|Year : 2012 | Volume
| Issue : 1 | Page : 41-46
Strength characteristics and marginal sealing ability of chlorhexidine-modified glass ionomer cement: An in vitro study
P Ahluwalia1, S Chopra2, AM Thomas2
1 Department of Pedodontics and Preventive Dentistry, Gian Sagar Dental College and Hospital, Ram Nagar, Banur, Patiala, India
2 Department of Pedodontics and Preventive Dentistry, Christian Dental College and Hospital, Ludhiana, Punjab, India
|Date of Web Publication||3-May-2012|
Department of Pediatric and Preventive Dentistry, Gian Dental College and Hospital, Ram Nagar, Banur, Patiala, Punjab
| Abstract|| |
Background: This study was done to compare and evaluate the compressive strength, diametral tensile strength, and microleakage of glass ionomer cement and chlorhexidine-modified glass ionomer cement. The glass ionomer cements used in the study were Fuji IX for group I and chlorhexidine-modified glass ionomer cement for group II. Materials and Methods: The strength characteristics (compressive and diametral tensile strengths) and microleakage of both the groups were evaluated after 24 h. Student's "t" test and Mann-Whitney test were used for statistical analysis of the difference in strength characteristics and microleakage. Results: There was no statistical difference (P>0.05) in the strength characteristics and microleakage of glass ionomer cement and chlorhexidine-modified glass ionomer cement. Conclusion: The present study suggests that strength characteristics and marginal sealing capability of chlorhexidine-modified glass ionomer cement were similar to those of glass ionomer cement (Fuji IX). So, chlorhexidine-modified glass ionomer can be considered as a substitute for glass ionomer cements, especially in pediatric dentistry.
Keywords: Chlorhexidine, compressive strength, diametral tensile strength, glass ionomer cement, microleakage
|How to cite this article:|
Ahluwalia P, Chopra S, Thomas A M. Strength characteristics and marginal sealing ability of chlorhexidine-modified glass ionomer cement: An in vitro study. J Indian Soc Pedod Prev Dent 2012;30:41-6
|How to cite this URL:|
Ahluwalia P, Chopra S, Thomas A M. Strength characteristics and marginal sealing ability of chlorhexidine-modified glass ionomer cement: An in vitro study. J Indian Soc Pedod Prev Dent [serial online] 2012 [cited 2013 May 25];30:41-6. Available from: http://www.jisppd.com/text.asp?2012/30/1/41/95580
| Introduction|| |
Dental caries is a disease that dates back to antiquity and is the most common disease afflicting mankind. Due to lack of oral health awareness, particularly in pediatric patients; the carious lesion tends to go unnoticed. Restoring the carious lesion at an early stage is an ideal treatment option. However, even a simple restorative treatment plan is likely to evoke anxiety in a pediatric patient. So, ART comes out to be a suitable option in such cases as less discomfort has been reported with the use of this technique. ART is a minimal intervention approach where demineralized tooth structure is removed using hand instruments and the cavity, including adjacent pits and fissures, is restored with adhesive restorative materials.  Atraumatic restorative treatment is currently referred to as Alternative restorative treatment. 
The material used for restoration of cavities in ART is usually Glass Ionomer Cement (GIC). It is also the principal element in the armamentarium of restorative materials used for children. Conventional GICs were introduced to the dental profession in 1970s by Wilson and Kent.  GIC provides a slow release of fluoride, which is responsible for its cariostatic action. It bonds chemically to enamel and dentin, thereby reducing the need for a retentive cavity preparation, and it is biocompatible with pulp tissue. Since all carious tooth structure is not removed from the hand-prepared cavity during ART, it is possible that the carious process may soon resume, as not all cultivable microorganisms are always removed.  Moreover, the use of GIC as a restorative material for sealing of caries is also questionable because of the possible microleakage and limitations associated with their physical properties. Therapeutic benefits may be gained by combining antibacterial agents with GICs. Therefore, the incorporation of an antimicrobial agent, which would increase the activity of GIC without significantly affecting its physico-mechanical properties, would add to the benefits of GIC as a restorative material for ART.
The idea of using antiseptics to control dental decay was originally suggested by Miller in 1890. However, it was only in 1964 that convincing evidence was produced that antimicrobial agents could reduce caries activity in humans. Subsequently, in 1970, it was reported that a safe antimicrobial agent called chlorhexidine, which had been widely used in medical field, could effectively reduce plaque formation and experimental gingivitis.  Different salts of chlorhexidine have been evaluated for their antimicrobial efficacy, which is present irrespective of the salt added to the dental restorative material. , The two chlorhexidine salts most commonly incorporated experimentally into dental cements for improving the antimicrobial efficacy are chlorhexidine digluconate and chlorhexidine diacetate. For the longevity of a restoration, it is necessary that the restorative material should have adequate strength and minimal microleakage. Since there are not many studies to assess microleakage and strength characteristics of chlorhexidine-modified GIC, this study was undertaken with a purpose of evaluating and comparing the compressive strength (CS), diametral tensile strength (DTS), and microleakage of chlorhexidine-modified GIC with GIC.
| Materials and Methods|| |
The materials used for the study were GIC (Fuji IX) and chlorhexidine-modified GIC. The control GIC (group I) was prepared with self-curing GIC (Fuji IX). The experimental cement (group II) was formulated from the same batch by incorporating 1% w/w chlorhexidine diacetate salt into the powder component of GIC (Fuji IX). The experimental cement thus obtained was stored in amber-colored bottles to prevent any alterations in the material due to light. For the purpose of the present study, 30 specimens were prepared for each group for compressive and DTS testing. For the assessment of microleakage, a total of 60 primary molar teeth were obtained from the Department of Pedodontics and Preventive Dentistry, Christian Dental College, Ludhiana.
Thirty specimens for CS testing for each of the groups were prepared by a single operator using standardized molds with inner dimensions of 6 mm thickness and 4 mm diameter. ,,, The specimens were prepared by mixing powder and liquid in the ratio 3.6:1 as specified by the manufacturer. The standardized ratio to be used was ensured by using a level scoop of powder with a drop of liquid obtained by holding liquid bottle vertically and gently squeezing the components. The Teflon molds used for preparing specimens were coated with polytetrafluoroethylene dry film lubricant before insertion of material to facilitate removal of hardened cements.  The material was mixed according to the manufacturer's instructions for a period of 25 sec and then inserted in excess into the Teflon molds within 2 minutes from the start of mixing. The samples were covered with acetate strips, isolated from atmosphere with a glass slab, and sealed with a clamp. The assembly was shifted to a water bath at 37 ± 1°C in not more than 120 sec after completion of mixing, to simulate oral conditions. One hour after the completion of mixing, the specimens were removed from the molds; the ends were ground using water as a lubricant on 500-grit Sic paper.  Specimens with non-uniform ends, residual surface defects, or visually apparent pores were discarded, and the remaining specimens stored in deionized water at 37°C for a further period of 23 h at which time the test specimens were compressive loaded (24 h after the completion of mixing). This is the storage procedure specified in both ISO and British Standards.  Prior to testing, the diameter of each specimen was determined using a dial calipers and specimens were placed with their flat ends up between the plates of universal testing machine ,, (UTM-01, Lloyd instruments, UK). A compressive load was applied along the long axis at a crosshead speed of 1 mm/min.  The maximum force applied when the specimen fractured was recorded, and the CS was calculated by the following equation: 
where F=force resulting in failure of specimen and d=diameter of the specimen.
Diametral tensile strength
Thirty specimens for DTS testing for each of the groups were prepared by a single operator using standardized molds with inner dimensions of 6 mm diameter and 3 mm thickness. , The specimens were prepared by mixing powder and liquid in the ratio 3.6:1 as specified by the manufacturer. The standardized ratio to be used was ensured by using a level scoop of powder with a drop of liquid obtained by holding liquid bottle vertically and gently squeezing the components. The Teflon molds used for preparing specimens were coated with polytetrafluoroethylene dry film lubricant before insertion of material to facilitate removal of hardened cements.  The material was mixed according to the manufacturer's instructions for a period of 25 sec and then inserted in excess into the Teflon molds within 2 minutes from the start of mixing. The samples were covered with acetate strips, isolated from atmosphere with a glass slab, and sealed with a clamp. The assembly was shifted to a water bath at 37 ± 1°C in not more than 120 sec after the completion of mixing, to simulate oral conditions. One hour after the completion of mixing, the specimens were removed from the molds; the ends were ground using water as lubricant on 500-grit Sic paper.  Specimens with non-uniform ends, residual surface defects, or visually apparent pores were discarded, and the remaining specimens stored in deionized water at 37°C for a further period of 23 h at which time the test specimens were compressive loaded (24 h after the completion of mixing). This is the storage procedure specified in both ISO and British standards.  Prior to testing, the diameter of each specimen was determined using a dial calipers and specimens were placed with their flat ends up between the plates of universal testing machine , (UTM-01, Lloyd instruments, UK). A compressive load was applied along the long axis at a crosshead speed of 1 mm/min. , The maximum force applied when the specimen fractured was recorded, and the DTS was calculated by the following equation: ,,
diametral tensile strength=2P/ΠDT,
where P=load applied, D=diameter of the specimen, and T=thickness of the specimen.
Sixty sound primary molar teeth were obtained for the purpose of this study after ethical approval, from the Department of Pedodontics and Preventive Dentistry, Christian Dental College. The teeth used for the study were obtained from patients having retained molars indicated for extraction, after taking parental consent for the treatment. The extracted teeth were cleaned of soft tissue and debris and stored in saline at room temperature.  The teeth were disinfected using 1% Chloramine T solution for 1 week and then washed and dried.  Class V cavities (4 mm wide ×2 mm high ×1.5 mm deep)  were prepared on the buccal surfaces of teeth, with no retentive features incorporated in the cavity design, using burs (no. 1 round bur, no. 57 straight fissure bur) with high-speed air rotor handpiece with water coolant. Burs were changed after every five preparations.  All cavosurface angles were kept at right angles with no bevels.  The depth of cavity was standardized at 1.5 mm with the help of premeasured and marked no. 57 straight fissure bur. The standardization of cavities was done using a divider with a locking system, dial calipers, and a graduated probe to further confirm the depth of cavity. The prepared cavity was rinsed thoroughly with air/water spray and dried. GC dentin conditioner was applied for 20 sec to the cavity walls using a brush with light scrubbing motion, rinsed with water, and then dried thoroughly by directing the air stream from the sides to avoid the dessication of dentin. Then, the cavities were restored with GIC and chlorhexidine-modified GIC, respectively. The teeth were restored with bulk placement. After setting, the restoration was finished and polished, keeping the restoration surface wet. After polishing, the restoration was lightly air dried and varnish was applied. After restoration, the teeth were stored in distilled water at 37°C for 24 h  and then subjected to 1500 thermocycles at 5°C and 60°C with 20 sec of dwell time in each bath. 
All the tooth surfaces except the restoration and a 1-mm zone adjacent to its margins were covered with two coats of varnish.  The root apices, if any, were sealed with sticky wax.  The coated teeth were then immersed in 2% methylene blue dye solution for a period of 24 h at 37°C.  The specimens were retrieved after the stipulated time period. After removal from the dye, the coatings were stripped from the teeth by peeling and, where necessary, by scraping.  The teeth were then thoroughly washed in water, dried, and embedded in self-curing resin. The teeth were sectioned into two halves buccolingually in an occlusoapical direction through the middle of restoration by using a diamond disk mounted on a straight handpiece with water coolant. Each section was then observed under stereo microscope. The degree of microleakage of both halves was assessed. The section showing the maximum degree of dye penetration was chosen for grading the microleakage.
The extent of the microleakage was noted according to the following scoring criteria: 
0: No marginal leakage
1: Up to 1/3 cavity depth
2: 1/3-2/3 cavity depth
3: >2/3 cavity depth, but not involving the axial wall
4: Involving the axial wall
The scores were tabulated, interpreted, and the resultant findings were statistically analyzed using Student's "t0" test for strength testing and Mann-Whitney test for microleakage.
| Results|| |
The mean CSs of GIC and chlorhexidine-modified GIC are depicted in [Table 1]. Student's "t" test showed that there was no significant difference (P>0.05) between the CSs of GIC and chlorhexidine-modified GIC.
|Table 1: Comparison of compressive strengths of glass ionomer cement and chlorhexidine-modified glass ionomer after 24 h|
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The mean DTSs of GIC and chlorhexidine-modified GIC are depicted in [Table 2]. Student's "t" test showed that there was no significant difference (P>0.05) between the DTSs of GIC and chlorhexidine-modified GIC.
|Table 2: Comparison of diametral tensile strengths of glass ionomer cement and chlorhexidine-modified glass ionomer cement after 24 h|
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The statistical analysis of microleakage scores using Mann-Whitney test revealed that there was no significant difference (P>0.05) between the microleakage scores of GIC and chlorhexidine-modified GIC [Table 3].
|Table 3: Comparison of microleakage observed with glass ionomer cement and chlorhexidine-modified glass ionomer cement|
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| Discussion|| |
Chlorhexidine has been extensively studied for its antimicrobial activity since past several decades and has been the most potent chemotherapeutic agent against Streptococcus mutans and dental caries, as stated by Emilson.  It is a cationic antiseptic belonging to the chemical group of bisbiguanides and consists of 1,6 bis-p-chlorophenyl-biguainidohexane. Chlorhexidine inhibits the metabolism of S. mutans by suppressing enzymes like glycosyltransferase as well as the phosphoenolpyruvate-phosphotransferase system.  Different salts of chlorhexidine have been evaluated for their antimicrobial efficacy which is present irrespective of the salt added. Chlorhexidine diacetate was chosen as the chlorhexidine salt of choice to be incorporated into GIC in the present study as it is more stable material, not prone to decomposition, and can be easily blended into the GIC. The addition of higher concentrations (5%) resulted in the deterioration of the material while addition of 1% chlorhexidine to dental cement exhibited optimal antimicrobial activity without affecting the strength characteristics.  So, in the light of previous studies, 1% chlorhexidine diacetate was used as the test cement with antibacterial properties in the study. Chlorhexidine as an additive into GICs gained popularity as it increased the antibacterial property of these cements whilst not interfering with their fluoride release, which accounted for the cariostatic action of the cement. ,
The clinical utility of a material is defined by its ability to endure the stresses and strains induced during mastication and function. Mechanical strength is an important property that controls the clinical success of restorative materials. Two of the most commonly used criteria to check the strength of GICs are CS and DTS. So, these two mechanical strength tests (compressive and diametral tensile) were used in this study. The CS is an important property of restorative materials, particularly in the process of mastication. This test is more suitable to compare brittle materials, which show a relatively low result when subject to tension. The DTS is a critical requirement because many clinical failures are due to tensile stress. As it is not possible to measure the tensile strength of brittle materials like GICs directly, the British Standards Institution adopted the DTS test. In this test, a compressive force is applied to a cylindrical specimen across the diameter by compression plates.  The statistical analysis revealed that there was no significant difference in the strengths of both control (group I) and the experimental cement (group II) [Table 1] [Figure 1]. This could be due to the presence of chlorhexidine at a low concentration in GIC, which does not hinder polyion chain formation. For both the groups, the CS values were much higher than the DTS values. This may be explained by the fact that the cohesion between the materials is identical in both the CS and DTS tests, but the direction of forces is reversed. The values of CS obtained in the present study were similar to those obtained by Takahashi and colleagues.  The DTS values [Table 2] were higher than those reported in a previous study by Bresciani and colleagues.  This could be due to the use of different variables, like the methodology and testing conditions.
|Figure 1: Group Ia: Compressive strength of glass ionomer cement. Group Ib: Diametral strength of glass ionomer cement. Group IIa: Compressive strength of chlorhexidine glass ionomer cement. Group IIb: Diametral tensile strength of chlorhexidine glass ionomer cement|
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Another important property responsible for the success of a material used for restorative purposes in the oral cavity is its ability to bond to tooth structure in a way that there is a complete and perfect seal between the margins of restorations and tissue of the tooth. A measure of this property is microleakage. Microleakage can be defined as the passage of bacteria, fluids, molecules, or ions between a cavity wall and the restorative material applied to it.  Microleakage poses a particular problem in the pediatric patient in whom the floor of the cavity preparation is closer to the pulp. The sample size in this study was fixed at 30 per group to make it statistically significant. In spite of the loss of a few samples because of dislodgement of fillings and breakage during sectioning, the number of samples was maintained at 30 by incorporating extra primary molars. The results revealed that group II had higher microleakage, but there was no statistically significant difference in the mean microleakage values between group I and group II [Table 3] [Figure 2]. This could have transpired because the minor amount of chlorhexidine did not hinder the formation of bond of glass ionomer with the tooth structure. Since there have been no previous studies evaluating the microleakage of chlorhexidine-modified GICs, the results could not be compared. These results are in harmony with the fact that Fuji IX has a coefficient of thermal expansion close to that of tooth. As is evident from the results, most of the samples showed dye penetration up to 1/3 cavity depth which could be due to enamel microcrazing, although no obvious enamel cracking was observed. Only one sample showed dye penetration involving axial wall which could be due to the failure of adhesion between GC Fuji IX and tooth because of incorporation of void/air bubble during the bulk placement of material into the cavity.
|Figure 2: Group Ic: Microleakage of glass ionomer cement. Group IIc: Microleakage of chlorhexidine modifi ed glass ionomer cement|
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The present study reveals that chlorhexidine-modified GIC could be a good substitute for GIC (Fuji IX) in ART and in primary dentition. Since in vitro studies do not reflect all variables present in the mouth, the results of this in vitro study may not be extrapolated to the clinical situation unless adequate clinical trials are conducted to test the in vivo efficacy of the material. Further tests should be undertaken to compare and evaluate the other strength characteristics like flexural strength, bond strength, and properties like hardness, setting, and working times of the experimental cement. The present study involved strength testing after 24 h only, while investigations should be done to test the strength of both the materials after prolonged periods of function and storage and wear rate of the experimental material. Studies should also be carried out to evaluate the shelf life and stability of chlorhexidine-modified GIC. So, in the present study, it can be concluded that the addition of chlorhexidine to GIC (Fuji IX) does not mar the strength characteristics and the marginal sealing ability of GIC.
| Conclusion|| |
The present study suggests that strength characteristics and marginal sealing capability of chlorhexidine-modified GIC were similar to those of GIC (Fuji IX). So, chlorhexidine-modified glass ionomer can be considered as a substitute for GICs.
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[Figure 1], [Figure 2]
[Table 1], [Table 2], [Table 3]