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 Table of Contents  
ORIGINAL RESEARCH
Year : 2018  |  Volume : 10  |  Issue : 3  |  Page : 138-142

Microleakage assessment of a new modified glass ionomer cement-nanozirconia-silica-hydroxyapatite restorative material


1 School of Dental Sciences, Universiti Sains Malaysia (Health Campus), Kota Bharu, Kelantan, Malaysia
2 Department of Conservative Dentistry, School of Dental Sciences, Universiti Sains Malaysia (Health Campus), Kota Bharu, Kelantan, Malaysia
3 Department of Biomaterials and Prosthodontics, School of Dental Sciences, Universiti Sains Malaysia (Health Campus), Kubang Kerian, Kelantan, Malaysia

Date of Web Publication14-Jun-2018

Correspondence Address:
Dr. Wan Zaripah Wan Bakar
School of Dental Sciences, 16150, Kubang Kerian, Kelantan
Malaysia
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/jioh.jioh_73_18

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  Abstract 

Aims: The purpose of this study was to evaluate the in vitro microleakage of new modified glass ionomer cement (GIC)-nanozirconia-silica-hydroxyapatite (GIC-nanoZrO2-SiO2-HA) hybrid material by comparing the depth of microleakage with conventional GIC (Fuji IX). Materials and Methods: Forty samples of standardized oval-shaped cavity preparation (4 mm × 3 mm × 2 mm) on buccal or lingual surfaces of freshly extracted human premolar and molar teeth were prepared. The samples were divided in two groups (n = 20) by simple random sampling method and restored with the new modified GIC-nanoZrO2-SiO2-HA hybrid material and Fuji IX (control), respectively; following the manufacturer's recommendations. All samples were then submitted to thermocycling (500 cycles at 5°C–55°C). The external surfaces of each tooth were coated with nail varnish except a 1 mm wide margin surrounding the restoration. Samples were then immersed in 2% methylene blue at room temperature for 24 h before rinsed under running water. Each sample was sectioned mesiodistally before microleakage evaluation was done using a stereomicroscope under × 20 magnifications and graded accordingly. Results: Differences in microleakage scores between materials were compared statistically using independent t-test. The new material shows significantly more microleakage compared to Fuji IX at P < 0.05. Conclusion: As conclusion, within the limitation of this study, the new modified GIC-nanoZrO2-SiO2-HA hybrid material was found to have more microleakage than conventional GIC.

Keywords: Glass ionomer, microleakage, restorative materials, zirconia


How to cite this article:
Hussin HM, Bakar WZ, Ghazali NA, Sajjad A. Microleakage assessment of a new modified glass ionomer cement-nanozirconia-silica-hydroxyapatite restorative material. J Int Oral Health 2018;10:138-42

How to cite this URL:
Hussin HM, Bakar WZ, Ghazali NA, Sajjad A. Microleakage assessment of a new modified glass ionomer cement-nanozirconia-silica-hydroxyapatite restorative material. J Int Oral Health [serial online] 2018 [cited 2019 Sep 22];10:138-42. Available from: http://www.jioh.org/text.asp?2018/10/3/138/234522


  Introduction Top


Since the introduction of glass ionomer cement (GIC) in 1972, they have been widely used as restorative materials, luting cement, and base materials.[1] These materials have widened the armamentarium of tooth-colored restorative materials, and in particular, they have been successfully used for restoration of primary teeth. Their main advantages are relative ease of use, bonding potential to enamel, and dentin and fluoride ion release. However, the disadvantages include the low wear resistance, opacity, and microleakage.[2] A good seal at tooth surface-restoration interface is very essential for an ideal restorative material to minimize the microleakage. Poor adaptation can lead to marginal discoloration, postoperative sensitivity, bacterial penetration, secondary caries, failure of restoration, and pulpal inflammation.

The main components of GIC are glass, polyacid, tartaric acid, and water. Tartaric acid is an important component of the GIC, as it has significant influence on the working and setting time.[3] The glass can be made from variety of materials allowing for a range of properties. The glasses contain three major components; silica (SiO2), alumina, and a flux of calcium fluoride (CaF2).

Microleakage which is a passage of bacteria, fluids, and ions along the tooth-restoration interface is among the most common cause of restorative materials failure. It leads to secondary caries and pulpal irritation which could be at micron or nanometer level.[4],[5] Microleakage could also be defined as the ingress of oral fluids into the space between tooth structure and restoration.[6] Youngson et al., Taylor and Lynch, and Matharu et al. stated that the microleakage could be at micron level or nanometer level.[7],[8],[9] This leakage might be not detected clinically, but it is a major influencing factor for the longevity of dental restoration as it can cause several biological effects on the restored tooth including recurrent caries, pulp pathology, hypersensitivity, and marginal break down.[10] The study shows that once cariogenic bacteria gain an entrance to the tooth-restoration interface, they are capable of proliferating along this area successfully with the potential to cause an adverse response from the pulp and recurrent caries.[11]

It has been reported that recurrent caries rates significantly increased with the extent of marginal gap.[12] A crevice at the tooth-restoration interface between 250 and 400 μm is considered as major problem in terms of recurrent caries.[4] Criteria that were established by McLean and von Fraunhofer (1971) were used by many researchers who suggested that 120 μm was maximum tolerable marginal opening.[13]

The higher mineral content in enamel provides greater ionic bonding between the tooth and cement. However, the bonding on dentinal margins is not sufficient to resist marginal gap formation. Conventional GIC exhibits the advantage of a similar linear coefficient of thermal expansion (CTE) as the tooth structure. When a testing material contacts moisture early and insufficient tooth bonding has been established, the difference of volumetric change between the restoration and tooth would produce a stress. During the thermocycling test which is usually applied to simulate oral condition, the stress will be exaggerated directly affecting the marginal seal.[14] The long-term outcome of mechanical loading and thermal changes can cause elastic deformation and physical alterations of both tooth substances and restorations which results in microleakage.[6] Inappropriate manipulation of materials by operators also plays a role in causing microleakage.

As cited in an article by Moshaverinia et al., several studies have been conducted related to microleakage of conventional GIC.[15] For this newly modified GIC-nanoZrO2-SiO2-HA hybrid material, no study on microleakage has been done yet, and it is important to investigate this as an assessment of the properties for this new material. Thus, the objective of this study was to evaluate the in vitro microleakage of a newly synthesized GIC-nanoZrO2-SiO2-HA composite material and compare it with the commonly used conventional GIC (Fuji IX).

The hybrid material was synthesized at Dental Biomaterial Laboratory, School of Dental Sciences, Universiti Sains Malaysia (USM), aimed at improving the strength and esthetics of conventional GIC by the addition of nano-zirconia.[16] It was expected to retain the desirable properties of conventional GIC which include better esthetics and true chemical bond with the tooth structure.


  Materials and Methods Top


This was an experimental study conducted at our Dental Biomaterial Laboratory over a period of 3 months (Jan 2018–Mar 2018), in order to evaluate the in vitro microleakage of a new modified GIC-nanoZrO2-SiO2-HA hybrid material by comparing the depth of microleakage of this new material with conventional GIC (Fuji IX ® Universal, GC Corp., Japan). Fuji IX ® was chosen as control because it is among the most preferred ionomeric restorative materials and is considered the gold standard for atraumatic restorative therapy.

Freshly extracted human permanent premolar teeth were collected according to the inclusion and exclusion criteria presented in [Table 1]. After cleaning with an ultrasonic scaler and polishing with rubber cups and pumice, the teeth were disinfected with 0.2% thymol solution for 48 h and stored in distilled water at room temperature until their usage in the experiment. Standardized oval-shaped cavity measuring 4 mm width × 3 mm height and 2 mm depth was prepared on the buccal or lingual surface of each tooth.
Table 1: Criteria for selection of extracted teeth for the study

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Following unbiased simple random sampling, the samples were divided into two groups, each containing 20 samples and after cavity preparation, rinsing and drying, a cotton pellet was placed in the cavity to avoid complete dehydration of the tooth.[2]

For sample in Group A, 10% polyacrylic acid conditioner (GC Dentin Conditioner, GC Corp., Japan) was applied to the cavity for 10 s before rinsing and dried without desiccation. The powder and liquid of conventional GIC (Fuji IX ® Universal, GC Corp., Japan) were mixed according to the manufacturer's instruction and placed into the cavity. The above steps were repeated for the new modified GIC-nanoZrO2-SiO2-HA hybrid material in Group B.

All samples were then submitted to thermocycling for 500 cycles at 5°C–55°C.[17] The external surface of each sample was coated with nail varnish except a 1 mm wide margin surrounding the restoration. Samples were immersed in 2% methylene blue at 37°C for 24 h and then rinsed under running water.[1] Later, the samples were partially immersed in epoxy resin for easy handling during sectioning. Each sample was then sectioned in the middle of the restoration parallel to the occlusal surface using a diamond band saw (Exakt 310 Cutting system, Exakt Technologies Inc., Germany).

The degree of marginal leakage was evaluated by the penetration of the dye stain from the surface margins to the base of cavity preparation. Each specimen were viewed under a stereomicroscope (Leica Imaging System, LEICA, UK) at ×20 magnification and graded according to the depth of dye penetration [Figure 1] and [Figure 2]. The scoring was done: following the scoring criteria as:
Figure 1: Dye penetration evaluation in conventional glass ionomer cement (Fuji IX)

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Figure 2: Dye penetration evaluation in new modified glass ionomer cement-nanoZrO2-SiO2-HA hybrid material

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0 – No evidence of dye penetration at tooth-restoration interface

1 – Dye penetration along the interface to ≤½ depth of cavity

2 – Dye penetration to full depth of cavity

3 – Dye penetration to base of cavity and beyond.[2],[18],[19]

The readings were recorded for each sectioned plane of the teeth which were two reading per specimen, one for each side. The views from the stereomicroscope were also photographed. Data were entered and analyzed using SPSS version 22.0 (SPSS Inc., Chicago, IL, USA) and tested with independent t-test.


  Results Top


The results show that the new modified GIC-nanoZrO2-SiO2-HA hybrid material had statistically significant microleakage when compared to GIC Fuji IX as shown in [Table 2].
Table 2: Comparison of microleakage between glass ionomer cement Fuji IX (Group A) and new modified glass ionomer cement-nanozirconia-silica-hydroxyapatite hybrid material (Group B)

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  Discussion Top


In assessing the microleakage of dental materials, there are a few testing methods available such as scanning electron microscopy, dye penetration, and chemical trace method. However, in this study, dye penetration method using methylene blue was chosen due to its cost-effectiveness, widespread use and popularity among researchers.[20],[21],[22],[23] The strength of the common dye penetration method following thermocycling for assessment of microleakage in this study lies in the fact that it has a close resemblance to what restorations are facing during their actual clinical service.[24]

The depth of dye penetration will convey the information on the degree of the microleakage which is observed under a stereomicroscope at ×20 magnification. The depth of penetration will be converted into 0–3 score which will describe the severity of microleakage.[2],[18],[19],[25] Another literature reported on calculating the volume of the dye penetrated into the sample where higher value meant a high degree of microleakage.[22] However, in this study, the scoring system will be used due to its simplicity and cost-effective.

To avoid fracture or missing middle part of the material for the proper reading, each sample was sectioned carefully. This new modified GIC-nanoZrO2-SiO2-HA was recently fabricated at the Biomaterial laboratory at School of Dental Sciences, USM, and has since shown superior results in terms of hardness and esthetics when compared to conventional GIC.[26] However, the result of this study shows that the new hybrid material had more microleakage than the conventional GIC where several factors could be considered to have caused this microleakage.

The integrity of the marginal seal is essential to increase the longevity of the restoration.[27] The higher mineral content in enamel provides greater ionic bonding between the tooth and cement, but the bonding on dentinal margins is not sufficient to resist marginal gap formation. Conventional GIC exhibits the advantage of a similar linear CTE as the tooth structure. When a testing material contacts moisture early and insufficient tooth bonding has been established, the difference of volumetric change between the restoration and tooth would produce stress. During the thermocycling test, the stress may be exaggerated and will directly affect the marginal seal.[14] According to previous literature, if poor bond strength exists between the tooth and restorative material, a failure of adhesion may be caused by polymerization shrinkage, and microscopic gaps at the tooth-restoration interface can subsequently form.[28] However, polymerization shrinkage occurs more for composite resin.

Restorations in the oral cavity are subjected to occlusal forces, moisture, and temperature variations from food or drink. For this study, the samples underwent thermal cycling which may contribute to the dislodgement of the restoration from the cavity walls, as a result of stress formation at the interface between the dentine and restoration.[29] Furthermore, since tooth and restoration have different CTE, the bond may be broken because of differences between contraction and expansion of tooth and restoration during thermal cycling. Thermal cycling can accelerate adhesive and/or cohesive failures or increase interface gap formation and dye penetration depths. In the thermocycling method, specimens are submitted to thermal cycles that simulate the intraoral temperature.

During the mixing procedure, this new material seems to have less consistency in compared to the conventional GIC which may be due to tartaric acid component. The action of (+)-tartaric acid which is the most important additive on the setting reaction depended on its concentration. Low concentrations accelerated the development of viscosity of the cement paste, while high concentrations retarded it. At intermediate concentrations, (+)-tartaric acid had an interesting, uniquely favorable effect on setting characteristics. First, it induced a lag period in the setting process during which the viscosity of the cement paste remained constant. This lag period was followed by a sharp, almost exponential, and increase in viscosity. Thus, tartaric acid was found to have a dual effect on setting, first inhibiting gelation and then accelerating it.[30]

Zirconium and its oxide, due to their good dimensional stability and toughness (on the same order as stainless steel alloys), have been used widely for the toughening and strengthening of brittle HA bioglasses in biomedical applications.[31] Gu et al. in their studies concluded that the mechanical properties of HA/ZrO2-GICs were found to be much better than those of HA-GICs because ZrO2 has the attributes of high strength, high modulus, and is significantly harder than glass and HA particles. Furthermore, ZrO2 does not dissolve with increasing soaking time.

Improper handling of the material by the operator might be causing the microleakage. Inconsistent powder and liquid mixing of the GIC by the operator can cause the mixed GIC become too liquidly or too hard causing unstandardized of the GIC before restoring into the cavity. Presence of moisture during handling the material may also affect the microleakage.

This study had one limitation, in that it evaluated the effect of thermocyclic wetting on the microleakage of the new hybrid material, but there are certain medical conditions such as Sjogren's syndrome, stroke, antidepressant, and irradiation therapies that result in excessive dryness of mouth. These conditions may result in recurrent caries and in some instances contraction of intra-oral hard tissues and dental restorations which could, in turn, hasten their degradation resulting in microleakage and stress at tooth-restoration interface as a result of wet and dry oral environment. Therefore, future studies must evaluate the adverse effect of cyclic wetting and forced drying, like in dry mouth conditions mentioned previously on the new hybrid material.

Another future recommendation, suggested by the authors is that clinical studies be designed to evaluate the effect of adding nanoZrO2-SiO2-HA to conventional GIC and resin-modified GIC in vivo or oral conditions be simulated using thermocyclic loading in conjunction with different commonly consumed beverages and acidic liquids.


  Conclusion Top


Within the limitations of this study, the new modified GIC-nanoZrO2-SiO2-HA hybrid material was shown to have slightly higher microleakage when compared with the conventional GIC.

Acknowledgment

This research was supported by Universiti Sains Malaysia RUI grant No. 1001/PPSG/812164.

Financial support and sponsorship

This research study was financially supported by USM short-term grant: 304/PPSG/61311041.

Conflicts of interest

There are no conflicts of interest.



 
  References Top

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