Study of the bismuth oxide concentration required to provide Portland cement with adequate radiopacity for endodontic use

Transcription

1 Study of the bismuth oxide concentration required to provide Portland cement with adequate radiopacity for endodontic use Carlos Eduardo da Silveira Bueno, DDs, MSc, PhD, Eduardo Gregatto Zeferino, DDS, Luiz Roberto Coutinho Manhães, Jr., DDS, MSc, PhD, Daniel Guimarães Pedro Rocha, DDS, MSc, Rodrigo Sanches Cunha, DDS, MSc, PhD, and Alexandre Sigrist De Martin, DDS, MSc, PhD, Campinas, Brazil SÃO LEOPOLDO MANDIC UNIVERSITY Objective: The purpose of this study was to determine the ideal concentration of bismuth oxide in white Portland cement to provide it with sufficient radiopacity for use as an endodontic material (ADA specification #57). Study design: 2-mm thick standardized test specimens of white MTA and of white Portland cement, as controls, and of white Portland cement with the experimental addition of 5%, 10%, 15%, 20%, 25% or 30% of bismuth oxide were radiographed and compared with various thicknesses of pure aluminum, using optic density to determine the observed grayscale levels of radiopacity in a scale ranging from 0 to 255. The data was submitted to ANOVA (p 0.05) and the Ryan-Einot-Gabriel-Welch and Quiot test (REGWQ) for multiple comparison of the means. Results: White Portland cement with 0%, 5%, 10%, 15%, 20%, 25% and 30% of bismuth oxide presented mean readings of 63.3, 95.7, 110.7, 142.7, 151.3, and respectively. MTA presented a mean reading of The readings of MTA and white Portland cement with 15% bismuth oxide did not differ significantly from the reading observed for a thickness of 4 mm of aluminum (145.3), which is considered ideal for a test specimen by ADA specification #57 (2 mm above the thickness of the test specimen). Conclusion: White MTA and white Portland cement with 15% bismuth oxide presented the radiopacity required for an endodontic cement. (Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2009;107:e65-e69) Mineral trioxide aggregate (MTA) is a material that was developed at the University of Loma Linda in the 1990s. 1 Use of this material has yielded favorable results for cases of root perforation compared with other materials because of its good sealing ability. 2,3 MTA has also been used for capping of pulps with reversible pulpitis, for apexification, for repair of root perforations nonsurgically and surgically, as a root-end filling material, to protect the dental pulp directly in pulpotomies, as a coronal plug after complete obturation of the root canal system, and before internal bleaching of discolored teeth. 4 Suitable physical and biologic properties have been associated with this material, such as good tolerability in contact with bone and conjunctive tissues, 1,5-10 low cytotoxicity and genotoxity, 1,11,12 good sealing ability, 2,3,13-15 antimicrobial action, low solubility, 19 good setting and working time, 19 and radiopacity suitable for use as an endodontic material. 19 Endodontic Area, Center for Dental Research. Received for publication Jul 24, 2008; returned for revision Aug 11, 2008; accepted for publication Sep 22, /$ - see front matter 2009 Mosby, Inc. All rights reserved. doi: /j.tripleo Various studies have demonstrated that MTA and Portland cement have a very similar chemical composition, 1,11,20,21 except for the presence of bismuth oxide, which is contained in MTA and imparts radiopacity to the material. Other studies have compared Portland cement with MTA and observed that they had the same sealing ability in root-end fillings, 13,14 in perforations of the tooth s middle third, 22 and in furcation regions. 15 Both materials also produced good cellular responses in studies of subcutaneous and intrabone implantations in animals. 6-8,10 Studies comparing genotoxity and cytotoxicity 6,11,12 and studies of their use in the dental pulps of animals 5,9 and their antimicrobial action also provided similar results for both MTA and Portland cement. Radiopacity is an important property of an endodontic material for it to be distinguishable from that of either cortical bone or dentin, 23 so much so that the American Dental Association (ADA) establishes standards for researching the radiopacity of endodontic cements, set down in specification no. 57 (1984). 23 The ADA specifications state that because 1 mm of cortical bone or dentin has a radiopacity equivalent of 1 mm of 1100 aluminum alloy, and comparisons can be made with step wedges of this material, a clear image is e65

2 e66 Bueno et al. January 2009 producible with at least 2 mm of aluminum equivalent differential. Because the test specimens used in the present study were 2 mm thick, we adopted the radiopacity obtained with a thickness of 4 mm of aluminum as an equivalence standard. The aim of the present study was to determine what concentration of bismuth oxide must be added to white Portland cement to provide the cement with adequate radiopacity, as measured by the grayscale levels of digitized radiographic images, to comply with ADA specification no MATERIALS AND METHODS The methodology used in this study was based on ADA specification no. 57, 23 which determines the requirements for endodontic cements, one such requirement being radiopacity. This specification determines that research undertaken to determine radiopacity must be conducted by comparing the materials under study with different thicknesses of pure aluminum. Initially, standardized portions of each material under study were obtained: white MTA (Angelus Indústria de Produtos Odontológicos, Londrina, PR, Brazil), white Portland cement (Irajazinho Votorantim; Cimento Rio Branco, Rio de Janeiro, RJ, Brazil), and white Portland cement with 5%, 10%, 15%, 20%, 25%, and 30% bismuth oxide (Neon Comercial, São Paulo, SP, Brazil). Three portions of each material were obtained, all weighing 500 mg; they were weighed on an electronic analytic balance (Ohaus Corp., Pine Brook, NJ). Standardized test specimens of the materials were obtained by mixing them with one-third of the material s weight in distilled water (from the MTA kit), using a spatula. A syringe with 0.5 ml capacity was used to measure the water. The dimensions of the resulting test specimens were standardized to 10 mm in diameter and 2 mm in thickness. Standardization was performed using standard metal matrixes which were filled with the tested materials. Three test specimens were made for each material. After adequate drying, the test specimens were radiographed with occlusal films (Kodak Insight Speed E; Eastman Kodak Company, Rochester, NY) at a distance of 40 cm from the radiation source, using an apparatus (Gendex 765DC; Gendex Dental X-Ray Division, Dentsply International, Des Plaines, IL) set to work at 65 kv, 7 ma, and an exposure time of 0.25 s. Radiographic processing was performed with an automatic processing unit (Gendex GXP; Gendex Corporation, Des Plaines, IL). The test specimens were placed over the radiographic film in such a way that there was a test specimen of each material and a scale with different thicknesses (1-8 mm) of pure aluminum in each radiograph. Three radiographs were taken (each with a different test specimen of each material). The radiographs were then digitized using a digital camera (Sony W5; Tokyo, Japan). The photographs were obtained in macro mode (resolution of 5 megapixels) by placing the film on a light box and superimposing a totally black paper frame slightly overlapping the outside borders of the film to prevent any light from invading the area not covered by the frame. The camera was then maintained at a standard distance from the film so that only the film and an adjacent black paper strip were included in the picture. On the digital photographs, areas with a standardized size for each test specimen as well as each thickness of the aluminum scale were measured in grayscale levels (0 to 255) with the Adobe Photoshop computer program, version (Adobe Systems, San Jose, CA). Because there were 3 test specimens of each material, one for each X-ray, an arithmetic mean of the values obtained for these 3 samples was calculated. The results were subjected to statistical analysis. RESULTS Initially, analysis of variance was applied to assess the differences between the means of the grayscale levels of the materials evaluated. The null hypothesis was rejected by the analysis of variance, which strongly indicated significant differences in the grayscale levels of the materials. The Ryan-Einot-Gabriel-Welch and Quiot test was applied to allow multiple comparisons of the means (at a level of significance of 5%), by comparing them 2 by 2. The standard deviations and the highest and lowest interval of 95% confidence limits for each sample were also compared. The results of the study are presented in Table 1. Regarding MTA, it was observed that there were no statistically significant differences in the grayscale levels of the material in relation to the thicknesses of 4 mm and 5 mm of aluminum. Neither was there any statistically significant difference between MTA and the white Portland cement with additions of 20% and 25% bismuth oxide. No statistically significant difference was observed between the radiopacity obtained with white Portland cement with the addition of 15% and 20% bismuth oxide and that obtained with a 4-mm thickness of aluminum. A regression analysis (P.01) performed for bismuth oxide content (Fig. 1) mathematically represented the development of radiopacity as a function of the amount of bismuth oxide present. This analysis showed that 96.91% of the variation in radiopacity can be credited to bismuth oxide content. It also showed that a theoretic addition of 21.51% of bismuth oxide in white

3 Volume 107, Number 1 Bueno et al. e67 Table I. Results and statistical analysis Group Mean Standard deviation Limits of the interval of confidence (95%) Upper Lower Test of REGWQ alpha 5% (.05)* 8 mm Al A 7 mm Al AB 6 mm Al BC WPC/30%BO CD 5 mm Al DE WPC/25%BO EF MTA EFG WPC/20%BO FGH 4 mm Al GH WPC/15%BO H 3 mm Al I WPC/10%BO I WPC/5%BO J 2 mm Al K WPC L 1 mm Al M Al, aluminum; BO, bismuth oxide; MTA, mineral trioxide aggregate; REGWQ, Ryan-Einot-Gabriel-Welch and Quiot; WPC, white Portland cement. *Simple statistics and the 95% confidence interval of the means of the original data and the REGWQ test applied to the resulting data according to the method recommended by the study of assumptions. Means with the same letters do not differ among themselves according to the REGWQ test, with a 5% alpha level (.05) of significance. Radiopacity (Grayscale levels) y = x x (p < R 2 :96.91%) Grayscale value MTA (157.3) 4 mm of aluminum (145.3) Bismuth Oxide (%) Fig. 1. Polynomial quadratic regression to represent radiopacity (grayscale level) as a function of added bismuth oxide content. MTA, Mineral trioxide aggregate. Portland cement provided a radiopacity (grayscale level) equivalent to the mean observed for white MTA, and that a theoretic addition of 17.65% of bismuth oxide in white Portland cement provided a mean radiopacity equivalent to that obtained with a thickness of 4 mm of aluminum. DISCUSSION The aim of this study was to determine the concentration of bismuth oxide that must be added to Portland cement to give it the radiopacity needed to be used as an endodontic material. A recently published study 24 evaluated the radiopacity of Portland cement with the addition of different proportions of bismuth oxide (4:1, 6:1, and 8:1). The authors observed that with 20% bismuth oxide the material presented a radiopacity not significantly different from that of MTA, and they concluded that this proportion of bismuth oxide rendered Portland cement with a greater potential for being used as a root-end filling material compared with Porland cement with less bismuth oxide. Statistically similar cell viability was also observed for the different groups. Another study 25 demonstrated the adequate radiopacity of MTA and inadequate radiopacity of Portland cement for endodontic use, suggesting that this difference is due to the presence of bismuth oxide in MTA, but the concentration of bismuth oxide that should be added to Portland cement to produce adequate radiopacity in this material was not determined. Cellular responses in animals to subcutaneous implantations of MTA and Portland cement with additions of 20% and 30% bismuth oxide have been proven to be similar. 8 A study comparing tissue response to MTA and to Portland cement with the addition of iodoform found similar results for the experimental groups, suggesting the addition of iodoform to Portland cement as a radiopacity agent rather than bismuth oxide because of the greater availability of the former than of the latter. 10 Radiopacity is an important property of an endodontic material for it to be distinguishable from that of either cortical bone or dentin. 23 The ADA specification

4 e68 Bueno et al. January 2009 no establishes other properties required for endodontic materials in addition to radiopacity, such as the possibility of being sterilized, pureness of the material, biocompatibility, working time, setting time, resistance to the forces of compression and traction, dimensional stability, and resistance to solubility. Regarding radiopacity, this specification determines that the tests of the materials must be performed comparatively with different thicknesses of pure aluminum. However, the specification is not clear regarding the material dimensions of the test specimen or to the aluminum thicknesses with which the specimens must be compared. In the present study, a thickness of 2 mm was adopted for preparing the test specimens, as in other studies Regarding the comparison procedure, an aluminum thickness of 4 mm was adopted. 26,27 However, some authors had used test specimens with different thicknesses, such as 1 mm 24,30 or 1.5 mm. 31 There is also divergence regarding the comparison with aluminum, considering that some authors made comparisons with an aluminum thickness of 3 mm The use of 3 test specimens of each material instead of only 1 sample reduced the possibility of an operational error. Radiography was performed in the present study with a direct-current apparatus (that does not undergo variations of electrical current, guaranteeing stability to the radiation emission). The appliance also had a high voltage (65 kv), which allows better discrimination of grayscale levels (contrast) in the radiographic film. 31 Although many studies have demonstrated the similarity between MTA and Portland cement, the clinical use of Portland cement has not yet been accepted on human beings, owing to lack of quality control in producing Portland cement and the absence of radiopacity of this material. The major difference between MTA and Portland cement is the presence of bismuth oxide, which ensures the radiopacity of MTA. 20,21,25 Based on the results of the present study, new research on the physical and biologic aspects of MTA and Portland cement with bismuth oxide is recommended to assess whether the addition of bismuth oxide modifies the physical and biologic properties of the material and also to eventually authorize the use of Portland cement with the addition of bismuth oxide as an endodontic material in clinics. CONCLUSIONS Based on the methodology used and on the results obtained in this study, and based on the recommendations of ADA specification no. 57, it can be concluded that: 1. White MTA has a radiopacity (measured in grayscale levels) that allows it to be used as an endodontic material. 2. White Portland cement does not have sufficient radiopacity for it to be used as an endodontic material. 3. The addition of at least 15% of bismuth oxide to white Portland cement gives it sufficient radiopacity for it to be used as an endodontic material. REFERENCES 1. Camilleri J, Pitt Ford TR. Mineral trioxide aggregate: a review of the constituents and biological properties of the material. Int Endod J 2006;39: Torabinejad M, Watson TF, Pitt Ford, TR. Sealing ability of a mineral trioxide aggregate when used as a root-end filling material. J Endod 1993;19: Lee SJ, Monsef M, Torabinejad M. Sealing ability of a mineral trioxide aggregate for repair of lateral root perforations. 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