Abstracts

INTRODUCTION

The minimal intervention technique for the treatment of caries lesions has been widely used over the last few decades. In this technique, the recommendation is to remove the layer of infected, more disorganized dentin, and preserve the affected dentin that has the potential to be remineralized¹1. Mount GJ, Ngo H. Minimal intervention: a new concept for operative dentistry. Quintessence Int. 2000 Sep; 31(8):527-33. PMid:11203973. ^{, 2}2. Peters MC, McLean ME. Minimally invasive operative care. II. Contemporary techniques and materials: an overview. J Adhes Dent. 2001 Spring; 3(1):17-31.; 3: 17-31.

As the carious dentin is not completely removed, glass ionomer cement (GIC) has been indicated as the restorative material, due to its properties of chemical bonding to mineralized tooth structures, coefficient of heat expansion similar to that of dentin, adequate biocompatibility and fluoride ion release, which contribute to the remineralization process³3. Moshaverinia A, Chee WW, Brantley WA, Schricker SR. Surface properties and bond strength measurements of N-vinylcaprolactam (NVC) containing glass-ionomer cements. J Prosthet Dent. 2011 Mar; 105(3):185-93. http://dx.doi.org/10.1016/S0022-3913(11)60027-9
http://dx.doi.org/10.1016/S0022-3913(11)... ^{, 4}4. ten Cate JM, van Duinen RN. Hypermineralization of dentinal lesions adjacent to glass-ionomer cement restorations. J Dent Res. 1995 Jun; 74(6):1266-71. PMid:7629335. http://dx.doi.org/10.1177/00220345950740060501
http://dx.doi.org/10.1177/00220345950740... . However, the low mechanical strength of the conventional formulations of this material⁵5. Xie D, Brantley WA, Culbertson BM, Wang G. Mechanical properties and microstructures of glass-ionomer cements. Dent Mat. 2000 Mar;16(2):129-38. http://dx.doi.org/10.1016/S0109-5641(99)00093-7
http://dx.doi.org/10.1016/S0109-5641(99)... is a limiting factor for its use in cavities subjected to high masticatory stresses, such as extensive Class I and Class II restorations. This has led to the development of a new category of GICs with enhanced physical properties.

These GICs present greater wettability of the powder by the liquid component than the conventional GICs, which has resulted in easier and faster manipulation and greater viscosity of the product⁶6. Peez R, Frank S. The physical-mechanical performance of the new Ketac Molar Easymix compared to commercially available glass ionomer restoratives. J Dent. 2006 Sep; 34(8):582-7. PMid:16581174. http://dx.doi.org/10.1016/j.jdent.2004.12.009
http://dx.doi.org/10.1016/j.jdent.2004.1... . As a disadvantage, they present lower cumulative fluoride ion release⁷7. Frencken JE, Makoni F. A treatment technique for tooth decay in deprived communities. World Health. 1994; 1: 15-7.

8. Gao W, Smales R J, Gale M S. Fluoride release/uptake from newer glass ionomer cements used with the ART approach. Am J Dent. 2000 Aug; 13(4):201-4. PMid:11763931. ^{- 9}9. Smales RJ, Yip HK. The atraumatic restorative treatment (ART) approach for the management of dental caries. Quintessence Int. 2002 Jun; 33(6):427-32. PMid:12073723.. Although the effects of this lower fluoride ion release on the inhibition of residual caries lesions are not yet known, various researchers¹⁰10. Jedrychowski JR, Caputo AA, Kerper S. Antibacterial and mechanical properties of restorative materials combined with chlorhexidines. J Oral Rehabil. 1983 Sep; 10(5):373-81. PMid:6355413. http://dx.doi.org/10.1111/j.1365-2842.1983.tb00133.x
http://dx.doi.org/10.1111/j.1365-2842.19...

11. Hoszek A, Ericson D. In vitro fluoride release and the antibacterial effect of glass ionomers containing chlorhexidine gluconate. Oper Dent. 2008 Nov-Dec;33(6):696-701. PMid:19051864. http://dx.doi.org/10.2341/08-20
http://dx.doi.org/10.2341/08-20...

12. Takahashi Y, Imazato S, Kaneshiro AV, Ebisu S, Frencken JE, Tay FR. Antibacterial effects and physical properties of glass-ionomer cements containing chlorhexidine for the ART approach. Dent Mat. 2006 22(7):647-52. PMid:16226806. http://dx.doi.org/10.1016/j.dental.2005.08.003
http://dx.doi.org/10.1016/j.dental.2005....

13. Tüzüner T, Kuşgöz A, Er K, Taşdemir T, Buruk K, Kemer B. Antibacterial activity and physical properties of conventional glass-ionomer cements containing chlorhexidine diacetate/cetrimide mixtures. J Esthet Restor Dent. 2011 Feb; 23(1):46-55. PMid:21323839. http://dx.doi.org/10.1111/j.1708-8240.2010.00385.x
http://dx.doi.org/10.1111/j.1708-8240.20... ^{- 14}14. Yesilyurt C, Er K, Tasdemir T, Buruk K, Celik D. Antibacterial activity and physical properties of glass-ionomer cements containing antibiotics. Oper Dent. 2009 Jan-Feb; 34(1):18-23. PMid:19192833. http://dx.doi.org/10.2341/08-30
http://dx.doi.org/10.2341/08-30... have proposed the association of anti-septic agents with GICs, in order to improve their antibacterial properties.

Chlorhexidine (CHX) has been used in association with GICs, particularly in the forms of digluconate¹⁰10. Jedrychowski JR, Caputo AA, Kerper S. Antibacterial and mechanical properties of restorative materials combined with chlorhexidines. J Oral Rehabil. 1983 Sep; 10(5):373-81. PMid:6355413. http://dx.doi.org/10.1111/j.1365-2842.1983.tb00133.x
http://dx.doi.org/10.1111/j.1365-2842.19... ^{, 13}13. Tüzüner T, Kuşgöz A, Er K, Taşdemir T, Buruk K, Kemer B. Antibacterial activity and physical properties of conventional glass-ionomer cements containing chlorhexidine diacetate/cetrimide mixtures. J Esthet Restor Dent. 2011 Feb; 23(1):46-55. PMid:21323839. http://dx.doi.org/10.1111/j.1708-8240.2010.00385.x
http://dx.doi.org/10.1111/j.1708-8240.20... and diacetate¹²12. Takahashi Y, Imazato S, Kaneshiro AV, Ebisu S, Frencken JE, Tay FR. Antibacterial effects and physical properties of glass-ionomer cements containing chlorhexidine for the ART approach. Dent Mat. 2006 22(7):647-52. PMid:16226806. http://dx.doi.org/10.1016/j.dental.2005.08.003
http://dx.doi.org/10.1016/j.dental.2005.... ^{, 13}13. Tüzüner T, Kuşgöz A, Er K, Taşdemir T, Buruk K, Kemer B. Antibacterial activity and physical properties of conventional glass-ionomer cements containing chlorhexidine diacetate/cetrimide mixtures. J Esthet Restor Dent. 2011 Feb; 23(1):46-55. PMid:21323839. http://dx.doi.org/10.1111/j.1708-8240.2010.00385.x
http://dx.doi.org/10.1111/j.1708-8240.20... ^{, 15}15. Türkün LS, Türkün M, Ertugrul F, Ates M, Brugger S. Long-term antibacterial effects and physical properties of a chlorhexidine containing glass ionomer cement. J Esthet Restor Dent. 2008; 20(1):29-44. PMid:18237338. http://dx.doi.org/10.1111/j.1708-8240.2008.00146.x
http://dx.doi.org/10.1111/j.1708-8240.20... . Nevertheless, their antibacterial effect is concentration-dependent¹¹11. Hoszek A, Ericson D. In vitro fluoride release and the antibacterial effect of glass ionomers containing chlorhexidine gluconate. Oper Dent. 2008 Nov-Dec;33(6):696-701. PMid:19051864. http://dx.doi.org/10.2341/08-20
http://dx.doi.org/10.2341/08-20... , and at high concentrations, CHX may interfere in the physical and mechanical properties of GIC¹⁰10. Jedrychowski JR, Caputo AA, Kerper S. Antibacterial and mechanical properties of restorative materials combined with chlorhexidines. J Oral Rehabil. 1983 Sep; 10(5):373-81. PMid:6355413. http://dx.doi.org/10.1111/j.1365-2842.1983.tb00133.x
http://dx.doi.org/10.1111/j.1365-2842.19... ^{, 11}11. Hoszek A, Ericson D. In vitro fluoride release and the antibacterial effect of glass ionomers containing chlorhexidine gluconate. Oper Dent. 2008 Nov-Dec;33(6):696-701. PMid:19051864. http://dx.doi.org/10.2341/08-20
http://dx.doi.org/10.2341/08-20... .

In order to attain the clinical success of a restorative technique, it is important to point out that the modified material must present adequate physical properties, and its property of bonding to dental structures must not be altered, since the anticariogenic effect depends on a combination of antibacterial agent release and retention time of the material in the cavity¹¹11. Hoszek A, Ericson D. In vitro fluoride release and the antibacterial effect of glass ionomers containing chlorhexidine gluconate. Oper Dent. 2008 Nov-Dec;33(6):696-701. PMid:19051864. http://dx.doi.org/10.2341/08-20
http://dx.doi.org/10.2341/08-20... . As studies of the bond strength of GIC associated with chlorhexidine are scarce¹²12. Takahashi Y, Imazato S, Kaneshiro AV, Ebisu S, Frencken JE, Tay FR. Antibacterial effects and physical properties of glass-ionomer cements containing chlorhexidine for the ART approach. Dent Mat. 2006 22(7):647-52. PMid:16226806. http://dx.doi.org/10.1016/j.dental.2005.08.003
http://dx.doi.org/10.1016/j.dental.2005.... and there are no studies testing this property in caries-affected dentin, the aim of this study was to evaluate the influence of the addition of different concentrations of CHX diacetate, on the bond strength of a high viscosity GIC to sound and caries-affected dentin.

MATERIAL AND METHOD

1. Selection and Preparation of Teeth

Eighty sound extracted human third molars were obtained from the Tooth Bank of the Araraquara School of Dentistry - UNESP, with approval from the Research Ethics Committee (Report 68.388, of August 07, 2012). After the removal of tissue remainders, prophylaxis and washing, only teeth without anatomical and structural defects were selected. These were stored in a 0.1% thymol solution, under refrigeration (4 °C) up to the time of being used. The teeth were randomly divided into eight groups (n=10) according to the condition of the substrate (caries-affected dentin and sound dentin) and concentration of chlorhexidine diacetate added to the material (0%, 0.5%, 1% and 2%). The material used was a high viscosity GIC (Ketac Molar Easymix - 3M-ESPE Dental Products, St. Paul, MN, USA) (Table 1).

1.1. Obtaining the dentin surface

The teeth were cut in the transverse direction in the occlusal third of the crown, for the purpose of producing a flat surface in dentin. The cut was made with a metallographic cutter (ISOMET 1000, Buehler Ltd., Lake Bluff, IL, EUA) equipped with a diamond disc (No.11-4254, Buehler LTD., Lake Bluff IL, USA), at a speed of 300 rpm and force of 200 gf, under constant cooling. The surfaces were inspected under a stereomicroscopy (Model SZX7, Olympus, São Paulo, Brazil) at 40x magnification to prove the absence enamel remainders on the dentin surface.

1.2. Artificial induction of caries lesions

In half of the selected teeth (n=40) one of the roots of each tooth was perforated and transfixed with orthodontic wire to enable the teeth to be suspended. The teeth were sealed with two layers of acid resistant enamel, leaving only the dentin surface exposed, and were then sterilized with ethylene oxide. After this, the teeth were suspended in a cariogenic solution (BHI broth supplemented with 2% sucrose, 1% glucose and 0.5% yeast extract; 25 mL/tooth) and inoculated with 10⁵ 5. Xie D, Brantley WA, Culbertson BM, Wang G. Mechanical properties and microstructures of glass-ionomer cements. Dent Mat. 2000 Mar;16(2):129-38. http://dx.doi.org/10.1016/S0109-5641(99)00093-7
http://dx.doi.org/10.1016/S0109-5641(99)... CFU/mL of Streptoccocus mutans ATCC 25175 (Tropical Culture Collection - André Toselo Foundation). The set was incubated under microaerophilic conditions at 37 °C for 14 days, with changes of cariogenic solution every 48 hours, without the inoculation of new microorganisms. After the incubation period, the biofilm was removed with gauze and the sealing material with the aid of scalpel blades. The teeth were abundantly washed in deionized water and the dentin surface was found to be darkened and softened when it was touched with an exploratory probe without using pressure¹⁶16. Ricci HA, Scheffel DLS, Santos FJ, Jafelicci-Junior M, Hebling J. Influência da clorexidina na capacidade de umectablidade da dentina hígida e afetada por cárie por um sistema adesivo. ROBRAC: Rev Odontol Brasil Central. 2011; 20 (53): 119-124..

1.3. Carious tissue removal and obtainment of dies

In the teeth with artificially induced caries lesions, the infected dentin was manually removed with 320 grain silicon carbide abrasive papers, until hardened dentin, resistant to the touch of a sharp exploratory probe, without using pressure, was obtained (affected dentin). In an attempt to obtain a similar dentin depth among the caries-affected teeth and the teeth that were maintained sound, the latter were also worn with the same type of abrasive paper.

After this, the teeth were washed in an ultrasonic bath, embedded in self-polymerizing acrylic resin, using a cylindrical PVC tube as matrix, with an external diameter of 20 mm by 18 mm high, so that the dentin surface would be centralized and parallel to the base of the tube. After complete polymerization of the acrylic resin, all the teeth were carefully abraded manually with 320 grit silicon carbide abrasive papers lubricated with water, for 15 seconds, in order to produce a standardized smear layer¹⁶16. Ricci HA, Scheffel DLS, Santos FJ, Jafelicci-Junior M, Hebling J. Influência da clorexidina na capacidade de umectablidade da dentina hígida e afetada por cárie por um sistema adesivo. ROBRAC: Rev Odontol Brasil Central. 2011; 20 (53): 119-124.. All the procedures were carried out by one single, previously trained operator.

2. Test Specimen Fabrication

On the dentin surface of each tooth a test specimen was constructed. Initially, the bonding area was delimited using double-faced acid resistant adhesive tape (3M do Brasil, Sumaré, SP, Brazil) with a perforation (1.0 mm in diameter) made with a rubber mat perforator (model Ainsworth, Wilcos do Brasil Indústria e Comércio Ltda, Petrópolis, RJ, Brazil). After this, the dentin surfaces were etched with polyacrylic acid for 10 seconds and then washed with a jet of water-air for 10 seconds and dried with cotton wool balls. A transparent cylindrical silicone matrix 1 mm high with an orifice 1 mm in diameter obtained from a disposable urethral probe (Embramed, São Paulo, SP, Brazil) was placed so that its internal diameter would coincide with the perforation in the adhesive tape, and this was used as a matrix for fabricating the test specimens. The material was manipulated manually at a controlled room temperature (24 ± 1 °C), in accordance with the Manufacturer's recommendations (3M - ESPE Dental Products, St. Paul, MN,USA) and was inserted into the matrix with the aid of a Centrix syringe (DFL, Indústria e Comércio S.A, Jacarepaguá, RJ, Brazil). The test specimens were protected with vaseline on their top portion and the set (die + microtube + test specimen) was stored at 37 °C with 100% humidity for 24 hours. After this the matrix were removed with the aid of a scalpel blade no.15 (Embramed, Jurubatuba, SP, Brazil). The test specimens were observed under a stereomicroscopy at 40x magnification to certify the absence of defects at the bond interface.

2.1. Bond Strength Determination by means of the microshear test

The mechanical microshear test was performed in a mechanical testing machine (DL-Digital Line, EMIC, Paraná, Brazil), previously adjusted for tensile forces. To perform the test, a metal wire 0.2 mm in diameter was used simultaneously lassoing the test specimen as closely as possible to the material/dentin bond and prolongation of the load cell. The movements of traction were made at a speed of 0.5 mm/min. The tests were started by means of a specific computerized program (Tesc-Test Script, EMIC Equipamentos de Ensaio Ltda, São José dos Pinhais, Paraná, Brazil) and proceeded until fracture. The maximum stress values in MegaPascal withstood by the dentin/material bond were recorded.

3. Fracture Pattern Analysis

The fracture pattern of each specimen was evaluated by a single trained examiner, with the aid of light microscope (Model SZX7 Olympus, São Paulo, Brazil) at a magnification that would allow adequate analysis (approximately 40x). The fractures were classified as adhesive (failure between the substrate and restorative material), cohesive in dentin or in material (failure in dentin or in material, respectively) and mixed (combination of adhesive and cohesive failures). The operator was blind to the group to which each test specimen belonged.

4. Analysis of the Results

The bond strength data (in MPa) were evaluated as regards the normality and homogeneity of variance. As these conditions were not met, the non parametric Kruskall-Wallis test was applied, complemented with the Mann-Whitney test. The level of significance adopted for decision making was 5%. Fracture pattern analysis was done in a descriptive manner.

RESULT

The bond strength values considering the variables chlorhexidine diacetate concentration and condition of the substrate are presented in Table 2. In affected dentin, two specimens (one from Group GIC and the other from Group GIC+2%CHX) fractured during removal of the matrix and were excluded from the analysis.

Condition of the substrate (sound and caries-affected dentin) had no influence on the immediate bond strength values (p>0.05). For both conditions, the addition of chlorhexidine diacetate to GIC in the concentrations of 0.5% and 1% showed statistically similar bond strength results to those of the control group without the addition of chlorhexidine (GIC) (p>0.05), and all the groups presented higher bond strength than the group in which CHX diacetate at the concentration of 2% was added (p<0.025), (Table 2).

The distribution of the fracture types for each study group may be observed in Figura 1. The cohesive in material and mixed fractures were predominant for all groups, irrespective of the condition of the substrate. No cohesive failure was observed in dentin.

In addition, it may be observed that when CHX diacetate was added to GIC, there was an increase in the percentage of the adhesive failures in caries-affected dentin, and this was proportional to the increase in concentration. For sound dentin, the increase in the percentage of adhesive failures occurred only when 2% CHX diacetate was used.

DISCUSSION

Bonding is a phenomenon by which two surfaces remain attached by means of chemical or chemical-physical interactions. One of the main characteristics of GICs is the bond to dental structures without any pre-treatment of the surface¹⁴14. Yesilyurt C, Er K, Tasdemir T, Buruk K, Celik D. Antibacterial activity and physical properties of glass-ionomer cements containing antibiotics. Oper Dent. 2009 Jan-Feb; 34(1):18-23. PMid:19192833. http://dx.doi.org/10.2341/08-30
http://dx.doi.org/10.2341/08-30... . However, this property may be affected by the conditions of the substrate¹⁷17. Glasspole EA, Erickson RL,Davidson CL. Effect of surface treatments on bond strength of glass ionomers to enamel. Dent Mater. 2002 Sep; 18(6):454-62. http://dx.doi.org/10.1016/S0109-5641(01)00068-9
http://dx.doi.org/10.1016/S0109-5641(01)...

18. Gordan VV. Effect of conditioning times on resin-modified glass-ionomer bonding. Am J Dent. 2000 Feb; 13(1):13-6. PMid:11763896. ^{- 19}19. Kobayashi CA, Fujishima A, Miyasaki T, Kimura Y, Matsumoto K, Osada T, et al. Efect of Nd:YAG laser irradiation on shear bond strength of glass-ionomer luting cement to dentin surface. Int J Prothodont. 2003 Sep-Oct; 16(5):493-8. PMid:14651233..

Previous studies have shown that the values of shear bond strength of GICs to sound dentin are low, generally between 1 and 3 MPa and they rarely exceed 5 MPa²⁰20. Berry EA, Powers JM. Bond strength of glass ionomers to coronal and radicular dentin. Oper Dent. 1994 Jul-Aug;19(4):122-6. PMid:9028230.

21. Cattani-Lorente MA, Godin C, Meyer JM. Early strength of glass ionomer cements. Dent Mater. 1993 Jan; 9(1):57-62. http://dx.doi.org/10.1016/0109-5641(93)90107-2
http://dx.doi.org/10.1016/0109-5641(93)9... ^{- 22}22. Czarnecka B, Deregowska-Nosowicz P, Limanowska-Shaw H, Nicholson JW. Shear bond strengths of glass-ionomer cements to sound and to prepared carious dentine. J Mater Sci: Mater Med. 2007 May; 18(5):845-9. PMid:17203413. http://dx.doi.org/10.1007/s10856-006-0085-y
http://dx.doi.org/10.1007/s10856-006-008... . These values tend to be higher in microtensile tests due to the differences in stress distribution and reduction in bonding area when compared with shear tests²³23. Choi K, Oshida Y, Platt JA, Cochran MA, Matis BA, Yi K. Microtensile bond strength of glass ionomer cements to artificially created carious dentin. Oper Dent. 2006 Sep-Oct;31(5):590-7. PMid:17024948. http://dx.doi.org/10.2341/05-108
http://dx.doi.org/10.2341/05-108... ^{, 24}24. Garcia FCP, Terada RSS, Carvalho RM. Testes mecânicos para a avaliação laboratorial da união resina /dentina. Rev Fac Odontol Bauru. 2002; 10(3): 118. In the present study, the option taken was to use the microshear test, with the purpose of obtaining specimens with a reduced area, without the need for a great deal of manipulation of the specimens, as occurs during their obtainment for the microtensile test. In spite of this, the bond strength medians were lower than 5 MPa.

Low bond strength values may have occurred because before the mechanical test, the plastic matrix used for fabrication of the test specimens was removed with the aid of a scalpel blade, and the pressure exerted for cutting may have been transferred to the cylinder of material, forming cracks in it, and also cause some level of stress at the bond interface, thus interfering in the real bond strength²⁵25. Andrade AM, Garcia E, Moura SK, Reis A, Loguercio A, Silva LM, et al. Do the microshear test variables affect the bond strength values?. Int J Dent. 2012. doi: 10.1155/2012/618960. http://dx.doi.org/10.1155/2012/618960
http://dx.doi.org/10.1155/2012/618960... . Maintaining the plastic matrix would be an alternative, however, it is resilient and capable of absorbing stress during the test. Andrade et al.²⁵25. Andrade AM, Garcia E, Moura SK, Reis A, Loguercio A, Silva LM, et al. Do the microshear test variables affect the bond strength values?. Int J Dent. 2012. doi: 10.1155/2012/618960. http://dx.doi.org/10.1155/2012/618960
http://dx.doi.org/10.1155/2012/618960... (2012) evaluating the bond strength of a resin composite to dentin, with two adhesive systems, verified no significant difference between the groups either with maintaining or removing the plastic matrix. Higher bond strength values were obtained by the authors when the resin composite was pre-polymerized in the matrix and it was removed before the bond to dentin was performed. As the application of this methodology is not possible when it concerns the GIC/dentin bond, which is chemically determined during the setting reaction of the material, the option was taken to remove the plastic matrix before performing the microshear test, which is the method most frequently used in the literature.

The influence of the addition of CHX diacetate in different concentrations on the bond strength of a high viscosity GIC to sound and caries-affected dentin was evaluated in this study. The results showed that the condition of the substrate did not significantly influence the immediate bond strength of the material, irrespective of whether or not CHX was added.

Up to now, few studies have evaluated the bond strength of GIC to carious dentin. As was demonstrated in the present study, Way et al.²⁶26. Way JL, Caputo AA, Jedrychowski JR. Bond strength of light-cured glass ionomers to carious primary dentin. J Dent Child. 1996 Jul-Aug; 63(4):261-4. PMid:8893978. (1996) using resin-modified GIC, and Palma-Dibb et al.²⁷27. Palma-Dibb RG, de Castro CG, Ramos RP, Chimello DT, Chinelatti MA. Bond strength of glass-ionomer cements to carious-affected dentin. J Adhes Dent. 2003 Spring; 5(1):57-62. PMid:12729084. (2003) using conventional and resin-modified GICs, also observed no significant difference in the bond strength to caries-affected and sound dentin. On the other hand, Choi et al.²³23. Choi K, Oshida Y, Platt JA, Cochran MA, Matis BA, Yi K. Microtensile bond strength of glass ionomer cements to artificially created carious dentin. Oper Dent. 2006 Sep-Oct;31(5):590-7. PMid:17024948. http://dx.doi.org/10.2341/05-108
http://dx.doi.org/10.2341/05-108... (2006) using a conventional GIC and another resin-modified GIC verified a significantly lower microtensile bond strength to caries-affected dentin. Although the bond mechanism of GICs to dental structure has not yet been well elucidated, these authors considered that the loss of calcium ions in carious dentin is unfavorable to bonding, because in the first moment the chemical bond of GICs to mineralized dental tissues involves the chelation of the carboxylic groups of polyalkenoic acid with the calcium of hydroxyapatite²⁸28. Yoshida Y, Van Meerbeek B, Nakayama Y, Snauwaert J, Hellemans L, Lambrechts P, et al. Evidence of chemical bonding at biomaterial-hard tissue interfaces. J Dent Res. 2000 Feb; 79(2):709-14. PMid:10728971. http://dx.doi.org/10.1177/00220345000790020301
http://dx.doi.org/10.1177/00220345000790... . Moreover, the affected-dentin surface is more porous and capable of retaining traces of lactic acid involved in the caries lesion²²22. Czarnecka B, Deregowska-Nosowicz P, Limanowska-Shaw H, Nicholson JW. Shear bond strengths of glass-ionomer cements to sound and to prepared carious dentine. J Mater Sci: Mater Med. 2007 May; 18(5):845-9. PMid:17203413. http://dx.doi.org/10.1007/s10856-006-0085-y
http://dx.doi.org/10.1007/s10856-006-008... ^{, 29}29. Sano H. Relationship between caries detector staining and structural characteristics of carious dentin. J. Stomatol. Soc. Jpn. 1987 Mar; 54(1):241-70. http://dx.doi.org/10.5357/koubyou.54.241
http://dx.doi.org/10.5357/koubyou.54.241... . The GICs rapidly react with this acids³⁰30. Nicholson JW, Aggarwal A, Czarnecka B, Limanowska-Shaw H. The rate of change of pH of lactic acid exposed to glass-ionomer dental cements. Biomaterials. 2000 Oct; 21(19):1989-93. http://dx.doi.org/10.1016/S0142-9612(00)00085-5
http://dx.doi.org/10.1016/S0142-9612(00)... and this may be the reason why the bond of some cements to sound and caries-affected dentin is different.

In the present study, as in the study of Palma-Dibb et al.²⁷27. Palma-Dibb RG, de Castro CG, Ramos RP, Chimello DT, Chinelatti MA. Bond strength of glass-ionomer cements to carious-affected dentin. J Adhes Dent. 2003 Spring; 5(1):57-62. PMid:12729084. (2003) the softened dentin was removed until a surface well resistant to touch (affected dentin) was obtained. After the teeth were embedded in acrylic resin, this dentin was again abraded with 320 grit silicon carbide abrasive papers for 15 seconds to produce a standardized smear layer on all the test specimens¹⁶16. Ricci HA, Scheffel DLS, Santos FJ, Jafelicci-Junior M, Hebling J. Influência da clorexidina na capacidade de umectablidade da dentina hígida e afetada por cárie por um sistema adesivo. ROBRAC: Rev Odontol Brasil Central. 2011; 20 (53): 119-124.. This procedure may have contributed to obtaining a dentin surface with characteristics close those of sound dentin. Therefore, it is considered that the loss of calcium ions in this dentin was not enough to determine a significant reduction in bond strength with GIC when compared with that obtained to sound dentin. When comparing the bond strength of GIC to sound dentin and dentin after the process of erosion, Cruz et al.³¹31. Cruz JB, Lenzi TL, Tedesco TK, Guglielmi Cde A, Raggio DP. Eroded dentin does not jeopardize the bond strength of adhesive restorative materials. Braz Oral Res. 2012 Jul-Aug; 26(4):306-12. PMid:22714927. http://dx.doi.org/10.1590/S1806-83242012005000009
http://dx.doi.org/10.1590/S1806-83242012... (2012) also observed no statistically significant differences. Although dentin that has gone through the process of erosion would be highly demineralized, with a low calcium and hydroxyapatite content, this condition did not affect the bond of the material, but it may be related to the alterations in the fracture patterns³¹31. Cruz JB, Lenzi TL, Tedesco TK, Guglielmi Cde A, Raggio DP. Eroded dentin does not jeopardize the bond strength of adhesive restorative materials. Braz Oral Res. 2012 Jul-Aug; 26(4):306-12. PMid:22714927. http://dx.doi.org/10.1590/S1806-83242012005000009
http://dx.doi.org/10.1590/S1806-83242012... .

High viscosity glass ionomer cements, such as Ketac Molar Easymix were especially developed for use in the Atraumatic Restorative Treatment technique. These materials present high performance physical properties⁶6. Peez R, Frank S. The physical-mechanical performance of the new Ketac Molar Easymix compared to commercially available glass ionomer restoratives. J Dent. 2006 Sep; 34(8):582-7. PMid:16581174. http://dx.doi.org/10.1016/j.jdent.2004.12.009
http://dx.doi.org/10.1016/j.jdent.2004.1... , however, they have demonstrated a lower level of fluoride release in comparison with the conventional GICs⁸8. Gao W, Smales R J, Gale M S. Fluoride release/uptake from newer glass ionomer cements used with the ART approach. Am J Dent. 2000 Aug; 13(4):201-4. PMid:11763931. ^{, 9}9. Smales RJ, Yip HK. The atraumatic restorative treatment (ART) approach for the management of dental caries. Quintessence Int. 2002 Jun; 33(6):427-32. PMid:12073723.. Since the effect of this lower level of fluoride release on residual bacteria has not yet been well elucidated, the association of these GICs with antimicrobial agents such as chlorhexidine, ciprofloxacin, metronidazol and minocycline¹⁰10. Jedrychowski JR, Caputo AA, Kerper S. Antibacterial and mechanical properties of restorative materials combined with chlorhexidines. J Oral Rehabil. 1983 Sep; 10(5):373-81. PMid:6355413. http://dx.doi.org/10.1111/j.1365-2842.1983.tb00133.x
http://dx.doi.org/10.1111/j.1365-2842.19...

11. Hoszek A, Ericson D. In vitro fluoride release and the antibacterial effect of glass ionomers containing chlorhexidine gluconate. Oper Dent. 2008 Nov-Dec;33(6):696-701. PMid:19051864. http://dx.doi.org/10.2341/08-20
http://dx.doi.org/10.2341/08-20...

12. Takahashi Y, Imazato S, Kaneshiro AV, Ebisu S, Frencken JE, Tay FR. Antibacterial effects and physical properties of glass-ionomer cements containing chlorhexidine for the ART approach. Dent Mat. 2006 22(7):647-52. PMid:16226806. http://dx.doi.org/10.1016/j.dental.2005.08.003
http://dx.doi.org/10.1016/j.dental.2005....

13. Tüzüner T, Kuşgöz A, Er K, Taşdemir T, Buruk K, Kemer B. Antibacterial activity and physical properties of conventional glass-ionomer cements containing chlorhexidine diacetate/cetrimide mixtures. J Esthet Restor Dent. 2011 Feb; 23(1):46-55. PMid:21323839. http://dx.doi.org/10.1111/j.1708-8240.2010.00385.x
http://dx.doi.org/10.1111/j.1708-8240.20... ^{- 14}14. Yesilyurt C, Er K, Tasdemir T, Buruk K, Celik D. Antibacterial activity and physical properties of glass-ionomer cements containing antibiotics. Oper Dent. 2009 Jan-Feb; 34(1):18-23. PMid:19192833. http://dx.doi.org/10.2341/08-30
http://dx.doi.org/10.2341/08-30... has been suggested in order to increase their antibacterial properties. In this study, CHX in the form of diacetate was chosen because of being more stable than CHX digluconate, and because it is presented in the form of power that would be more easily added to the GIC powder¹⁵15. Türkün LS, Türkün M, Ertugrul F, Ates M, Brugger S. Long-term antibacterial effects and physical properties of a chlorhexidine containing glass ionomer cement. J Esthet Restor Dent. 2008; 20(1):29-44. PMid:18237338. http://dx.doi.org/10.1111/j.1708-8240.2008.00146.x
http://dx.doi.org/10.1111/j.1708-8240.20... . Türkün et al.¹⁵15. Türkün LS, Türkün M, Ertugrul F, Ates M, Brugger S. Long-term antibacterial effects and physical properties of a chlorhexidine containing glass ionomer cement. J Esthet Restor Dent. 2008; 20(1):29-44. PMid:18237338. http://dx.doi.org/10.1111/j.1708-8240.2008.00146.x
http://dx.doi.org/10.1111/j.1708-8240.20... (2008) using CHX digluconate and diacetate in the concentrations of 0.5%, 1.25% and 2.5% verified that 1.25% CHX diacetate presented better antibacterial properties without altering the mechanical properties of GIC. Mixed with GIC in the concentrations of 0.5% and 1% in the present study, CHX diacetate presented similar bond strength to dentin results to those obtained with GIC without any association, and higher than those presented for the concentration of 2%. These results are compatible with those obtained in the study of Takahashi et al.¹²12. Takahashi Y, Imazato S, Kaneshiro AV, Ebisu S, Frencken JE, Tay FR. Antibacterial effects and physical properties of glass-ionomer cements containing chlorhexidine for the ART approach. Dent Mat. 2006 22(7):647-52. PMid:16226806. http://dx.doi.org/10.1016/j.dental.2005.08.003
http://dx.doi.org/10.1016/j.dental.2005.... (2006), in which statistically significant difference in the bond strength of a GIC with the addition of various concentrations of CHX diacetate were found only in the groups with 2% and 3% CHX. These authors demonstrated that the incorporation of 1% CHX diacetate was excellent for increasing the antibacterial activity, without affecting the mechanical properties and bonding capacity. Other studies have also verified an increase in antibacterial activity of GIC when both CHX diacetate and CHX digluconate were added in concentrations as from 0.5%¹⁰10. Jedrychowski JR, Caputo AA, Kerper S. Antibacterial and mechanical properties of restorative materials combined with chlorhexidines. J Oral Rehabil. 1983 Sep; 10(5):373-81. PMid:6355413. http://dx.doi.org/10.1111/j.1365-2842.1983.tb00133.x
http://dx.doi.org/10.1111/j.1365-2842.19... ^{, 11}11. Hoszek A, Ericson D. In vitro fluoride release and the antibacterial effect of glass ionomers containing chlorhexidine gluconate. Oper Dent. 2008 Nov-Dec;33(6):696-701. PMid:19051864. http://dx.doi.org/10.2341/08-20
http://dx.doi.org/10.2341/08-20... ^{, 13}13. Tüzüner T, Kuşgöz A, Er K, Taşdemir T, Buruk K, Kemer B. Antibacterial activity and physical properties of conventional glass-ionomer cements containing chlorhexidine diacetate/cetrimide mixtures. J Esthet Restor Dent. 2011 Feb; 23(1):46-55. PMid:21323839. http://dx.doi.org/10.1111/j.1708-8240.2010.00385.x
http://dx.doi.org/10.1111/j.1708-8240.20... . Nevertheless, the physical and mechanical properties of GIC were compromised by the addition of CHX in concentrations higher than 2%.

The addition of CHX in high concentrations appears to interfere in fluoride release. According to Hoszek, Ericson¹¹11. Hoszek A, Ericson D. In vitro fluoride release and the antibacterial effect of glass ionomers containing chlorhexidine gluconate. Oper Dent. 2008 Nov-Dec;33(6):696-701. PMid:19051864. http://dx.doi.org/10.2341/08-20
http://dx.doi.org/10.2341/08-20... (2008), GICs with additions of CHX in concentrations of 3% release up to 30% less fluoride in 60 days than GIC without CHX. A possible explanation for this is that the molecules of CHX may interact with those of the fluoride ions, resulting in the precipitation of salts with low solubility, leading to a lower level of its release¹¹11. Hoszek A, Ericson D. In vitro fluoride release and the antibacterial effect of glass ionomers containing chlorhexidine gluconate. Oper Dent. 2008 Nov-Dec;33(6):696-701. PMid:19051864. http://dx.doi.org/10.2341/08-20
http://dx.doi.org/10.2341/08-20... . This factor, associated with the cationic properties of CHX salts, which interfere in the reaction of polyacrylic acid with the glass particles¹²12. Takahashi Y, Imazato S, Kaneshiro AV, Ebisu S, Frencken JE, Tay FR. Antibacterial effects and physical properties of glass-ionomer cements containing chlorhexidine for the ART approach. Dent Mat. 2006 22(7):647-52. PMid:16226806. http://dx.doi.org/10.1016/j.dental.2005.08.003
http://dx.doi.org/10.1016/j.dental.2005.... , may harm the mechanical properties of the material when high concentrations of CHX are added. It is therefore suggested that the mechanical properties of the material depend on the concentration of CHX added to it, and that concentrations equal to or higher than 2% may cause a significant reduction in the bond strength of GIC to sound and caries-affected dentin.

1. Fracture Pattern Analysis

In this study, cohesive in material and mixed fractures were predominant. To Cruz et al.³¹31. Cruz JB, Lenzi TL, Tedesco TK, Guglielmi Cde A, Raggio DP. Eroded dentin does not jeopardize the bond strength of adhesive restorative materials. Braz Oral Res. 2012 Jul-Aug; 26(4):306-12. PMid:22714927. http://dx.doi.org/10.1590/S1806-83242012005000009
http://dx.doi.org/10.1590/S1806-83242012... (2012), fracture patterns are related to the properties of all components of the bonded joint: material, bonding interface and substrate, in addition to the mechanics of the test assembly. Higher prevalence of cohesive in material fractures has also been observed in other studies¹⁰10. Jedrychowski JR, Caputo AA, Kerper S. Antibacterial and mechanical properties of restorative materials combined with chlorhexidines. J Oral Rehabil. 1983 Sep; 10(5):373-81. PMid:6355413. http://dx.doi.org/10.1111/j.1365-2842.1983.tb00133.x
http://dx.doi.org/10.1111/j.1365-2842.19... ^{, 23}23. Choi K, Oshida Y, Platt JA, Cochran MA, Matis BA, Yi K. Microtensile bond strength of glass ionomer cements to artificially created carious dentin. Oper Dent. 2006 Sep-Oct;31(5):590-7. PMid:17024948. http://dx.doi.org/10.2341/05-108
http://dx.doi.org/10.2341/05-108... ^{, 27}27. Palma-Dibb RG, de Castro CG, Ramos RP, Chimello DT, Chinelatti MA. Bond strength of glass-ionomer cements to carious-affected dentin. J Adhes Dent. 2003 Spring; 5(1):57-62. PMid:12729084. and has been related to the low tensile strength and low cohesive strength of GICs, as well as to the low values of bond strength. This in the majority of instances does not represent the real bond strength of the material to dentin²³23. Choi K, Oshida Y, Platt JA, Cochran MA, Matis BA, Yi K. Microtensile bond strength of glass ionomer cements to artificially created carious dentin. Oper Dent. 2006 Sep-Oct;31(5):590-7. PMid:17024948. http://dx.doi.org/10.2341/05-108
http://dx.doi.org/10.2341/05-108... .

In the present study, although no statistically significant difference was detected between the median of the bond strength values of GIC to sound dentin (4.55 MPa) and to caries-affected dentin (3.25 MPa), the latter was shown to be numerically lower. When the bond to affected dentin was established, there was an increase in the percentage of adhesive fractures proportional to the increase in concentration of CHX diacetate added to the GIC, whereas for sound dentin the increase in the percentage of adhesive fractures occurred only for 2% CHX. This may be explained by a lower degree of bond of the modified material to dentin, particularly when it is affected by caries.

Although low bond strength values have been observed for both sound dentin and caries-affected dentin when high viscosity GIC modified by the addition of CHX diacetate, or not, was used, these results cannot yet be considered conclusive, and further studies are necessary, using other tests, including determination of the real advantage in the reduction of microorganisms determined by this modification of the material.

CONCLUSION

The addition of CHX diacetate in the concentrations of 0.5% and 1% did not negatively influence the bond strength of a high viscosity GIC to sound or caries-affected dentin, and this may be a good option for improving the antibacterial activity of this cement.

REFERENCES

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