Solubility and Disintegration of New Calcium Aluminate Cement ...

Basic Research—Technology

Solubility and Disintegration of New Calcium Aluminate Cement (EndoBinder) Containing Different Radiopacifying Agents Lucas da Fonseca Roberti Garcia, DDS, MSc, PhD,* Michelle Alexandra Chinelatti, DDS, MSc, PhD,* Hebert Luis Rossetto, B Eng, MSc, PhD,† and Fernanda de Carvalho Panzeri Pires-de-Souza, DDS, MSc, PhD* Abstract Introduction: The aim of this study was to evaluate the solubility and disintegration of EndoBinder (EB) containing 3 different radiopacifying agents, bismuth oxide (Bi2O3), zinc oxide (ZnO), or zirconium oxide (ZrO2), in comparison with gray mineral trioxide aggregate (GMTA) and white MTA (WMTA). Methods: Ten specimens of each cement were made in a stainless steel matrix (20 1.5 mm) according to Specification no. 57 of American National Standards Institute/American Dental Association: EB + Bi2O3, EB + ZrO, EB + ZnO, WMTA, and GMTA. The specimens were weighed on an accurate analytical scale and immersed in 50 mL distilled and deionized water at 37 C for 7 days. Afterwards, specimens were dried and weighed again to determine mass loss (%). Resulting solutions were analyzed in an atomic absorption spectrophotometer for identification and quantification of chemical elements released. Results: All cements presented mean values of solubility and disintegration above the American National Standards Institute/American Dental Association Specification no. 57. EB + Bi2O3 presented the lowest mass loss (5.08%) and WMTA (6.65%) the highest, with no statistically significant difference (P > .05). The release of several chemical elements was observed, mostly metal ions. Only GMTA and EB + Bi2O3 showed the presence of Cr, with significant difference (P < .05). EB + ZnO presented the highest levels of Pb, followed by WMTA (P < .05). For As, the cements presented different release levels, with EB + ZnO showing the highest and GMTA the lowest levels (P < .05). However, the amounts of As and Pb released were lower than the safe limit proposed by ISO 9917-1. Conclusions: Irrespective of the radiopacifying agents used, EndoBinder presented similar behavior to MTA. (J Endod 2014;40:261–265)

Key Words Arsenic, calcium aluminate cement, lead, MTA, solubility

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ertain procedures performed during endodontic therapy require a specific sealing cement to obtain a successful treatment (1). This cement must be biocompatible (2), noncarcinogenic and non-genotoxic (3), must not stain dental structures (4), must be radiopaque (5), and be insoluble in oral fluids (6). Mineral trioxide aggregate (MTA) was originally developed for retrograde filling and treatment of radicular and furcal perforations (1), and because of its good clinical performance, it has been used in several other applications such as pulpotomy and pulp capping (1). However, some of the negative features of MTA must be pointed out, such as the long setting time (1), poor handling characteristics (7), low compressive strength (8), low flow capacity (9), high incidence of dental structure staining (4), high solubility (6), and presence and release of arsenic (2, 10), with levels above those recommended by the ISO 9917-1 standard (11). MTA has undergone a series of modifications in its original formulation because of its poor handling characteristics and long setting time (7). Studies in which these cement compositions have been analyzed have demonstrated that Angelus MTA presents a higher quantity of calcium carbonate, calcium silicate, and zinc-barium phosphate than the conventional types, thus contributing to a significant improvement in its physicochemical properties (1). Although the MTA setting time is lower than that of Portland cement, it is still considered long enough to make the material unstable when in contact with moisture before it has completely hardened (7, 9). Considering effects such as these, the development of new materials with adequate biological and physicochemical properties is justified (6). Therefore, a new calcium aluminate–based cement called EndoBinder (Binderware, S~ao Carlos, SP, Brazil) was developed by the Federal University of S~ao Carlos (UFSCar-Brazil, patent number PI0704502-6) to preserve the properties and clinical applications of MTA without its negative features. EndoBinder is composed of (% by weight) Al2O3 ($68.0), CaO (#31.0), SiO2 (0.3–0.8), MgO (0.4–0.5), and Fe2O3 ( .05). The mean values of different chemical elements released by the cements after the solubility and disintegration test are shown in Table 3. The release of several chemical elements was observed, mostly metal ions. Only GMTA and EB + Bi2O3 showed the presence of Cr, with statistically significant difference (P < .05). EB + ZnO presented the highest levels of Pb, followed by WMTA (P < .05). For As, the cements presented different levels of release, with the highest shown by EB + ZnO and the lowest by GMTA (P < .05). However, the amounts of As and Pb released were below the safe limit proposed by the ISO 9917-1 Specification (11). With regard to Ca release, WMTA presented the highest levels and GMTA the lowest, with significant difference between them and in comparison with the other cements (P < .05). EndoBinder presented intermediate values, with the highest being shown by EB + ZnO, with statistically significant difference from the other cements (P < .05).

Discussion Radiopacity is one of the most important properties of materials used in endodontic therapy (5). Therefore, cements used for this JOE — Volume 40, Number 2, February 2014

Basic Research—Technology TABLE 2. Mean Values (%) and Standard Deviation for the Solubility and Disintegration Test Cements EB + Bi2O3 5.08 (0.010)

EB + ZrO2 5.65 (0.009)

EB + ZnO 5.13 (0.008)

GMTA 5.74 (0.022)

WMTA 6.65 (0.022)

There was no statistically significant difference among groups (1-way ANOVA, Bartlett test, P < .05).

purpose must have a radiopacifying agent in their composition, which allows them to be observed radiographically (5). The ideal radiopacifying agent should be inert, and the minimum possible quantity of it should be added to cement formulation (5), taking into account that this minimum quantity must be of a material composed of elements with high atomic numbers. The Bi2O3 used in the MTA composition increases its radiopacity, with values higher than the Al scale (5). However, Bi2O3 is not inert and interferes in the hydration mechanism of the material, decreasing calcium ion release by the cement, altering its reparative capacity and several physicochemical properties (20, 21). Therefore, alternative radiopacifying agents have been proposed (5), with emphasis on zinc and zirconium oxides. These agents are widely used in prosthodontics and in dental implant areas because of their biocompatibility and because they do not promote changes in the chemical and physico-mechanical properties of these materials (22). A sealing cement should promote hermetic sealing close to the area of application to prevent bacterial migration to pulp and periodontal tissues, thereby controlling infection and preventing its recurrence (18). Solubility and disintegration is a physicochemical property directly related to this sealing capacity, because it is responsible for maintaining the dimensions of the cement after it has been applied (18). According to the results of the present study, the sealing capacity of both MTA and EndoBinder, irrespective of the radiopacifying agents used, would be compromised, because the tested cements presented similar behavior, with a mass loss exceeding 3%, a value above the limit proposed by Specification no. 57 of ANSI/ADA (19). However, studies have demonstrated that this solubilization does not contraindicate the use of MTA, because its good biological performance is related to the ability to release Ca and hydroxyl ions into the medium during its continuous hydration process (18). Studies have reported that Ca ions are the main components detected in soluble and insoluble residues released by MTA, demonstrating that the cement solubility is an important phenomenon in the delivery of Ca and

hydroxyl ions to periodontal and pulp tissues (17, 23). When used as root-end filling material, Ca ion release promotes an alkaline pH of the medium, leading to a biochemical process, which in turn accelerates the reparative process (1). In many clinical situations, the application of wet cotton wool on a restoration performed with MTA is recommended, because it improves its biological performance in shorter periods of time, favoring the separation of particles that come in contact with tissues, initiating an inflammatory process that leads to their repair (24). The same can be observed for EndoBinder, a hydraulic cement similar to MTA, in which the physicochemical interaction of the cement with moisture is essential, especially as far as its reparative capacity is concerned (25). During the hydration process of MTA, calcium silicate hydrate, a by-product of calcium hydroxide, is formed (21). The reaction of calcium silicate in moist conditions promotes hydrogenation of CaO and Ca(OH)2, releasing a high concentration of Ca ions (21). The Ca ions released are produced from the Ca(OH)2 present and from the decomposition of calcium silicate hydrate, which is released at a slower rate in comparison with Ca(OH)2 (21). The hydration process of calcium aluminate–based cements, such as EndoBinder, leads to the formation of hydrates of calcium aluminate and aluminum hydroxide (26). Thus, the release of Ca ions by cement occurs as a result of decomposition of calcium aluminate hydrate at a slower rate than in MTA, which could explain the higher levels of release for WMTA than for EndoBinder after 7 days of immersion in distilled and deionized water (25). The same cannot be said about GMTA, which obtained the lowest levels, leading us to believe that the higher concentration of Fe2O3 in this cement may have an influence on Ca ion release (21). Therefore, it is worth emphasizing that control of the levels of impurities such as Fe2O3, which the EndoBinder synterization process allows, plays a relevant role in the release of Ca ions by the cement (25). The hydration process of hydraulic cements such as EndoBinder presents 3 different phases: ion dissolution, nucleation, and

TABLE 3. Mean Values (mg/kg - ppm) and Standard Deviation of Chemical Elements Released by the Different Cements Chemical element Ru Pb Ni Cr As Cu Cd Ca

Cements EB + Bi2O3 0.00036A (0.00003) 0.000074A (0.00004) 0.00454A (0.00116) 0.00009A (0.00048) 0.00020A (0.00003) —

EB + ZrO2 0.00023B (0.00001) 0.000090A (0.000054) 0.00451A (0.00224) —

EB + ZnO 0.00025B (0.00001) 0.000916C (0.000239) 0.00641A (0.00201) —

GMTA 0.00013C (0.00007) 0.000069A (0.000061) —

0.00026B (0.00002) —

0.00035C (0.00005) —

0.00303B (0.00226) 0.00009D (0.00002) —

0.000009A (0.000005) 122.758A (4.61)

0.000065B (0.000032) 122.146A (10.15)

0.000043B (0.000027) 192.528B (15.75)

0.000007A (0.000008) 23.279C (11.09)

WMTA 0.00077D (0.00007) 0.000419B (0.000092) 0.01960B (0.00164) — 0.00014E (0.00004) 0.00009 (0.00227) 0.000008A (0.000005) 571.743D (30.45)

Different uppercase letters indicate statistically significant difference (1-way ANOVA, Tukey test, P < .05).

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Basic Research—Technology precipitation of hydrated phases (25). As EndoBinder particles come into contact with water, anhydrous phases of calcium aluminate are dissociated, releasing Ca and hydroxyl ions into the medium (27). Dissolution continues until the concentration of ions is saturated, initiating their precipitation in the form of calcium aluminate hydrates, by the mechanisms of nucleation and growth (25). The precipitation of hydrated cement particles reduces the concentration of ions in the solution at levels below the saturation point, allowing dissociation and formation of anhydrous phases. This fact results in a continuous process of dissolution/precipitation until most or all of the anhydrous phase has reacted (25). Nevertheless, with respect to EndoBinder, the water/cement ratio and temperature are crucial for formation of the resulting phases of the hydration process (25). Under experimental conditions (temperature = 37 C and cement/water ratio = 0.21), more stable phases, AH3 (Al2O3.3H2O) and C3AH6 (3CaO.Al2O3.6H2O), are favored (27). Therefore, it is understood that not only the humid medium in which the cement is used but also the handling conditions of the material before it is applied are important factors for an adequate release of hydroxyl and Ca ions (27). In the present study, several other elements, mostly heavy metals, were detected in the resulting solutions from the solubility and disintegration test, with emphasis on As, Cr, and Pb, because of their cytotoxic potential (2, 28). According to the ISO 9917-1 Standard (11), materials used for dental procedures should not present more than 2 mg/kg As. As is a metalloid element found in air, soil, and water, in organic and inorganic forms, and in different oxidation levels (29). Its toxicity depends on its chemical form and oxidation state, with the trivalent and pentavalent stages of oxidation being the most toxic (29). The carcinogenic effect of As could be explained by the alterations that occur in DNA repair. Trivalent arsenic compounds such as arsenite may strongly bond to sulfhydryl and dithiol groups, subsequently leading to genetic mutations and increased cellular proliferation, inducing subsequent mutations because of DNA repair inhibition (29). Some studies have demonstrated the presence and release of As in levels exceeding the safe limit proposed by the ISO 9917-1 Standard (11) for Portland cements (10) and MTA (30). However, Duarte et al (2), who evaluated many different types of Portland and MTA cements, including Gray ProRoot-MTA and Angelus MTA, the same cements as those used in the present study, observed levels right below the limit suggested by ISO 9917-1 (11). It is valid to emphasize that Duarte et al evaluated the release by and not the presence of As in these cements, leaving unanswered the question of whether the As levels in these materials are within the safe standard limits (10). Moreover, the amount of As present in Portland cement and MTA is directly related to differences in the material formulations and manufacturing processes (10). The higher As content does not necessarily indicate a greater release of As into the medium. In the case of GMTA, the higher concentration of Fe2O3, which is responsible for the dark color of the cement, stabilizes the As content, decreasing As release (10). This fact may explain the contradictory results obtained in different studies with regard to As release from different forms of MTAs and Portland cements. Few studies have reported levels of contamination with Pb and Cr for MTA (30, 31). Pb has also been reported as cytotoxic and genotoxic (28); however, the levels for EndoBinder and MTA observed in the present study were below the safe limit suggested by ISO 9917-1 (11), which is 11 mg/kg; these results are similar to those found by Chang et al (31). With respect to Cr, another carcinogenic and mutagenic element (32), ISO 9917-1 (11) does not specify the safe limit for dental application. However, a Material Safety Data Sheet (33) reported that the 264

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lethal dose of Cr, enough to kill a rat, would be 1.790 mg/kg (ppm). Furthermore, Gad (34) reported that the human body has an efficient disintoxication mechanism when exposed to some degree of Cr. In the present study only EB + Bi2O3 and GMTA showed the presence of Cr in the resulting solutions, with values below the one proposed by the Material Safety Data Sheet (33). Therefore, it could be stated that the Cr released from the tested cements would not lead to a serious health problem, because the amount released was negligible (32). Another relevant situation, not only in regard to the elements listed above but for all those detected in the resulting solutions, is that most of the releasing occurs in the first 15 days of cement hydration process (30). Clinically, this situation is important because it demonstrates that in long-term, there are no problems caused by the continuous release of metal ions to the adjacent tissues (30). On the basis of the results obtained in this study, the tested hypothesis was rejected. Irrespective of the radiopacifying agent used, EndoBinder and MTA presented similar solubility and disintegration, with values exceeding the limit proposed by ANSI/ADA. In addition, the cements showed the release of heavy metal ions, within safe limits.

Acknowledgments The authors deny any conflicts of interest related to this study.

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