The effect of mixing method on tricalcium. silicate-based cements.

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1 doi: /iej The effect of mixing method on tricalcium silicate-based cement J. A. Duque 1, S. L. Fernandes 1, J. P. Bubola 1, M. A. H. Duarte 1, J. Camilleri 2 & M. A. Marciano 3 1 Department of Dentistry, Dental School of Bauru, University of S~ao Paulo (USP), Bauru, SP, Brazil; 2 Department of Restorative Dentistry, Faculty of Dental Surgery, University of Malta, Msida, Malta; and 3 Piracicaba Dental School, State University of Campinas, Piracicaba, SP, Brazil Abstract Duque JA, Fernandes SL, Bubola JP, Duarte MAH, Camilleri J, Marciano MA. The effect of mixing method on tricalcium silicate-based cement.. Aim To evaluate the effect of three methods of mixing on the physical and chemical properties of tricalcium silicate-based cements. Methodology The materials evaluated were MTA Angelus and Portland cement with 20% zirconium oxide (PC-20-Zr). The cements were mixed using a 3 : 1 powder-to-liquid ratio. The mixing methods were manual (m), trituration (tr) and ultrasonic (us) activation. The materials were characterized by means of scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy. Flowability was analysed according to ANSI/ADA 57/2012. Initial and final setting times were assessed following ASTM C266/08. Volume change was evaluated using a micro-ct volumetric method. Solubility was analysed according to ADA 57/2012. ph and calcium ion release were measured after 3, 24, 72 and 168 h. Statistical analysis was performed using two-way analysis of variance. The level of significance was set at P = Results The SEM analysis revealed that ultrasonic activation was associated with a homogeneous distribution of particles. Flowability, volume change and initial setting time were not influenced by the mixing method (P > 0.05). Solubility was influenced by the mixing method (P < 0.05). For ph, at 168 h, significant differences were found between MTA-m and PC-20-Zr-m (P < 0.05). For calcium ion release, PC-20-Zr-tr had higher values than MTA-m at 3 h, and MTA-tr had higher values than PC-20-Zr-m at 168 h (P < 0.05). Conclusions The ultrasonic and trituration methods led to higher calcium ion release and ph compared with manual mixing for all cements, whilst the ultrasonic method produced smaller particles for the PC-20-Zr cement. Flow, setting times and volume change were not influenced by the mixing method used; however, it did have an impact on solubility. Keywords: mixing methods, scanning electron microscopy, solubility, tricalcium silicate. Received 18 May 2016; accepted 24 March 2017 Introduction Tricalcium silicate-based cements (MTA) are largely used as repair materials (Torabinejad et al. 1995, Correspondence: Marco Antonio Hungaro Duarte, Department of Dentistry, Dental School of Bauru, University of S~ao Paulo (USP) Bauru, SP, Brazil (Tel.: ; mhungaro@fob.usp.br) Farsi et al. 2006, Bortoluzzi et al. 2007) and come into direct contact with pulpal or apical tissues. The biological properties of tricalcium silicate-based cements favour tissue repair. Bioactivity is a characteristic of MTA and tricalcium silicate-based cements (Camilleri et al. 2013, Cornelio et al. 2017). Furthermore, their physical and chemical properties such as solubility, ph and calcium ion release have been found to be satisfactory for a root-end material (Torabinejad et al. 1993, 1995). The low solubility assures 69

2 Effect of mixing methods on cements Duque et al. that the cement remains at the site where it is placed, promoting adequate filling and preventing bacterial leakage (Danesh et al. 2006). Alkaline ph and calcium ion release stimulate tissue repair and provide an antimicrobial environment (Estrela et al. 2000, Duarte et al. 2003). The mixing process of tricalcium silicate-based cements is performed manually to blend the powder and water on a glass slab, using a metal spatula. The mixture is complete when the cement is homogeneous (Darvell & Wu 2011). This consistency of MTA has been criticized in the literature (Holland et al. 2007, Duarte et al. 2012, Milani et al. 2013). Some authors have proposed changing the liquid of MTA to improve its handling (Ber et al. 2007, Holland et al. 2007, Hsieh et al. 2009, Duarte et al. 2012). Propylene glycol (20 80%) dissolved in distilled water increases the flowability of MTA (Duarte et al. 2012). This was later tested as liquid for tricalcium silicate-based cements with various radiopacifiers (Marciano et al. 2016). The mixing method has been also tested as a possible factor to enhance the handling characteristics of MTA (Nekoofar et al. 2010, Basturk et al. 2014). Trituration is a method of mixing used for preparing dental materials including amalgam, glass ionomer and even root canal sealers (Youdelis 1967, Miller et al. 1995, Zielinski et al. 2008). Trituration is mechanical agitation of a capsule containing the powder and liquid until they form a completely uniform mixture (Nekoofar et al. 2010). The use of ultrasonic agitation to mix materials has been also proposed (Nekoofar et al. 2010, Shahi et al. 2012, Basturk et al. 2014). This method for mixing MTA is associated with high surface microhardness (Nekoofar et al. 2010), but did not change the flexural strength, porosity or push-out bond strength (Shahi et al. 2012, Basturk et al. 2014). It is possible that the acoustic micro-streaming and/or cavitation promoted by ultrasonic activation (Roy et al. 1994), reduces the size of cement particles and consequently increases the area available to react with water during the hydration process. The aim of the study was to compare three mixing methods: manual, trituration and ultrasonic activation on flowability, setting time, volume change, solubility, ph and calcium ion release of two tricalcium silicatebased cements. The null hypothesis was that trituration and ultrasonic activation would not improve hydration, flowability, setting time, solubility, ph and calcium ion release nor reduce the volume change. Materials and methods The materials used in the study were MTA (Angelus, Londrina, Parana, Brazil) mixed with distilled water and Portland cement (PC, Irajazinho, Cimento Rio Branco, Rio de Janeiro, Brazil) with 20% of zirconium oxide (Sigma-Aldrich, St. Louis, MO, USA; PC-20-Zr), proportioned by weight, mixed with a liquid composed of 80% water (DW) and 20% propylene glycol (PG) (C 3 H 8 O 2 Pharmacia Specıfica, Bauru, S~ao Paulo, Brazil). The cements were divided according to the method of mixing: MTA-m MTA manually mixed using a spatula (control); MTA-tr MTA mixed using trituration; MTA-us MTA mixed using ultrasonic agitation; PC-20-Zr-m Portland cement with zirconium oxide manually mixed using a spatula; PC-20-Zr-tr Portland cement with zirconium oxide mixed using trituration; PC-20-Zr-us Portland cement with zirconium oxide mixed using ultrasonic agitation. For all the groups and tests, the cements were prepared using 3 : 1 powder-to-liquid ratio (1 g powder to 0.3 ml liquid). Manual mixing The liquid was added to the powder on a glass slab, and the cement was blended using a metal spatula. The cement was mixed for 1 min, until a homogeneous consistency was obtained. Trituration The liquid was added to the powder in an empty amalgam capsule. The capsule was closed and immediately triturated for 30 s, using an amalgamator (Gnatus, Ribeir~ao Preto, SP, Brazil) at 4500 rpm as proposed by Nekoofar et al. (2010). Ultrasonic activation The liquid was added to the powder on a glass slab, and the cement was blended using a metal spatula. After this, the cement was inserted in an empty and clean amalgam capsule. The cement was then agitated with a CPR-2D ultrasonic tip (Obtura Spartan, Fenton, MO, USA) coupled to an ultrasonic device (Suprasson P5; Satelec, Merignac, France) at a power setting of five and activated for 30 s. 70

3 Duque et al. Effect of mixing methods on cements Characterization of materials One disc 10 mm in diameter and 2 mm high was prepared with each material. After 24 h, the samples were stored in Hank s Balanced Salt Solution (HBSS, H6648, Sigma-Aldrich) at 37 C, for 28 days. At the end of the storage period, the specimens were removed from the solution and dried in a vacuum desiccator. They were then attached to aluminium stubs and viewed by scanning electron microscopy (Personal SEM (PSEM) express TM ; Aspex Corporation, Hillsboro, OR, USA). Scanning electron micrographs of the microstructural components at 5009 magnification in back-scatter electron mode were captured, and energy dispersive spectroscopy (EDS) was performed at a determined point (cement particle). Flowability A volume of 0.5 ml of cement, measured with a syringe, was placed on a glass plate according to ANSI/ ADA specification No. 57/2012. Three minutes after starting the mixing procedure, another plate with a mass of 20 2 g and a load of 100 g plus was applied centrally on top of the sample mass. Ten minutes after starting the mixing procedure, the load was removed, and the mean values of the largest and smallest diameters of the compressed cement were measured using a digital calliper with a precision of 0.01 mm (Mitutoyo MTI Corporation, Tokyo, Japan). Three measurements were performed for each material. Setting time The setting time was determined according to the American Society for Testing and Materials specifications (ASTM C266-08), but the samples were made in accordance with the International Standard Organization (ISO 6876:2012) specifications. The cements were mixed and placed into stainless steel rings with an internal diameter of 10 and 1 mm high. Three stainless steel rings were filled with each material. Then, a g Gillmore needle was used to determine the initial setting time. The final setting time was determined with a g Gillmore needle. This procedure was repeated at 60-s intervals. The setting times were considered to be the time when the needle did not leave any indentation on the specimen surface. Volume change The volume change test was performed using volumetric micro-ct measurements (Cavenago et al. 2014). Sixty acrylic teeth (n = 10) with a standardized root-end cavity 3 mm deep and 1.5 mm in diameter were used. The cavities were filled with the freshly mixed cement, and the samples were scanned using a desktop X-ray microfocus CT scanner (SkyScan 1174v2; SkyScan, Kontich, Belgium). The scanning was performed using 50 kv X-ray tube voltages, 800 la anode current. Four samples were scanned at a time. The image capture parameters used were a voxel size of 14.1 lm, with 1.1 rotation step in a 360 rotation. Each scan consisted of.tif images with pixels. Digital data were further transformed by reconstruction software (NReconv , SkyScan), and the CTan software (CTan v , SkyScan) was used for the volume measurements. In the CTan software, the total volume of cement was calculated in mm 3. After scanning, the samples were individually immersed in flasks containing 15 ml of ultrapure water and stored at 37 C for 7 and 14 days. After each time interval of immersion, the samples were dried with a gauze, scanned and immersed in a new flask containing 15 ml of ultrapure water. The volume change was determined in percentage, by calculating the volume of cement that was lost during immersion. Solubility Solubility of the cements was determined according to ADA Specification 57. Three cylindrical Teflon moulds 1.5 mm in thickness and 20 mm in internal diameter were filled with the material. An impermeable nylon thread was placed inside the material with the aim of keeping the specimens suspended and immersed in distilled water during the trial period. The moulds were placed on a glass plate covered with cellophane film, and after filling, another glass plate also covered with cellophane film was placed on the moulds and the assembly was placed in an incubator at 37 C and relative humidity of 95%, for a period corresponding to three times that of the setting time. Next, the samples were removed from the mould and residues and loose particles were removed with the use of a brush. The samples were weighed on an analytical balance with accuracy of g (UMark 210; Bel Engineering, Monza, Italy) and placed inside a plastic 71

4 Effect of mixing methods on cements Duque et al. vessel containing 50 ml of distilled water with care taken so that the samples were entirely immersed in water, without contact between the sample and the walls of the containers. The samples remained for 7 days and were then removed, thoroughly dried with filter paper, placed in desiccators for 24 h and reweighed. The solubility values were determined by the difference between the weight before and after water immersion, expressed in percentages. ph and calcium ion release Sixty acrylic teeth (n = 10) with a cavity 3 mm deep and 2 mm of diameter were filled with the materials and immediately immersed individually in 10 ml of deionized water and stored at 37 C. To avoid any interference with the results, all glass flasks were pretreated with nitric acid. After 3, 24, 72 and 168 h, the teeth were placed in new flasks containing an equal volume of new deionized water. The ph of the water in which the teeth had been kept was measured with a ph meter with a precision of 0.01 (model 371; Micronal, S~ao Paulo, SP, Brazil), previously calibrated using buffer solutions of ph 4, 7 and 14. After removing the specimens, the container was placed in a shaker (model 251; Farmem, S~ao Paulo, SP, Brazil) for 5 s before measuring. The room temperature during the readout was 25 C. Calcium ion release was determined using an atomic absorption spectrophotometer (AA6800; Shimadzu, Tokyo, Japan) equipped with a calcium-specific hollow cathode lamp under the following operating conditions: lamp current: 3 ma; fuel: acetylene; support: oxygen; stoichiometry: reducing; wavelength: nm; slit: 0.2 nm. The water in which calcium ion release was measured was the same used in the ph measurements. For determination of calcium ion release, an atomic absorption spectrophotometer (AA6800; Shimadzu, Tokyo, Japan) equipped with a calcium-specific hollow cathode lamp was used. The calcium ion release readouts were compared to a standard curve obtained from standard solutions. The calcium ion release was measured after time intervals of 3, 24, 72 and 168 h. Statistical analysis Statistical analysis was performed with two-way analysis of variance because of the presence of normal distribution confirmed by the D Agostino & Pearson analysis (P < 0.05). Results The scanning electron micrographs and EDS analysis of the hydrated MTA and PC-20-Zr are shown in Fig. 1(a,b). The MTA contained particles rich in calcium and silicon with traces of aluminium. Particles of bismuth were interspersed with the cement particles. The particles were more compacted when ultrasonic activation was applied. For PC-20-Zr, the group in which ultrasonic activation was used for mixing also had smaller particles. The PC-20-Zr was composed of cement particles of variable size with small zirconium oxide particles interspersed in the cement matrix. Figure 2 shows the representative micro-ct three-dimensional reconstructions to visualize the samples. The results for physical tests are represented in Table 1. The flowability of MTA and PC-20-Zr was not influenced by the mixing method (P > 0.05). The setting times (initial and final) varied amongst the test groups and two materials. The PC-20-Zr-m cement had the highest mean initial setting time values (109 65), whilst MTA-m showed the lowest values (37 2). Despite the high variability, no significant differences were verified for initial setting time amongst the groups (P > 0.05). For the final setting time, the PC-20-Zr-us cement (277 1) was significantly longer values than MTA-us (73 13; P < 0.05). For volume change, at 7 days of analysis, MTA-m had the lowest and at 14 days, MTA-us percentages were the lowest. No significant differences were verified amongst groups in all the periods of analysis (P > 0.05). For solubility, the mixing methods influenced the results compared to the conventional method (P < 0.05), except for the PC-20-Zr-tr group, which was not significantly different to the PC-20-Zr-m group (P > 0.05). The results of ph and calcium ion release are represented in Table 2. The ph at 3, 24 and 72 h was about 9 for all the groups evaluated (P > 0.05). At 168 h, significant differences were found between MTA-m ( ) and PC-20-Zr-m ( ; P < 0.05). The MTA-us ( ) values were significantly high at this period in comparison with PC-20-Zr-m ( ) and PC-20-Zr-us ( ; P < 0.05). The calcium ion release was higher at 3 h. The cement PC-20-Zr-tr ( ) released more calcium in this period with significant differences in relation to MTA-m ( ; P < 0.05). At 24 and 72 h, no significant differences were seen amongst 72

5 Duque et al. Effect of mixing methods on cements (a) (A) (B) (C) Figure 1 (a) Back-scatter scanning electron micrographs and EDS plots showing elemental composition of hydrated MTA cements (A MTA-m, B MTA-tr and C MTA-us), 5009 magnification. (b) Back-scatter scanning electron micrographs and EDS plots showing elemental composition of hydrated PC-20-Zr cements (A PC-20-Zr-m, B PC-20-Zr-tr and C PC-20-Zr-us), 5009 magnification. 73

6 Effect of mixing methods on cements Duque et al. (b) (A) (B) (C) Figure 1 Continued the groups (P > 0.05). At 168 h, MTA-tr ( ) had higher calcium release than PC-20-Zr-m ( ; P < 0.05). In the intragroup analysis, calcium ion release decreased as the period increased. Discussion Tricalcium silicate-based cements are hydraulic due to the reaction of particles with water (Darvell & Wu 74

7 Duque et al. Effect of mixing methods on cements Figure 2 Representative micro-ct three-dimensional reconstructions: Initial (green) and after 7 (blue) and 14 (red) days of immersion in the water. 2011). The Angelus manufacturer recommends covering the mixed cement with humid gauze to reduce evaporation and prolong the working time (Darvell & Wu 2011). MTA has been reported to have a consistency similar to that of wet sand after mixing (Holland et al. 2007, Duarte et al. 2012, Milani et al. 2013). These characteristics are considered unfavourable in clinical practice (Duarte et al. 2012). Trituration and ultrasonic activation are techniques that have been tested previously for MTA mixing (Nekoofar et al. 2010, Shahi et al. 2012, Basturk et al. 2014). In the present study, MTA was tested for flowability, setting time, volume change, solubility, ph and calcium ion release. Additionally, an experimental tricalcium silicate-based cement was tested (PC-20-Zr; Marciano et al. 2015). The results revealed that the mixing techniques did not influence the flowability of the cements. No differences were found amongst the groups (P > 0.05). Trituration or ultrasonic activation in the PC-20-Zr groups did not improve the flow in comparison with MTA groups. In the description of the test, the mean diameter of the cement interposed between two glass slabs was considered as the flowability of the material. However, according to the ISO standard 6876:2012, a material has to present a value of 20 mm and the MTA-tr, MTA-us and the PC-20-Zr-tr groups had values of 17 mm. The other groups performed below the minimum flow recommended by the ISO 6876:2012. Although the fluidity of the cement is evaluated using this methodology, the handling is not assessed. The setting time was determined according to the ASTM C standard; however, the size of the moulds was in accordance with the ISO 6876:2012 standard, to enable the use of a reasonable amount of cement (Duarte et al. 2012, Cavenago et al. 2014). The setting time of manually mixed MTA Angelus varies considerably in the literature. Cavenago et al. (2014) reported higher values than those found in the present study: 104 and 135 min for initial and final setting times, other studies have reported lower values: 15 and 30 min for initial and final setting (Duarte et al. 2012). The initial and final setting time of PC was approximate from that reported in literature using manual mixing. Duarte et al. (2003) reported 90 and 307 min for PC-20-Zr initial and final setting time. The mixing methods trituration and ultrasonic agitation did not significantly change the setting time compared with the manual mixing method. Significant differences were found only Table 1 Mean and standard deviation of physical tests. Different letters in each column indicate significant differences (P < 0.05) Group Flowability (mm) Initial setting time (min) Final setting time (min) Volume change 7 days (%) Volume change 14 days (%) Solubility 7 days (%) MTA-m a a ab a a a 0.11 MTA-tr a a ab a a b 0.34 MTA-us a a 5 73 a a a b 0.03 PC-20-Zr-m a a ab a a a 0.21 PC-20-Zr-tr a a ab a a a 0.61 PC-20-Zr-us a a b a a c 0.25 In solubility, negative values indicate an increase in weight. 75

8 Effect of mixing methods on cements Duque et al. Table 2 Mean and standard deviation of ph tests. Different lower cases in each column indicate statistically significant differences between materials (P < 0.05). Different upper cases in each row indicate significant differences in periods (P < 0.05) ph (ppm) Calcium release (mg L 1 ) 3 h 24 h 72 h 168 h 3 h 24 h 72 h 168 h Group MTA-m aa aa aa aca aa aac ab abbc MTA-tr ba aa aba aca aba aa aa aa MTA-us aba aa aba aa aba aa aa aba PC-20-Zr-m ba aa bb bb aba aac abc bb PC-20-Zr-tr aba aab abb bcb ba aab ab abb PC-20-Zr-us bab aa abb bcb aba aa aab abb between PC-us and MTA-us groups, where the PC-us group had a long final setting time than those of MTA-us (P > 0.05). This probably occurred because the liquid used to mix PC-20-Zr was composed of 80% water and 20% propylene glycol. Moreover, the particles of PC are coarser and contain calcium sulphate which could prolong the setting time (Duarte et al. 2003, Bortoluzzi et al. 2006). These factors together may explain why the setting times of PC-20- Zr specimens were longer than those of the MTA (Vivan et al. 2010, Duarte et al. 2012, Marciano et al. 2016). In the present study, the volume change was studied using a methodology proposed by Cavenago et al. (2014). In this test, the volume of material lost was measured. The design of the samples simulated clinical conditions with root-end cavities in acrylic teeth. For both cements, the mixing method did not influence the volume change at 7 and 14 days of immersion (P > 0.05). Shahi et al. (2015) observed that alternative mixing methods increased the solubility of cements. However, in the present study, the volume was considered. This variance in methodology may be the reason for the different results verified. ADA standard 57 was used to test the solubility of the cements. There was an increase of weight after 7 days in all groups. This may have occurred due to the fact that the cements used are hydrophilic, that is, they have the capacity to absorb water (Danesh et al. 2006, Bortoluzzi et al. 2009). This can lead to a false impression that these cements do not suffer from dissolution of particles; however, as seen in the volume change test, it is known that these cements, even in small proportions, suffer loss of particles. In the comparison between the groups, it was verified that the proposed mixing methods promoted a significant increase in the weight percentage of the cement compared to conventional manipulation (P < 0.05), with the exception of the PC-20-Zr-tr group, which was not different to the PC-20-Zr-m group (P > 0.05). Alkaline ph and calcium ion release are properties characteristic of tricalcium silicate-based cements. These properties are related to biological activity and induction of repair (Duarte et al. 2003, Vivan et al. 2010). The release of calcium ions was higher with trituration in comparison with manual method at 3 h and 168 h (P < 0.05). The ph results revealed an alkaline ph, irrespective of the mixing methods used. The ph values were very close amongst groups 76

9 Duque et al. Effect of mixing methods on cements (around 9), suggesting that the mixing method did not influence this property. Variable results can be found in literature using similar methodology, with some studies reporting similar results for manually mixed MTA Angelus (Duarte et al. 2003, De Vasconcelos et al. 2009), whilst others found lower values (Duarte et al. 2012, Cavenago et al. 2014). The lower ph values observed in other studies (Duarte et al. 2012, Cavenago et al. 2014) could be related with the manipulation that is difficult to be standardized in the studies. Another reason can be related with the diameter of the root-end cavity. In the present study, root-end cavities 2 mm in diameter were used. Statistical differences in ph could be found at 168 h differing from the results observed by Shahi et al. (2015) where alternative methods of manipulation have not different to manual methods. The MTA-us group had the greatest hydroxyl ion release than the PC-m group (P < 0.05). Although the capacity of the material to release calcium and hydroxyl ions is directly related to their solubility, alternative mixing methods increased release of these ions, without a substantial increase in solubility. Conclusion The ultrasonic and trituration methods were associated with higher ion calcium release and ph compared with manual mixing. The ultrasonic method produced more homogeneous distribution of particles. The ultrasonic and trituration methods promoted greater weight gain than the manual method in the solubility test. The other properties evaluated were not influenced by the mixing method used. Acknowledgements This work was supported by the State of S~ao Paulo Research Foundation (FAPESP 2015/ and 2014/ ). Conflict of interest The authors have stated explicitly that there are no conflict of interests in connection with this article. References Basturk FB, Nekoofar MH, Gunday M, Dummer PM (2014) Effect of various mixing and placement techniques on the flexural strength and porosity of mineral trioxide aggregate. Journal of Endodontics 40, Ber BS, Hatton JF, Stewart GP (2007) Chemical modification of ProRoot MTA to improve handling characteristics and decrease setting time. Journal of Endodontics 33, Bortoluzzi EA, Broon NJ, Bramante CM, Garcia RB, Moraes IG, Bernardineli N (2006) Sealing ability of MTA and radiopaque portland cement with or without calcium chloride for root-end filling. Journal of Endodontics 32, Bortoluzzi EA, Araujo GS, Guerreiro Tanomaru JM, Tanomaru-Filho M (2007) Marginal gingiva discoloration by gray MTA: a case report. Journal of Endodontics 33, Bortoluzzi EA, Broon NJ, Bramante CM, Felippe WT, Tanomaru Filho M, Esberard RM (2009) The influence of calcium chloride on the setting time, solubility, disintegration, and ph of mineral trioxide aggregate and white Portland cement with a radiopacifier. Journal of Endodontics 35, Camilleri J, Sorrentino F, Damidot D (2013) Investigation of the hydration and bioactivity of radiopacified tricalcium silicate cement, Biodentine and MTA Angelus. Dental Materials 29, Cavenago BC, Pereira TC, Duarte MA et al. (2014) Influence of powder-to-water ratio on radiopacity, setting time, ph, calcium ion release and a micro-ct volumetric solubility of white mineral trioxide aggregate. International Endodontic Journal 47, Cornelio AL, Rodrigues EM, Salles LP et al. (2017) Bioactivity of MTA Plus, Biodentine and experimental calcium silicate-based cements in human osteoblast-like cells. International Endodontic Journal 50, Danesh G, Dammaschke T, Gerth HU, Zandbiglari T, Sch afer E (2006) A comparative study of selected properties of ProRoot mineral trioxide aggregate and two Portland cements. International Endodontic Journal 39, Darvell BW, Wu RC (2011) MTA -an Hydraulic Silicate Cement: review update and setting reaction. Dental Materials 27, De Vasconcelos BC, Bernardes RA, Cruz SML et al. (2009) Evaluation of ph and calcium ion release of new root-end filling materials. Oral Surgery Oral Medicine Oral Pathology Oral Radiology and Endodontology 108, Duarte MA, Demarchi AC, Yamashita JC, Kuga MC, de Fraga SC (2003) ph and calcium ion release of 2 root-end filling materials. Oral Surgery Oral Medicine Oral Pathology Oral Radiology and Endodontology 95, Duarte MA, Alves de Aguiar K, Zeferino MA et al. (2012) Evaluation of the propylene glycol association on some physical and chemical properties of mineral trioxide aggregate. International Endodontic Journal 45, Estrela C, Bammann LL, Estrela CR, Silva RS, Pecora JD (2000) Antimicrobial and chemical study of MTA, Portland cement, calcium hydroxide paste, Sealapex and Dycal. Brazilian Dental Journal 11, 3 9. Farsi N, Alamoudi N, Balto K, Al Mushayt A (2006) Clinical assessment of mineral trioxide aggregate (MTA) as direct 77

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