Year : 2008 | Volume
: 26 | Issue : 6 | Page : 56--61
Comparison of antibacterial activity of three fluorides- and zinc-releasing commercial glass ionomer cements on strains of mutans streptococci: An in vitro study
KK Shashibhushan1, N Basappa2, VV Subba Reddy1,
1 Department of Pediatric Dentistry, College of Dental Sciences and Hospital, Davangere-577 004, India
2 Department of Pediatric Dentistry, Bapuji Dental College and Hospital, Davangere-577 004, India
K K Shashibhushan
Department of Pediatric Dentistry, College of Dental Sciences & Hospital, Davangere-577004, Karnataka
The purpose of present study was to investigate the antibacterial activity of three commercially available fluoride- and zinc-releasing glass ionomer cements on strains of mutans streptococci. Three glass ionomers (Fuji II Conventional, Fuji II Light Cure, and Fuji IX) were used. The antibacterial effect of glass ionomer cements were estimated by anaerobically growing mutans streptococci on a selective medium by inoculating human saliva and measuring the inhibition zones around the glass ionomer discs on the medium. Fluoride and zinc release were measured and compared with the antibacterial activity. The results, when statistically analyzed, showed a direct correlation between fluoride release and antibacterial activity, but there was no correlation between zinc release and antibacterial activity.
|How to cite this article:|
Shashibhushan K K, Basappa N, Subba Reddy V V. Comparison of antibacterial activity of three fluorides- and zinc-releasing commercial glass ionomer cements on strains of mutans streptococci: An in vitro study.J Indian Soc Pedod Prev Dent 2008;26:56-61
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Shashibhushan K K, Basappa N, Subba Reddy V V. Comparison of antibacterial activity of three fluorides- and zinc-releasing commercial glass ionomer cements on strains of mutans streptococci: An in vitro study. J Indian Soc Pedod Prev Dent [serial online] 2008 [cited 2020 Sep 18 ];26:56-61
Available from: http://www.jisppd.com/text.asp?2008/26/6/56/43533
Secondary caries is reported to be one of the main causes of the replacement of amalgam and composite restorations. It is a well-documented fact ,,, that optimum levels of fluorides in any form reduces dental caries. Low incidence of secondary caries was observed ,, when the restorations were made with fluoride-containing restorative materials.
Since their introduction in 1972 by Wilson and Kent, glass ionomers have progressed greatly to achieve their current status and now include conventional, dual-cure, and tri-cure systems. One useful property of glass ionomer is its ability to release of fluoride and other trace elements such as zinc.  It is established, ,,,,,,,, that there is a continuous release of low levels of fluoride and zinc by glass ionomers; these accumulate in dental plaque and modulate the population of mutans streptococci and also inhibit their growth around restorative margins, ,,, thus preventing initiation of secondary caries and failure of restoration.
The ability of glass ionomer cements to release fluoride and zinc to the surrounding environment could be a measure of their antibacterial activity. Recently introduced glass ionomers contain fluoride and also have superior physical properties,  which is important in the prevention of secondary caries. It would be advantageous if such materials possess antimicrobial potential.
Hence this study was planned to evaluate the antibacterial activity against strains of mutans streptococci of three commercially available glass ionomer cements (viz., Fuji II Conventional, Fuji II Light Cure (tri-cure), and Fuji IX) that release zinc along with fluoride.
The present study was carried out in two parts: evaluation of antibacterial activity of glass ionomer cements on mutans streptococci and analysis of the amount of zinc and fluoride release.
Cements used were Fuji II Conventional (type II glass ionomer), Fuji II Light Cure (type II Light Cure), and Fuji IX (Designed for ART) manufactured by G.C. Corporation, Tokyo, Japan.
Preparation of glass ionomer specimens
Specimens of the three glass ionomer cements were prepared by using an acrylic template containing six holes measuring 6 mm (diameter) × 2 mm (height) and three holes measuring 3 mm (diameter) × 2 mm (height). Two specific holes measuring 6 mm × 2 mm and one hole measuring 3 × 2 mm were used for preparing specimens of each cement; the holes were never interchanged for the preparation of glass ionomer cements.
For preparing glass ionomer specimens a glass slab was placed under the template and the glass ionomers were mixed according to the manufacturer's instruction and loaded into the specific holes as labeled on the template. Glass cover slips were placed on the material to flush out excess material and the light cure glass ionomer (Fuji II Light Cure) was light cured for 20 s. Set discs were pushed into an empty petri dish with a glass rod.
The antibacterial effect of glass ionomer cements on agar plates was estimated by anaerobically growing mutans streptococci on selective medium by inoculating human saliva. Once growth was obtained, they were reinoculated on to agar plates and glass ionomer discs measuring 6 × 2 mm were placed in predesignated areas. The agar plates were then incubated in an anaerobic jar.
Under these conditions, the inhibition zone [Figure 1] was recorded in millimeters using a magnifying glass and a measuring scale. Each experiment was done in triplicate. Inhibition zones were measured in all three experiments and mean was recorded and used for the analysis. The antibacterial effect of glass ionomer cements on strains of mutans streptococci was statistically analyzed.
Fluoride and zinc release
For measuring fluoride and zinc release from each of the cements, seven discs measuring 6 × 2 mm and one disc measuring 3 × 2 mm of each cement were prepared and placed in a 100-ml jar containing 30 ml of deionised distilled water and the jars were incubated at 37°C for 8 days. On the morning of each day the specimens were removed, washed with distilled water, and dried with blotting paper, before being transferred to a fresh jar containing 30 ml of distilled water. The procedure was continued up to 8 days and fluoride and zinc release were measured daily.
Fluoride release was measured using a fluoride-specific electrode (9609 Orion Research Inc, Boston, MI, USA). Zinc release was measured using an atomic absorption spectrophotometer (1800 Hitachi Model, Japan).
For each sample, analysis was done three times and the mean was taken to obtain accurate results. The results were statistically analyzed.
Antibacterial activity was determined by measuring the size of the growth inhibition zone on the agar plate. The amount of fluoride and zinc release was measured in parts per million released over a period of 8 days. The antibacterial activity was correlated with the amount of fluoride and zinc release and this was compared among the three cements.
Fuji II Light Cure exhibited the greatest amount of antibacterial activity, producing the largest inhibitory zones. These inhibitory zones for mutans streptococci ranged from 6-7.6 mm, with a mean of 6.87 ± 0.81 mm [Figure 1], after 48 h of exposure. Fuji II Conventional exhibited similar inhibitory ability, ranging from 2-3 mm with a mean of 2.30 ± 0.58 mm. The least growth inhibition was seen in the case of Fuji IX; the inhibitory zone ranged from 1.5-, with a mean of 1.23 ± 0.25 mm [Table 1] and [Graph 1].
The fluoride release was maximal on day one for all the three cements, reduced drastically on the second day, and then decreased gradually thereon. On the seventh and eighth day fluoride release was almost constant [Table 2], [Graph 2].
Fluoride release was greater with Fuji II Light Cure on all days when compared to Fuji II Conventional and Fuji IX. The least amount of fluoride was released by Fuji IX [Table 2], [Graph 2].
Zinc release was highest on day one for all the cements, after which it gradually decreased [Table 3], [Graph 3]. Fuji IX exhibited the greatest amount of zinc release among the three cements tested. The least amount of zinc release was seen in case of Fuji II Conventional [Table 3], [Graph 3].
The greatest degree of antibacterial activity was exhibited by Fuji II Light Cure. The antibacterial activity of the cements appeared to be directly related to the amount of fluoride release. Even though zinc was released by all the three glass ionomer cements, there did not seem to be any direct correlation between antibacterial activity and the amount of zinc release.
Present study indicates that some degree of growth inhibition of mutans streptococci was exhibited by all the tested glass ionomers. There was significant difference in antibacterial activity of the three glass ionomers. This antibacterial activity of the cements may be due to the release of fluoride and zinc into an aqueous medium, which may inhibit growth of mutans streptococci. The release of fluoride and zinc from glass ionomer cement occurs through three mechanisms: , a rapid surface elution, diffusion through cracks, and dissolution. The release of these ions from glass ionomer cements are governed by intrinsic and extrinsic factors. , The intrinsic factors are related to the preparation of the material, its powder / liquid ratio, manipulation time, temperature, specimen geometry, surface protection, and the finish and permeability of the material. The extrinsic factors are related to the storage / dissolution of the medium (volume of storage solution and frequency of solution change and stirring) and the analytic method used. ,
Fluoride contributes to caries inhibition in the oral environment by means of both physiochemical and biological mechanisms.  Physicochemically, fluoride inhibits demineralization through formation of fluorapatite and enhances remineralization of carious noncavitated enamel. The biologic mechanisms include inhibition of carbohydrate metabolism by acidogenic plaque microflora. Fluoride enters microorganisms against a concentration gradient and accumulates intracellularly as the extracellular pH decreases, the transport of hydrogen fluoride into cells leads to dissociation of HF into H+ and F− in the alkaline cytoplasm. Ionic fluoride then induces enzymatic inhibition of acid production. Meanwhile, the fluoride increases cell permeability, allowing it to rapidly diffuse out of the bacterium; this fluoride again contributes to the fluoride content within the plaque matrix. Sublethal concentrations of fluoride alter bacterial adhesion and the acid tolerance of mutans streptococcus, leading to less acidogenic plaque flora.
Zinc is known to interfere with substrate transport and oxidation and to react with the thiol group on the bacterial cell wall. Zinc also changes the protein structure ,,, and leads to inhibition of specific metabolic enzymes, thereby causing growth inhibition.
Fuji II Light Cure showed maximum inhibition (6.87 ± 0.81 mm) of mutans streptococci when compared to Fuji II Conventional (2.30 ± 0.58 mm) and Fuji IX (1.23 ± 0.25 mm). This may be related to fluoride release because it contributes to caries inhibition by means of both physicochemical and biological mechanisms  ; similar observations were also made by other authors. ,
The present study showed that both fluoride and zinc were continuously released from all the tested glass ionomer cements. The release of fluoride was maximal on the first day for all the three test cements and decreased by almost four times on the second day. Later, the fluoride release decreased gradually, reaching a constant level on the seventh and eight day. Similar findings were reported by other investigators. ,,
The maximum fluoride release was seen with Fuji II Light Cure when compared to Fuji II Conventional and Fuji IX. This may be because of the difference in chemical composition and physical properties; the lower sensitivity of the cement to moisture during early setting, which results in leaching of more and more fluoride and other ions from the powder by acid attack; and also due to the shorter mixing time of Fuji II Light Cure (20-25 s) when compared to Fuji II Conventional and Fuji IX (25-30 s). Fluoride release was least with Fuji IX, which may be because of the differences in the chemical composition, physical properties, and the consistency of the mix (3.6 : 1 P/L). 
In this study, zinc was released by all the three test cements. The maximum zinc release was seen on the first day, after which it gradually tapered off. The highest amount of zinc release was seen with Fuji IX (4.25 ± 0.47 to 0.47 ± 0.04 ppm) when compared to Fuji II Conventional (1.47 ± 0.40 to 0.15 ± 0.17 ppm) and Fuji II Light Cure (3.22 ± 1.47 to 0.39 ± 0.07 ppm). This difference in zinc release may be because of the differences in the chemical compositions of the three test cements; also, variable amounts of the zinc may be present as complexed salts, making it unavailable for estimation.
Even though other studies ,,, have shown that zinc has an antibacterial action, in this study there was no correlation between zinc release and the antibacterial activity of the three test cements. Fuji IX showed highest amount of zinc release but it exhibited the least amount of antibacterial action; Fuji II Light Cure released the second greatest amount of zinc and showed the highest antibacterial action; Fuji II Conventional showed the least amount of zinc release and second highest antibacterial activity. This lack of correlation between zinc release and antibacterial activity may be because of the following reasons:
The amount of zinc released may not be sufficient to produce growth inhibition. Zinc may be released as a complexed salt and not in the ionic form which is required for growth inhibition.The normal constituents used for preparing bacterial culture media such as inorganic salts, amino acids, and proteins strongly interact with metal ions and modify their antibacterial properties. ,, Zinc may play its role only by inhibiting acid production and not by inhibiting growth of mutans streptococci.
This study indicates that there is a direct correlation between the amount of fluoride release and the antibacterial activity of all the three test glass ionomers. This suggests that the antibacterial effect of glass ionomer cements may be a consequence of synergistic action by fluoride and zinc. It also appears that release of zinc alone by glass ionomer may not bring about direct bacterial inhibition, but it does play a role in the inhibition of acid production by mutans streptococci.
Fluoride and zinc were released by all the three cements in varying concentrations.Direct correlation was observed between fluoride release and antibacterial activity. No correlation was found between zinc release and antibacterial activity. It appears that the antibacterial effect is a consequence of the synergistic action of fluoride and zinc released in certain amounts. Further studies are needed to determine the exact role of zinc and find out the minimum amount of fluoride release required to bring about sufficient growth inhibition.
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