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 Table of Contents  
ORIGINAL RESEARCH
Year : 2019  |  Volume : 11  |  Issue : 6  |  Page : 357-362

Microleakage evaluation of novel nano-hydroxyapatite-silica glass ionomer cement


1 Biomaterial Unit, School of Dental Sciences, Universiti Sains Malaysia, Kelantan, Malaysia
2 Department of Prosthodontics, School of Dental Sciences, Universiti Sains Malaysia, Kelantan, Malaysia
3 Department of Conservative Dentistry, Lincoln University College, Kelantan, Malaysia
4 Human Genome Centre, School of Dental Sciences, Universiti Sains Malaysia, Kelantan, Malaysia
5 Department of Conservative Dentistry, School of Dental Sciences, Universiti Sains Malaysia, Kelantan, Malaysia

Date of Web Publication26-Nov-2019

Correspondence Address:
Assoc. Prof. Dr. Norhayati Luddin
Restorative dentistry (Prosthodontic Unit), School of Dental Sciences, Health Campus, Universiti Sains Malaysia, Kubang Kerian, 161 50, Kelantan.
Malaysia
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/jioh.jioh_132_19

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  Abstract 

Aims and Objectives: To analyze the microleakage of nano-hydroxyapatite-silica glass ionomer cement (nano-HA-SiO2-GIC) and compare it with conventional glass ionomer cement (cGIC). Materials and Methods: Twenty caries-free human premolar teeth were used. A standardized box-shaped class V cavity was prepared on the buccal surfaces at the cemento-enamel junction, with the occlusal margin (OM) set on enamel and gingival margin (GM) was placed on the cementum. Teeth were randomly assigned to two experimental groups of 10 teeth each and restored as follows: group 1, cGIC (Fuji IX) and group 2, nano-HA-SiO2 GIC. After 24h of immersion in distilled water, the teeth were thermocycled (500 cycles and 5°C–55°C). Following that, the teeth were placed in 2% methylene blue solution and stored at room temperature for 24h. The microleakage along the tooth-restoration interface was recorded. Independent sample t-test (two-tailed) was used to analyze the data. Results with P < 0.5 were considered statistically significant. Results: Microleakage in general was greater at GMs as compared to OMs for both the materials. Nano-HA-SiO2-GIC exhibited lower microleakage at occlusal level (0.2 ± 0.42) as compared to cGIC (0.5 ± 0.71), whereas, at GM nano-HA-SiO2-GIC displayed significantly less microleakage (2.7 ± 0.67) compared to cGIC (3 ± 0.00). Conclusion: Nano-HA-SiO2 glass ionomers showed less microleakage both at OMs and GMs compared to that at cGIC (Fuji IX).

Keywords: Bonding, glass ionomer cement, microleakage, nano-HA, nano-HA-Si, nano-Si


How to cite this article:
Moheet IA, Luddin N, Rahman IA, Masudi SM, Kannan TP, Abd Ghani NN. Microleakage evaluation of novel nano-hydroxyapatite-silica glass ionomer cement. J Int Oral Health 2019;11:357-62

How to cite this URL:
Moheet IA, Luddin N, Rahman IA, Masudi SM, Kannan TP, Abd Ghani NN. Microleakage evaluation of novel nano-hydroxyapatite-silica glass ionomer cement. J Int Oral Health [serial online] 2019 [cited 2020 Aug 12];11:357-62. Available from: http://www.jioh.org/text.asp?2019/11/6/357/271773


  Introduction Top


As a result of lack of oral health awareness and regular ingestion of refined carbohydrates, caries is the one of the most common diseases affecting the population of various age groups.[1] Restoration of carious teeth at an early stage is an ideal treatment choice to preserve the oral health status.[1] By preserving the natural teeth, healthy oral environment can be maintained by safeguarding the aesthetics, mastication, and speech.[2],[3]

A simple restorative treatment plan is likely to arouse anxiety in a patient that may provide challenge to a clinician in a clinical setup. Hence, when a choice of the restorative material is made, simplicity of clinical application of the material should be considered along with other properties of the restorative material.[4] The interest in the clinical application of conventional glass ionomer cements (cGICs) surfaced mainly from their advantage of requirement of minimum drilling as well as short time to fill the cavity, which is a desirable property while treating patients.[2]

Apart from that, an important aspect that is associated with the success of any restorative material in oral cavity is the ability of the material to bond to tooth structure. The hard tissue structures that are more commonly available for adhesion in restorative dentistry are enamel and dentin. These mineralized substrates present distinct ultra-morphologies and compositions.[5] A good adhesion between restorative material and enamel and dentin results in a complete and perfect seal between the restoration and tooth cavity walls. A measure of the materials ability to adhere with tooth structure is assessed through microleakage evaluation.[3]

Microleakage is defined as the undetectable movement of bacteria, fluids, molecules, or ions, and even air between the prepared cavity walls and the subsequently applied dental restorative material.[6] Microleakage is one of the most common causes of failure of various restorative materials because it is a leading causative factor for secondary caries and pulpal irritation.[7],[8] Consequently, there is a growing concern in finding a dental restorative material, which has good bonding characteristics, thus reducing microleakage and minimizing the potential for caries development and pulpal irritation. cGIC is one dental material that bonds chemically to tooth structure, and thus the use of cGIC has been reported to reduce the microleakage at occlusal margins (OMs) and gingival margins (GMs) as compared to other restorative materials.[9]

Glass ionomer cements (GICs) are the material of choice for atraumatic restorative technique because of their advantageous properties such as fast setting, adequate strength, and self-adhesiveness to natural tooth. However because of low mechanical properties, the risk of fracture exists for larger restorations.[10],[11] GIC is still inferior to other restorative materials when it comes to mechanical properties.[12] Hence, there has been an ongoing pursuit for further improvement in the properties of GIC. However, it should be borne in mind that the addition of any filler into a restorative material should not impart any negative effect on the desirable properties of the original material.[8] Some researchers have shown that nano-hydroxyapatite and nano-silica have a great potential for a broad range of uses because of their adaptable chemical and physical properties such as biodegradability, biocompatibility, remineralization potential, antimicrobial activity, and nontoxicity.[13],[14],[15],[16],[17],[18],[19],[20],[21]

Previously, Moheet et al.[22] evaluated the Vickers hardness, compressive strength and flexural strength, and shear bond strength of nano-hydroxyapatite-silica GIC (nano-HA-SiO2 GIC) The authors reported a significant increase in Vickers hardness, compressive strength, flexural strength, and shear bond strength of nano-HA-SiO2-cGIC (approximately 36%, 19.7%, 53.4%, and 17.34%, respectively) compared to that of cGIC (Fuji IX GP).[22] In addition, Noorani et al.[15] showed favorable cytotoxic response for nano-HA-SiO2-cGIC on using human dental pulp stem cells. Even though nano-HA-SiO2 GIC has shown an improvement in mechanical properties with favorable cytotoxic response, data related to microleakage are yet to be reported. Therefore, the objective of this study was to analyze the microleakage of nano-HA-SiO2 added GIC and compare it with cGIC. The null hypotheses tested in this study were that no difference is observed in microleakage property of nano-HA-SiO2 added GIC when compared to cGIC.


  Materials and Methods Top


The study protocol was granted approval by the Jawatankuasa Etika Penyelidikan Manusia (JEPeM) of the Universiti Sains Malaysia (USM/JEPeM/18080371).

Materials: Commercialized GIC (Fuji IX GP; GC International, Japan) in powder and liquid state were used in this study. The rest of the chemicals used were of analytical grade. The chemicals used in this study were calcium hydroxide (<98%, RM Chemicals, India), phosphoric acid (<99%, Sigma-Aldrich, Germany), tetraethyl orthosilicate (TEOS, 99%, Fluka, Germany), ethanol (99%, Systerm, Malaysia), ammonia (99%, Sigma-Aldrich, Germany), and total ionic strength buffer III (TISAB, Sigma-Aldrich, Germany).

Synthesis of nano-hydroxyapatite-silica: Nano-hydroxyapatite-silica powder was synthesized by a one-pot sol-gel technique.[22],[23] A quantity of 7.408g of calcium hydroxide was dissolved in 100mL of distilled water. This suspension was mixed with a magnetic stirrer for 30min. A total of 4.104mL of phosphoric acid was added dropwise to calcium hydroxide suspension.[22] This suspension was stirred for 48h. Liquid ammonia was used to maintain the pH of the suspension between 11 and 12. A quantity of 20mL TEOS was dissolved in 10mL of absolute ethanol and was added dropwise to calcium hydroxide suspension after 12h. After 48h, the sol produced was centrifuged (Eppendorf Centrifuge 5804, Germany) followed by freeze-drying (ScanVac CoolSafe, Denmark) and calcined (WiseTherm, Germany) at 600°C. The calcined powder was grounded manually using a mortar and pestle for 10min.[22]

Selection of teeth: The teeth collected for the experimentations were not extracted specifically for this study. Rather they were routinely collected from the dental clinics in the Hospital Universiti Sains Malaysia (HUSM) dental clinics. The teeth are being routinely extracted by undergraduate students, and faculty members for various reasons such as caries, periodontal problem, and orthodontic treatment. Among these extracted teeth, specific teeth were selected based on the inclusion criteria for our study.

Inclusion criteria were sound teeth (premolar/molars), crack-free teeth, and teeth storage time of less than 6 months. Teeth with permanent stains, teeth with abrasion, teeth with erosion, teeth with hypoplastic enamel, and teeth not stored in normal saline or distilled water were excluded from the study.

Microleakage sample preparation: Twenty caries-free maxillary first premolars extracted for orthodontic and periodontal reasons were used in this study for the evaluation of microleakage. The soft tissue debris and calculus were removed using ultrasonic scalers. The teeth were then polished using pumice and rubber cups. After cleaning and polishing, the teeth were placed in 0.5 chloramine solution for 1 week and stored in 0.9% sodium chloride solution at 37°C for not more than 4 weeks. The total storage time for the extracted teeth was less than 5 weeks before the testing. A standardized box-shaped class V cavity was prepared on the buccal surface of each tooth. A high-speed handpiece mounted with a round diamond bur was used for the preparation of class V cavity with copious amount of water irrigation. Each cavity prepared measured 3 ± 0.3mm in occluso-gingivally and mesiodistally. The depth of the cavity was kept at 1.5 ± 0.3mm [[Figure 1]]. The box-shaped cavity was located at the cemento-enamel junction (CEJ), with the OM finish on enamel and GM was placed on cementum. The dimensions of the cavity were checked with a digital gauge, with a level of 0.3mm tolerance was considered acceptable.
Figure 1: Cavity design for microleakage evaluation

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Following cavity preparation, the teeth were randomly divided into two groups consisting of 10 teeth per group. The cavities were conditioned for 10s and rinsed with water and air dried. The teeth were then restored with a nano-hydroxyapatite-silica glass ionomer cement (nano-HA-SiO2-GIC) and cGIC. Polishing was performed with a superfine diamond bur (Komet 859 EF.314.014; Komet, Denmark) mounted on a handpiece with a speed of 20,000rpm. The surface of the restoration was then covered by cocoa butter. Following restoration placement and polishing, the teeth were stored in 100% relative humidity in a water bath at 37°C.

The teeth were then subjected to 500 thermal cycles between 4°C and 60°C, with a dwell time of 15s. After that, the teeth were then coated with nail polish, except for 2mm surrounding the restoration margins. Following that, they were immersed in a 2% methylene blue solution and stored at room temperature for 24h. After storage, the specimens were abundantly washed with physiological solution (normal saline) and air dried. The teeth were then embedded in acrylic resin to prepare the samples for sectioning. A diamond saw fixed in a hard tissue cutter (EXAKT, Germany) was used to section the tooth specimen, for obtaining two buccolingual halves (mesial and distal), by cutting the teeth in a buccolingual direction under constant water irrigation.

The tooth sections prepared for microleakage evaluation were observed under a stereomicroscope (Leica Imaging System, Leica, UK) at 40× magnification. [Figure 2] shows the graphical presentation of the scoring and the measurement system. Microleakage score for the experimental materials was evaluated by two independent operators at the occlusal and gingival walls for each tooth section according to the following scoring system as suggested by Umer et al.[24]:
Figure 2: Schematic diagram showing microleakage scores on a buccolingual section of class V cavity

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  • 0. No penetration of the dye solution


  • 1. Infiltration of the dye up to the enamel-dentin junction in the occlusal wall or penetration up to one-fourth of the length of the gingival wall


  • 2. Penetration of the dye up to half of the length of the cavity wall


  • 3. Penetration of the dye extending for the total depth of the cavity wall


Statistical analysis: All the data were analyzed using the Statistical Package of the Social Services software (SPSS), version 23 (IBM, USA). Independent sample t-test (two-tailed) was used to analyze the significant difference for microleakage between nano-HA-SiO2-GIC and conventional GIC at 95% confidence interval. A value of α = 0.05 was considered statistically significant.


  Results Top


The scoring for microleakage testing and their means with P value are presented in [Table 1] and [Table 2], respectively. In general, microleakage was greater at GMs as compared to OMs for both the materials [Figure 3]. Nano-HA-SiO2-GIC showed lower microleakage at occlusal level (0.2 ± 0.42) as compared to cGIC (0.5 ± 0.71), whereas, significantly less microleakage was shown at GM for nano-HA-SiO2-GIC (2.7 ± 0.67) compared to that for cGIC (3 ± 0.00) [Table 2].
Table 1: Microleakage scores for conventional glass ionomer cement and nano-hydroxyapatite-silica glass ionomer cement

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,
Table 2: Intergroup microleakage comparison

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,
Figure 3: Dye penetration evaluation (A) conventional glass ionomer cement and (B) nano-hydroxyapatite-silica glass ionomer cement

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  Discussion Top


In restoration of a class V cavity, the coronal margins of these cervical lesions normally occur in enamel, whereas the cervical or GMs lie in dentin or cementum.[25] A restorative dentist is faced with a great amount of challenge in restoring a cervical lesion (class V cavity) occurred as a result of erosion, caries, or abrasion. These challenges include the restoration placement and isolation of teeth with rubber dam and clamp.[26] Another challenge is eliminating or reducing gap formation between the restoration and the gingival wall.[26]

To prolong the clinical outcome, a dental restorative material is required to adhere firmly to various types of tooth tissues. Microleakage and lack of marginal integrity of dental restorations has been associated with percolation of fluid, dentinal sensitivity, secondary caries formation, corrosion or dissolution of restorative materials, and discoloration of restorative materials and surrounding tooth structure.[27] Microleakage is also characterized by the permeation of bacteria, acids, and enzymes into the cavity margins. This infiltration of acids and bacteria is responsible for the discoloration of restoration, postoperative sensitivity, secondary caries, and pulpal damage.[28]

Microleakage is an important property that has been used in evaluating the success of a dental restorative material. There are several techniques or methods to evaluate or detect microleakage. These techniques involve the use of dyes, chemical tracers, radioactive tracers, scanning electron microscopy, neutron activation analysis, and fluid filtration.[9] In this study, the dye penetration method was used. Dye penetration method is a simple, inexpensive, and a fast technique, and does not require the utilization of complex laboratory equipment.[9] The use of organic dyes to record microleakage is one of the oldest and among the most frequently used in vitro methods for evaluation of microleakage in a tooth.[29] The shortcoming of dye penetration technique is that this method is basically a qualitative assessment of microleakage. A slight modification in evaluation by application of a nonparametric scale transforms this technique into a semiquantitative evaluation method.[30] To simulate in vivo aging, thermocycling protocol (cyclic hot and cold exposures) has been used to evaluate the bonded restorative material.[31]

In this study, cGIC (Fuji IX) showed a mean microleakage of 0.5 ± 0.71 at OM (enamel) after performing thermocycling followed by 24h of dye immersion. This was in accordance with the study carried out by Virmani et al.[32], Shruthi et al.[33], and Hussin et al.[34] All authors investigated microleakage of GIC in molars and reported almost similar microleakage results with GC Fuji IX.[32],[33],[34] Virmani et al.[32] also concluded that the use of additional application of sealant over the material gave the lowest degree of microleakage. This microleakage behavior would probably have been because of the high viscosity of GIC not allowing the proper wetting of the tooth surface. As a result, formation of good seal between tooth restoration interface has been affected.[7] cGIC (Fuji IX) showed a mean microleakage of 3 ± 0.00 at GM (cementum). Not enough data are available to compare microleakage of GIC with respect to cementum as most work has been focused on microleakage evaluation with enamel and dentin. This higher microleakage can be linked to the fact that GIC has the least bonding capability with cementum as compared to enamel and dentin.[35] This is because of the presence of highest organic content in cementum among all the hard tissues of the teeth.[36][Figure 4] shows the graphical representation of microleakage between nano-HA-SiO2-GIC and cGIC.
Figure 4: Graphical representation of microleakage between nano-hydroxyapatite-silica glass ionomer cement and conventional glass ionomer cement

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The results obtained in this study showed that both cGIC and nano-HA-SiO2-GIC showed greater microleakage on the GMs as compared to that on the OMs [Figure 4]. However, none of the experimental materials were able to completely eliminate microleakage at the enamel or gingival (cementum) margin. This finding is in agreement with other studies, which reported that cavity preparations resting on enamel margin results in consistently stronger bonds, and thus exhibiting less microleakage. Exceptional challenges are encountered with cementum surface bonding as compared to that with enamel and dentin, as enamel is approximately 92% inorganic hydroxyapatite, dentin is 45%–50% inorganic, and cementum is approximately 40% by volume.[37],[38] Furthermore, it has been reported that GIC has the least bonding capability with cementum as compared to enamel and dentin.[35] This fact was evident in this study whereby greater microleakage was reported at the GMs (cementum) as compared to that at the OMs (enamel). Both groups in this study showed high levels of dye penetration at the GMs. The dye penetration has extended to the full depth of the cavity as well as on to the axial wall. Similar findings were seen in previous studies, but the dye penetration occurred to a lesser extent.[38],[39]

Nano-HA-SiO2-GIC showed a mean microleakage of 0.2 ± 0.42 at OM (enamel), which is significantly lower as compared to cGIC (P < 0.05). Microleakage score of 0.96 ± 0.56 was reported for a nano-Zr-HA-SiO2 added GIC, which is significantly higher as compared to nano-HA-SiO2-GIC reported in this study.[34] In another study, microleakage was analyzed for nanoionomer. The author reported a mean score of 1.3, which is also significantly higher as compared to nano-HA-SiO2-GIC.[40] Nano-HA-SiO2-GIC showed a mean microleakage of 2.7 ± 0.67 at GM (cementum). As mentioned earlier, not enough data are available to compare microleakage at GM (cementum). The higher microleakage at GM can be linked to less bond strength with cementum.[35]

This study showed that the nano-HA-SiO2-GIC demonstrated less microleakage than cGIC at occlusal as well as GMs. This could be because of the higher filler loading in the nano-HA-SiO2-GIC that may have resulted in lower polymerization shrinkage and lower coefficient of thermal expansion, thus improving the long-term bonding to tooth structure.[41] Other factor that may have contributed to the lower microleakage at the OM could be explained by the fact that the nanostructure of the nano-HA-SiO2 added glass ionomer type allowed for better wetting and adaptability of the cement to the tooth surface, hence enhancing the chemical bonding, which can be evident by the increased shear bond strength reported previously by Moheet et al.[22]

Within the limitations of this study, it is concluded that none of the experimental materials were free from microleakage. The degree of microleakage in the GMs of each group was greater than that of OMs. Nano-HA-SiO2-GIC showed less microleakage as compared to cGIC both at OMs and GMs. Microleakage at GM was significantly lower for nano-HA-SiO2-GIC as compared to that for cGIC. Therefore, nano-HA-SiO2-GIC is a better restorative material for restoring cavities with respect to microleakage compared to cGIC (Fuji IX). The major innovation of this study involves the addition of nanotechnology by adding nano-HA-SiO2 synthesized by one-pot sol-gel method into GIC.

Financial support and sponsorship

This work was supported by the Ministry of Higher Education under Fundamental Research Grant Scheme (FRGS/203/PPSGi6171173)

Conflicts of interest

There are no conflicts of interest.

 
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