| Abstract|| |
Background and Objective: Glass ionomer cements (GICs) are the most commonly used restorative material in pediatric dentistry. They have numerous advantages; however, they show some marginal microleakage at the restoration–tooth interface. Various conditioning agents have been tested for alteration or dissolution of smear layer which has been attributed to the occurrence of microleakage; however, very limited studies have been done using primary teeth. Aims: To evaluate and compare the effect of 10% polyacrylic acid and 17% EDTA on marginal microleakage of high-viscosity GIC. Settings and Design: Experimental, in vitro study. Methodology: Class V cavities of standardized dimensions were prepared on 60 primary anterior teeth and were randomly divided into three groups. Except Group I, the cavities of Groups II and III were conditioned with 10% polyacrylic acid and 17% EDTA, respectively. All the 60 teeth were then restored with high-viscosity GIC. The samples were thermocycled and immersed in methylene blue solution for 24 h. The teeth were removed from the stain, rinsed, and sectioned buccolingually and were observed under stereomicroscope at 30× to score the marginal microleakage. Statistical Analysis Used: Kruskal–Wallis test followed by Mann–Whitney post hoc analysis were used to compare the mean marginal leakage scores between the three study groups. Results: Statistical significance difference was found between all the three groups (P < 0.05). The mean marginal microleakage score was maximum for Group I (control group; 3.00), whereas it was the least for Group II (1.30) where 10% polyacrylic was used for conditioning the cavity surface. Conclusion: Among the study groups, none of them was completely devoid of microleakage in all its samples. 10% polyacrylic acid emerged as a better conditioning agent when compared with 17% EDTA in altering or removing the smear layer thereby resulting in better adhesion.
Keywords: Adhesion, adhesive restorative materials, conditioning agents, smear layer
|How to cite this article:|
Unnikrishnan S, Krishnamurthy NH, Nagarathna C. Marginal microleakage of glass ionomer cement with two different cavity conditioners on primary anterior teeth – An in vitro study. Indian J Dent Res 2019;30:267-72
|How to cite this URL:|
Unnikrishnan S, Krishnamurthy NH, Nagarathna C. Marginal microleakage of glass ionomer cement with two different cavity conditioners on primary anterior teeth – An in vitro study. Indian J Dent Res [serial online] 2019 [cited 2019 Jun 20];30:267-72. Available from: http://www.ijdr.in/text.asp?2019/30/2/267/259234
| Introduction|| |
Invented and originally described by Wilson and Kent, glass ionomer cements (GICs) have been used in dentistry as a restorative material for more than 45 years. They are composed of a basic glass powder, calcium (or strontium) alumina fluorosilicate, and a water-soluble acidic polymer, such as polyacrylic acid. GICs have been used extensively in pediatric dentistry for restoration of carious teeth as they have additional advantages of chemical adhesion to tooth structure, fluoride release, and the possibility of relatively quick placement while treating young children.,
Today, one of the prime problems pertaining to restorations is the failure to obtain a complete bond of adhesive restorative material with enamel and dentin. The mechanism of adhesion of GIC to tooth structure is through the development of ionic crosslinks at the tooth–restorative interface and it was proposed by Wilson et al. in 1983. However, despite good adhesion, even GICs show some microleakage at the margins of restorations.
Microleakage may be defined as the passage of bacteria, fluids, molecules, or ions between a cavity wall and the restorative material applied to it. Microleakage between the restoration and the tooth interface can result in occurrence of postoperative pain, discoloration of the cavity edges, secondary caries, and pulpal inflammation resulting in postoperative failure.
The presence of smear layer is one of the factors which may lead to reduction of GICs' adhesion to the tooth surface particularly to dentinal surfaces. At first, researchers believed that the smear layer should be preserved to protect pulp from the toxic stimuli. However, today it is emphasized that the smear layer does not provide a stable substrate for adhesion and bonding of the restorative material to the tooth surface and dissolves under restorative material as a result of microleakage. Therefore, the smear layer should be either modified or completely dissolved and removed using various conditioning agents.
In literature, conditioning agents of varying concentrations such as 5% and 12% citric acid, 10%, 20%, and 25% acrylic acid, 17% EDTA, and 35% phosphoric acid have been used to condition dental surfaces thereby decreasing the marginal microleakage. Currently, in the literature, the effect of conditioning agents such as 10% acrylic acid and 17% EDTA on bonding of conventional high-viscosity GIC in primary anterior restorations is scarce. Therefore, the aim of this study was to evaluate and compare the effect of 10% polyacrylic acid and 17% EDTA on microleakage of high-viscosity GIC.
| Methodology|| |
This in vitro experimental study was conducted by the Department of Pedodontics and Preventive Dentistry, Rajarajeswari Dental College and Hospital, Bangalore. The study included 60 intact primary anterior teeth with no caries, restorations, fractures, or developmental anomalies, with root resorption of <1/2 root length that were extracted, which were collected from pediatric dentists' private offices in a 6-month period. The teeth were later stored in normal saline solution at room temperature.
Standard Class V cavities were prepared on all labial tooth surfaces using a sharp diamond flat fissure bur with high-speed rotary airotor with water spray. The cavity dimensions were standardized as follows: 2 mm incisogingival in length, 3 mm mesiodistal in width, and 1.5 mm in depth. All teeth were placed in distilled water after cavity preparation.
Later, the teeth were rinsed and dried, and moist cotton pellet was placed in the cavity to prevent complete dehydration of the tooth; the teeth were divided into three groups of 20 teeth in each.
- Group I – Prepared teeth with no cavity conditioners used
- Group II – Prepared teeth conditioned with 10% polyacrylic acid conditioner (Gc Dentin Conditioner; GC, Japan)
- Group III – Prepared teeth conditioned with 17% EDTA gel (RC Help; PDP, India).
Cavity conditioning in all the groups, except Group I, was carried out according to the manufacturer's instructions. Then, the cavity was rinsed using water spray for 15 s and water and air spray for another 15 s. Following rinsing, a piece of cotton pellet was placed in the cavity and gently dried before the cavity was filled with GIC.
After the cavity was restored and polished and coated with varnish (GC Fuji, Japan), the teeth were stored in distilled water for 24 h; the specimens were subjected to thermocycling procedures 500 times at a range of 5°C–55°C with an immersion time of 30 s (first, 5°C ± 2°C; then, room temperature; next, 55°C ± 5°C; after that, back to room temperature; and finally, 5°C ± 2°C). Subsequently, all the teeth apices were sealed with sticky wax, and all the teeth surfaces as well as the mesial and distal margins of the restoration up to 1 mm of the incisal and gingival margins were covered with two layers of nail polish to eliminate any unwanted dye penetration.
Furthermore, each tooth was embedded up to cementoenamel junction in autopolymerizing acrylic resin and later was immersed in 1% aqueous solution of methylene blue for 24 h. Diamond disc attached to straight handpiece at slow speed was used to section the teeth longitudinally in a buccolingual direction.
The amount of microleakage was determined by the amount of dye penetration at the tooth–restoration interface using a stereomicroscope at 30× magnification by an examiner who was blinded to the study groups.
The scoring criteria used for marginal microleakage assessment at the tooth–restorative material interface were as follows:
- Score 0 – No dye penetration in tooth–restoration interface [Figure 1]
- Score 1 – Dye penetration in tooth–restoration interface which at most has spread till dentinoenamel junction (DEJ) [Figure 2]
- Score 2 – Dye penetration in tooth–restoration interface which at most has passed DEJ, but has not reached the axial wall of the cavity [Figure 3]
- Score 3 – Dye penetration in tooth restoration interface which at most has reached the axial wall of the cavity [Figure 4]
- Score 4 – Lateral dye penetration in enamel that has reached the dentin [Figure 5].
|Figure 2: Score 1: Dye penetration in tooth restoration interface which at most has spread till dentino-enamel junction (DEJ)|
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|Figure 3: Score 2: Dye penetration in tooth restoration interface which at most has passed DEJ, but has not reached the axial wall of the cavity|
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|Figure 4: Score 3: Dye penetration in tooth restoration interface which at most has reached the axial wall of the cavity|
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|Figure 5: Score 4: Lateral dye penetration in enamel that has reached the dentin|
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The highest score for each sample was considered and tabulated. Statistical analysis was done using Statistical Package for Social Sciences (SPSS) for Windows, version 22.0. Descriptive statistics includes expression of the marginal leakage scores in mean, standard deviation (SD), and standard error. Kruskal–Wallis test followed by Mann–Whitney post hoc analysis were used to compare the mean marginal leakage scores between three study groups. The level of significance (P-value) was set at P < 0.05.
| Results|| |
Kruskal–Wallis test revealed statistical significance (P < 0.001) between the mean marginal leakage of all the three groups; Group I with maximum mean marginal leakage and Group II with the least mean marginal leakage, which suggest the alteration or removal of smear layer by conditioning agents affects the amount of microleakage [Table 1] and [Graph 1].
|Table 1: Comparison of mean marginal microleakage between three groups using Kruskal-Wallis test|
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Mann–Whitney U-test was carried out for multiple comparisons of mean marginal microleakage scores between the three groups. Statistical significance (P < 0.001) was found with the mean difference of 1.70 when Groups I and II were compared. On comparison of Groups I and III, the mean difference was 0.95 which showed statistical significance (P = 0.005). Similarly, statistical significance (P = 0.02) was found on comparison of Groups II and III with a mean marginal microleakage difference of 0.75 [Table 2].
|Table 2: Multiple comparison of mean marginal microleakage scores between groups using Mann-Whitney U-test|
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| Discussion|| |
GICs were discovered originally by Wilson and Kent as a result of the search for a replacement for the silicate cements that had been used in dentistry for about hundred years. Restoration of the primary dentition is considered less demanding, because the restoration will be in use for lesser time and also lower biting forces experienced than in adults., Glass ionomers are well suited for these uses because of the possibility of relatively quick placement, and the additional advantages of fluoride release and chemical adhesion. With years, the original GIC has evolved with better physical and mechanical properties, and in the early 1990s a fast-setting, high-strength conventional GIC was introduced. This variant of GIC found its application in treating Class V cavities in primary and permanent dentition. GC Gold Label IX, which is one such improved conventional GIC, was used in this microleakage study.
During cavity preparation, tooth structure is cut by rotary instruments, that is, diamond or carbide burs, and this procedure generates a large amount of energy locally, which results in collagen degeneration and alters surfaces chemically and physically. These microcrystalline debris that coat the dentin and clog the orifices of the dentinal tubules are termed the smear layer which can influence the adhesion between the tooth structure and dental materials. In this study, diamond straight fissure (SF-41) burs were used for Class V cavity preparation on all the samples in each group which could have resulted in significant smear layer formation on the cut tooth surface. This was in accordance with a study by Di Nicolo et al. who concluded that surfaces cut with diamond burs presented more irregularities and thicker smear layer when compared with the dentin surface cut with carbide burs.
The smear layer thus formed during cavity preparation does not constitute a stable substrate for the restorative material to bond to the tooth surface and may undergo hydrolysis with time resulting in bacterial penetration at the tooth–restoration interface. Studies have reported that conditioning of the tooth surface increases the bond strength of GICs to dental hard tissues, thereby decreasing the marginal microleakage by reducing the smear layer.,
In our study, Group I restorations without any cavity conditioners showed significantly higher mean marginal microleakage score of 3.0 when compared with teeth where conditioning of cavity walls was done prior to restoration with high-viscosity GIC [Graph 1]. These findings were in agreement with the study by Castro and Feigal in which the primary molars with and without a conditioner agent application were restored with Fuji IX, and it was found that cavities that had a conditioner agent application presented with less microleakage.
Different materials such as citric acid, acrylic acid, EDTA, and phosphoric acid have been tested and used at different concentrations to condition tooth surfaces. Among these various conditioning agents used, 10% polyacrylic acid and 17% EDTA were used as conditioning agents in this study to modify or remove the smear layer. Polyacrylic acid is the most commonly used conditioner for conventional GICs as it increases the bonding efficiency by cleansing effect which removes loose cutting debris following cavity preparation; partial demineralization effect which increases the surface area and creates microporosities; and chemical interaction of the polyalkenoic acid with residual hydroxyapatite. EDTA was selected for dentine pretreatment as it has been previously used to dissolve the mineral phase of dentine without altering dentine proteins and also it has been claimed to produce a mild demineralization that may facilitate dentine infiltration or adhesion to residual mineral located within the collagen fibrils.
In vitro studies to detect the marginal microleakage include the uses of dyes, chemical tracers, radioactive isotopes, air pressure, neutron activation analysis, scanning electron microscopy, artificial caries techniques, and electrical conductivity. We have used 2% methylene blue dye in our study because of its ease of manipulation, convenience, low cost, and also the low-molecular weight of the dye which is smaller than bacteria and could detect leakage where bacteria could not penetrate. The specimens were soaked in the dye for 24 h which is considered to be a standard time span for the dye to penetrate.
Before immersing the specimen in the dye, the specimens were subjected to thermocycling, a standard procedure done in microleakage studies for 500 cycles with a temperature range from 5°C to 55°C for thermocycling.
After sectioning of the study samples, stereomicroscope, a qualitative method, which is considered as the gold standard, had been used in this study at 30× magnification for evaluating the marginal microleakage at the tooth–restoration interface of each sectioned sample. Chen et al. concluded that the best images were obtained from stereomicroscopy compared with other latest methods, and hence is considered as the gold standard for marginal microleakage assessment.
The results of this study [Table 1] and [Graph 1] showed that the mean microleakage score of Group I (control group) was 3.0 with an SD of 0.97, for Group II (10% polyacrylic acid) 1.30 with an SD of 1.03, and 2.05 mean marginal microleakage score with an SD of 0.89 for Group III (17% EDTA); none of these considered groups was completely devoid of marginal microleakage, and the use of conditioners resulted in significantly lower microleakage compared with the control group. This could be due to the elimination of debris, removal of smear layer, enamel rod exposure, partial demineralization, and formation of microporosities in the enamel and dentinal surfaces, which result in an increased surface for chemical and microchemical bonding. Glasspoole et al. showed that using 10% polyacrylic acid for 20 s or 35% phosphoric acid for 15 s on enamel surface results in higher bond strength in Fuji II conventional GIC. Scanning electron microscopic (SEM) studies by Castro and Feigal and Yilmaz et al. showed a decreased microleakage and a close contact at the enamel–restoration interface following the application of different conditioners in cavities filled by Fuji IX glass ionomer., However, several studies have demonstrated that cavity conditioner had no effect on the bond strength and microleakage of self-cured GICs.
In this study, the effect of conditioning agents 10% polyacrylic acid (Group II) and 17% EDTA (Group III) on the marginal microleakage of high-viscosity GICs was compared [Table 2], and it was found that the mean marginal microleakage of 17% EDTA was 2.05 and was significantly higher than 10% polyacrylic acid with a mean score of 1.30 and the mean difference of 0.75 between the two groups. This was similar to the study by Mazaheri et al.
Tanumiharja et al. in an SEM study reported that there was no smear layer in dentinal tubules and Fuji IX cement matrix had penetrated into the demineralized dentin following the use of polyacrylic acid as conditioning agent. A study by Stephen M disagreed with the results of our study as it concluded greater microleakage in glass ionomer restorations that had received polyacrylic acid as a conditioner to the control group where no conditioners were used. The higher microleakage in EDTA group when compared with polyacrylic group in this study might be due to the fact that application of 17% EDTA on dentin for 60 s is capable of only partially removing the smear layer with maintenance of about 30% of the smear plugs.
This study made a sincere attempt to investigate the effect of two different cavity conditioners on marginal microleakage of GIC in primary anterior teeth. However, because the teeth in the laboratory setting were not subjected to mechanical forces or biologic factors which could affect the marginal seal of a restorative material, further long-term in vivo studies are recommended considering all the factors responsible for marginal microleakage of a restorative material for better clinical application and practice.
| Conclusion|| |
The following conclusions can be drawn from this study:
- Dye penetration was seen in all the three groups considered in the study
- Cavities restored without the use of cavity conditioners showed the highest mean marginal microleakage
- Even with the use of cavity conditioners, not all samples of experimental groups showed complete elimination of marginal microleakage
- Use of 10% polyacrylic acid was more efficient than 17% EDTA in reducing the marginal microleakage at the GIC–tooth surface interface
- Conventional GICs can be used even without removal of the smear layer; however, the use of cavity conditioners which remove or alter the smear layer can be used to reduce the marginal microleakage of the restoration thereby improving the longevity of the restoration.
The authors would like to thank the Department of Oral Pathology and Microbiology, for granting access to the stereomicroscope and providing with methylene blue stain, for successful conductance of this study.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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Dr. Surej Unnikrishnan
Department of Pedodontics and Preventive Dentistry, Rajarajeswari Dental College and Hospital, Ramohalli Cross, Mysore Road, Kumbalgodu, Bangalore - 560 074, Karnataka
Source of Support: None, Conflict of Interest: None
[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5]
[Table 1], [Table 2]