing Portland cement like MM-MTA, the calcium carbonate reacts with the ettringite, which is a hydration product of the aluminate phase in Portland cement, replacing the sulphate ions with carbonate ions and thus modifying the hydration mechanisms (16). AH Plus was composed of zirconium oxide and calcium tungstate. The characterization techniques used are suitable for detecting inorganic materials; thus, any organic substance present in the materials under study would not be elucidated. Bio MM was mixed at a high water-to-powder ratio. Most tricalcium silicate–based materials are mixed at a water-to-powder ratio of 0.35. High water-to-powder ratios result in materials that are too wet with a tendency to flocculate and exhibit poor physical properties. Regardless of the high water-to-powder ratio, the resultant mixture was stable and homogenous. This could have resulted from the presence of organic compounds that help stabilize water-based cement mixtures. Bio MM and BioRoot RCS had a comparable setting time (32 and 27 minutes, respectively) that was much shorter than that of AH Plus 6
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(1154 minutes). The results achieved for the setting time of BioRoot RCS and AH Plus are in accordance to that reported in the literature (3, 11, 17, 18). BioRoot RCS contains a chloride accelerator (11). The calcium carbonate present in Bio MM could also accelerate tricalcium silicate hydration (19, 20). Bio MM and BioRoot RCS had a lower flow and a higher film thickness than what is specified for sealers in ISO 6876 (2012). The importance of a specific film thickness and compliance to ISO norms may not be important for new sealers based on tricalcium silicate cement, particularly if the single-cone technique is advocated. These sealer types aim at bonding to dentin and bioactivity; thus, forming a thicker film may not jeopardize the sealing ability of the root canal filling. The formation of a mineral infiltration zone has been shown even for BioRoot RCS (13). This was observed by confocal microscopy in which the presence of sealer was verified as part of the dentin at the interface. This observation was similar to that shown for Biodentine (7). All the sealers had adequate radiopacity, with Bio MM being the least radiopaque (4.5 mm Al thickness). The radiopacity of AH Plus is imparted by 2 radiopacifying agents, thus the high radiopacity recorded (18.4 mm Al thickness). BioRoot RCS contains zirconium oxide; Bio MM contains tantalum oxide as shown by the EDS and phase analyses. Tantalum oxide is also present in a new MTA type called Neo MTA (Avalon Biomed, Bradenton, FL). It was introduced to replace the bismuth oxide because the latter causes tooth discoloration when used in the coronal part of the tooth as in pulpotomies (21). Both BioRoot RCS and Bio MM exhibited alkalinizing pH immediately, which increased after 28 days in physiological solution. BioRoot RCS exhibited a calcium hydroxide peak that intensified after 28 days. Calcium hydroxide was also evident in the material matrix seen under the scanning electron microscope. This would explain the alkalinizing pH. Bio MM did not show formation of calcium hydroxide. The presence of calcium carbonate has been shown to impede the crystallization of portlandite. Noncrystalline portlandite cannot be detected by XRD analysis because XRD only detects crystalline phases (22, 23). This was also demonstrated with MM-MTA (14). Bio MM contained a phosphate phase evident in its matrix on scanning electron microscopic/EDS analysis. This phase was not present in the XRD scans, indicating its amorphous nature. The presence of additives, namely, calcium carbonate and calcium phosphate, modified the reaction kinetics of the tricalcium silicate in Bio MM. Although crystalline calcium hydroxide was not formed on hydration as shown from the XRD scans and less calcium was leached in solution, the material was alkalinizing, and it interacted with the physiological solution because phosphorus was depleted in greater amounts in the bioceramic sealer. The new Bio MM interacted with physiologic solution, thus showing potential for bioactivity. The sealer properties were acceptable, and this sealer could be developed further for prospective clinical use.
Acknowledgments The authors deny any conflicts of interest related to this study. JOE — Volume -, Number -, - 2016
Basic Research—Technology References 1. Moinzadeh AT, Zerbst W, Boutsioukis C, et al. Porosity distribution in root canals filled with gutta percha and calcium silicate cement. Dent Mater 2015;15: 185–92. 2. Camilleri J. Characterization and hydration kinetics of tricalcium silicate cement for use as a dental biomaterial. Dent Mater 2011;27:836–44. 3. Camilleri J. Sealers and warm gutta-percha obturation techniques. J Endod 2015;41: 72–8. 4. Reyes-Carmona JF, Felippe MS, Felippe WT. Biomineralization ability and interaction of mineral trioxide aggregate and white portland cement with dentin in a phosphatecontaining fluid. J Endod 2009;35:731–6. 5. Sarkar NK, Caicedo R, Ritwik P, et al. Physicochemical basis of the biologic properties of mineral trioxide aggregate. J Endod 2005;31:97–100. 6. Tay FR, Pashley DH, Rueggeberg FA, et al. Calcium phosphate phase transformation produced by the interaction of the portland cement component of white mineral trioxide aggregate with a phosphate-containing fluid. J Endod 2007;33:1347–51. 7. Atmeh AR, Chong EZ, Richard G, et al. Dentin-cement interfacial interaction: calcium silicates and polyalkenoates. J Dent Res 2012;91:454–9. 8. Viapiana R, Guerreiro-Tanomaru JM, Hungaro-Duarte MA, et al. Chemical characterization and bioactivity of epoxy resin and Portland cement-based sealers with niobium and zirconium oxide radiopacifiers. Dent Mater 2014;30:1005–20. 9. International Organization for Standardization. Dentistry-Root Canal Sealing Materials. ISO 6876. London, UK: British Standards Institution; 2012. 10. Viapiana R, Guerreiro-Tanomaru JM, Tanomaru-Filho M, Camilleri J. Investigation of the effect of sealer use on the heat generated at the external root surface during root canal obturation using warm vertical compaction technique with System B heat source. J Endod 2014;40:555–61. 11. Xuereb M, Vella P, Damidot D, et al. In situ assessment of the setting of tricalcium silicate-based sealers using a dentin pressure model. J Endod 2015;41:111–24.
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12. Zhou HM, Shen Y, Zheng W, et al. Physical properties of 5 root canal sealers. J Endod 2013;39:1281–6. 13. Viapiana R, Moinzadeh AT, Camilleri L, et al. Porosity and sealing ability of root fillings with gutta-percha and BioRoot RCS or AH Plus sealers. Evaluation by three ex vivo methods. Int Endod J 2016;49:774–82. 14. Khalil I, Naaman A, Camilleri J. Investigation of a novel mechanically mixed mineral trioxide aggregate MM-MTA. Int Endod J 2015;48:757–67. 15. Camilleri J, Sorrentino F, Damidot D. Investigation of the hydration and bioactivity of radiopacified tricalcium silicate cement, Biodentine and MTA Angelus. Dent Mater 2013;29:580–93. 16. Bushnell-Watson SM, Sharp JM. The detection of the carboaluminate phase in hydrated high alumina cements by differential thermal analysis. Thermochim Acta 1985;93:613–6. 17. Arias-Moliz MT, Ruiz-Linares M, Cassar G, et al. The effect of benzalkonium chloride additions to AH Plus sealer. Antimicrobial, physical and chemical properties. J Dent 2015;43:846–54. 18. Ruiz-Linares M, Bailon-Sanchez ME, Baca P, et al. Physical properties of AH Plus with chlorhexidine and cetrimide. J Endod 2013;39:1611–4. 19. Pera J, Husson S, Guilhot B. Influence of finely ground limestone on cement hydration. Cem Conc Comp 1999;21:99–105. 20. Ramachandran VS. Thermal analysis of cement components hydrated in the presence of calcium carbonate. Thermochim Acta 1988;127:385–94. 21. Camilleri J. Staining potential of Neo MTA Plus, MTA Plus, and Biodentine used for pulpotomy procedures. J Endod 2015;41:1139–45. 22. Gabrovsek R, Vuk T, Kaucic V. Evaluation of the hydration of Portland cement containing various carbonates by means of thermal analysis. Acta Chim Slov 2006;53: 159–65. 23. Hawkins P, Tennis PD, Detwiler R. The Use of Limestone in Portland Cement: A State-of-the-Art Review. Skokie, IL: EB 227 Portland Cement Association; 2003:44.
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Properties of Tricalcium Silicate Sealers Issam Khalil, DDS, MSc, PhD,* Alfred Naaman, DDS, MSc, PhD,* and Josette Camilleri, BChD, MPhil, PhD, FIMMM, FADM† Abstract Introduction: Sealers based on tricalcium silicate cement aim at an interaction of the sealer with the root canal wall, alkalinity with potential antimicrobial activity, and the ability to set in a wet field. The aim of this study was to characterize and investigate the properties of a new tricalcium silicate–based sealer and verify its compliance to ISO 6876 (2012). Methods: A new tricalcium silicate–based sealer (Bio MM; St Joseph University, Beirut, Lebanon), BioRoot RCS (Septodont, St Maure de Fosses, France), and AH Plus (Dentsply, DeTrey, Konstanz, Germany) were investigated. Characterization using scanning electron microscopy, energy-dispersive spectroscopy, and X-ray diffraction analysis was performed. Furthermore, sealer setting time, flow, film thickness, and radiopacity were performed following ISO specifications. pH and ion leaching in solution were assessed by pH analysis and inductively coupled plasma. Results: Bio MM and BioRoot RCS were both composed of tricalcium silicate and tantalum oxide in Bio MM and zirconium oxide in BioRoot RCS. In addition, the Bio MM contained calcium carbonate and a phosphate phase. The inorganic components of AH Plus were calcium tungstate and zirconium oxide. AH Plus complied with the ISO norms for both flow and film thickness. BioRoot RCS and Bio MM exhibited a lower flow and a higher film thickness than that specified for sealer cements in ISO 6876. All test sealers exhibited adequate radiopacity. Conclusions: Bio MM interacted with physiologic solution, thus showing potential for bioactivity. Sealer properties were acceptable and comparable with other sealers available clinically. (J Endod 2016;-:1–7)
Key Words BioRoot RCS, Bio MM, characterization, physical testing, sealer, tricalcium silicate-based sealers
From the *Department of Endodontics, Saint Joseph University, Beirut, Lebanon; †Department of Restorative Dentistry, Faculty of Dental Surgery, University of Malta, Msida, Malta. Address requests for reprints to Dr Issam Khalil, Department of Endodontics, Saint-Joseph University, Damascus Street, Beirut, Lebanon. E-mail address: [email protected] 0099-2399/$ - see front matter Copyright ª 2016 American Association of Endodontists. http://dx.doi.org/10.1016/j.joen.2016.06.002
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illing a root canal is Significance classically performed Single-cone obturation in combination with a biousing a gutta-percha solid ceramic sealer resulted in less porosity; rather cone in combination with than aiming for a hermetic seal of the root canal, a sealer. Initially, this was a more biological approach is being undertaken done using lateral condenin which the sealers interact with the dentin, resultsation, which was eventuing in biomineralization. ally superseded by warm vertical compaction. More recently, rather than aiming for a hermetic seal of the root canal, a more biological approach is being undertaken in which the sealers aim at interacting with the root dentin, resulting in bioactivity. Single-cone obturation in combination with a tricalcium silicate–based sealer resulted in significantly less porosity, particularly coronally compared with lateral compaction–filled teeth (1). Materials based on tricalcium silicate used in combination with a radiopacifying material are used as sealers. These sealers were developed because they induce bioactivity on the material surface when in contact with tissue fluids as a result of the interaction of calcium hydroxide produced as a reaction product of tricalcium silicate hydration (2, 3) with phosphates present in tissue fluids (4–6). The interaction of these materials with dentin has been termed the mineral infiltration zone (7). The first sealer based on tricalcium silicate was MTA Fillapex (Angelus, Londrina, Brazil). This sealer is mainly composed of a salicylate resin matrix, silica, and mineral trioxide aggregate, with the mineral trioxide aggregate being a minor component. Although the main scope of using a tricalcium silicate–based sealer is the release of calcium hydroxide from the material, hydration MTA Fillapex has been shown to be inert, and no calcium hydroxide was formed when the material set (8). However, MTA Fillapex complies with ISO 6876 (9) and is also stable when used with warm vertical compaction techniques (10). Other tricalcium silicate–based sealers have been developed. Endosequence BC Sealer (Brasseler, Savannah, GA) is a biphasic sealer because it also contains calcium phosphate monobasic together with the tricalcium silicate phase (11). It is premixed and dispensed through a syringe. It possesses comparable flow and dimensional stability to MTA Fillapex but higher film thickness and solubility than AH Plus (Dentsply, DeTrey, Konstanz, Germany) (12). BioRoot RCS (Septodont, St Maure de Fosses, France) is also based on tricalcium silicate with zirconium oxide added for radiopacity. This sealer is water based; thus, it should be used with a single-cone obturation technique rather than warm vertical compaction because the sealer properties are changed when heated (3). BioRoot RCS exhibited a significantly higher percentage of voids than AH Plus using micro–computed tomographic analysis, but there was no difference in fluid flow and microsphere penetration. A different pattern of sealer penetration and interaction with the dentin walls was observed when compared with AH Plus (13). Although a number of tricalcium silicate–based sealers are available to the clinician, none of them fulfills all the necessary criteria of stability and interaction with the dentin. The aim of this study was the development of a novel tricalcium silicate–based sealer based on tricalcium silicate that fulfills the criteria set by ISO 6876 (2012) (9) and also exhibits bioactivity potential. In the current study, the novel sealer is compared with BioRoot RCS, which is a tricalcium silicate–based sealer that does not contain any additives to the powder except for the zirconium oxide radiopacifier, and AH Plus, which is an epoxy-based sealer that has been considered the gold standard and has been used as a control material in most studies on sealers.
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Basic Research—Technology Materials and Methods Three sealers were investigated: 1. Bio MM (developed at St Joseph University, Beirut, Lebanon) 2. BioRoot RCS 3. AH Plus
Sealer Characterization Bio MM was mixed at a water to powder ratio of 0.75. BioRoot RCS and AH Plus were mixed according to the manufacturers’ instructions. After preparation, the materials were allowed to set for 24 hours at 37 C and 100% humidity. Then, they were immersed in 5 mL Hank’s balanced salt solution (HBSS [H6648; Sigma-Aldrich, St Louis]) at 37 C for 1 and 28 days. The sealers were characterized by scanning electron microscopy and energy-dispersive spectroscopy (EDS) and X-ray diffraction analysis (XRD). Scanning Electron Microscopy and EDS. Disc-shaped specimens (10 mm in diameter and 2-mm high) were prepared from each sealer type. After 1 and 28 days, they were removed from HBSS and placed in acetone for 48 hours followed by desiccation in a vacuum desiccator for 24 hours. Samples were impregnated in resin (Epoxyfix; Struers GmbH, Ballerup, Denmark) under a vacuum. The resin blocks were then ground with progressively finer diamond discs and pastes using an automatic polishing machine (Tegramin 20; Struers GmbH, Ballerup, Denmark). Specimens were mounted on aluminum stubs, carbon coated, and viewed under a scanning electron microscope (SI SS40; ISI, Tokyo, Japan). Scanning electron micrographs of the different material microstructural components at different magnifications in the back-scatter electron mode were captured, and EDS of the different phases was performed. XRD Analysis. Disc-shaped specimens 15 mm in diameter and 2-mm high were prepared and allowed to set. They were immersed in HBSS for either 1 or 28 days; after which, they were retrieved, dried, and crushed to a fine powder using a mortar and pestle. Phase analysis was performed with a Bruker D8 diffractometer (Bruker Corp, Billerica, MA) with Co Ka radiation (1.78 A ). The X-ray patterns were acquired in 2q (15 –45 ) with a step of 0.02 and 0.6 seconds per step. Phase identification was accomplished using search-match software using the International Centre for Diffraction Data database (ICDD) (International Centre for Diffraction Data, Newtown Square, PA). Assessment of Setting Time The setting time of sealers was evaluated by dispensing the sealers into stainless steel molds measuring 10 mm in diameter and 2-mm high. A stopwatch was started, and the molds were placed in an incubator at 37 C and 100% humidity until the end of setting. Testing for setting was performed using an indentation technique with a weighted needle of a round cross section size of 2 0.1 mm with a total mass of 100 0.5 g. The sealers were considered to have set when the needle was lowered gently onto the material surface and did not leave a complete round indentation on it. The testing was conducted in triplicate. Assessment of Sealer Flow The materials were mixed, and, using a graduated pipette, 0.05 0.005 mL of the material was dispensed on a glass plate measuring 40 40 mm and 5 mm in thickness. The second glass plate weighing 20 g was placed centrally on top of the sealer followed by the 100-g weight. The assembly was left in place for 10 minutes from the start of mixing; after which, the maximum and minimum diameters of the compressed disc of sealer were measured using a vernier caliper 2
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to an accuracy of 0.1 mm. The mean diameter was calculated if the diameters agreed to within 1 mm. If not, the test was repeated. The testing was conducted in triplicate.
Assessment of Film Thickness For the film thickness test, the combined thickness of 2 glass plates each measuring 5 mm in thickness and having a surface area of 200 mm2 was measured by using a micrometer to an accuracy of 1 mm. The materials were mixed and placed on a glass plate, and the other plate was placed over the sealer and inserted in a loading device (Triaxial; ELE International, Leighton Buzzard, UK). A load of 150 N was applied until the sealer filled the area in between the glass plates. After 10 minutes from the start of mixing, the thickness of the combined glass plates and sealer was measured using a micrometer. Radiopacity Assessment Three specimens 10 1 mm in diameter and 1 0.1 mm thick were prepared of each sealer type. The specimens were radiographed by placing them directly on a photostimulable phosphor plate adjacent to a calibrated aluminium step wedge (Everything X-ray Ltd, High Wycombe, UK) with 3-mm increments. A standard X-ray machine (GEC Medical Equipment Ltd, Middlesex, UK) was used to irradiate X-rays onto the specimens using an exposure time of 1.60 seconds at 10 mA, a tube voltage of 65 5 kV, and a cathode target film distance of 300 10 mm. The radiographs were processed (Clarimat 300; Gendex Dental Systems, Medivance Instruments Ltd, London, UK), and a digital image of the radiograph was obtained. The gray pixel value on the radiograph of each step in the step wedge was determined using an imaging program (Photoshop; Adobe, San Jose, CA), and a graph of thickness of aluminum versus the gray pixel value on the radiograph was plotted with the best-fit logarithmic trend line. The equation of the trend line gave the gray pixel value of an object on the image as a function of the object’s thickness in millimeters of aluminum. The gray pixel values of the cement specimens were then determined, and the relevant thickness of aluminum was calculated. Assessment of pH and Mineral Ion Leaching Specimens measuring 10 mm in diameter and 1-mm high were prepared from each sealer type and were weighed to an accuracy to 0.0001 g. They were then immersed in HBSS until testing. The pH of the HBSS and HBSS after immersion of the test sealers for 1 day and 28 days was assessed. The pH meter (Hanna HI 3221; Hanna Instruments, Woonsocket, RI) and single-junction (Ag/AgCl) ceramic pH electrode (HI 1131, Hanna Instruments) using a glass probe (HI 1230, Hanna Instruments) were calibrated at 3 points (pH = 4.00, = 7.00, and = 10.00) using standard calibrating solutions (Scharlau; Scharlab, Sentimenat, Spain) with temperature compensation (HI 7662, Hanna Instruments). Calibration was performed before measurement of the pH values of the soaking solutions. The results in triplicate were recorded, and the mean and standard deviation of each were calculated. The HBSS and HBSS exposed to the test sealers for 28 days were assessed for the presence of calcium, silicon, tungsten, zirconium, tantalum, and phosphorus using inductively coupled plasma.
Results Sealer Characterization The scanning electron micrographs and EDS analysis of the test sealers showing the material microstructure and elemental analysis for the different microstructural components are presented in Figure 1A JOE — Volume -, Number -, - 2016
Basic Research—Technology
Figure 1. (A) Scanning electron micrographs and EDS plots of a particular location of test sealers after immersion for 1 day in Hank’s balanced salt solution. (B) Scanning electron micrographs and area EDS plots of test sealers after immersion for 28 days in Hank’s balanced salt solution.
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Figure 1. (continued).
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Basic Research—Technology BioRoot RCS
Bio MM TO
CH
15
intensity cps
intensity cps
TO
TO CC TCS
20
25
TCS
30 degrees 2 theta 1 day
CC
35
ZO
ZO
CC
TCS
ZO
40
15
45
20
25
28 days
CH ZO
30 degrees 2 theta 1 day
35
ZO
40
45
28 days
AH Plus
intensity cps
CT CT
CT ZO
15
20
25
ZO CT
ZO CT
30 35 degrees 2 theta
1 day
CT
40
45
28 days
Figure 2. X-ray diffraction plots of test sealers showing the minimum crystalline phases present after immersion in Hank’s balanced salt solution for 1 day and 28 days. CC, calcium carbonate; CH, calcium hydroxide; CT, calcium tungstate; TCS, tricalcium silicate; ZO, zirconium oxide.
for 1 day. Figure 1B portrays the material microstructure after 28 days of immersion in HBSS with area EDS analysis. The microstructure of Bio MM sealer at 1 and 28 days did not change. It was composed of a range of particles with variable sizes. The particles rich in calcium and silicon were small (labeled 1) compared with the particles rich in calcium (labeled 2). Other particles rich in calcium and phosphorus were also present (labeled 3). The matrix was also interspersed with small white particles and large particles both consisting of tantalum and oxygen (labeled 4). BioRoot RCS was composed of calcium and silicon together with white particles rich in zirconium. Areas consisting of needlelike crystals were present both at 1 day and 28 days of immersion, with more crystals being present at 28 days. AH Plus was composed of white particles composed of tungsten and calcium, which varied in size and particles composed of zirconium. The phase analysis of the sealers is shown in Figure 2. Both Bio MM and BioRoot RCS contained a tricalcium silicate phase. The peaks at 32 and 34 2q were more obvious for Bio MM according to the 1-day and 28-day analyses when compared with BioRoot RCS, indicating less reaction of the Bio MM. In addition, the faster reaction of BioRoot RCS
was evident by the calcium hydroxide peaks at 18 and 34 2q. The peak at 18 2q was more intense than that at 1 day, indicating a more advanced reaction at the later time point. Bio MM did not exhibit a presence of calcium hydroxide at both time periods. Both BioRoot RCS and Bio MM exhibited the presence of a radiopacier phase, namely, zirconium oxide (ICDD: 04-005-7378) and tantalum oxide (ICDD: 01-0818067), respectively. Bio MM had an additional phase, namely, calcium carbonate (ICDD: 04-005-6528), with the main peak at 29 2q. The crystalline phases in AH Plus were calcium tungstate (ICDD: 01-0759478) and zirconium oxide (ICDD: 04-013-4343). There was a reduction in peak intensity at 18 and 29 2q for AH Plus after 28 days. These peaks represent the calcium tungstate.
Sealer Physical Properties The test sealer physical properties are shown in Table 1. Table 1 also shows the ISO 6876 (2012) norms for sealer cements. AH Plus complied with the ISO norms for both flow and film thickness. Both BioRoot RCS and Bio MM exhibited a lower flow and a higher film thickness
TABLE 1. Physical and Chemical Properties of Test Sealers and Compliance to ISO 6876 (2012) pH Sealer type
Setting time (min)
Flow (mm)
Film thickness (mm)
Radiopacity (mm Al)
1 day
28 days
Bio MM BioRoot RCS AH Plus ISO 6876
32 4.4 27.4 2.8 1154 48.1 /
13 1.1 16 1.6 17 1.6 >17
212 32 52 17 15 5 <50
4.5 0.44 8.3 0.99 18.4 0.39 >3
10.9 0.1 12.1 0.1 8.4 0 /
11.9 0.2 12.7 0.1 8.7 0.1 /
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Basic Research—Technology TABLE 2. Concentration of Elements Leached in Hank’s Balanced Salt Solution after 1 or 28 Days* Concentration of element (mg/g) Sealer Bio MM BioRoot RCS AH Plus
Soaking time (d)
Calcium
1 28 1 28 1 28
7200 2333 19,789 28,682 40 39
Phosphorus 119 417 33 106 25 8
Silicon
Tantalum
Tungsten
Zirconium
121 168 164 0 53 0
2.1 1.6 0 0 0 0
0 0 0 0 4.6 12.3
0 0 0.2 0.2 0.5 0.4
*HBSS blank contained calcium 2.9 mg/L and phosphorus: 24 mg/L.
than that specified for sealer cements in ISO 6876 (2012). All the test sealers exhibited adequate radiopacity, with AH Plus being the most radiopaque sealer.
Sealer Chemical Properties The pH levels of all the sealers tested after 1 day and 28 days in HBSS are shown in Table 1. Both Bio MM and BioRoot RCS were alkalinizing, and the pH increased with time. The ion leaching from all sealers at 1 and 28 days is shown in Table 2. Both tricalcium silicate–based sealers leached high levels of calcium compared with AH Plus. BioRoot RCS leached more calcium at both time intervals than Bio MM, with the 28-day calcium leaching higher than the 1 day, as opposed to Bio MM in which the 28-day leaching of calcium was lower than the early-age calcium ion release. In comparison, the depletion of phosphorus from the solution was higher in Bio MM than BioRoot RCS. The tantalum and zirconium release in solution was low for both tricalcium silicate–based sealers, whereas increasing levels of tungsten were leached from AH Plus.
Discussion The materials used for this study included 2 sealers that were based on tricalcium silicate. BioRoot RCS has been launched recently by Septodont and is composed of a powder made up of tricalcium silicate and zirconium oxide and a liquid that is water based with additives of calcium chloride and a polymer. This has been shown in this study, which verifies earlier work characterizing this sealer (3, 11). The new sealer, Bio MM, was also composed of tricalcium silicate but included calcium carbonate in the formulation. Additions of calcium carbonate have also been reported for MM-MTA by Micromega (Besancon, France) (14) and Biodentine (Septodont). The calcium carbonate is added as a filler and acts as a nucleating agent. The nucleating agent’s role is to provide more reaction sites for cement hydration. In Biodentine, it has been shown to enhance the physical properties of the material (15). In formulations containing Portland cement like MM-MTA, the calcium carbonate reacts with the ettringite, which is a hydration product of the aluminate phase in Portland cement, replacing the sulphate ions with carbonate ions and thus modifying the hydration mechanisms (16). AH Plus was composed of zirconium oxide and calcium tungstate. The characterization techniques used are suitable for detecting inorganic materials; thus, any organic substance present in the materials under study would not be elucidated. Bio MM was mixed at a high water-to-powder ratio. Most tricalcium silicate–based materials are mixed at a water-to-powder ratio of 0.35. High water-to-powder ratios result in materials that are too wet with a tendency to flocculate and exhibit poor physical properties. Regardless of the high water-to-powder ratio, the resultant mixture was stable and homogenous. This could have resulted from the presence of organic compounds that help stabilize water-based cement mixtures. Bio MM and BioRoot RCS had a comparable setting time (32 and 27 minutes, respectively) that was much shorter than that of AH Plus 6
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(1154 minutes). The results achieved for the setting time of BioRoot RCS and AH Plus are in accordance to that reported in the literature (3, 11, 17, 18). BioRoot RCS contains a chloride accelerator (11). The calcium carbonate present in Bio MM could also accelerate tricalcium silicate hydration (19, 20). Bio MM and BioRoot RCS had a lower flow and a higher film thickness than what is specified for sealers in ISO 6876 (2012). The importance of a specific film thickness and compliance to ISO norms may not be important for new sealers based on tricalcium silicate cement, particularly if the single-cone technique is advocated. These sealer types aim at bonding to dentin and bioactivity; thus, forming a thicker film may not jeopardize the sealing ability of the root canal filling. The formation of a mineral infiltration zone has been shown even for BioRoot RCS (13). This was observed by confocal microscopy in which the presence of sealer was verified as part of the dentin at the interface. This observation was similar to that shown for Biodentine (7). All the sealers had adequate radiopacity, with Bio MM being the least radiopaque (4.5 mm Al thickness). The radiopacity of AH Plus is imparted by 2 radiopacifying agents, thus the high radiopacity recorded (18.4 mm Al thickness). BioRoot RCS contains zirconium oxide; Bio MM contains tantalum oxide as shown by the EDS and phase analyses. Tantalum oxide is also present in a new MTA type called Neo MTA (Avalon Biomed, Bradenton, FL). It was introduced to replace the bismuth oxide because the latter causes tooth discoloration when used in the coronal part of the tooth as in pulpotomies (21). Both BioRoot RCS and Bio MM exhibited alkalinizing pH immediately, which increased after 28 days in physiological solution. BioRoot RCS exhibited a calcium hydroxide peak that intensified after 28 days. Calcium hydroxide was also evident in the material matrix seen under the scanning electron microscope. This would explain the alkalinizing pH. Bio MM did not show formation of calcium hydroxide. The presence of calcium carbonate has been shown to impede the crystallization of portlandite. Noncrystalline portlandite cannot be detected by XRD analysis because XRD only detects crystalline phases (22, 23). This was also demonstrated with MM-MTA (14). Bio MM contained a phosphate phase evident in its matrix on scanning electron microscopic/EDS analysis. This phase was not present in the XRD scans, indicating its amorphous nature. The presence of additives, namely, calcium carbonate and calcium phosphate, modified the reaction kinetics of the tricalcium silicate in Bio MM. Although crystalline calcium hydroxide was not formed on hydration as shown from the XRD scans and less calcium was leached in solution, the material was alkalinizing, and it interacted with the physiological solution because phosphorus was depleted in greater amounts in the bioceramic sealer. The new Bio MM interacted with physiologic solution, thus showing potential for bioactivity. The sealer properties were acceptable, and this sealer could be developed further for prospective clinical use.
Acknowledgments The authors deny any conflicts of interest related to this study. JOE — Volume -, Number -, - 2016
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12. Zhou HM, Shen Y, Zheng W, et al. Physical properties of 5 root canal sealers. J Endod 2013;39:1281–6. 13. Viapiana R, Moinzadeh AT, Camilleri L, et al. Porosity and sealing ability of root fillings with gutta-percha and BioRoot RCS or AH Plus sealers. Evaluation by three ex vivo methods. Int Endod J 2016;49:774–82. 14. Khalil I, Naaman A, Camilleri J. Investigation of a novel mechanically mixed mineral trioxide aggregate MM-MTA. Int Endod J 2015;48:757–67. 15. Camilleri J, Sorrentino F, Damidot D. Investigation of the hydration and bioactivity of radiopacified tricalcium silicate cement, Biodentine and MTA Angelus. Dent Mater 2013;29:580–93. 16. Bushnell-Watson SM, Sharp JM. The detection of the carboaluminate phase in hydrated high alumina cements by differential thermal analysis. Thermochim Acta 1985;93:613–6. 17. Arias-Moliz MT, Ruiz-Linares M, Cassar G, et al. The effect of benzalkonium chloride additions to AH Plus sealer. Antimicrobial, physical and chemical properties. J Dent 2015;43:846–54. 18. Ruiz-Linares M, Bailon-Sanchez ME, Baca P, et al. Physical properties of AH Plus with chlorhexidine and cetrimide. J Endod 2013;39:1611–4. 19. Pera J, Husson S, Guilhot B. Influence of finely ground limestone on cement hydration. Cem Conc Comp 1999;21:99–105. 20. Ramachandran VS. Thermal analysis of cement components hydrated in the presence of calcium carbonate. Thermochim Acta 1988;127:385–94. 21. Camilleri J. Staining potential of Neo MTA Plus, MTA Plus, and Biodentine used for pulpotomy procedures. J Endod 2015;41:1139–45. 22. Gabrovsek R, Vuk T, Kaucic V. Evaluation of the hydration of Portland cement containing various carbonates by means of thermal analysis. Acta Chim Slov 2006;53: 159–65. 23. Hawkins P, Tennis PD, Detwiler R. The Use of Limestone in Portland Cement: A State-of-the-Art Review. Skokie, IL: EB 227 Portland Cement Association; 2003:44.
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