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Compressive and diametral tensile strength of glass ionomer cements

Compressive and diametral tensile strength of glass ionomer cements J Appl Oral Sci 2004; 12(4): 344-8 www.fob.usp.br - www.scielo.br COMPRESSIVE AND DIAMETRAL TENSILE STRENGTH OF GLASS IONOMER CEMENTS RESISTÊNCIA À COMPRESSÃO E À TRAÇÃO DIAMETRAL DE CIMENTOS DE IONÔMERO DE VIDRO 1 1 2 Eduardo BRESCIANI , Terezinha de Jesus Esteves BARATA , Ticiane Cestari FAGUNDES , 3 3 4 Akimi ADACHI , Marina Martins TERRIN , Maria Fidela de Lima NAVARRO 1- DDS, MSc, PhD, Graduate Student, Department of Operative Dentistry, Bauru Dental School, University of São Paulo, Brazil. 2- DDS, MSc, Graduate Student, Department of Operative Dentistry, Bauru Dental School, University of São Paulo, Brazil. 3- Undergraduate Student of Bauru Dental School, University of São Paulo, Brazil. 4- Associate Professor of Operative Dentistry, Dean of Bauru Dental School, University of São Paulo, Brazil. Corresponding address: Profa. Dra. Maria Fidela de Lima Navarro - Department of Operative Dentistry, Bauru Dental School University of São Paulo - Alameda Dr. Octávio Pinheiro Brisolla 9-75, CEP: 17.012-101 - Bauru - São Paulo- Brazil Phone: 55-14-3224-7688 - Fax: 55 14 3223-4679 - E-mail: mflnavar@usp.br Received: July 28, 2004 - Returned for modification: August 27, 2004 - Accepted: September 28, 2004 ABSTRACT he aim of this study was to compare, in different periods of time, the compressive and diametral tensile strength of a traditional high viscous glass ionomer cement: Fuji IX (GC Corporation), with two new Brazilian GIC’s: Vitro-Molar (DFL) and Bioglass R (Biodinamica), all indicated for the Atraumatic Restorative Treatment (ART) technique. Fifteen disk specimens (6.0mm diameter x 3.0mm height) for the diametral tensile strength (DTS) test and fifteen cylindrical specimens (6.0mm diameter x 12.0mm height) for the compressive strength (CS) test were made of each GIC. Specimens were stored in deionized water at 37º C and 100% of humidity in a stove until testing. Five specimens of each GIC were submitted to CS and DTS test in each period, namely 1 hour, 24 hours and 7 days. The specimens were tested in a testing machine (Emic) at a crosshead speed of 1.0mm/min for CS and 0.5mm/min for the DTS test until failure occurred. The data were submitted to two-way ANOVA and Tukey tests (α=0.05). The mean CS values ranged from 42.03 to 155.47MPa and means DTS from 5.54 to 13.72 MPa, with test periods from 1h to 7 days. The CS and DTS tests showed no statistically significant difference between Fuji IX and Vitro Molar, except for CS test at 1-hour period. Bioglass R had lowest mean value for CS of the cements tested. In DTS test Bioglass R presented no statistically significant differences when compared with all others tested GICs at 1-hour period and Bioglass R presented no difference at 24-hour and 7-day periods when compared to Vitro-Molar. Further studies to investigate other physical properties such as fracture toughness and wear resistance, as well as chemical composition and biocompatibility, are now needed to better understand the properties of these new Brazilian GIC’s. Uniterms: Glass ionomer cements, mechanical properties; Atraumatic Restorative Treatments; Compressive strength; Diametral tensile strength. RESUMO C omparou-se a Resistência à Compressão (RC) e à Tração Diametral (TD) de um cimento de ionômero de vidro de alta viscosidade [Fuji IX (GC Corporation)] e de dois novos cimentos Brasileiros [Vitro Molar (DFL) e Bioglass R (Biodinamica)], recentemente lançados no mercado, ambos indicados para o Tratamento Restaurador Atraumático (ART), em diferentes períodos de tempo. Foram confeccionados quinze corpos-de-prova com 6,0 mm de diâmetro x 3,0 mm de altura para o teste de TD e quinze com 6,0 mm de diâmetro e 12,0 mm de altura para o teste de RC, para cada ionômero a ser testado. Os corpos-de-prova foram armazenados em recipientes plásticos, com água deionizada, e mantidos em estufa a 37ºC e 100% de umidade, até a realização dos testes. Cinco corpos-de-prova de cada material foram submetidos aos testes de TD e RC em cada período de tempo: 1-hora, 24-horas e 7-dias, em uma máquina de testes universal (EMIC – DL 500) a uma velocidade de 1,0 mm/min para RC e 0,5mm/min para TD. Os dados obtidos foram submetidos aos testes ANOVA a dois critérios e Tukey (á=0,05). Os valores médios de RC e TD variaram de 42,03 a 155.47 MPa e de 5,54 a 13,72 MPa, respectivamente para os períodos analisados. O Fuji IX e o Vitro Molar não apresentaram diferenças em relação aos testes de RC e TD, exceto para RC no período de 1-hora. O Bioglass R apresentou os menores valores de RC dos cimentos testados. Na TD o Bioglass R não apresentou diferença em relação aos outros cimentos testados no período de 1-hora e não foi diferente do Vitro-Molar nos períodos de 24-horas e 7-dias. Mais estudos são necessários para avaliar outras propriedades mecânicas desses novos cimentos de ionômero de vidro brasileiros, tais como: tenacidade e desgaste, bem como composição química e biocompatibilidade Unitermos: Cimentos de ionômero de vidro, propriedades mecânicas; Tratamento Restaurador Atraumático; Resistência à compressão; Resistência à tração diametral. 344 COMPRESSIVE AND DIAMETRAL TENSILE STRENGTH OF GLASS IONOMER CEMENTS INTRODUCTION As Brazilian GIC indicated for ART technique are commercially available and no previous study was performed Conventional Glass Ionomer Cements (GICs) were with these materials, the aim of this study was to compare the introduced to the dental professional in 1971 by Wilson & compressive and diametral tensile strengths of a traditional Kent as materials consisting of a base-usually an ion- Glass-Ionomer Cement (GIC): Fuji IX-GC Corporation, with two leachable, calcium-aluminum-fluorosilicate glass powder – that Brazilian marketed GICs: Vitro-Molar (DFL) and Bioglass R is combined with polyacrylic acid or its copolymers . These (Biodinamica), all indicated for Atraumatic Restorative cements possess certain unique properties that make them Treatment (ART) technique. useful as restorative and adhesive materials, including adhesion to moist tooth structure and base metals, anticariogenic properties due to release of fluoride, thermal compatibility with MATERIAL AND METHODS tooth enamel because of low coefficient of thermal expansion similar to those of tooth structure, biocompatibility and low The three chemically-cured glass-ionomer cements (GICs) 7,16 cytotoxicity . The limitations include the brittleness and poor tested in this study are listed on Table 1. 7,15 1 fracture toughness of the materials . In accordance with ADA specifications 66 five specimens Due to their considerable advantages and improvement, were prepared for each material and for each of three periods of GICs have been widely indicated in the Atraumatic Restorative time: 1 hour, 24 hours and 7 days, to evaluate compressive (CS) 9,12 Treatment (ART) technique . The ART is an approach of and diametral tensile strengths (DTS). The cylinder dimensions caries removal using only hand instruments, and restoring the were 6.0mm diameter x 12.0mm height for the CS test and 6.0mm cavity and sealing any associated fissures and pits with an diameter x 3.0mm height for the DTS test. adhesive restorative material, such as the currently used GICs. The powder/liquid ratios were used according to the The approach combines a preventive component with a manufacturers’ instructions for all materials. The material restorative procedure, and has the potential to be minimally necessary to make each specimen was weighted in a precision 9,12 invasive and maximally preserve the tooth structure . balance and mixed with a plastic spatula (GC Corporation, Tokyo, But, due to inadequate physical properties of the glass Japan) on impermeable paper. ionomer materials to resist occlusal forces , efforts to improve The specimens were made at room temperature of 23±2ºC several aspects of this treatment have been made, involving and relative air humidity of 50±10%, as recommended by ADA different kinds of self-cured GICs, such as inclusion of more specification . After mixing, the materials were inserted with a reactive polyacids (e.g. copolymers of acrylic and maleic acid), Centrix syringe (Centrix, Shelton, USA) into metallic matrices, by pretreatment of the glass surfaces and with modified glass which were previously coated with a thin layer of petroleum 11,23 compositions . Besides all the developments in the hybrid jelly (Sidepal, Guarulhos, Brazil). The insertion was done slowly systems, there has been a potential development in the field of to adapt the material into the matrix and avoid bubble formation. conventional acid/glass systems with the development of high The matrices were slightly overfilled with the GIC; a polyester 8,10,11 viscosity GICs, as Fuji IX (GC Corporation) . The particular strip (Proben, Catanduva, Brazil) covered with a thin layer of ways of improving conventional GICs consisted mainly of petroleum jelly was placed on the material and a coverslip was optimizing the concentration and molecular weight of the placed on top of it. Hand pressure was then applied for 20 polyacid as well as the particle size distribution of the glass . seconds while excess material was extruded from the top of the The compressive and diametral tensile strengths are matrices for DTS test. For CS test matrices were compressed in common tests to determine the mechanical properties of glass a device. Two minutes after the start of the mix, the matrices 4,6,9,10,19,21,23,24 ionomers . were placed in an oven at 37±1ºC and 95±5% relative humidity, TABLE 1- Materials, manufacturers, GIC classification, powder:liquid (P:L) ratio, and batch numbers Materials Manufacturers Classification P:L ratio Batch numbers- valid Bioglass R Biodinamica Restorative 3.0:1.0 157/04-03/2006 Ibiporã, Brazil Conventional Fuji IX GC Corporation Restorative 3.6: 1.0 0309051- 09/2006 Tokyo, Japan Conventional High Viscositiy Vitro Molar DFL Restorative 3.0:1.0 020144-11/2006 Rio de Janeiro Conventional Brazil 345 BRESCIANI E, BARATA T de J E, FAGUNDES T C, ADACHI A, TERRIN M M, NAVARRO M F de L for 15 minutes. Then, the specimens were ejected from the incident on the long axis (Figure 2). The CS was calculated by matrices and the excess material was removed with a carver the following formula: P/πr . Where: P= load at fracture, r= the and petroleum jelly was applied to protect the GIC during the radius of sample cylinder, and π= (constant) 3.14. CS values initial setting reaction. The specimens were afterward stored in [kgf/cm ] were converted into MPa as follows: CS 6mL of deionized water at 37±1ºC. Tests were made in an Emic [MPa]=CS[Kgf/cm ] x 0.09807. Universal Testing Machine (Emic- DL 5000/10000, São José The data were submitted to two-way ANOVA (GICs and dos Pinhais-PR-Brazil) at a crosshead speed of 1.0mm/min for time) and Tukey-Kramer test for individual comparison with a CS and 0.5mm/min for the DTS test. 0.05 level of significance. For the DTS test, the specimens were compressed diametrically introducing tensile stress in the material in the plane of the force application by the test (Figure 1). This was RESULTS calculated by the formula: 2P/ =πDT, where: P= load applied; D= diameter of the cylinder, T= thickness of the cylinder, π= The CS and DTS test results for the GICs are shown in (constant) 3,14. DTS values [kgf/cm ] were converted into MPa Tables 2 and 3. as follows: DTS[MPa]=DTS[Kgf/cm2] x 0.09807. For the CS test, the specimens were placed in vertical position, with force Compressive Strength · All GICs tested presented a significant increase in CS between the 1-hour and 7-day periods (p<0.001). · Bioglass R and Vitro Molar and Fuji IX presented statistically significant difference between 1-hour and 24-hour periods. There were no differences between the 24-hour and 7- day periods. · There were statistically significant differences between all GICs at the 1-hour period. · Bioglass R and Fuji IX showed statistically significant difference at the 24-hour and 7-day periods. · Vitro Molar and Fuji IX showed no statistically significant FIGURE 1- Schematic illustration of Diametral Tensile difference at the 24-hour and 7-day periods. · Bioglass R presented lower strengths than the others GICs Strength adapted from Darvell , 2000. included in this study at the 3 tested periods. How diametral tensile is envisaged ideally tension acting smoothly over the entire diameter, peak at the center . Diametral Tensile Strength · Two-way analysis showed significant differences among materials, where Bioglass R < Vitro Molar < Fuji IX (p = 0.00) and among periods of evaluation, where 1 hour < 1 day < 1 week (p = 0.00). · Bioglass R and Vitro Molar presented no statistically significant differences between the 3 analyzed periods (1 hour, 24 hours and 7 days) · Fuji IX presented lower DTS at 1-hour when compared to 24-hour and 7-day periods. · At 1 hour there were no differences among the materials. · At 24 hours and 7 days, Bioglass R presented statistically significant lower DTS than Fuji IX · At 24 hours and 7 days, Vitro Molar presented no statistical difference when compared to Bioglass R and Fuji IX. DISCUSSION The resistance to fracture within a restorative material is FIGURE 2- Schematic illustration of Compressive Strength specified by a fracture stress, which is often referred to as the 7 24 adapted from Darvell , 2000. strength of the material . Two mechanical strength tests (Compressive and Diametral Tensile) were used in this study. The stress and causes of failure in a cylindrical specimen The compressive strength (CS) is an important property in loaded axially are no different from those in the diametral restorative materials, particularly in the process of mastication. case except that the pattern is radially symetrical . 346 COMPRESSIVE AND DIAMETRAL TENSILE STRENGTH OF GLASS IONOMER CEMENTS This test is more suitable to compare brittle materials, which lower values are significantly different, but assumptions can 7,17 show relatively low result when subject to tension . To test be made and the lower values can be attributed to different compressive strength of a material, two axial sets of force are variants of the study. applied to a sample in an opposite direction, in order to In this study, Bioglass R and Vitro Molar showed an approximate the molecular structure of the material . increased in CS between 1 hour and 7 days and between 1 hour The diametral tensile strength (DTS) is a critical requirement, and 24 hours, but no significant difference in strength was because many clinical failures are due to tensile stress . As it observed between 24 hours and 7 days. This increase in CS is not possible to measure the tensile strength of brittle materials can be analyzed by the setting reaction of GICs. The calcium like Glass Ionomer Cements (GICs) directly, the British Standards polycarboxylate is formed in the first 5-7 minutes after mixing. Institution adopted the diametral tensile strength test . In this The aluminum polycarboxylate, which is more stable and test, a compressive force is applied to a cylindrical specimen improves the mechanical properties of the cement, takes 24 across the diameter by compression plates. While the stresses hours to be formed in the average. The setting reaction 18,21 in the contact regions are indeterminate, there is evidence of a continues for at least 24 hours and probably much longer . compressive component that hinders the propagation of the In contrast, the Fuji IX did not show statistically significant tensile crack . Large shear stresses that exist locally under the differences when CS was evaluated (1 hour, 24 hours and 7 contact area may also induce a shear failure before tensile failure days). This may be explained by the faster setting reaction of 6,7 at the center of the specimen . the high viscosity GICs (Fuji IX). According to the manufacturer, For all cements, CS values were much higher than DTS the relatively higher viscosity is the result of the addition of values. Compressive strength was about 8-13 times greater poly (acrylic acid) to the powder and finer grain-size 8,11 than DTS. This may be explained because cohesion between distribution improved the mechanical properties of these the materials is identical in both compressive and diametral cements mainly in the first hours . No significant difference in tensile strength tests, but the direction of forces is reversed . strengths was observed between Fuji IX and Vitro Molar at 24- The results observed in this study were comparable to those hour and 7-day periods. presented in the literature concerning the Fuji IX DTS and CS In relation to the DTS, also theoretically Fuji IX should be 19,23 values , probably due to standardization of procedures, stronger at all time intervals, as the maturation of the cement especially those involved with measuring powder/liquid and takes place at a faster rate. The use of smaller particles to manipulation according to manufacturers’ instructions. This increase the setting reaction may, however, have a observation is of great importance to validate the present results compromising effect on strength. The smaller irregularly shaped and observations. There are studies with lower DTS values for particles used could increase the risk for local stress Fuji IX, for example Iazzetti et al , in 2001. This happens due to concentrations and as a result of that facilitate local crack different variables, as operators and measuring and growth and decrease strength. This may be attributed to no manipulating the material. It is not possible to perform a significant differences observed in DTS among the three GICs statistical analysis between these two studies to check if the tested at 1 hour. TABLE 2- Mean Compressive Strength (CS) of GIC’s in MPa and standard deviations (SD) Glass-Ionomer Cements 1 hour 24 hours 7 days A 1 A 2 A 2 Bioglass R 42.03 (6.83) 83.39 (16.60) 95.67(15.27) B 1 B 2 B 2 Vitro Molar 70.26(6.05) 125.67(6.95) 148.03(17.80) C 1 B 2 B 2 Fuji IX 99.51(7.91) 147.93(18.18) 155.47(9.02) Results designated with the same superscript characters are not statistically different (p<0.05). Letters are for comparisons between GIC’s; numbers are for comparisons between times of the same material TABLE 3- Mean Diametral Tensile Strength (DTS) of GIC’s in MPa and standard deviations (SD) Glass-Ionomer Cements 1 hour 24 hours 7 days A 1 B 1 D 1,2,3 Bioglass R 5.54(0.529) 6.58(0.808) 8.74(1.396) A 2 B,C 2 D,E 2,4 Vitro Molar 8.27(0.475) 9.43(0.822) 10.76(3.072) A 3 C 4 E 4 Fuji IX 7.24(0.699) 1 1.96(1.514) 13.72(2.834) Results designated with the same superscript characters are not statistically different (p<0.05). Letters are for comparisons between GIC’s; numbers are for comparisons between times of the same material 347 BRESCIANI E, BARATA T de J E, FAGUNDES T C, ADACHI A, TERRIN M M, NAVARRO M F de L 5- Cefaly DFG, Franco EB, Mondelli RFL, Francisconi PAS, Navarro At 24-hour and 7-day periods, Bioglass R presented MFL. Diametral tensile strength and water sorption of glass-ionomer statistically significant lower DTS than Fuji IX, but Vitro Molar cements used in Atraumatic Restorative Treatment. J Appl Oral Sci presented no statistical difference when compared to Bioglass 2003;11:96-101. R and Fuji IX. This may be explained in part by the low cohesive 6- Craig RG. Mechanical properties. In:________. Restorative dental condition . The DTS measures the cohesive strength of the materials. 10th. St. Louis:Mosby; c1997. p. 56-103. material, and the most brittle the material, the faster will be the occurrence of fracture. The cohesive properties of the material 7- Darvell BW. Mechanical testing. In:________. Materials Science for will influence the load necessary to produce fracture, Dentistry. 6th ed. Hong Kong : University of Hong Kong;2000. p.1- 18.34. independently of the deformation values. The CS of amalgam is in the range of 300-450MPa, while 8- Frankenberger R.; Sindel J.; Kramer N. Viscous glass-ionomer cements: that for composite resin is between 210-340 MPa . In addition, a new alternative to amalgam in the primary dentition? Quintessence the DTS of amalgam and composite resin has been reported to Int 1997; 28: 667-76. be between 43-58MPa and 40-70MPa respectively . In this 9- Frencken JE, Holmgren CJ. How effective is ART in the management study, the mean CS and DTS at 24 hours of the GICs tested, of dental caries? Community Dent Oral Epidemiol 1999; 27(6): 423- was still lower than that of the amalgam and composite resin, between 83.39 –147.93MPa and 6.58-11.96MPa, respectively. 10- Gladys S, Van Meerbeek B, Braem M, Lambrechts P, Vanherle G. It must be reiterated that, of the GICs tested, only Bioglass R Comparative physico-mechanical characterization of new hybrid showed a CS below the minimum strength at 24-hours periods restorative materials with conventional glass-ionomer and resin of 125MPa required by British Standards . The mean CS of composite restorative materials. J Dent Res 1997;76:883-94. Bioglass R at 1 hour, 24 hours and 7 days was very low, namely 11- Guggenberger R, May R, Stefan KP. New trends in glass-ionomer 42.03 - 83.39 - 95.67MPa, respectively. chemistry. Biomaterials 1998;19: 479-83. 12- Horowitz AM. Introduction to the symposium on minimal CONCLUSIONS intervention techniques for caries. J Public Hlth Dent 1996; 56(sp. Issue):133-4. The CS and DTS tests showed no significant difference 13- Iazzetti G, Burgess JO, Gardiner D. Selected mechanical properties of between Fuji IX and Vitro Molar, except for CS test at 1-hour fluoride-releasing restorative materials. Oper Dent 2001;26:21-6. period. Bioglass R had lowest mean value for CS of the cements 14- Kerby RE, Knobloch L. Strenght characteristics of glass-ionomer tested. In DTS test Bioglass R presented no statistically cements. Oper Dent 1992; 17:170-4. significant difference when compared to all others tested GICs at 1-hour period and Bioglass R presented no difference at 24- 15- McKinney JE, Antonucci JM, Rupp NW. Wear and microhardness hour and 7-day periods when compared to Vitro-Molar. Further of glass-ionomer cements. J. Dent. Res. 1987;66:1134-39. studies to investigate other physical properties such as fracture 16- McLean JW. Glass-ionomer cement. Br Dent J 1988;164:293-300. toughness and wear resistance as well as chemical composition and biocompatibility are now needed to better understand the 17- Naasan MA; Watson TF. Conventional glass ionomers as posterior properties of these new Brazilian GICs. restorations. A status report for the American Journal of Dentistry. Am J Dent 1998;11:36-45. 18- Pearson GJ, Atkinson AS. Long-term flexural strength of glass ACKNOWLEDGEMENT ionomer cements. Biomaterials 1991;12:658-60. This study was partially supported by CAPES (Coordenação 19- Pereira LC, Nunes MC, Dibb RG, Powers JM, Roulet JF, Navarro MF. de Aperfeiçoamento de Pessoal de Nível Superior). The authors Mechanical properties and bond strength of glass-ionomer cements. J would like to thank the manufacturers (Biodinamica, DFL, GC Adhes Dent 2002;4:73-80. Corporation) for their generous supply of dental materials. 20- Wang L, D’Alpino PHP, Lopes GL, Pereira JC. Mechanical properties of dental restorative materials: relative contribution of laboratory tests. J Appl Oral Sci 2003;11:162-7. REFERENCES 21- Williams JA, Billington RW. Changes in compressive strength of 1- American Dental Association, Specification n 66 for dental glass glass ionomer restorative materials with respect to time periods of 24 h ionomer cements. Council on Dental Materials, Instruments and to 4 months. J Oral Rehabil 1991;18:163-8. Equipment. J Am Dent Assoc 1989;119:205. 22- Wilson AD, Kent BE. The glass ionomer cement. A new translucent 2- Anusavice KJ. Does ART have a place in preservative dentistry? cement for dentistry. J Appl Chem Biotechnol 1971;21:313. Community Dent Oral Epidemiol 1999;27: 442-8. 23- Xie D, Brantley WA, Culbertson BM, Wang G. Mechanical properties 3- British Standards Institution, British Standards Specification for Dental and microstructures of glass-ionomer cements. Dent Mater 2000;16:129- Glass Ionomer Cement BS 6039, 1981:4 38. 4- Cattani-Lorente MA, Godin C, Meyer JM. Mechanical behavior of 24- Yap AUJ, Pek YS, Cheang P. Physico-mechanical properties of a glass ionomer cements affected by long-term storage in water. Dent fast-set highly viscous GIC restorative. J Oral Rehabil 2003;30:1-8. Mater 1994;10:37-44. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Journal of Applied Oral Science Unpaywall

Compressive and diametral tensile strength of glass ionomer cements

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J Appl Oral Sci 2004; 12(4): 344-8 www.fob.usp.br - www.scielo.br COMPRESSIVE AND DIAMETRAL TENSILE STRENGTH OF GLASS IONOMER CEMENTS RESISTÊNCIA À COMPRESSÃO E À TRAÇÃO DIAMETRAL DE CIMENTOS DE IONÔMERO DE VIDRO 1 1 2 Eduardo BRESCIANI , Terezinha de Jesus Esteves BARATA , Ticiane Cestari FAGUNDES , 3 3 4 Akimi ADACHI , Marina Martins TERRIN , Maria Fidela de Lima NAVARRO 1- DDS, MSc, PhD, Graduate Student, Department of Operative Dentistry, Bauru Dental School, University of São Paulo, Brazil. 2- DDS, MSc, Graduate Student, Department of Operative Dentistry, Bauru Dental School, University of São Paulo, Brazil. 3- Undergraduate Student of Bauru Dental School, University of São Paulo, Brazil. 4- Associate Professor of Operative Dentistry, Dean of Bauru Dental School, University of São Paulo, Brazil. Corresponding address: Profa. Dra. Maria Fidela de Lima Navarro - Department of Operative Dentistry, Bauru Dental School University of São Paulo - Alameda Dr. Octávio Pinheiro Brisolla 9-75, CEP: 17.012-101 - Bauru - São Paulo- Brazil Phone: 55-14-3224-7688 - Fax: 55 14 3223-4679 - E-mail: mflnavar@usp.br Received: July 28, 2004 - Returned for modification: August 27, 2004 - Accepted: September 28, 2004 ABSTRACT he aim of this study was to compare, in different periods of time, the compressive and diametral tensile strength of a traditional high viscous glass ionomer cement: Fuji IX (GC Corporation), with two new Brazilian GIC’s: Vitro-Molar (DFL) and Bioglass R (Biodinamica), all indicated for the Atraumatic Restorative Treatment (ART) technique. Fifteen disk specimens (6.0mm diameter x 3.0mm height) for the diametral tensile strength (DTS) test and fifteen cylindrical specimens (6.0mm diameter x 12.0mm height) for the compressive strength (CS) test were made of each GIC. Specimens were stored in deionized water at 37º C and 100% of humidity in a stove until testing. Five specimens of each GIC were submitted to CS and DTS test in each period, namely 1 hour, 24 hours and 7 days. The specimens were tested in a testing machine (Emic) at a crosshead speed of 1.0mm/min for CS and 0.5mm/min for the DTS test until failure occurred. The data were submitted to two-way ANOVA and Tukey tests (α=0.05). The mean CS values ranged from 42.03 to 155.47MPa and means DTS from 5.54 to 13.72 MPa, with test periods from 1h to 7 days. The CS and DTS tests showed no statistically significant difference between Fuji IX and Vitro Molar, except for CS test at 1-hour period. Bioglass R had lowest mean value for CS of the cements tested. In DTS test Bioglass R presented no statistically significant differences when compared with all others tested GICs at 1-hour period and Bioglass R presented no difference at 24-hour and 7-day periods when compared to Vitro-Molar. Further studies to investigate other physical properties such as fracture toughness and wear resistance, as well as chemical composition and biocompatibility, are now needed to better understand the properties of these new Brazilian GIC’s. Uniterms: Glass ionomer cements, mechanical properties; Atraumatic Restorative Treatments; Compressive strength; Diametral tensile strength. RESUMO C omparou-se a Resistência à Compressão (RC) e à Tração Diametral (TD) de um cimento de ionômero de vidro de alta viscosidade [Fuji IX (GC Corporation)] e de dois novos cimentos Brasileiros [Vitro Molar (DFL) e Bioglass R (Biodinamica)], recentemente lançados no mercado, ambos indicados para o Tratamento Restaurador Atraumático (ART), em diferentes períodos de tempo. Foram confeccionados quinze corpos-de-prova com 6,0 mm de diâmetro x 3,0 mm de altura para o teste de TD e quinze com 6,0 mm de diâmetro e 12,0 mm de altura para o teste de RC, para cada ionômero a ser testado. Os corpos-de-prova foram armazenados em recipientes plásticos, com água deionizada, e mantidos em estufa a 37ºC e 100% de umidade, até a realização dos testes. Cinco corpos-de-prova de cada material foram submetidos aos testes de TD e RC em cada período de tempo: 1-hora, 24-horas e 7-dias, em uma máquina de testes universal (EMIC – DL 500) a uma velocidade de 1,0 mm/min para RC e 0,5mm/min para TD. Os dados obtidos foram submetidos aos testes ANOVA a dois critérios e Tukey (á=0,05). Os valores médios de RC e TD variaram de 42,03 a 155.47 MPa e de 5,54 a 13,72 MPa, respectivamente para os períodos analisados. O Fuji IX e o Vitro Molar não apresentaram diferenças em relação aos testes de RC e TD, exceto para RC no período de 1-hora. O Bioglass R apresentou os menores valores de RC dos cimentos testados. Na TD o Bioglass R não apresentou diferença em relação aos outros cimentos testados no período de 1-hora e não foi diferente do Vitro-Molar nos períodos de 24-horas e 7-dias. Mais estudos são necessários para avaliar outras propriedades mecânicas desses novos cimentos de ionômero de vidro brasileiros, tais como: tenacidade e desgaste, bem como composição química e biocompatibilidade Unitermos: Cimentos de ionômero de vidro, propriedades mecânicas; Tratamento Restaurador Atraumático; Resistência à compressão; Resistência à tração diametral. 344 COMPRESSIVE AND DIAMETRAL TENSILE STRENGTH OF GLASS IONOMER CEMENTS INTRODUCTION As Brazilian GIC indicated for ART technique are commercially available and no previous study was performed Conventional Glass Ionomer Cements (GICs) were with these materials, the aim of this study was to compare the introduced to the dental professional in 1971 by Wilson & compressive and diametral tensile strengths of a traditional Kent as materials consisting of a base-usually an ion- Glass-Ionomer Cement (GIC): Fuji IX-GC Corporation, with two leachable, calcium-aluminum-fluorosilicate glass powder – that Brazilian marketed GICs: Vitro-Molar (DFL) and Bioglass R is combined with polyacrylic acid or its copolymers . These (Biodinamica), all indicated for Atraumatic Restorative cements possess certain unique properties that make them Treatment (ART) technique. useful as restorative and adhesive materials, including adhesion to moist tooth structure and base metals, anticariogenic properties due to release of fluoride, thermal compatibility with MATERIAL AND METHODS tooth enamel because of low coefficient of thermal expansion similar to those of tooth structure, biocompatibility and low The three chemically-cured glass-ionomer cements (GICs) 7,16 cytotoxicity . The limitations include the brittleness and poor tested in this study are listed on Table 1. 7,15 1 fracture toughness of the materials . In accordance with ADA specifications 66 five specimens Due to their considerable advantages and improvement, were prepared for each material and for each of three periods of GICs have been widely indicated in the Atraumatic Restorative time: 1 hour, 24 hours and 7 days, to evaluate compressive (CS) 9,12 Treatment (ART) technique . The ART is an approach of and diametral tensile strengths (DTS). The cylinder dimensions caries removal using only hand instruments, and restoring the were 6.0mm diameter x 12.0mm height for the CS test and 6.0mm cavity and sealing any associated fissures and pits with an diameter x 3.0mm height for the DTS test. adhesive restorative material, such as the currently used GICs. The powder/liquid ratios were used according to the The approach combines a preventive component with a manufacturers’ instructions for all materials. The material restorative procedure, and has the potential to be minimally necessary to make each specimen was weighted in a precision 9,12 invasive and maximally preserve the tooth structure . balance and mixed with a plastic spatula (GC Corporation, Tokyo, But, due to inadequate physical properties of the glass Japan) on impermeable paper. ionomer materials to resist occlusal forces , efforts to improve The specimens were made at room temperature of 23±2ºC several aspects of this treatment have been made, involving and relative air humidity of 50±10%, as recommended by ADA different kinds of self-cured GICs, such as inclusion of more specification . After mixing, the materials were inserted with a reactive polyacids (e.g. copolymers of acrylic and maleic acid), Centrix syringe (Centrix, Shelton, USA) into metallic matrices, by pretreatment of the glass surfaces and with modified glass which were previously coated with a thin layer of petroleum 11,23 compositions . Besides all the developments in the hybrid jelly (Sidepal, Guarulhos, Brazil). The insertion was done slowly systems, there has been a potential development in the field of to adapt the material into the matrix and avoid bubble formation. conventional acid/glass systems with the development of high The matrices were slightly overfilled with the GIC; a polyester 8,10,11 viscosity GICs, as Fuji IX (GC Corporation) . The particular strip (Proben, Catanduva, Brazil) covered with a thin layer of ways of improving conventional GICs consisted mainly of petroleum jelly was placed on the material and a coverslip was optimizing the concentration and molecular weight of the placed on top of it. Hand pressure was then applied for 20 polyacid as well as the particle size distribution of the glass . seconds while excess material was extruded from the top of the The compressive and diametral tensile strengths are matrices for DTS test. For CS test matrices were compressed in common tests to determine the mechanical properties of glass a device. Two minutes after the start of the mix, the matrices 4,6,9,10,19,21,23,24 ionomers . were placed in an oven at 37±1ºC and 95±5% relative humidity, TABLE 1- Materials, manufacturers, GIC classification, powder:liquid (P:L) ratio, and batch numbers Materials Manufacturers Classification P:L ratio Batch numbers- valid Bioglass R Biodinamica Restorative 3.0:1.0 157/04-03/2006 Ibiporã, Brazil Conventional Fuji IX GC Corporation Restorative 3.6: 1.0 0309051- 09/2006 Tokyo, Japan Conventional High Viscositiy Vitro Molar DFL Restorative 3.0:1.0 020144-11/2006 Rio de Janeiro Conventional Brazil 345 BRESCIANI E, BARATA T de J E, FAGUNDES T C, ADACHI A, TERRIN M M, NAVARRO M F de L for 15 minutes. Then, the specimens were ejected from the incident on the long axis (Figure 2). The CS was calculated by matrices and the excess material was removed with a carver the following formula: P/πr . Where: P= load at fracture, r= the and petroleum jelly was applied to protect the GIC during the radius of sample cylinder, and π= (constant) 3.14. CS values initial setting reaction. The specimens were afterward stored in [kgf/cm ] were converted into MPa as follows: CS 6mL of deionized water at 37±1ºC. Tests were made in an Emic [MPa]=CS[Kgf/cm ] x 0.09807. Universal Testing Machine (Emic- DL 5000/10000, São José The data were submitted to two-way ANOVA (GICs and dos Pinhais-PR-Brazil) at a crosshead speed of 1.0mm/min for time) and Tukey-Kramer test for individual comparison with a CS and 0.5mm/min for the DTS test. 0.05 level of significance. For the DTS test, the specimens were compressed diametrically introducing tensile stress in the material in the plane of the force application by the test (Figure 1). This was RESULTS calculated by the formula: 2P/ =πDT, where: P= load applied; D= diameter of the cylinder, T= thickness of the cylinder, π= The CS and DTS test results for the GICs are shown in (constant) 3,14. DTS values [kgf/cm ] were converted into MPa Tables 2 and 3. as follows: DTS[MPa]=DTS[Kgf/cm2] x 0.09807. For the CS test, the specimens were placed in vertical position, with force Compressive Strength · All GICs tested presented a significant increase in CS between the 1-hour and 7-day periods (p<0.001). · Bioglass R and Vitro Molar and Fuji IX presented statistically significant difference between 1-hour and 24-hour periods. There were no differences between the 24-hour and 7- day periods. · There were statistically significant differences between all GICs at the 1-hour period. · Bioglass R and Fuji IX showed statistically significant difference at the 24-hour and 7-day periods. · Vitro Molar and Fuji IX showed no statistically significant FIGURE 1- Schematic illustration of Diametral Tensile difference at the 24-hour and 7-day periods. · Bioglass R presented lower strengths than the others GICs Strength adapted from Darvell , 2000. included in this study at the 3 tested periods. How diametral tensile is envisaged ideally tension acting smoothly over the entire diameter, peak at the center . Diametral Tensile Strength · Two-way analysis showed significant differences among materials, where Bioglass R < Vitro Molar < Fuji IX (p = 0.00) and among periods of evaluation, where 1 hour < 1 day < 1 week (p = 0.00). · Bioglass R and Vitro Molar presented no statistically significant differences between the 3 analyzed periods (1 hour, 24 hours and 7 days) · Fuji IX presented lower DTS at 1-hour when compared to 24-hour and 7-day periods. · At 1 hour there were no differences among the materials. · At 24 hours and 7 days, Bioglass R presented statistically significant lower DTS than Fuji IX · At 24 hours and 7 days, Vitro Molar presented no statistical difference when compared to Bioglass R and Fuji IX. DISCUSSION The resistance to fracture within a restorative material is FIGURE 2- Schematic illustration of Compressive Strength specified by a fracture stress, which is often referred to as the 7 24 adapted from Darvell , 2000. strength of the material . Two mechanical strength tests (Compressive and Diametral Tensile) were used in this study. The stress and causes of failure in a cylindrical specimen The compressive strength (CS) is an important property in loaded axially are no different from those in the diametral restorative materials, particularly in the process of mastication. case except that the pattern is radially symetrical . 346 COMPRESSIVE AND DIAMETRAL TENSILE STRENGTH OF GLASS IONOMER CEMENTS This test is more suitable to compare brittle materials, which lower values are significantly different, but assumptions can 7,17 show relatively low result when subject to tension . To test be made and the lower values can be attributed to different compressive strength of a material, two axial sets of force are variants of the study. applied to a sample in an opposite direction, in order to In this study, Bioglass R and Vitro Molar showed an approximate the molecular structure of the material . increased in CS between 1 hour and 7 days and between 1 hour The diametral tensile strength (DTS) is a critical requirement, and 24 hours, but no significant difference in strength was because many clinical failures are due to tensile stress . As it observed between 24 hours and 7 days. This increase in CS is not possible to measure the tensile strength of brittle materials can be analyzed by the setting reaction of GICs. The calcium like Glass Ionomer Cements (GICs) directly, the British Standards polycarboxylate is formed in the first 5-7 minutes after mixing. Institution adopted the diametral tensile strength test . In this The aluminum polycarboxylate, which is more stable and test, a compressive force is applied to a cylindrical specimen improves the mechanical properties of the cement, takes 24 across the diameter by compression plates. While the stresses hours to be formed in the average. The setting reaction 18,21 in the contact regions are indeterminate, there is evidence of a continues for at least 24 hours and probably much longer . compressive component that hinders the propagation of the In contrast, the Fuji IX did not show statistically significant tensile crack . Large shear stresses that exist locally under the differences when CS was evaluated (1 hour, 24 hours and 7 contact area may also induce a shear failure before tensile failure days). This may be explained by the faster setting reaction of 6,7 at the center of the specimen . the high viscosity GICs (Fuji IX). According to the manufacturer, For all cements, CS values were much higher than DTS the relatively higher viscosity is the result of the addition of values. Compressive strength was about 8-13 times greater poly (acrylic acid) to the powder and finer grain-size 8,11 than DTS. This may be explained because cohesion between distribution improved the mechanical properties of these the materials is identical in both compressive and diametral cements mainly in the first hours . No significant difference in tensile strength tests, but the direction of forces is reversed . strengths was observed between Fuji IX and Vitro Molar at 24- The results observed in this study were comparable to those hour and 7-day periods. presented in the literature concerning the Fuji IX DTS and CS In relation to the DTS, also theoretically Fuji IX should be 19,23 values , probably due to standardization of procedures, stronger at all time intervals, as the maturation of the cement especially those involved with measuring powder/liquid and takes place at a faster rate. The use of smaller particles to manipulation according to manufacturers’ instructions. This increase the setting reaction may, however, have a observation is of great importance to validate the present results compromising effect on strength. The smaller irregularly shaped and observations. There are studies with lower DTS values for particles used could increase the risk for local stress Fuji IX, for example Iazzetti et al , in 2001. This happens due to concentrations and as a result of that facilitate local crack different variables, as operators and measuring and growth and decrease strength. This may be attributed to no manipulating the material. It is not possible to perform a significant differences observed in DTS among the three GICs statistical analysis between these two studies to check if the tested at 1 hour. TABLE 2- Mean Compressive Strength (CS) of GIC’s in MPa and standard deviations (SD) Glass-Ionomer Cements 1 hour 24 hours 7 days A 1 A 2 A 2 Bioglass R 42.03 (6.83) 83.39 (16.60) 95.67(15.27) B 1 B 2 B 2 Vitro Molar 70.26(6.05) 125.67(6.95) 148.03(17.80) C 1 B 2 B 2 Fuji IX 99.51(7.91) 147.93(18.18) 155.47(9.02) Results designated with the same superscript characters are not statistically different (p<0.05). Letters are for comparisons between GIC’s; numbers are for comparisons between times of the same material TABLE 3- Mean Diametral Tensile Strength (DTS) of GIC’s in MPa and standard deviations (SD) Glass-Ionomer Cements 1 hour 24 hours 7 days A 1 B 1 D 1,2,3 Bioglass R 5.54(0.529) 6.58(0.808) 8.74(1.396) A 2 B,C 2 D,E 2,4 Vitro Molar 8.27(0.475) 9.43(0.822) 10.76(3.072) A 3 C 4 E 4 Fuji IX 7.24(0.699) 1 1.96(1.514) 13.72(2.834) Results designated with the same superscript characters are not statistically different (p<0.05). Letters are for comparisons between GIC’s; numbers are for comparisons between times of the same material 347 BRESCIANI E, BARATA T de J E, FAGUNDES T C, ADACHI A, TERRIN M M, NAVARRO M F de L 5- Cefaly DFG, Franco EB, Mondelli RFL, Francisconi PAS, Navarro At 24-hour and 7-day periods, Bioglass R presented MFL. Diametral tensile strength and water sorption of glass-ionomer statistically significant lower DTS than Fuji IX, but Vitro Molar cements used in Atraumatic Restorative Treatment. J Appl Oral Sci presented no statistical difference when compared to Bioglass 2003;11:96-101. R and Fuji IX. This may be explained in part by the low cohesive 6- Craig RG. Mechanical properties. In:________. Restorative dental condition . The DTS measures the cohesive strength of the materials. 10th. St. Louis:Mosby; c1997. p. 56-103. material, and the most brittle the material, the faster will be the occurrence of fracture. The cohesive properties of the material 7- Darvell BW. Mechanical testing. In:________. Materials Science for will influence the load necessary to produce fracture, Dentistry. 6th ed. Hong Kong : University of Hong Kong;2000. p.1- 18.34. independently of the deformation values. The CS of amalgam is in the range of 300-450MPa, while 8- Frankenberger R.; Sindel J.; Kramer N. Viscous glass-ionomer cements: that for composite resin is between 210-340 MPa . In addition, a new alternative to amalgam in the primary dentition? Quintessence the DTS of amalgam and composite resin has been reported to Int 1997; 28: 667-76. be between 43-58MPa and 40-70MPa respectively . In this 9- Frencken JE, Holmgren CJ. How effective is ART in the management study, the mean CS and DTS at 24 hours of the GICs tested, of dental caries? Community Dent Oral Epidemiol 1999; 27(6): 423- was still lower than that of the amalgam and composite resin, between 83.39 –147.93MPa and 6.58-11.96MPa, respectively. 10- Gladys S, Van Meerbeek B, Braem M, Lambrechts P, Vanherle G. It must be reiterated that, of the GICs tested, only Bioglass R Comparative physico-mechanical characterization of new hybrid showed a CS below the minimum strength at 24-hours periods restorative materials with conventional glass-ionomer and resin of 125MPa required by British Standards . The mean CS of composite restorative materials. J Dent Res 1997;76:883-94. Bioglass R at 1 hour, 24 hours and 7 days was very low, namely 11- Guggenberger R, May R, Stefan KP. New trends in glass-ionomer 42.03 - 83.39 - 95.67MPa, respectively. chemistry. Biomaterials 1998;19: 479-83. 12- Horowitz AM. Introduction to the symposium on minimal CONCLUSIONS intervention techniques for caries. J Public Hlth Dent 1996; 56(sp. Issue):133-4. The CS and DTS tests showed no significant difference 13- Iazzetti G, Burgess JO, Gardiner D. Selected mechanical properties of between Fuji IX and Vitro Molar, except for CS test at 1-hour fluoride-releasing restorative materials. Oper Dent 2001;26:21-6. period. Bioglass R had lowest mean value for CS of the cements 14- Kerby RE, Knobloch L. Strenght characteristics of glass-ionomer tested. In DTS test Bioglass R presented no statistically cements. Oper Dent 1992; 17:170-4. significant difference when compared to all others tested GICs at 1-hour period and Bioglass R presented no difference at 24- 15- McKinney JE, Antonucci JM, Rupp NW. Wear and microhardness hour and 7-day periods when compared to Vitro-Molar. Further of glass-ionomer cements. J. Dent. Res. 1987;66:1134-39. studies to investigate other physical properties such as fracture 16- McLean JW. Glass-ionomer cement. Br Dent J 1988;164:293-300. toughness and wear resistance as well as chemical composition and biocompatibility are now needed to better understand the 17- Naasan MA; Watson TF. Conventional glass ionomers as posterior properties of these new Brazilian GICs. restorations. A status report for the American Journal of Dentistry. Am J Dent 1998;11:36-45. 18- Pearson GJ, Atkinson AS. Long-term flexural strength of glass ACKNOWLEDGEMENT ionomer cements. Biomaterials 1991;12:658-60. 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Published: Dec 1, 2004

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