Clin Oral Invest DOI 10.1007/s00784-015-1483-7
ORIGINAL ARTICLE
Physicochemical properties of calcium silicate cements associated with microparticulate and nanoparticulate radiopacifiers Roberta Bosso-Martelo 1 & Juliane M. Guerreiro-Tanomaru 1 & Raqueli Viapiana 1 & Fabio Luiz C. Berbert 1 & Marco Antonio Hungaro Duarte 1 & Mário Tanomaru-Filho 1
Received: 19 June 2014 / Accepted: 24 April 2015 # Springer-Verlag Berlin Heidelberg 2015
Abstract Objectives The objective of this paper was to evaluate the physicochemical properties of calcium silicate cements with different chemical compositions, associated with radiopacifying agents. Materials and methods Mineral trioxide aggregate (MTA) Angelus, calcium silicate cement with additives (CSC), and resinous calcium silicate cement (CSCR) were evaluated, with the addition of the following radiopacifiers: microparticles (micro) or nanoparticles (nano) of zirconium oxide (ZrO2), niobium oxide (Nb2O5), bismuth oxide (Bi2O3), or calcium tungstate (CaWO4). Setting time was evaluated using Gilmore needles. Solubility was determined after immersion in water. The pH and calcium ion release were analyzed after 3, 12, and 24 h and 7, 14, and 21 days. The data obtained were submitted to analysis of variance and Tukey’s test, at a level of significance of 5 %. Results CSC + CaWO4 and CSCR + ZrO2 micro, Nb2O5 and CaWO4 presented results similar to MTA, with a shorter final setting time than the other associations. CSC and CSCR+ ZrO2 micro presented a higher degree of flow. All the cements evaluated presented low solubility. The materials presented alkaline pH and released calcium ions. Conclusions ZrO2 micro radiopacifier may be considered a potential substitute for Bi2O3 when associated with CSC or CSCR. Clinical relevance The proposed materials, especially when associated with ZrO2, are potential materials for use as alternatives to MTA.
* Mário Tanomaru-Filho [email protected] 1
Araraquara School of Dentistry, Araraquara, São Paulo, Brazil
Keywords Portland cement . Radiopacity . Setting time . Calcium silicate cement . Radiopacifying agents
Introduction Mineral trioxide aggregate (MTA) is considered the ideal material for perforation treatment, retrograde filling, and other indications, due to its excellent biological and satisfactory physicochemical properties [1–3]. Asgary et al. [4] have reported that MTA and portland cement (PC) are calcium silicate cements (CSC) with a similar composition, except for bismuth oxide (Bi2O3), the radiopacifying agent of MTA. MTA has a long setting time [5] and is also difficult to manipulate and insert [6]. Different modifications to calcium silicate cements have been proposed, such as the addition of additives and resins to improve its manipulation and setting properties [7]. Camilleri [2] observed that the addition of radiopacifier Bi2O3 to MTA reduced the release of calcium hydroxide, increased solubility, and changed the dimensional stability of the material. The cell toxicity of Bi2O3 has been demonstrated by Gandolfi et al. [8]. New radiopacifiers have been evaluated as alternatives to Bi2O3 [9]. Húngaro Duarte et al. [9] observed that PC associated with Bi2O3, bismuth subnitrate, bismuth carbonate, iodoform, calcium tungstate (CaWO4), and zirconium oxide (ZrO2) provided adequate radiopacity for use as retrofilling material. Many studies investigated potential radiopacifying agents to replace Bi2O3 in MTA [10]. The replacement of Bi2O3 by ZrO2 in MTA may modify the mechanical properties of the material [11, 12]. Cutajar et al. [13] added different concentrations of ZrO2 to PC and observed that a combination of 30 % ZrO2 to PC had radiopacity, compressive strength, setting time, water absorption, and solubility similar to ProRoot MTA. They also showed that the addition of 30 % ZrO2 to PC
Clin Oral Invest
resulted in a material with properties comparable to MTA. Camilleri et al. [14] found that the hydration of PC with the addition of 30 % ZrO2 resulted in an increase in pH, calcium ion release, and bioactive potential. Antonijevic et al. [15] found that ZrO2 could be used as a substitute for Bi2O3 in MTA, because this radiopacifier does not alter the physical properties of MTA. Moreover, according to Liu et al. [11], the use of ZrO2 in nanoparticle form in bone cements has demonstrated bioactivity and cytocompatibility. Li et al. [16] have shown that the addition of 20 % ZrO2 nanoparticles to white PC improved its biocompatibility. ZrO2 is already present as a radiopacifying agent in Biodentine, a fast setting tricalcium silicate cement [17]. Another chemical element with favorable biological properties is niobium. Niobium oxide has been used in titanium alloys of endosseous implants, because of its excellent biocompatibility [18] and bioactive potential [19]. As a radiopacifying agent of PC, CaWO4 provided alkaline pH and calcium ion release [20], high compressive strength [21], antimicrobial activity [22], and biological compatibility [23]. Furthermore, when associated with PC in the proportion of 20 %, it provided a 3.11 mmAl radiopacity [9]. CaWO4 is a component of TheraCal, a resin-modified PC [17]. The physicochemical properties of experimental accelerated calcium silicate cements have been studied [24]. Calcium silicate cement with additives or resins may improve the consistency of the material and its association with ZrO2 or Nb2O5 microparticulate and nanoparticulate radiopacifiers. Its association with CaWO4 may improve the radiopacity and bioactive potential of the materials. The aim of this study was to evaluate the physicochemical and mechanical properties of two calcium silicate cements with different chemical compositions, associated with microparticulate or nanoparticulate radiopacifying agents.
Materials and methods Two cements with different chemical compositions were evaluated: a calcium silicate cement (Usina Fortaleza ICMF Ltda., Barueri, SP, Brazil), named in this study as CSC and composed of mineral aggregates, additives, and pigments, and a resinous calcium silicate cement (Ligatex Ind. e Com. Ltda., Rio Claro, SP, Brazil), named in this study as CSCR and composed of mineral aggregates, resins, additives, and pigments. They were used to formulate the experimental cements for the study. CSC and CSCR are type II portland cements. They contain calcium carbonate, tricalcium silicate, dicalcium silicate, tricalcium aluminate, tetracalcium aluminoferrite, and calcium sulfate. The additives used to accelerate the set cements are silicates, sodium carbonate, and calcium chloride. CSC and CSCR were evaluated in pure form or prepared in association with the following radiopacifying agents (% by
weight), which were mixed with distilled water using a powder/liquid ratio determined by pilot tests: & &
& &
& &
30 % microparticulated ZrO2 (ZrO2 micro, Sigma-Aldrich Brazil Ltda., São Paulo, SP, Brazil), mixed in a ratio of 1 g/ 200 μL for CSC and 1 g/235 μL for CSCR; 30 % nanoparticulated ZrO2 (ZrO2 nano, Nanotechnology Laboratory, Physics Institute, São Carlos, SP, Brazil), mixed in a ratio of 1 g/360 μL for CSC and 1 g/340 μL for CSCR; 30 % microparticulated Nb2O5 (Nb2O5 micro, SigmaAldrich Brasil Ltda., São Paulo, SP, Brazil), mixed in a ratio of 1 g/340 μL for CSC and 1 g/380 μL for CSCR; 30 % of nanoparticulated Nb 2 O 5 (Nb2O 5 nano, Nanotechnology laboratory, Physics Institute, São Carlos, SP, Brazil), mixed in a ratio of 1 g/390 μL for CSC and 1 g/380 μL for CSCR; 20 % Bi2O3 (Sigma-Aldrich Brazil Ltda., São Paulo, SP, Brazil), mixed in a ratio of 1 g/260 μL for CSC and 1 g/ 250 μL for CSCR; 30 % CaWO4 (Sigma Aldrich, St Louis, MO, USA), mixed in a ratio of 1 g/200 μL for CSC and 1 g/220 μL for CSCR.
According to the manufacturer, ZrO2 microparticles and Nb2O5 microparticles have a particle size of 5 and 1 μm, respectively. The nanoparticulate radiopacifiers were obtained by the polymeric precursor method performed by the São Carlos Physics Institute (University of São Paulo, São Carlos, Brazil). The zirconium oxide was prepared from precursor salt ZrO (NO3) 2·xH2O (Alfa Aesar). Aqueous solutions of this salt were prepared, mixed, and added to an aqueous solution of citric acid (at 60 °C), with constant stirring. Afterward, ethylene glycol (HOCH2CH2OH) was added to polymerize the citrate using a polyesterification reaction (at 120 °C). The citric acid/metal molar ratio was 3:1, whereas the citric acid/ethylene glycol mass ratio was 60:40. The resulting polymer resin was then calcined at 300 °C for 4 h, followed by 600 °C/2 h, to produce ZrO2 crystalline particles. As for producing the niobium oxide nanoparticles, an aqueous solution of niobium ammonium oxalate {NH4 [NbO (C2O4)2 (H2O)] (H2O) N (CBMM, Companhia Brasileira de Metalurgia e Mineração, Araxá, MG, Brazil) was prepared, and drops of ammonium hydroxide were then instilled in the solution. The niobium hydroxide precipitate was filtered and washed to eliminate oxalate ions, and then dissolved into a citric acid (CA) aqueous solution ([CA]/[Nb]=3). The niobium content in the solution was determined precisely by gravimetric analysis. The solution was stirred for 2 h at 70 °C to promote the complex reaction. Ethylene glycol (EG) was added to the mixture at a mass ratio of 60:40. The translucent solution was heated and stirred for several hours. A polymerization process started during water evaporation, resulting in a highly
Clin Oral Invest
viscous solution. This resin was heated in an electric furnace at 300 °C for 4 h. The resulting soft black mass was milled and calcined in an electric furnace for 2 h over alumina slabs at 700 °C for 2 h. A particle size of 74 nm was obtained for ZrO2, and 83 nm for Nb2O5, confirmed by the Brunauer-EmmettTeller surface area analysis.
Setting time Setting time was evaluated as follows: 6 test specimens were made for each material, using metal rings 10 mm in diameter and 1 mm high. A Gilmore needle having 100±0.5 g and a tip diameter of 2±0.1 mm was used to determine the initial setting time, as established by ISO 6876:2002 [25], and a Gilmore needle having 456±0.5 g and a tip diameter of 1± 0.1 mm was used to determine the final setting time, as established by ASTM standard C-266–03 [26]. The materials were kept in an oven at 37 °C and 95 % humidity throughout the analysis. The setting time of the cements was established by calculating the mean time elapsing from the time the materials were mixed up to when the Gillmore needle failed to leave an indentation on the surface of the specimens.
Solubility Carvalho-Júnior et al. [27] found that samples with smaller dimension could be a viable alternative for testing the solubility of root filling materials, based on Specification No. 57 of the American National Standard Institute/American Dental Association (ANSI/ADA) [28]. According to these findings, circular plastic molds measuring 1.5 mm high and 7.75 mm in diameter were fabricated, placed on a glass slide covered with cellophane film, and filled with one of the tested cements (n= 6). A nylon thread was embedded in the fresh mixture of the cement, and another glass slide also covered by cellophane was placed over the mold. The set was pressed manually and stored in an oven at a temperature of 37 °C for a period corresponding to three times the initial setting time of each material. The test specimens were removed from the molds, weighed on a precision balance (HM-200, A & D Engineering, Inc., Bradford, MA, USA), placed in plastic receptacles with lids and containing 7.5 mL of distilled and deionized water, and then suspended by nylon threads attached to the containers. The receptacles remained in the oven at 37 °C for 7 days, at which time the test specimens were removed from the distilled water, dried and placed in a dehumidifying chamber. The mass was measured before and after immersion of the samples in distilled water, and every 24 h thereafter, until attaining mass stabilization. The loss of mass was expressed as a percentage of the original mass.
Radiopacity The radiopacity test was performed based on ISO 6876 standards [25]. Teflon rings measuring 10 mm in diameter and 1 mm high were used to fabricate 6 test specimens of each material. The materials were kept at 37 °C and 100 % humidity for 48 h. After this period, they were placed on occlusal film (Insight—Kodak Comp, Rochester, NY, USA), next to an aluminum scale with a thickness ranging from 2 to 16 mm. Radiographs were taken with an X-ray appliance model GE 1000 (General Electric, Milwaukee, WI, USA), set to 50 kV, 10 mA, 18 pulses per second, and focal distance of 33 cm. The films were processed in an automatic developer (A/T 2000®XR, Air Techniques Inc., Hicksville, NY, USA). After digitizing the radiograph, the aluminum equivalence for each sample was determined in millimeters using the UTHSCSA ImageTool software for Windows version 3.0.
pH and calcium ion release The pH and calcium tests were performed by filling polyethylene tubes 10 mm long and 1 mm in diameter with each material (n=10). Each tube was immersed in 10 mL of distilled water and kept in an oven at 37 °C throughout the experimental periods. The tubes were removed from the flasks at each period and put into new flasks each containing 10 mL of distilled water. The experimental time periods were 3, 12, and 24 h and 7, 14, and 21 days. The pH of the solutions was measured immediately after the end of each experimental period, using a previously calibrated Ultrabasic pH meter (Denver Instrument Company, Arvada, CO, USA). The calcium ions were measured in an atomic absorption spectrophotometer H1170 Hilger & Watts (Rank Precision Industries Ltd. Analytical Division, London, UK). Distilled water was aspirated into a chamber, mixed with acetylene and an oxidant, and then burned (flame height=5 cm). The calcium released (mg/L) from the materials was quantified using a hollow cathode lamp specifically for calcium data readings (wavelength=422.7 nm and window of 0.7 nm), operated at 20 mA. The calcium ion readouts were compared with a standard curve, obtained with multiple calcium dilutions in ultrapure water.
Statistical analysis The results obtained for all the tests were submitted to the normality test. After proving the normality of the sample data distribution, the data were submitted to the parametric ANOVA statistical test and Tukey’s multiple comparisons test at a 5 % level of significance.
Clin Oral Invest
Results Setting time CSC associated with ZrO2 micro presented an initial setting time similar to that of MTA-Angelus. As regards to final setting time, CSC + CaWO4 was similar to MTA-Angelus. The use of Nb2O5 nano radiopacifier with CSC and pure CSC presented the longest initial and final setting times (p
ORIGINAL ARTICLE
Physicochemical properties of calcium silicate cements associated with microparticulate and nanoparticulate radiopacifiers Roberta Bosso-Martelo 1 & Juliane M. Guerreiro-Tanomaru 1 & Raqueli Viapiana 1 & Fabio Luiz C. Berbert 1 & Marco Antonio Hungaro Duarte 1 & Mário Tanomaru-Filho 1
Received: 19 June 2014 / Accepted: 24 April 2015 # Springer-Verlag Berlin Heidelberg 2015
Abstract Objectives The objective of this paper was to evaluate the physicochemical properties of calcium silicate cements with different chemical compositions, associated with radiopacifying agents. Materials and methods Mineral trioxide aggregate (MTA) Angelus, calcium silicate cement with additives (CSC), and resinous calcium silicate cement (CSCR) were evaluated, with the addition of the following radiopacifiers: microparticles (micro) or nanoparticles (nano) of zirconium oxide (ZrO2), niobium oxide (Nb2O5), bismuth oxide (Bi2O3), or calcium tungstate (CaWO4). Setting time was evaluated using Gilmore needles. Solubility was determined after immersion in water. The pH and calcium ion release were analyzed after 3, 12, and 24 h and 7, 14, and 21 days. The data obtained were submitted to analysis of variance and Tukey’s test, at a level of significance of 5 %. Results CSC + CaWO4 and CSCR + ZrO2 micro, Nb2O5 and CaWO4 presented results similar to MTA, with a shorter final setting time than the other associations. CSC and CSCR+ ZrO2 micro presented a higher degree of flow. All the cements evaluated presented low solubility. The materials presented alkaline pH and released calcium ions. Conclusions ZrO2 micro radiopacifier may be considered a potential substitute for Bi2O3 when associated with CSC or CSCR. Clinical relevance The proposed materials, especially when associated with ZrO2, are potential materials for use as alternatives to MTA.
* Mário Tanomaru-Filho [email protected] 1
Araraquara School of Dentistry, Araraquara, São Paulo, Brazil
Keywords Portland cement . Radiopacity . Setting time . Calcium silicate cement . Radiopacifying agents
Introduction Mineral trioxide aggregate (MTA) is considered the ideal material for perforation treatment, retrograde filling, and other indications, due to its excellent biological and satisfactory physicochemical properties [1–3]. Asgary et al. [4] have reported that MTA and portland cement (PC) are calcium silicate cements (CSC) with a similar composition, except for bismuth oxide (Bi2O3), the radiopacifying agent of MTA. MTA has a long setting time [5] and is also difficult to manipulate and insert [6]. Different modifications to calcium silicate cements have been proposed, such as the addition of additives and resins to improve its manipulation and setting properties [7]. Camilleri [2] observed that the addition of radiopacifier Bi2O3 to MTA reduced the release of calcium hydroxide, increased solubility, and changed the dimensional stability of the material. The cell toxicity of Bi2O3 has been demonstrated by Gandolfi et al. [8]. New radiopacifiers have been evaluated as alternatives to Bi2O3 [9]. Húngaro Duarte et al. [9] observed that PC associated with Bi2O3, bismuth subnitrate, bismuth carbonate, iodoform, calcium tungstate (CaWO4), and zirconium oxide (ZrO2) provided adequate radiopacity for use as retrofilling material. Many studies investigated potential radiopacifying agents to replace Bi2O3 in MTA [10]. The replacement of Bi2O3 by ZrO2 in MTA may modify the mechanical properties of the material [11, 12]. Cutajar et al. [13] added different concentrations of ZrO2 to PC and observed that a combination of 30 % ZrO2 to PC had radiopacity, compressive strength, setting time, water absorption, and solubility similar to ProRoot MTA. They also showed that the addition of 30 % ZrO2 to PC
Clin Oral Invest
resulted in a material with properties comparable to MTA. Camilleri et al. [14] found that the hydration of PC with the addition of 30 % ZrO2 resulted in an increase in pH, calcium ion release, and bioactive potential. Antonijevic et al. [15] found that ZrO2 could be used as a substitute for Bi2O3 in MTA, because this radiopacifier does not alter the physical properties of MTA. Moreover, according to Liu et al. [11], the use of ZrO2 in nanoparticle form in bone cements has demonstrated bioactivity and cytocompatibility. Li et al. [16] have shown that the addition of 20 % ZrO2 nanoparticles to white PC improved its biocompatibility. ZrO2 is already present as a radiopacifying agent in Biodentine, a fast setting tricalcium silicate cement [17]. Another chemical element with favorable biological properties is niobium. Niobium oxide has been used in titanium alloys of endosseous implants, because of its excellent biocompatibility [18] and bioactive potential [19]. As a radiopacifying agent of PC, CaWO4 provided alkaline pH and calcium ion release [20], high compressive strength [21], antimicrobial activity [22], and biological compatibility [23]. Furthermore, when associated with PC in the proportion of 20 %, it provided a 3.11 mmAl radiopacity [9]. CaWO4 is a component of TheraCal, a resin-modified PC [17]. The physicochemical properties of experimental accelerated calcium silicate cements have been studied [24]. Calcium silicate cement with additives or resins may improve the consistency of the material and its association with ZrO2 or Nb2O5 microparticulate and nanoparticulate radiopacifiers. Its association with CaWO4 may improve the radiopacity and bioactive potential of the materials. The aim of this study was to evaluate the physicochemical and mechanical properties of two calcium silicate cements with different chemical compositions, associated with microparticulate or nanoparticulate radiopacifying agents.
Materials and methods Two cements with different chemical compositions were evaluated: a calcium silicate cement (Usina Fortaleza ICMF Ltda., Barueri, SP, Brazil), named in this study as CSC and composed of mineral aggregates, additives, and pigments, and a resinous calcium silicate cement (Ligatex Ind. e Com. Ltda., Rio Claro, SP, Brazil), named in this study as CSCR and composed of mineral aggregates, resins, additives, and pigments. They were used to formulate the experimental cements for the study. CSC and CSCR are type II portland cements. They contain calcium carbonate, tricalcium silicate, dicalcium silicate, tricalcium aluminate, tetracalcium aluminoferrite, and calcium sulfate. The additives used to accelerate the set cements are silicates, sodium carbonate, and calcium chloride. CSC and CSCR were evaluated in pure form or prepared in association with the following radiopacifying agents (% by
weight), which were mixed with distilled water using a powder/liquid ratio determined by pilot tests: & &
& &
& &
30 % microparticulated ZrO2 (ZrO2 micro, Sigma-Aldrich Brazil Ltda., São Paulo, SP, Brazil), mixed in a ratio of 1 g/ 200 μL for CSC and 1 g/235 μL for CSCR; 30 % nanoparticulated ZrO2 (ZrO2 nano, Nanotechnology Laboratory, Physics Institute, São Carlos, SP, Brazil), mixed in a ratio of 1 g/360 μL for CSC and 1 g/340 μL for CSCR; 30 % microparticulated Nb2O5 (Nb2O5 micro, SigmaAldrich Brasil Ltda., São Paulo, SP, Brazil), mixed in a ratio of 1 g/340 μL for CSC and 1 g/380 μL for CSCR; 30 % of nanoparticulated Nb 2 O 5 (Nb2O 5 nano, Nanotechnology laboratory, Physics Institute, São Carlos, SP, Brazil), mixed in a ratio of 1 g/390 μL for CSC and 1 g/380 μL for CSCR; 20 % Bi2O3 (Sigma-Aldrich Brazil Ltda., São Paulo, SP, Brazil), mixed in a ratio of 1 g/260 μL for CSC and 1 g/ 250 μL for CSCR; 30 % CaWO4 (Sigma Aldrich, St Louis, MO, USA), mixed in a ratio of 1 g/200 μL for CSC and 1 g/220 μL for CSCR.
According to the manufacturer, ZrO2 microparticles and Nb2O5 microparticles have a particle size of 5 and 1 μm, respectively. The nanoparticulate radiopacifiers were obtained by the polymeric precursor method performed by the São Carlos Physics Institute (University of São Paulo, São Carlos, Brazil). The zirconium oxide was prepared from precursor salt ZrO (NO3) 2·xH2O (Alfa Aesar). Aqueous solutions of this salt were prepared, mixed, and added to an aqueous solution of citric acid (at 60 °C), with constant stirring. Afterward, ethylene glycol (HOCH2CH2OH) was added to polymerize the citrate using a polyesterification reaction (at 120 °C). The citric acid/metal molar ratio was 3:1, whereas the citric acid/ethylene glycol mass ratio was 60:40. The resulting polymer resin was then calcined at 300 °C for 4 h, followed by 600 °C/2 h, to produce ZrO2 crystalline particles. As for producing the niobium oxide nanoparticles, an aqueous solution of niobium ammonium oxalate {NH4 [NbO (C2O4)2 (H2O)] (H2O) N (CBMM, Companhia Brasileira de Metalurgia e Mineração, Araxá, MG, Brazil) was prepared, and drops of ammonium hydroxide were then instilled in the solution. The niobium hydroxide precipitate was filtered and washed to eliminate oxalate ions, and then dissolved into a citric acid (CA) aqueous solution ([CA]/[Nb]=3). The niobium content in the solution was determined precisely by gravimetric analysis. The solution was stirred for 2 h at 70 °C to promote the complex reaction. Ethylene glycol (EG) was added to the mixture at a mass ratio of 60:40. The translucent solution was heated and stirred for several hours. A polymerization process started during water evaporation, resulting in a highly
Clin Oral Invest
viscous solution. This resin was heated in an electric furnace at 300 °C for 4 h. The resulting soft black mass was milled and calcined in an electric furnace for 2 h over alumina slabs at 700 °C for 2 h. A particle size of 74 nm was obtained for ZrO2, and 83 nm for Nb2O5, confirmed by the Brunauer-EmmettTeller surface area analysis.
Setting time Setting time was evaluated as follows: 6 test specimens were made for each material, using metal rings 10 mm in diameter and 1 mm high. A Gilmore needle having 100±0.5 g and a tip diameter of 2±0.1 mm was used to determine the initial setting time, as established by ISO 6876:2002 [25], and a Gilmore needle having 456±0.5 g and a tip diameter of 1± 0.1 mm was used to determine the final setting time, as established by ASTM standard C-266–03 [26]. The materials were kept in an oven at 37 °C and 95 % humidity throughout the analysis. The setting time of the cements was established by calculating the mean time elapsing from the time the materials were mixed up to when the Gillmore needle failed to leave an indentation on the surface of the specimens.
Solubility Carvalho-Júnior et al. [27] found that samples with smaller dimension could be a viable alternative for testing the solubility of root filling materials, based on Specification No. 57 of the American National Standard Institute/American Dental Association (ANSI/ADA) [28]. According to these findings, circular plastic molds measuring 1.5 mm high and 7.75 mm in diameter were fabricated, placed on a glass slide covered with cellophane film, and filled with one of the tested cements (n= 6). A nylon thread was embedded in the fresh mixture of the cement, and another glass slide also covered by cellophane was placed over the mold. The set was pressed manually and stored in an oven at a temperature of 37 °C for a period corresponding to three times the initial setting time of each material. The test specimens were removed from the molds, weighed on a precision balance (HM-200, A & D Engineering, Inc., Bradford, MA, USA), placed in plastic receptacles with lids and containing 7.5 mL of distilled and deionized water, and then suspended by nylon threads attached to the containers. The receptacles remained in the oven at 37 °C for 7 days, at which time the test specimens were removed from the distilled water, dried and placed in a dehumidifying chamber. The mass was measured before and after immersion of the samples in distilled water, and every 24 h thereafter, until attaining mass stabilization. The loss of mass was expressed as a percentage of the original mass.
Radiopacity The radiopacity test was performed based on ISO 6876 standards [25]. Teflon rings measuring 10 mm in diameter and 1 mm high were used to fabricate 6 test specimens of each material. The materials were kept at 37 °C and 100 % humidity for 48 h. After this period, they were placed on occlusal film (Insight—Kodak Comp, Rochester, NY, USA), next to an aluminum scale with a thickness ranging from 2 to 16 mm. Radiographs were taken with an X-ray appliance model GE 1000 (General Electric, Milwaukee, WI, USA), set to 50 kV, 10 mA, 18 pulses per second, and focal distance of 33 cm. The films were processed in an automatic developer (A/T 2000®XR, Air Techniques Inc., Hicksville, NY, USA). After digitizing the radiograph, the aluminum equivalence for each sample was determined in millimeters using the UTHSCSA ImageTool software for Windows version 3.0.
pH and calcium ion release The pH and calcium tests were performed by filling polyethylene tubes 10 mm long and 1 mm in diameter with each material (n=10). Each tube was immersed in 10 mL of distilled water and kept in an oven at 37 °C throughout the experimental periods. The tubes were removed from the flasks at each period and put into new flasks each containing 10 mL of distilled water. The experimental time periods were 3, 12, and 24 h and 7, 14, and 21 days. The pH of the solutions was measured immediately after the end of each experimental period, using a previously calibrated Ultrabasic pH meter (Denver Instrument Company, Arvada, CO, USA). The calcium ions were measured in an atomic absorption spectrophotometer H1170 Hilger & Watts (Rank Precision Industries Ltd. Analytical Division, London, UK). Distilled water was aspirated into a chamber, mixed with acetylene and an oxidant, and then burned (flame height=5 cm). The calcium released (mg/L) from the materials was quantified using a hollow cathode lamp specifically for calcium data readings (wavelength=422.7 nm and window of 0.7 nm), operated at 20 mA. The calcium ion readouts were compared with a standard curve, obtained with multiple calcium dilutions in ultrapure water.
Statistical analysis The results obtained for all the tests were submitted to the normality test. After proving the normality of the sample data distribution, the data were submitted to the parametric ANOVA statistical test and Tukey’s multiple comparisons test at a 5 % level of significance.
Clin Oral Invest
Results Setting time CSC associated with ZrO2 micro presented an initial setting time similar to that of MTA-Angelus. As regards to final setting time, CSC + CaWO4 was similar to MTA-Angelus. The use of Nb2O5 nano radiopacifier with CSC and pure CSC presented the longest initial and final setting times (p
